Marvelous!!! On behalf of me and all our students trying to apply ziplines without trees to impoverished communities in the highlands of Columbia we thank you!
Thank you Ryan that was an outstanding explanation I was planning a similar installation. I was considering 6 5/8 “ galvanized pipe. So glad I saw this post since the cost of building materials are through the roof!
I have a 500ft zipline in my backyard and we just used a string as a rough estimate of the height we needed. For some 250lb riders, they will bottom out in one spot, so we use a shorter leash for them to fix that issue and with really small kids we use two leashes so they can reach the platform at the end.
This was Awesome, thank you for this excellent Video, I have a handyman side gig and need to build a Zipline for a customer. I actually have a mechanical engineering degree as well so was able to follow along with your formulas.
Man, that is an expensive cable but it seems like a reasonable diameter for that length. Your anchor points are going to need to exert 3 or 4 tons of force, those are going to be expensive anchors also. Good luck, and I look forward to seeing the video!
Did you check the margin of strength on the cable (and connections)? At what rider weight does the cable start to yield? If it yields, is it still usable afterwards if you tighten it? Do you know if cable work-harden? I am considering a zipline for my grandkids, and appreciate your engineering. I am a retired aerospace engineer, and make similar videos on various projects. The more math, the fewer the views, unfortunately.
Naw - I didn't calculate anything with the cable. It came as part of a kit and the manufacturer's instructions said it was rated for a 300-lb rider (I think?). I am 200 lbs, and it didn't yield under the stretch loads caused by my weight. I imagine there's a good chance that the cable supplier already work-hardens the cable, because I calculate that a 200-lb rider ride puts it well beyond 0.2% strain. Or maybe the first couple of rides stretch-harden it like you are asking. It's not an issue, don't worry about it. Look up what other people suggest. Good luck.
Fair enough Ryan. I was rounding up from 7.5" to 8". I know the website I showed you recommends 12" and 8"...I am just trying to figure out if the 12" for the main pole is overkill, but I understand that your patience is exhausted.
Chris, the ziplinegear guidance presents your options as "either-or". Re-read it again carefully. Option 1 is to install a standalone post with a 12" diameter minimum. You are not choosing that installation type. So forget it. Pretend that you never saw the number 12. Option 2 is a double-post guy-wire system where *the main post and the support post are each are 8" diameter minimum.* If you are doing guy-wire, then yes - 12" would be overkill. *BUT FINALLY -* don't do any rounding up. I want you to say the following words in quotes out loud ten times: "7.28 is less than 8. 7.5 is less than 8. I will not skimp on the number 8 because I am committed to following the guidance of both ziplinegear.com and the guidance of Ryan, who fully endorses that same guidance and he told me now four times to follow the guidance and don't skimp." Fill up a chalkboard like bart simpson.
Very useful video - thanks Ryan. Like Luke below I also based my calculations on a 200lb rider over a 120' distance and the deflection was coming out at over 2", which is higher than I'd like. I don't have the space to use a guy anchor so I figured I would use two 2x12 beams in series in line with the run, with 12" to 18" between them and bolt the beams together at the top and middle with a couple of pieces of 2x12 - think of it as something like this |=|. Each beam will be set in it's own (4' 5" deep) concreted hole so I'm hoping that will provide more than enough strength/rigidity.
Paul, I like the idea of two 2x12 in series. That will work well. However - do not bolt them together in rectangular fashion ( I=I as you say). Rather, take advantage of how triangles enable much much stiffer connections. Google search "triangles for stiffness" and you'll get explanations. So, I recommend tying your 2x12s together like IXI, ok?
@@BILLYSHED This might be a silly question, but wouldn't that require cutting one of the boards in half? Potentially adding a new weak point of failure where the split board buckles apart from the other board. This could cause the entire post to torque, very quickly resulting in a smaller diameter "tree" within the cable. I guess as a cloud platform engineer I'm used to searching for worst case scenarios, but I am intrigued at how this structure would actually be built. I built a 40 foot zip line at my old house using 2x10x12's after watching this video and it came out fantastic! I am so happy that I found you here! I am about to build a 95' zip line this weekend, so I am really glad that your calculations come pretty close to mine, although I humbly ask you to take a gander at arwrester141's question above about one side being 12' high. I am building the posts to take off of the balcony of this: paulsplayhouses.com/collections/playground-plans/products/pauls-clubhouse-play-set-plan
Thanks for posting this Ryan. I was going through the calculations myself, and I used a 200 lbs rider (if I'm going to build it, I want to be able to use it myself too :) and I found that for two 2 x 12 planks, the shear stress was 1305 psi engineersedge.com/beam_bending/calculators_protected/beam_deflection_9.htm. The shear strength for pines is between 885-1500 psi www.engineeringtoolbox.com/timber-mechanical-properties-d_1789.html, so I wasn't comfortable with that. I found a lumber yard that sells locus logs (don't have to pay for having it finished :) If it works well, I'll post again. I see that you had a good 4 year run with your design - that's cool.
Luke Bissell Thanks for the comment and in the name of science, you should post your results regardless!! I’m sure it will be fine. I’m also a 200 lb rider. I think the compressive stress on the front side of the beam started to approach published limits with a 200 lb rider, but there was still some safety factor. I find it hard to believe that shear would be anywhere close... maybe I’ll run the calculations for myself. Anyway, I’d love to see your system when you get it online. Godspeed
I have a customer who wants me to install a zip line inside their house from second floor to first floor I don’t think it’s possible any suggestions on how to do it so nobody get hurt
This sounds like a fun idea at first (assuming your client has a huge space?) but if you sit down and sketch some rough dimensions of the line and anchor points, and the rider hanging off the trolley, and if you think about how zip lines work, you will quickly reveal to yourself that, at best it's a bad idea and at worst it's pretty much impossible. Sounds like maybe you already have reached that conclusion. All zip lines have a downhill part (at the beginning), and an uphill part (near the end). This is how you slow down. If you don't have an uphill part, then you need a substantial braking mechanism. Is your client's house like a normal family residence, or more like an industrial warehouse?
