Constant-Torque Spring-Balanced Actuator
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- Опубліковано 5 лют 2025
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I've often been asked about adding springs to openDog to balance the actuators and assist with power saving. However, this would also make it harder to take steps as the feet lift off the ground. But what if we could develop a constant-torque spring-balanced actuator which didn't require more and more force the more the spring stretches?
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XROBOTS
Former toy designer, current UA-cam maker and general robotics, electrical and mechanical engineer, I’m a fan of doing it yourself and innovation by trial and error. My channel is where I share some of my useful and not-so-useful inventions, designs and maker advice. Iron Man is my go-to cosplay, and 3D printing can solve most issues - broken bolts, missing parts, world hunger, you name it.
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Hi
How do i be a member bc the jpin button is bot here ??
Lucky guys, they have money to donate.
@@tanjiro3285 Yep. On the other hand, you're not really missing it, just having it a bit later and with some commercials. Yet, Patrons and Channel members support James, and help him continue Making for him and us. (And YES, I, Patron, DO acknowledge that I'm privileged, and having the money to donate is a luxury that' I'm well aware of.)
@@thesfreader3068 hmm👍😇
"open dog works just about okay" as its dancing around in the background footage lol. Your robots may not be as advanced as boston dynamics but what you're doing by yourself is pretty incredible still!!!
i wish people would buy a Google dog and dissasemble it so we could see how the legs and body works.
It will be just as good someday!
@@Francois_Dupont There is a LOT done in motion control software. The body is just a body without a brain.
@@nrdesign1991 without the mouvement capability it woudnt work anyway. just tie a one meter rope between your two legs and try to walk. you will still trip sometimes.
and he is doing it open source! wich allows everyone interested in developing such things to go off a preatty advanced startingpoint, without spending upwards of 50k$for a boston dynamics dog(and probably getting spyed on by boston dynamics via some software, and not being allowed to change the hardware). Just by doing this he will advance the field of robotics, by allowing others to learn quicker.
I was literally just working to solve this same problem last night for a different application, and I think I know why your cams don't give as flat a response as you wanted. Spring force (ideally) varies by the linear displacement of the spring, which (I think) means that you need to set the stations on your cam profile by distance along the circumference, not by angle, and set your radius at each station based on the spring's pulling force for that displacement multiplied by the ratio of pulley radius / cam radius to get the return force you want. I used an excel spreadsheet to solve for cam radius to give a constant force ratio at stations a fixed distance apart, and when I plotted those out, it gave a ear-shaped result that closely resembles a compound bow's cam, rather than the neat nautiloid spiral of a constant or exponential cam profile.
don't forget, unless he's using a specific linear spring the force exerted per unit displacement will not increase linearly. But, you are correct about circumference. Something like a Vulcan Conforce spring would actually package excellently in this application. Hope your application works out!
@@zachbrown7272 Thanks! And yeah, I know spring force is never ideal (welcome to engineering, right?). Luckily, my application doesn't require a perfectly linear force response as long as it stays within reasonable bounds, so I'm confident it'll work out. We'll see how close I got once I get everything printed and test it out :)
Does the friction as the bungee wraps around the pulley/cam affect the system? 10:20
@@TheRainHarvester I don't think so..I feel the friction exerted is not static it's dynamic since the coefficient is relative to the motion of the cam so it declines as the spring force reduces
@@createwithbido just to clarify... i mean the sliding friction of the bungee on the cam. As the bungee wraps more, onto the cam, the sliding friction increases.
You could use vacuum to help the joints, something like a large syringe with the end closed, the amount of force would always be the same no matter the extension of the plunger, check it how the exercise machines from the space station works
Also the same way office chairs work. Good suggestion.
Or even just gas struts, which can have close to 1 K factor.
@@nophead - THIS!! Except there is the issue of added weight, size and movement restriction.
Air shocks don’t have a constant force but springs do. As the air compresses or decompresses the pressure changes making it behave differently. Springs have a constant force (at least good ones). You could try springs from bike shocks.
@@elihamaker3694 that depends on the ratio of system volume relative to the change in system volume
I should use this for my robot arm elbow (and probably for shoulder too). Great video!
hello syynnnntyafiiiiicccckk
it is good to see you here Skyentific :)
but what about the negative gravity?
İf the robot flips around then this mechanism would still work?
is it useful at all angles? I don't think so.
for your arm, maybe.