@@BILLYSHED just a normal residential house hallway 3.5 ft at top 4 ft at bottom. I have built a lot of crazy projects but I think this out of any realm
Using telephone poles. 5% decline in terrain with 100’ run. Thought larger pole should go at top. Does it matter? 10” diameter pole vs 12” diameter. Concrete will be poured 4’ deep holes 3’ W x 6’ L
Ahem... size matters, of course ! But not like I think you are implying. The pole at the top of your run isn't going to experience much more cantilever load than that at the bottom just because it's at the topside of the run. If either the top or the bottom pole needs to stick-up higher out of the ground, use the larger diameter pole for that end. Good luck, and I'd love to see pics / vids...
As I watch your calculations (with gratitude and fascination, trying to relearn the math!) I realize that if the downward deflection is between 3 and 4 feet (37.5" to 48") our IBC tank anchored zipline system isn't going to be all that successful given that an IBC tank is only 3 feet tall and we would be putting the cable sling somewhere lower than that... Hmmm. A failure? Or can we increase the tension (since nobody will be riding on it but it will be used for transporting cacao pod baskets). Any ideas?
The short answer (specific to a 90-foot zipline with 3/16" diameter cable) is "Nah, not so much". The preload force needed to pull the sag to a reasonably small amount is significantly less than the load once a rider jumps on. If you have the preload pulled so tight that it significantly loads the endpoints, your rider is probably going to plow hard into the end of the ride. Consider that ziplines are designed around stiffness / deflection. Anyway, longer runs with heavier cables... yeah you will probably start to need worrying about the cable weight (or the preload force).
Thanks for the kind words. But sorry - no checklist or links. I'm not sponsored and there's anything special about the kit I used. None of it is hard to find...
Regarding alternative materials: Nope. 2 x 12's were readily available and cheap. But if you can find a source of metal poles, then you can still use my cantilevered-beam calculations, you would just need to change your modulus of elasticity (E) to either 70 GPa (aluminum) or 210 GPa (steel), and you would need to re-figure your cross-sectional moment of inertia (I) based on an annular cross section rather than a solid rectangle. Regarding guy wires: That's a great option if you are willing to deal with more anchor points and a larger footprint, including wires that are a trip hazard. Wifey nixed guy wires so I went cantilever.
Hi Ryan, I am an engineer myself but haven't dabbled in structural work since my University days so have just been refreshing myself to help with design of a post to fix a zipline and/or slackline to and stumbled across your video. The product manual I have for the slackline recommends designing the post to handle a load of 11.5kN (appears to be the rated capacity of the line). Just wondering if you gave any consideration to the force on the post generated from setting the zipline to the required tension for use, prior to loading from users. This is probably more applicable to the slackline installation which comes with a ratcheting strap and needs to be set quite taught for use. Thanks
Hey Evan thanks for your comment. Yes I gave thought to the force needed to set the line. Just like the website I for calculating cable stretch (which I showed in the video) there are online tools for calculating sag. If I remember, I calculated that it was a little over 500N (110lbf) to get the line sagging less than 100mm (4") over the 27m (90') run -- not much force. The instructions with my zipline kit advised to use a "trial and error" approach for setting the tension. In practice, the kids were the ones that said "more/less", and I found that even relatively small changes made a huge difference in the ride. Every installation is different and different kids have different appetites for speed. I wayyyy overthought the whole thing because it was fun for me, but you really can just follow the manufacturer's instructions and you'll be fine.
Thanks for the response. I will check out the online tools and see what force would be required to minimize cable sag for the slackline to say 1inch and see how this compares to the manufactures recommendation of 11.5kN which i think is a bit excessive. Cheers
Hi Ryan, I stand corrected. The manufacturer's recomendation for the slackline does cross check! I assummed a sag of approx. 0.25m over the 10m span and adopted a tension force of 11.5kN. This equated to a load at mid span of approx. 120kg the rated max weight of the system. Thanks for the discussion.
Thanks for the engineering. It is refreshing to see this applied rather than people blindly hooking stuff up and saying "good enough". The only calculation question I had is if the mass of the cable needed to be factored as part of the weight? I have a decent 40cm yellow birch tree at the top, and nothing at the bottom 70m away and 12m lower. I was wondering if you had considered running an additional cable down at about a 45-60 degree angle to a ground anchor in order to minimize load on the post/tree? From an engineering standpoint, this seems like it may be better with significantly higher loads from the longer run.
Hey Michael, in my case (a 27 meter long run) the cable only weighed a few pounds so it's negligible. For longer runs where the cable weighs as much or more than a rider, well yeah, the cable weight itself becomes important or even dominant. As far as a guy cable - yeah I did consider it but I preferred to avoid the extra "junk" around the installation. I didn't want dogs or kids to get snagged up and possibly injured if they were running around and not paying attention. BUT a guy cable definitely would have reduced the requirements for my main anchor posts if I had chosen to use them.
@@BILLYSHED Would having a small frame diagonal down from the post to ground in front helps much, if at all? Say post is 8' tall, adds a diagonal lumber from 4' height of post to 4' ground in front (which also has concrete in ground). Thanks
Hi Ryan, I really appreciate your video. I have one question. You solved for tension this way 2*T*sin(theta) = 100 lbs (mass?). My question is this. Isn't tension a force? Shouldn't the equation be be 2*T*sin(theta) = 32.17405 ft/s^2 *100 lbs and then solve for T? If I'm right the horizontal load on the post is 1433.1795 lbf. I'm not trying to be a smarty pants, I'm just trying to make sure I understand. Thanks for the video its well done.
Hi John. Thanks for appreciating the video. I see *three* question marks in your comment and you seem to be asking in earnest so here goes: 1) 100 lbs is not a mass, it is a force. Around the three minute mark in my video, I perform a simple *static force balance* to approximate line tension. Compared to free-fall acceleration like jumping out of an airplane or being launched out of a cannon (in both cases where the object is in free-fall towards the center of the earth at 32.2 ft/s^2), a zipline ride is pretty well approximated with a static vertical analysis. The downward force (rider weight) is balanced by the vertical component of the tension in the line. Force equals force. Not Force = mass* acceleration. Quick google search on "static force balance" finds this page for a quick lesson: www.physicsclassroom.com/class/vectors/Lesson-3/Equilibrium-and-Statics 2) Yes, tension is a force. 3) No, the equation should not be as you have it written. No need to bring Mr. Newton into this analysis. See answer (1.) above... Cheers.
This video was really insightful, thank you for posting it and especially breaking down the math. This may be a dumb question, but would the same calculations work if the numbers were different values? For example, if I wanted one that was longer and higher, I could use my numbers in place of the ones you plugged in and still get an accurate amount of slack and tension?
Yes - the formulas apply to different dimensions, etc. For instance, if you wanted to increase the height (L) of your towers from 8' to 10', that 25% increase would double your deflection (delta is proportional to L^3). So, to keep deflection the same you would need four 2x12's at each end (ouch), or would need to substitute the wood with a stiffer (E) material, say, steel. Or you could figure some way to laminate a beam with more section stiffness (I
Hi. You assumed at 1:40 that the rider is gonna drop 4ft over a 90ft run. Why did you assume 4ft? Is that from the sloap of your yard that is 4ft and bems at 8' tall?
I assumed four feet in order to roughly estimate the tension in the line. And, 4 feet is a decent estimate just considering how my zip line worked. If I assumed 3 or 5 feet, the rest of the math wouldn't change much. The slope of my yard over 90 feet was about 6 feet.
Amazing video! Thanks for the calculations! I was planning on using the clubhouse I was building until I determine how much lateral force would be acting on my wall. One point of clarification on your calculations. 2x12 is nominally 1.5 x 11.25, not 11.5. It jumps down between 2x8 and 2x10's 1.5 x 7.5 and 1.5 x 9.25. Weird, huh? Do you think it would be possibly to anchor the wall back to a tree, if the wall were in the same line as the zip line on the other side of the wall?
William Jackson Indeed it is weird, the dimensions. We are getting ripped off! Somebody should talk to somebody about this. Regarding your question about putting a clubhouse in the middle of your load path, I don’t know. It might work just fine - you probably will end up with more deflection compared to a standard installation. You will know pretty quickly if it is going to work, or if it is going to rip itself apart over time. Good luck and shoot some video and share! Honestly, one of the biggest lessons I learned at the end of my zip line project is that it is a pretty forgiving system. You really don’t need to overthink it.
Thanks for the video, really enjoyed it. I'm attempting to put a zip line in my garden for my kids to play with and plan to use 12x2 timber laminated together like you did. Was the 4ft depth of the end points based on a calculation? Im digging by hand in hard stony soil and am wondering if 3ft will be deep enough? What do you think?
Hey Graeme - I assume that the 4ft depth recommendation that you find all over the place is based on calculations, but not mine. Check out www.ziplinegear.com/pages/how-to-build-a-zip-line-section-one-concepts (.) I strongly advise you to just bite the bullet and abide the 4ft recommendation. I also HIGHLY recommend that you either use a power auger or better yet make a few phone calls and find someone who offers auger service. The dude who dug my 18-inch diameter, 4-foot deep holes charged me $50... for two holes!! Best $50 I ever spent. Philosophically I believe that if you don't know what you're doing, your best results are to trust the people who do. That's why I did 4-foot holes.
I am doing the same. Rocky ground. I'm down 36" inchs and it's getting very difficult to remove the dirt. I'm using 2 3x12 instead as I want a go on it😂
Hello Ryan, I am going to build the same set up in my back yard for a 75' run. I have no slope and was hoping to have the ending height at 8' and starting point at 12' to 11'6" depending on the speed. Using 16' post on high side and 12' on low side. I ran through all the calculations with similar assumptions for a 8' at the end and 12' height at the start. Drop of 4' and the same stats for the wood. I used a 160lb as the rider for me, kids only 50 - 80lbs. T = 754lbs of force, degrees are 6.1. I calculated deflection at 1.35" for the 12' and .4" for the 8' side with 2.3" of cable stretch. Total deflection of 1.75", I am not sure how to feel about this, and if this is too much for the posts. . Solving for B^2 I got 42.74". This seems like the it within parameters, would you recommend a guy anchor on either side for additional support? I was thinking about adding one to at least the 12' side, do you think it is needed? I can always add after if i get more deflection than I calculated. Would you be satisfied with these result doing the same set up you did, but just a higher starting point? With 3 2x12's on the high side I get Total deflection of .9" + .4" = 1.3", would you think the post can sustain this amount? Thanks for the formulas and example to help calculate. .
Hi, thanks so for much for the video, currently helping someone build one. Three quick questions: 1. How much elevational difference is needed (or ideal?) between the two 'trees'? 2. Depending on your answer to #1, if someone is on flatter ground might they need to allow for less sag so that momentum is not lost? 3. Lastly, for the dimensional lumber, do the proportions matter at all or strictly the cross-sectional area? Is a 6x6 post as good as a 2x12 for this? I am working with one natural tree at the high end & one man-made 'tree' at the low end. So if the connection point on the actual tree is at 3.4m I am trying to figure out what height is ideal for the low end with about 600mm of actual elevational difference in the ground. Thanks!
1. Depends depends depends… on the length of the run, on how stiff your endpoints are, on how much fun you wanna have, do you have a brake, etc. 2. Yes. 3. Cross sectional proportions matter big time. It’s not cross sectional area. That Doesn’t mean anything. Re-Watch my video. The “h” matters way more than the “b”
Hey Scott- yes the bottom end was 4 feet lower than the top end, in a global sense because the yard sloped 4 feet over the run. But At each end, the cable was attached to each anchor approx 8 feet high off the local patch of ground.
I noticed that the beam bend equation you used assumes the load on the beam is at a 90 degree angle. I suppose that not completely accurate since the cable tension would NOT be exerting force on the beam at a 90degree angle. But I suppose assuming the force is exerted at 90degrees would be the worse case scenario. Is that what you were thinking?
The questions you are asking are great! The fact that you are asking them means that you are thinking along the right lines. And I believe you will find many answers yourself. But I'll answer your question... My thinking was along the lines of getting an approximation, not doing a "worst-case". All force vectors can be analytically decomposed into combinations of other vectors. Google the topic "decomposing force vectors" to get a better explanation, then get a piece of scratch paper and a calculator play with decomposition a little and you'll see what I mean. In your reference frame, the sine of 85 degrees is within one percent of the sine of 90 degrees. So: close enough!!
Is this missing in your calculations? -- cable weight -- shouldn't the weight of steel cable itself be added to load mg? my cable weighs as much as my 100 lb son so would that not double the tension required to hold son AND cable? Thanks, (currently building 450 footer)
Yeah - for longer runs like yours the weight of the cable itself (without a rider) will become significant. In my case I neglected such effects because the cable was pretty light over my 90-foot run.