@@myetis1990 in current design it is not usable at all the angles, but it is still usable at some angles. And for many applications this is enough.
check out the limbless crossbow video on the slingshot channel as well
I can't wait to see the video!
Ive been following your work for 8 years or so now, Ive got to say, you've gotten really really good. Its astonishing how much you've progressed in both complexity of your projects as well as the speed at which you complete them. Really impressive.
@@kruleworld no kidding.
Probably pay for people better than me to do the projects
@@kruleworld I think budgetary restrictions are actually very good for projects like these. The open-source community in general is awesome in that people are finding ways for average people to make things that they wouldn't be able to ever have if the only way to get them was by purchasing them outright.
On top of that, the design process of open-source stuff favors efficiency and practicality. The big R&D facilities start with a problem and are given immense resources to build a solution. This seems to lead to designs that are impractically expensive that inevitably have to wait for costs to go down to become practical. Development like what Mr. Bruton is doing basically starts off an idea to build a thing and then works within practicality restraints until a solution is found. If Boston Dynamics was working on this project, they would've just made a more complicated motor for the knee joints because they have no incentive to make the robot less expensive. They would've probably tried to water-cool the battery or something.
@@jamesbruton lool
A few comments that spring (sic) to mind:
1) you don't want constant torque, because your legs are variable geometry levers! The torque on the motor will depend on the angle of the leg to the ground. Standing with a perfect vertical leg takes no torque, standing crouched with a bent leg takes the most torque (as humans, we "lock out" our legs/joints when we stand for long periods to achieve exactly the same effect). There fore you need to profile your torque assist system to match this characteristic. The worst case you have to avoid is at max leg bend but with no weight on the leg (fully pulled up) and you motors must be able to overcome your static assistance load at this point. This normally isn't a problem because that sort of posture is not often held for long, being used to temporarily pick up individual legs over obsticles etc
2) The power disipated whilst stationary is the holding current, multipled by the forward voltage, which is the voltage required to push that current through the phase. Because the motor is static, there is no back emf, so that fwd voltage is simply the total dc resistance of the phase (motor phase + phase cables + inverter switch resistance). Because that total voltage will be small the turn down ratio to the battery is high, so battery current, and hence battery power is pretty small, despite the high phase current. For example, with the following arbitrary numbers: 100 amps phase
60 mOhms total resistance (High fet + phase cable in + phase winding + phase cable out + low fet)
24v supply (battery)
V = IR, so clearly the foward voltage wouold be 100 * 0.06 = 6v
Turn down ratio = 24/6 which is 4, so ignoring inverter efficiency (typically 90% or more) you'd expect 100 / 4 = 25 amps being pulled from the battery.
the powers clearly balance (100 x 6 = 600 and 24 * 25 = 600)
What this neatly shows is the efficiency of a motor is dominated at zero speed by it's dc resistance, which is why we try to minimise that characteristic (the motor will have a large inductance, ie a large AC impedance in order to have a small torque ripple from a modulated supply (PWM))
3) if standing for a long period, it may make sense to provide an "Over centre" lock to the leg geometry, ie a mechanical back stop to which the motor can rotate to lock the legs vertically, meaning motor can be then turned off.
Excellent info, thanks for sharing!
You can tell James is an engineer, "I need some form of spring that will apply a constant force" proceeds to design his own using a 3D printer and random bungees, most other people "How much are constant force springs on amazon?"
That is a good idea! The way you "played" around with those cams was a wonderful display of your engineering mindset 😁
That is an ingenious solution. I love it, and the dog is walking really well. I also learned that constant force springs exist.
James, you may actually want not to have a constant force because while the weight of the robot is relatively constant for each leg, each joint will need different amounts of torque depending on how bent it is. Really great innovation though. I would imagine making the robot significantly light would also be of aid to the overheating. Keep inspiring others. Thumbs up!
Hi James, I have to say that you're a great inspiration to me. I just started to watch this series and I'm astonished by the progress you've made with this robot. Keep it up it's incredible!
I see your dishwasher is happier this week!
The walking demo is so quite! Very impressive for having a nearly silent drive system on opendog :) definitely has inspired me! Thanks, James!
You're so close to 1 million subscribers!!!
I have a 5 year old and a 3 year old and need to figure out how to guide them towards this direction! Wow what an great video, thank you.