I have a slackline that has multiple hanging obstacles from it. It requires a 12" tree which I do not have. Could I use these same size posts to connect it? It states it needs to hold 2500 lbs.
Steel beams would work, sure. Size them with appropriate section stiffness (EI in my calculations) and make sure you include some kind of gentle attachment mechanism so you don’t crimp the steel cable on the steel beams.
Yeah - the compressive stress on the bottom/inside of the anchors is pretty high - almost as high as the compressive strength values for lumber that I can find on the web.
I feel like the 12 foot long boards were minimum. I would not recommend your 10 foot boards. What a shame it would be to go through all the trouble of installing and then wish you had a few more feet. Don’t do it. Get the 12-foot long boards.
I showed the rebar in my other video... verrrry briefly around the 3:30 mark. Looking back at it, i maybe didn't do a great job. Anyway, I bent the rebars in a "horseshoe" shape like you see. The horseshoes were located near the top of the hole (maybe 2 inches below the surface) on the insides of the run. Looking down from a birds eye view, the left and right rebars were in a "D" and "C" orientation... if that makes sense.
Naw, at least not the way I used it. I just used the cheap quick set stuff from Lowe’s and it never had a problem. Zero cracking over four years of service.
Hey Ryan thank you for the video, my brother in law did exactly what you suggested, I just don't like the look of 2 2x12's coming out of ground, I was thinking 2 4x6's bolted together. Please tell me your thoughts
Ok, you asked for my thoughts: So, you “Don’t like the look…” ? Awww. Too bad. Also, don’t waste your time with 4x6’s. Do the math for yourself (I gave you all the equations) and you’ll see that 4x6s aren’t even close to being sufficiently stiff (unless you bolt them short side together, essentially making a 4x12- then you’re right back at my original suggestion) but apparently you don’t like that look?
Hi Ryan. Did you do any calculation on the depth that you buried the post and diameter of the hole? I found an equation, "Eq. (7)", in the following article, which results in about 19,000 N to push over your post. Compared to the 2,500 N generated by the 100 lb child, this seems really safe. Maybe, a smaller hole would work. A 12 inch diameter hole results in 8,500 N to push over. I am considering using a steel pole and smaller hole. Article: digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1206&context=usarmyresearch Google sheet with my calculation: docs.google.com/spreadsheets/d/1xNHCyY33ueuB8tualJnHPk1vvi34AXowaCzkakxISpo/edit?usp=sharing
Luke, awesome, thanks for sharing the article, interesting adjacent study done by our friends at the Army... No - I didn't calculate anything about the holes, their depth, etc. The way that I arrived at the set of choices and constraints that defined my system, I knew they were going to be absolute beasts that I didn't need to worry about. And I had the luxury of a big yard so who cares if there's a ton (literally) of buried concrete out there. So many ways to skin this cat, I just shared my way. You should carry forward with your system design, experimentally validate, shoot it on video and share on youtube!
@@BILLYSHED The concrete quantity is the most intimidating element for me, but I am not sure I get to a ton. I calculate a net hole volume of 6 ft^3/hole or 12 ft^3 for two holes, i.e., 2 [ ( pi * 48 * 9^2) - (3 * 11.5 * 48)] / (12 * 12 * 12). This equals 20 bags of 80 lbs concrete at 0.6 ft^3 per bag (1,600 lbs plus a little water weight for about 1,800 lbs). Reducing the hole diameter from 18 inches to 12 inches drops this to about 7 bags of 80 lbs concrete. I will let you know if I move forward.
@@lukecampbell8598 Your concrete quantities sound about right. Don't be intimidated. It's cheap and it's hard to screw up (too badly). Definitely a little bit of sweat involved but just jump in. *Don't over-think it!*
Hi Luke what kind of metal post were you going to use? I was considering a metal post or a using a utility pole. I was also going to add a guy wire to both ends either way. Ryan awesome video. I’m not engineer but I appreciate the time you put into showing your work. It’s been very helpful to help plan my zip line.
@@lukecampbell8598 , I'd like to see your calculations for the effective stiffness comparison of steel pipe versus lumber. I suspect you made an error in your calculations. I have requested access to your google spreadsheet so I can find it. When I compare EI to EI, a 1.25-inch OD steel pipe (with 1/8 inch wall thickness) is about 250 times less stiff than a pair of wood 2x12's. In fact, to get a steel pipe close to a pair of wood 2x12s, I calculate that you have to get to outer diameter near 6 inches, with a 1/4 inch wall thickness.
you and I are similar weight. I rode my zipline many times, just had to tuck my legs up so that my feet didn't touch the ground near the midpoint. If your ground level has a dip in the middle, then you're fine.
Marvelous!!! On behalf of me and all our students trying to apply ziplines without trees to impoverished communities in the highlands of Columbia we thank you!
Thank you Ryan that was an outstanding explanation I was planning a similar installation. I was considering 6 5/8 “ galvanized pipe. So glad I saw this post since the cost of building materials are through the roof!
You are a legend, thank you so much Ryan! (repeat on blackboard 100 times)
I have a 500ft zipline in my backyard and we just used a string as a rough estimate of the height we needed. For some 250lb riders, they will bottom out in one spot, so we use a shorter leash for them to fix that issue and with really small kids we use two leashes so they can reach the platform at the end.
500 feet! Awesome. Yeah, the big takeaway from my zipline experience is don't overthink it (if you have decent anchor points).
This was Awesome, thank you for this excellent Video, I have a handyman side gig and need to build a Zipline for a customer. I actually have a mechanical engineering degree as well so was able to follow along with your formulas.
I'm am trying to model our proposed solution using Blender 3D physics simulations and animations -- great to see you using Sketchup!
Thank you for this video! Thanks for sharing your knowledge! Very helpful!
When I'm just interested on how to build a zipline post by myself but I ended up learning physics and all. Win:win situation
I’ve build 1000 feet long zip line with 5/8 cable. Is diameter sufficient? Thank you !
Man, that is an expensive cable but it seems like a reasonable diameter for that length. Your anchor points are going to need to exert 3 or 4 tons of force, those are going to be expensive anchors also. Good luck, and I look forward to seeing the video!
@@BILLYSHED it’s on my channel already! But video in Russian language)
I just wanna make sure the diameter is safe.
@@misty_mountain Awesome zip line! That was a lot of work. Do you plan to sell rides on your zip line someday?
@@BILLYSHED no, just for fun.
Thank you Ryan, you answered all doubts..Dan
Did you check the margin of strength on the cable (and connections)? At what rider weight does the cable start to yield? If it yields, is it still usable afterwards if you tighten it? Do you know if cable work-harden?
I am considering a zipline for my grandkids, and appreciate your engineering. I am a retired aerospace engineer, and make similar videos on various projects. The more math, the fewer the views, unfortunately.
Naw - I didn't calculate anything with the cable. It came as part of a kit and the manufacturer's instructions said it was rated for a 300-lb rider (I think?). I am 200 lbs, and it didn't yield under the stretch loads caused by my weight. I imagine there's a good chance that the cable supplier already work-hardens the cable, because I calculate that a 200-lb rider ride puts it well beyond 0.2% strain. Or maybe the first couple of rides stretch-harden it like you are asking. It's not an issue, don't worry about it. Look up what other people suggest. Good luck.
Fair enough Ryan. I was rounding up from 7.5" to 8". I know the website I showed you recommends 12" and 8"...I am just trying to figure out if the 12" for the main pole is overkill, but I understand that your patience is exhausted.
Chris, the ziplinegear guidance presents your options as "either-or". Re-read it again carefully. Option 1 is to install a standalone post with a 12" diameter minimum. You are not choosing that installation type. So forget it. Pretend that you never saw the number 12. Option 2 is a double-post guy-wire system where *the main post and the support post are each are 8" diameter minimum.* If you are doing guy-wire, then yes - 12" would be overkill. *BUT FINALLY -* don't do any rounding up. I want you to say the following words in quotes out loud ten times: "7.28 is less than 8. 7.5 is less than 8. I will not skimp on the number 8 because I am committed to following the guidance of both ziplinegear.com and the guidance of Ryan, who fully endorses that same guidance and he told me now four times to follow the guidance and don't skimp." Fill up a chalkboard like bart simpson.
Very useful video - thanks Ryan. Like Luke below I also based my calculations on a 200lb rider over a 120' distance and the deflection was coming out at over 2", which is higher than I'd like. I don't have the space to use a guy anchor so I figured I would use two 2x12 beams in series in line with the run, with 12" to 18" between them and bolt the beams together at the top and middle with a couple of pieces of 2x12 - think of it as something like this |=|. Each beam will be set in it's own (4' 5" deep) concreted hole so I'm hoping that will provide more than enough strength/rigidity.
Paul, I like the idea of two 2x12 in series. That will work well. However - do not bolt them together in rectangular fashion ( I=I as you say). Rather, take advantage of how triangles enable much much stiffer connections. Google search "triangles for stiffness" and you'll get explanations. So, I recommend tying your 2x12s together like IXI, ok?
Of course - I should have thought of that! Thanks again.
@@BILLYSHED This might be a silly question, but wouldn't that require cutting one of the boards in half? Potentially adding a new weak point of failure where the split board buckles apart from the other board. This could cause the entire post to torque, very quickly resulting in a smaller diameter "tree" within the cable.
I guess as a cloud platform engineer I'm used to searching for worst case scenarios, but I am intrigued at how this structure would actually be built.
I built a 40 foot zip line at my old house using 2x10x12's after watching this video and it came out fantastic! I am so happy that I found you here!
I am about to build a 95' zip line this weekend, so I am really glad that your calculations come pretty close to mine, although I humbly ask you to take a gander at arwrester141's question above about one side being 12' high. I am building the posts to take off of the balcony of this: paulsplayhouses.com/collections/playground-plans/products/pauls-clubhouse-play-set-plan
Thank you. Very thorough. Building mine soon!
Thanks for posting this Ryan. I was going through the calculations myself, and I used a 200 lbs rider (if I'm going to build it, I want to be able to use it myself too :) and I found that for two 2 x 12 planks, the shear stress was 1305 psi engineersedge.com/beam_bending/calculators_protected/beam_deflection_9.htm. The shear strength for pines is between 885-1500 psi www.engineeringtoolbox.com/timber-mechanical-properties-d_1789.html, so I wasn't comfortable with that. I found a lumber yard that sells locus logs (don't have to pay for having it finished :) If it works well, I'll post again. I see that you had a good 4 year run with your design - that's cool.
Luke Bissell Thanks for the comment and in the name of science, you should post your results regardless!! I’m sure it will be fine. I’m also a 200 lb rider. I think the compressive stress on the front side of the beam started to approach published limits with a 200 lb rider, but there was still some safety factor. I find it hard to believe that shear would be anywhere close... maybe I’ll run the calculations for myself. Anyway, I’d love to see your system when you get it online. Godspeed
I have a customer who wants me to install a zip line inside their house from second floor to first floor I don’t think it’s possible any suggestions on how to do it so nobody get hurt
This sounds like a fun idea at first (assuming your client has a huge space?) but if you sit down and sketch some rough dimensions of the line and anchor points, and the rider hanging off the trolley, and if you think about how zip lines work, you will quickly reveal to yourself that, at best it's a bad idea and at worst it's pretty much impossible. Sounds like maybe you already have reached that conclusion. All zip lines have a downhill part (at the beginning), and an uphill part (near the end). This is how you slow down. If you don't have an uphill part, then you need a substantial braking mechanism. Is your client's house like a normal family residence, or more like an industrial warehouse?
@@BILLYSHED just a normal residential house hallway 3.5 ft at top 4 ft at bottom. I have built a lot of crazy projects but I think this out of any realm
@@drumnmachn19 It's not in anyone's realm. It's a busted idea.
Using telephone poles. 5% decline in terrain with 100’ run. Thought larger pole should go at top. Does it matter? 10” diameter pole vs 12” diameter. Concrete will be poured 4’ deep holes 3’ W x 6’ L
Ahem... size matters, of course ! But not like I think you are implying. The pole at the top of your run isn't going to experience much more cantilever load than that at the bottom just because it's at the topside of the run. If either the top or the bottom pole needs to stick-up higher out of the ground, use the larger diameter pole for that end. Good luck, and I'd love to see pics / vids...
As I watch your calculations (with gratitude and fascination, trying to relearn the math!) I realize that if the downward deflection is between 3 and 4 feet (37.5" to 48") our IBC tank anchored zipline system isn't going to be all that successful given that an IBC tank is only 3 feet tall and we would be putting the cable sling somewhere lower than that... Hmmm. A failure? Or can we increase the tension (since nobody will be riding on it but it will be used for transporting cacao pod baskets). Any ideas?