Hey James, you can measure high currents easily with a clamp meter or hall effect sensor. Or you could fully charge your battery run your robot for 10 minutes recharge and measure the Ah you've charged in your battery and this way estimate your average current draw. BTW I love your channel 👍🏻
I remember suggesting a solution like that in a humanoid robot forum back in 2012. The problem was that the knees on those type of robots are direct driven by servos and the knees get the most torque making the servos move slow or not at all. The typical solution was a sort of crouch-walk, but I suggested a sort of spiral Bungie like the one used on the bow-flex (obviously much smaller) but being an animation major and not any type of engineering or math guy I couldn't quite explain my idea to the technical guys there and found out how unfriendly that forum could be.
I've always liked how you solve engineering issues the same way I do. Well, honestly I don't know if you really do, but you sure do explain them in my language, and I appreciate that.
Wow, this idea is ingenious! This is perfect for my active suspension RC car project. I’ve been struggling with using a spring based counter balance so the motors aren’t always drawing current. Thanks for sharing!
And a thermal camera picture could be interesting to see heat distribution after running the bot for a bit.
Perhaps one that plugs into a smartphone
I had a constant force spring mechanism design at one time. I used a rack and pinion gear setup where the pinion had an irregular profile. The pitch diameter followed an archimedian spiral. It's been years, I forget the details, but I also had a cam groove behind the teeth to hold the rack (which was on a pivot) in place meshed with the pinion. Spring on the rack, pinion shaft was the output.
To reduce the torque the motors have to exert when lifting the leg, would it make sense to attach some kind of clutch to the bungee cord that only engages when the weight of the robot rests on the leg? I was thinking: The upper arm could be made of two parts that are joined with linear glide bearing rods and a tiny bit of longitudinal play. The top end of the bungee cord would run in between the two parts and get clamped by the weight of the robot whenever it rests on the leg, but would slip through whenever it lifts the leg. The end of the cord could be connected to a much weaker bungee cord where it comes out on the other side of the "clutch". This weaker cord could be attached some distance away, e.g. close to the knee. Its purpose is to keep the thick bungee cord somewhat taught and pull it back through the "clutch" when the leg is straightened before it the foot touches the floor. I hope this makes sense!
Following
Big fan of the PCBway sponsorships, I wasn't aware that custom PCB's were so cheap.
This robot is already very impressive. DARPA would hire you in the blink of an eye.
I saw some other people mention it too. It was really cool watching you solve this problem, but constant force springs are something that exist.
For constant force spring you can also use vacuum - just plug shut one end of pneumatic actuator.
A spiral wound clock spring is what you need.
A tape measure has near constant force. Copy that sort of mechanism.
Maybe you could use the spring out of a seat belt retractor or something like that and build it into the leg joint?
God you really do absolutely pump out these!! How on earth do you design and print so many large pieces and complete all this testing within the time that you do?! Keep it up!
Mild note about the cams: when the radius of the cam gets longer, the angle of contact changes as well, because the angle between the weight side cam and height of the Bungie side cam changes
jesus how impressive are you! forever innovating and working, love watching
Cable-driven joints are the upcoming innovations in robotics. I can see you going in that direction. great !! keep up the good work.
I am planning a design project that will require constant force extension and I've never once though of using cams! Thanks for another great video!
The cam seem to function sort of like the patella in a human knee. Thanks for your video, I am trying to planning to use a spring to allow a stationary robot-arm to lift a large load even with relatively low-torque servos. Now I know it can work and probably even work better with a cam system.
It never ceases to surprise me how quiet this bot is. :) Stealth dog. :D
PS. It's not readily apparent, but I believe the dog sways less when it comes to a stop now.
This man makes me proud to be a human
About the current measurement, have you looked into hall effect current sensors? I have used ACS758ECB-200U-PFF-T for very heavy drones, and it worked really great. With two of these in parallel you could measure up to 400A using some ADC on your controller (and maybe a voltage divider).
Open dog progress is by far my favourite content of yours, cheers!
This level of power is terrifying
In case you don't know, there are constant force springs (I've typically found their use in quill feeds for drills). They're typically a fairly small, round spring meant for these kind of rotational loads. Searching "leespring constant force springs" should give good results.
Absolutely incredible! I love learning mechanical concepts and this just blew my mind. can't wait to use this on my own projects
Can't wait for the motors to come back in stock, this build will be so great with the new reductions!