Sorry friend - no ideas. I am sure you will figure it out. "Necessity is the mother of invention" - someone famous
do you need to consider the weight of the cable in the force applied to the end points? 100ft of decent cable is pretty heavy.
The short answer (specific to a 90-foot zipline with 3/16" diameter cable) is "Nah, not so much". The preload force needed to pull the sag to a reasonably small amount is significantly less than the load once a rider jumps on. If you have the preload pulled so tight that it significantly loads the endpoints, your rider is probably going to plow hard into the end of the ride. Consider that ziplines are designed around stiffness / deflection. Anyway, longer runs with heavier cables... yeah you will probably start to need worrying about the cable weight (or the preload force).
The joy of math and the comfort of science! - excellent explanation. Do you have a checklist of items &links to purchase.
Thanks for the kind words. But sorry - no checklist or links. I'm not sponsored and there's anything special about the kit I used. None of it is hard to find...
Great explanation! Did you look at using alternate materials such as steel or aluminum posts with or without guy wires?
Regarding alternative materials: Nope. 2 x 12's were readily available and cheap. But if you can find a source of metal poles, then you can still use my cantilevered-beam calculations, you would just need to change your modulus of elasticity (E) to either 70 GPa (aluminum) or 210 GPa (steel), and you would need to re-figure your cross-sectional moment of inertia (I) based on an annular cross section rather than a solid rectangle. Regarding guy wires: That's a great option if you are willing to deal with more anchor points and a larger footprint, including wires that are a trip hazard. Wifey nixed guy wires so I went cantilever.
@@BILLYSHED Not set in stone yet, looking at 6" square alum column, if not then wood. Got it, thanks
Hi Ryan, I am an engineer myself but haven't dabbled in structural work since my University days so have just been refreshing myself to help with design of a post to fix a zipline and/or slackline to and stumbled across your video. The product manual I have for the slackline recommends designing the post to handle a load of 11.5kN (appears to be the rated capacity of the line). Just wondering if you gave any consideration to the force on the post generated from setting the zipline to the required tension for use, prior to loading from users. This is probably more applicable to the slackline installation which comes with a ratcheting strap and needs to be set quite taught for use. Thanks
Hey Evan thanks for your comment. Yes I gave thought to the force needed to set the line. Just like the website I for calculating cable stretch (which I showed in the video) there are online tools for calculating sag. If I remember, I calculated that it was a little over 500N (110lbf) to get the line sagging less than 100mm (4") over the 27m (90') run -- not much force. The instructions with my zipline kit advised to use a "trial and error" approach for setting the tension. In practice, the kids were the ones that said "more/less", and I found that even relatively small changes made a huge difference in the ride. Every installation is different and different kids have different appetites for speed. I wayyyy overthought the whole thing because it was fun for me, but you really can just follow the manufacturer's instructions and you'll be fine.
Thanks for the response. I will check out the online tools and see what force would be required to minimize cable sag for the slackline to say 1inch and see how this compares to the manufactures recommendation of 11.5kN which i think is a bit excessive. Cheers
Hi Ryan, I stand corrected. The manufacturer's recomendation for the slackline does cross check! I assummed a sag of approx. 0.25m over the 10m span and adopted a tension force of 11.5kN. This equated to a load at mid span of approx. 120kg the rated max weight of the system. Thanks for the discussion.
Evan Johnson -- Excellent!
Thanks for the engineering. It is refreshing to see this applied rather than people blindly hooking stuff up and saying "good enough". The only calculation question I had is if the mass of the cable needed to be factored as part of the weight?
I have a decent 40cm yellow birch tree at the top, and nothing at the bottom 70m away and 12m lower.
I was wondering if you had considered running an additional cable down at about a 45-60 degree angle to a ground anchor in order to minimize load on the post/tree? From an engineering standpoint, this seems like it may be better with significantly higher loads from the longer run.
Hey Michael, in my case (a 27 meter long run) the cable only weighed a few pounds so it's negligible. For longer runs where the cable weighs as much or more than a rider, well yeah, the cable weight itself becomes important or even dominant.
As far as a guy cable - yeah I did consider it but I preferred to avoid the extra "junk" around the installation. I didn't want dogs or kids to get snagged up and possibly injured if they were running around and not paying attention. BUT a guy cable definitely would have reduced the requirements for my main anchor posts if I had chosen to use them.
@@BILLYSHED Would having a small frame diagonal down from the post to ground in front helps much, if at all? Say post is 8' tall, adds a diagonal lumber from 4' height of post to 4' ground in front (which also has concrete in ground). Thanks
@@6ahyw yep that would help to reduce deflections a lot.
Hi Ryan, I really appreciate your video. I have one question. You solved for tension this way 2*T*sin(theta) = 100 lbs (mass?). My question is this. Isn't tension a force? Shouldn't the equation be be 2*T*sin(theta) = 32.17405 ft/s^2 *100 lbs and then solve for T? If I'm right the horizontal load on the post is 1433.1795 lbf. I'm not trying to be a smarty pants, I'm just trying to make sure I understand. Thanks for the video its well done.
Hi John. Thanks for appreciating the video. I see *three* question marks in your comment and you seem to be asking in earnest so here goes:
1) 100 lbs is not a mass, it is a force. Around the three minute mark in my video, I perform a simple *static force balance* to approximate line tension. Compared to free-fall acceleration like jumping out of an airplane or being launched out of a cannon (in both cases where the object is in free-fall towards the center of the earth at 32.2 ft/s^2), a zipline ride is pretty well approximated with a static vertical analysis. The downward force (rider weight) is balanced by the vertical component of the tension in the line. Force equals force. Not Force = mass* acceleration. Quick google search on "static force balance" finds this page for a quick lesson:
www.physicsclassroom.com/class/vectors/Lesson-3/Equilibrium-and-Statics
2) Yes, tension is a force.
3) No, the equation should not be as you have it written. No need to bring Mr. Newton into this analysis. See answer (1.) above...
Cheers.
@@BILLYSHED Haha, sorry for all the question marks. Thanks for your reply.