My dog would be terrified by your robot XD, great video !
Now this is a robot dog I'm not scared of. Damn you, Boston Dynamics!
Great success! You could always measure the heat of the battery with a temperature gun with and without the springs and use that data to give you an idea but amazing job on the analysis and the implementation.
Dude, closing in on that 1 million subs. LET'S GOOOOO!
nearly!
There are constant force springs that unroll, and you could replace the bungee cords with
I feel like I'm kind of looking at a compound bow. At least one half of one.
And?
@@smashyrashy He's making a comment on the similarity, in the comment section, like the comment section is meant for. Problem?
@@tatertotjrdude yes. Massive problem
@@smashyrashyI'm sorry to hear that. Gives you something to talk with your therapist tomorrow.
@@tatertotjrdude 🤞🤞
Awesome! Such a simple and accessible solution. It would be cool to see an apples to apples comparison of how long the robot lasts while running in place with and without the bungees. This way you could get a rough value to say "the bungees increase power efficiency by X%".
would this be significantly more or less complex if you were to use a constant force spring instead of the cam/bungees?
His system is very easy and cheap to build, and it's also light weight. As long as you can tolerate the tiny bit of bulk, it would be hard to gain much without more expensive and heavier parts.
you deserve atleast 10 million subscriber..sorry man i dnt know why you still have less than a million..anyway great job genius
Compared to the previous version this is a massive improvement. Also the dog even sounds like a dog on your hard floor.
Check out "variable pivot point" design used in mountain bike rear shock absorbers.
They are disigned to eliminate the "bounce" while pushing the pedal (which would waste your peddling energy, as the bike would otherwise bounce as you pedal).
Also, a cam moves the pivot point as well, changing the angle of force from vertical to diagonal, something you may need to compensate for, or can utilize for benefit.
Gas struts or springs like the ones that hold open the lid of your car trunk are nearly constant rate. Available in lots of sizes and force levels for cabinetry.
Also constant rate springs are a thing look kinda like a tape measure.
This is absolutely brilliant 👍 for anyone thinking of being an engineer it is great inspiration!
The new kneecaps touching: seems nature had the same issue and evolved into knees facing the same direction.
Yeah either that or they evolved to stand (or nearly be able to)
Its probably why lizards havent evolved to stand upright (On all fours, not biped)
Aside from their very long bodies and itty bitty legs, their knees face each other. So if they did ever have a body plan more optimal to evolve locomotion that isnt skittering, their fat knees would be bonking into each other.
have you ever seen a dog? the knees/elbows do face together, natures solution was slanting the hindlegs outward.
What are you talking about?
Name one!
All large 4 limbed animals, including humans, have knees and elbows pointing to each other.
It works well; look at horses, tigers, cheetahs, basilisks, alligators (which can sprint very fast!),
Side note: Birds have their "knees" close to their ribs, practically internally. What we see as their knee is really their ankle (which is why it faces backwards, as ankles do), and their shin and "feet" are elonged into their legs, and the "ball" of their foot is their whole foot area. Check out their skeletons, especially of long, thinned-legged, wading birds (it's more obvious), it's fascinating!
@@pauldeddens5349 horses have the same leg design...
Worth noting that the restoring force from an elastomer is also temperature-dependent, and that shape changes alter the temperature. The relaxed state of the polymer has more entropy, and the stretched one less, such that higher temperature results in more force. This also makes for some hysteresis.
glad to see your dishwasher's doing ok
Great science in this video. Lots of brain food.
"Warm compared to unpleasently hot" sounds like a win to me!
what about a constant force spring? I think you can get spiral shaped ones, which you could just put on the joints. You can find some on McMaster
Just happy to see the dishwasher got fixed 😅
what do you do with all the leftover plastic from failed outdated parts?
Coil springs can give constant torque over a limited range, eg. a few rotations. Actually any spring is relatively linear over a small range of the maximum spring extension. Also coil springs are much more compact and can go over your motor since the motors only do a few turns anyway. The spring size could be adjusted to give the necessary nonlinearity to somewhat match the torque needed as the knees bend.
At those currents you should be able to use a clamp on ammeter, or build one and tie it into the uC so it can monitor for faults
For Current Sensing: Allegro makes some really small current sensors. Pololu has a board(ACS724 Current Sensor Carrier) for the smallest series(up to 50A) in a tiny 20x18mm size. Might be worth a look. Next bigger Sensorsize goes up to 400A(Battery Protection is no joke) but I dont know of any available breakout boards.
I wonder how gyroscopic feedback work towards stability.
Cause it to flop over?
Amazing! Unrelated idea, you should make a robot/machine that makes your bed. I think that would be dope, and manipulating fabric seems like a fun challenge for you
This modification crossed my mind again, and it made me think of something. Have you ever seen "power stilts?" What if you were to add something like that to the lower leg? Anyway, it seems to fit with the system of cams somehow to me.
You know, I think one of the reasons I love robots so much is because it forces companies to be fucking creative again for once in their lives.
Youve seen the shit we had back in the 60s to early 2000s, everything was mechanical, and overengineered.
I can understand the shift away from mechanisms, since points of movement equals failure points, and extra cost, _but god damn they are so cool._
And as is turns out, its not easy to just make a robot out of a bunch of motors and pieces of metal, _you need alot of over engineered joints, pulleys, gears, and shit like that._
Good stuff - would be nice to see some charts showing the streach/force curves as things go along
Great idea and design.
For other alternatives maybe something like nature does it where the joints lock at the end, or a system that can lock/unlock using friction when idle could work.
Do you have a thermal camera? You could surely do a nice demonstration by setting up a fixed, repeatable exercise routine for the robot, then run it with, and without the constant-force springs. The difference in temperature rise would be a clear indication of power savings.
Flipping the elbows around so they face the same way forward with the knees might help the gate be less bouncy and would also stop the joints from knocking
There are constant force springs often used in robotics they might be a pain because you would need a bearing to hold the spooled spring steal wrap but they would work and would be way easier in to long run to optimize.
Problems from an earlier project come to mind ---
Wondering if larger versions of the constant force spring from tape measures may help here? Could drastically reduce the bulk at the knee while applying a relatively constant torque during rotation/tension?
Id say that the next step of improvement would be making some sort of an artificial muscle to replace the bungee and remove the cams entirely, but the new problem would be finding a compressor or pump (i think) powerful enough to quickly work the muscles and also small and light enought to be placed on the robot. Ive also realised that this would just over complicate things when a simple band and variable cam can just do the same job without adding more weight and simplicity, so yea lol
There's a guy on UA-cam that's basically made exactly what you're talking about: artificial hydraulic (or is it pneumatic?) muscles without using a compressor motor. I believe he's using some kind of chemical reaction with hydrogen (yikes) to power the the muscles. I can't remember the details though, I'll see if I can find the video and link it here.
Edit: found it ua-cam.com/video/07oVoABYr10/v-deo.html
Apparently he's using a portable electrolyzer to create a hydrogen-air mixture. The hydrogen mixture has something like over 1000x the volume of the (water, I believe?) It's made from. Very complex, and dangerous, but it is technically possible.
You could safe power when you make the joints breakable, at least if the robot is standing. Or would it add to much weight? If the motors are outrunners you could try to break at the motor with some sort of bands that are pulled tight by a servo.
Otherwise great video, it makes alot of fun to watch your videos.👍
Brakeable. You don't want them to break. ;-)
Nifty start... I think an improvement would be to change the cam profile just a bit so that the spring is exerting the correct force to balance the weight at the angle of the foreleg (eg, if the leg were straight, the spring should be putting out near zero because the T=sin(theta) * mg (where theta=0 for vertical -- pure compression).
Of course you need to translate all that into your coordinate system for the servos... and do what James Pray recommended below to compensate for the difference in length as the cam size increases...
But this is pretty cool man!
On a completely weird idea, you could put the "top end" of the bungee on a screw-adjusting hook to be able to adjust the preload (slowly) and could rig that so that "adjust preload to minimize current when the knee is at this angle" (ie, standing at rest). Then the dog could adapt to carrying different weights without a lot more current being expended -- fido, fetch the keg for me!...
You missed a key consideration. The force required to straighten the knee under load is greatest when it's fully bent (squat), and decreases as it straightens. You overthought this one. A spring (or bungee) naturally behaves favourably.
This is why walking is easy and can be done for hours, but squats will have you burning in just minutes.
Great consideration!
Yes, I think you are correct. Of course the point was to provide a predictable load, I am indeed curious if removing the cam will be even more efficient (and making sure your kinematics / motion controls still work).