This video was really insightful, thank you for posting it and especially breaking down the math. This may be a dumb question, but would the same calculations work if the numbers were different values? For example, if I wanted one that was longer and higher, I could use my numbers in place of the ones you plugged in and still get an accurate amount of slack and tension?
Yes - the formulas apply to different dimensions, etc. For instance, if you wanted to increase the height (L) of your towers from 8' to 10', that 25% increase would double your deflection (delta is proportional to L^3). So, to keep deflection the same you would need four 2x12's at each end (ouch), or would need to substitute the wood with a stiffer (E) material, say, steel. Or you could figure some way to laminate a beam with more section stiffness (I
Hi. You assumed at 1:40 that the rider is gonna drop 4ft over a 90ft run. Why did you assume 4ft? Is that from the sloap of your yard that is 4ft and bems at 8' tall?
I assumed four feet in order to roughly estimate the tension in the line. And, 4 feet is a decent estimate just considering how my zip line worked. If I assumed 3 or 5 feet, the rest of the math wouldn't change much. The slope of my yard over 90 feet was about 6 feet.
You just made my head explode.🤯
I feel like my brain is scrambled eggs rn. 🫣😵💫
Amazing video! Thanks for the calculations! I was planning on using the clubhouse I was building until I determine how much lateral force would be acting on my wall. One point of clarification on your calculations. 2x12 is nominally 1.5 x 11.25, not 11.5. It jumps down between 2x8 and 2x10's 1.5 x 7.5 and 1.5 x 9.25. Weird, huh? Do you think it would be possibly to anchor the wall back to a tree, if the wall were in the same line as the zip line on the other side of the wall?
William Jackson Indeed it is weird, the dimensions. We are getting ripped off! Somebody should talk to somebody about this. Regarding your question about putting a clubhouse in the middle of your load path, I don’t know. It might work just fine - you probably will end up with more deflection compared to a standard installation. You will know pretty quickly if it is going to work, or if it is going to rip itself apart over time. Good luck and shoot some video and share! Honestly, one of the biggest lessons I learned at the end of my zip line project is that it is a pretty forgiving system. You really don’t need to overthink it.
Thanks for the video, really enjoyed it. I'm attempting to put a zip line in my garden for my kids to play with and plan to use 12x2 timber laminated together like you did. Was the 4ft depth of the end points based on a calculation? Im digging by hand in hard stony soil and am wondering if 3ft will be deep enough? What do you think?
Hey Graeme - I assume that the 4ft depth recommendation that you find all over the place is based on calculations, but not mine. Check out www.ziplinegear.com/pages/how-to-build-a-zip-line-section-one-concepts (.) I strongly advise you to just bite the bullet and abide the 4ft recommendation. I also HIGHLY recommend that you either use a power auger or better yet make a few phone calls and find someone who offers auger service. The dude who dug my 18-inch diameter, 4-foot deep holes charged me $50... for two holes!! Best $50 I ever spent. Philosophically I believe that if you don't know what you're doing, your best results are to trust the people who do. That's why I did 4-foot holes.
I am doing the same. Rocky ground. I'm down 36" inchs and it's getting very difficult to remove the dirt. I'm using 2 3x12 instead as I want a go on it😂
Hello Ryan, I am going to build the same set up in my back yard for a 75' run. I have no slope and was hoping to have the ending height at 8' and starting point at 12' to 11'6" depending on the speed. Using 16' post on high side and 12' on low side. I ran through all the calculations with similar assumptions for a 8' at the end and 12' height at the start. Drop of 4' and the same stats for the wood. I used a 160lb as the rider for me, kids only 50 - 80lbs. T = 754lbs of force, degrees are 6.1. I calculated deflection at 1.35" for the 12' and .4" for the 8' side with 2.3" of cable stretch. Total deflection of 1.75", I am not sure how to feel about this, and if this is too much for the posts. . Solving for B^2 I got 42.74". This seems like the it within parameters, would you recommend a guy anchor on either side for additional support? I was thinking about adding one to at least the 12' side, do you think it is needed? I can always add after if i get more deflection than I calculated. Would you be satisfied with these result doing the same set up you did, but just a higher starting point? With 3 2x12's on the high side I get Total deflection of .9" + .4" = 1.3", would you think the post can sustain this amount? Thanks for the formulas and example to help calculate. .
Try this video. It's easier to understand.
ua-cam.com/video/FwAiJtqGUQs/v-deo.html&feature=emb_logo&ab_channel=ZipLineGear
excellent, thank you!
Hi, thanks so for much for the video, currently helping someone build one. Three quick questions:
1. How much elevational difference is needed (or ideal?) between the two 'trees'?
2. Depending on your answer to #1, if someone is on flatter ground might they need to allow for less sag so that momentum is not lost?
3. Lastly, for the dimensional lumber, do the proportions matter at all or strictly the cross-sectional area? Is a 6x6 post as good as a 2x12 for this?
I am working with one natural tree at the high end & one man-made 'tree' at the low end. So if the connection point on the actual tree is at 3.4m I am trying to figure out what height is ideal for the low end with about 600mm of actual elevational difference in the ground. Thanks!
1. Depends depends depends… on the length of the run, on how stiff your endpoints are, on how much fun you wanna have, do you have a brake, etc.
2. Yes.
3. Cross sectional proportions matter big time. It’s not cross sectional area. That Doesn’t mean anything. Re-Watch my video. The “h” matters way more than the “b”
The one thing that wasn't clear was that because of slop in your line your zip line was 4 feet lower at one point?
Hey Scott- yes the bottom end was 4 feet lower than the top end, in a global sense because the yard sloped 4 feet over the run. But At each end, the cable was attached to each anchor approx 8 feet high off the local patch of ground.
I noticed that the beam bend equation you used assumes the load on the beam is at a 90 degree angle. I suppose that not completely accurate since the cable tension would NOT be exerting force on the beam at a 90degree angle. But I suppose assuming the force is exerted at 90degrees would be the worse case scenario. Is that what you were thinking?
The questions you are asking are great! The fact that you are asking them means that you are thinking along the right lines. And I believe you will find many answers yourself. But I'll answer your question... My thinking was along the lines of getting an approximation, not doing a "worst-case". All force vectors can be analytically decomposed into combinations of other vectors. Google the topic "decomposing force vectors" to get a better explanation, then get a piece of scratch paper and a calculator play with decomposition a little and you'll see what I mean. In your reference frame, the sine of 85 degrees is within one percent of the sine of 90 degrees. So: close enough!!
Is this missing in your calculations? -- cable weight -- shouldn't the weight of steel cable itself be added to load mg? my cable weighs as much as my 100 lb son so would that not double the tension required to hold son AND cable? Thanks, (currently building 450 footer)
Yeah - for longer runs like yours the weight of the cable itself (without a rider) will become significant. In my case I neglected such effects because the cable was pretty light over my 90-foot run.
I have a slackline that has multiple hanging obstacles from it. It requires a 12" tree which I do not have. Could I use these same size posts to connect it? It states it needs to hold 2500 lbs.
I think it would be fine to substitute my anchoring system for a 12" tree, yes. Good luck!
Hi Ryan,
Great info and great video. Have seen many people use your guidance videos.
Would steel RSJ type beams work?
Thank you.
Steel beams would work, sure. Size them with appropriate section stiffness (EI in my calculations) and make sure you include some kind of gentle attachment mechanism so you don’t crimp the steel cable on the steel beams.
How high could I make these anchors? Would I be able to use 20' lengths for a 90' span?
Short answer, no. You can calculate it. I recommend you use guy wires. Good luck!
Really nice calcs, ¿did you check the estress on the cantilevered beam?
Yeah - the compressive stress on the bottom/inside of the anchors is pretty high - almost as high as the compressive strength values for lumber that I can find on the web.
Any reason why 2x12x10s wouldnt work. If end height needs to be 78inches, with 3ft in ground that leaves enough out, no?
I feel like the 12 foot long boards were minimum. I would not recommend your 10 foot boards. What a shame it would be to go through all the trouble of installing and then wish you had a few more feet. Don’t do it. Get the 12-foot long boards.
Ok thank you!
can you please show /tell us how the rebar was used in the base hole? thanks
I showed the rebar in my other video... verrrry briefly around the 3:30 mark. Looking back at it, i maybe didn't do a great job. Anyway, I bent the rebars in a "horseshoe" shape like you see. The horseshoes were located near the top of the hole (maybe 2 inches below the surface) on the insides of the run. Looking down from a birds eye view, the left and right rebars were in a "D" and "C" orientation... if that makes sense.
@@BILLYSHED thanks a lot,, very helpful... RD
Any particular PSI recommended for the concrete?
Naw, at least not the way I used it. I just used the cheap quick set stuff from Lowe’s and it never had a problem. Zero cracking over four years of service.
Call these guys, they know (ziplinegear.com)
Two 2x12’s are better than one 4x12?
heidi saldana I guess they are essentially the same. Just much easier most places to source 2x12s.
I think you'd experience less warping, over time, out of two 2x12s then you would from one 4x12. Especially if the boards were not center cuts.
Hey Ryan thank you for the video, my brother in law did exactly what you suggested, I just don't like the look of 2 2x12's coming out of ground, I was thinking 2 4x6's bolted together. Please tell me your thoughts
Ok, you asked for my thoughts: So, you “Don’t like the look…” ? Awww. Too bad. Also, don’t waste your time with 4x6’s. Do the math for yourself (I gave you all the equations) and you’ll see that 4x6s aren’t even close to being sufficiently stiff (unless you bolt them short side together, essentially making a 4x12- then you’re right back at my original suggestion) but apparently you don’t like that look?
@@BILLYSHED I lub you
Hi Ryan. Did you do any calculation on the depth that you buried the post and diameter of the hole? I found an equation, "Eq. (7)", in the following article, which results in about 19,000 N to push over your post. Compared to the 2,500 N generated by the 100 lb child, this seems really safe. Maybe, a smaller hole would work. A 12 inch diameter hole results in 8,500 N to push over. I am considering using a steel pole and smaller hole.
Article: digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1206&context=usarmyresearch
Google sheet with my calculation: docs.google.com/spreadsheets/d/1xNHCyY33ueuB8tualJnHPk1vvi34AXowaCzkakxISpo/edit?usp=sharing
Luke, awesome, thanks for sharing the article, interesting adjacent study done by our friends at the Army... No - I didn't calculate anything about the holes, their depth, etc. The way that I arrived at the set of choices and constraints that defined my system, I knew they were going to be absolute beasts that I didn't need to worry about. And I had the luxury of a big yard so who cares if there's a ton (literally) of buried concrete out there. So many ways to skin this cat, I just shared my way. You should carry forward with your system design, experimentally validate, shoot it on video and share on youtube!
@@BILLYSHED The concrete quantity is the most intimidating element for me, but I am not sure I get to a ton. I calculate a net hole volume of 6 ft^3/hole or 12 ft^3 for two holes, i.e., 2 [ ( pi * 48 * 9^2) - (3 * 11.5 * 48)] / (12 * 12 * 12). This equals 20 bags of 80 lbs concrete at 0.6 ft^3 per bag (1,600 lbs plus a little water weight for about 1,800 lbs). Reducing the hole diameter from 18 inches to 12 inches drops this to about 7 bags of 80 lbs concrete. I will let you know if I move forward.
@@lukecampbell8598 Your concrete quantities sound about right. Don't be intimidated. It's cheap and it's hard to screw up (too badly). Definitely a little bit of sweat involved but just jump in. *Don't over-think it!*
Hi Luke what kind of metal post were you going to use? I was considering a metal post or a using a utility pole.
I was also going to add a guy wire to both ends either way.
Ryan awesome video. I’m not engineer but I appreciate the time you put into showing your work. It’s been very helpful to help plan my zip line.
@@lukecampbell8598 , I'd like to see your calculations for the effective stiffness comparison of steel pipe versus lumber. I suspect you made an error in your calculations. I have requested access to your google spreadsheet so I can find it. When I compare EI to EI, a 1.25-inch OD steel pipe (with 1/8 inch wall thickness) is about 250 times less stiff than a pair of wood 2x12's. In fact, to get a steel pipe close to a pair of wood 2x12s, I calculate that you have to get to outer diameter near 6 inches, with a 1/4 inch wall thickness.
I'm like.. 210# (me) T= mid 1100's dang.. "..were going to need a bigger boat".
you and I are similar weight. I rode my zipline many times, just had to tuck my legs up so that my feet didn't touch the ground near the midpoint. If your ground level has a dip in the middle, then you're fine.
🤔🫨😵💫🥴
What the fuuu??