Its important to note that bungy cords and other elastomers are not linear, they take more force to extend than to hold and let them retract. There also can be variances with the speed and acceleration in which they are pulled. Its probably not to important when used passively like you are here, but it may begin to matter if you incorporate them into any models.
You made the cams such that it produces constant torque, but I think it would be much better to shape them to create a constant vertical force. Because the torque required when the dog is lower to the ground is far greater. It would already be better to make the cams just round, as it creates more torque when it is lower and therefore keeping a more constant vertical force
please keep up the good work I'm definitely going to need things of your nature to crush
Another great video, many thanks.
Have you looked at Compound Bow Cams, as used in archery?
Something in this video reminded me of clockwork, where they also really wanted to have constant-torque springs so the clock doesn't tick slower as the spring winds down. Bit of wiki-reading led to en.wikipedia.org/wiki/Fusee_(horology) which is essentially a longer, coiled up version of the cam you have. If you had a spring-loaded helical cam on the shoulder instead of putting the cam on the knee it might free up some space between the knees.
What about constant force springs?
was gonna sat exactly the same thing.
Those tend to be much more expensive
I was thinking the same thing. This is a really cool idea, but it seems to be solving a probem that already has a solution...
@@quinnfoster4671 Definitely, but it's cost saves a lot of time and other problems. Who knows, maybe he used bungee for a fun challenge.
@@quinnfoster4671 you can get them for cheap in those window shade cord rollers :)
All that effort spent on making the response linear, whereas I suspect the nonlinearity could actually be used as a feature to reduce the bounce for example.
12:15 its like a special puppy lol
Seems like measuring the temperature of the motors beyond "not hot to the touch" anymore would be a good controlled way to monitor load. Furthermore, what old CNC drives did to reduce the heat of holding torque was to incorporate a brake. Seems like a combination of the two might be the best case for idle and mobile energy reduction.
Is constant force really the best solution, since the torque of the joint will increase as the dog gets lower
Can we all take a moment to appreciate the fact that technology has advanced to the point where we can call a 3-D printed robot dog made at home only OK when just 10 years ago that would have blown somebody's mind
I agree with some of the other comments, I don't think you actually need constant torque since the torque applied changes as the force vector changes when it bends referenced to the floor. (I probably didn't explain that very well.)
If the assisting force will be constant, wouldn't it be best to tension the joints with the bungee so they support the weight of the dog mid travel? Not sure where the force balance point is with the current setup. That is an awesome idea on the assist!
great idea to use cams to create a dynamic lever depending on the angular :)
James, Measuring the current shouldn't be too difficult. Just use any piece of wire that is sufficiently thick, with currents on the order of 200A you'll find a measurable voltage across them!
For example, you can use the negative lead of your battery. Use the black wire of your balancing lead for one end of the voltage measurement, and the first "junction" where multiple wires connect as the other.
The reactions that allow a LIPO to charge require some extra energy that is provided as heat to the charging LIPO. Thus a charging LIPO should get COLD. Now that effect is offset by the resistive losses around the system, so it might be unnoticable. But on the other end of the charge/discharge cycle.... the discharging lipo also produces heat that is added to the resistive losses. So a discharging LIPO should get warmer from the discharge.
Last, that 60C rating of your LIPO battery is determined by checking that the battery doesn't overheat when you apply that much current. So if you're near the limit, I certainly expect the battery to be hot afterwards. You don't need to exceed the limit to heat them up.
Using constant force springs would have been better but sourcing them is very difficult this method of counterweight with an exponential gearing is best for low cost solution.. I wonder how big (volume) the setup would be as compared to the mass added and the load reduced whole using springs on open dog..
Cancelling the nonlinear spring force with a nonlinear cam is such a clever approach.
How about measuring the amperage from the battery and comparing the power requirement before and after? Maybe try amp clamps (inductive) for the absulte current from the battery. Cheers
Does open dog have any active cooling? Maybe a small 40mm noctua fan like off a 3d printer blowing across key components would be low enough draw while improving part longevity?
Great job! To my untrained eye, the movements seem a bit more fluid.
You know, it kinda reminds me of the Achilles tendon in a hind leg of a biological dog or other four-legged mammal. Makes me wonder if their Achilles tendon performs a similar function.
It doesn’t
@@johnm91326 Thanks
i think you could make use of some sort of scale that will record data continuously over a short period of time. Then you could profile the resistance force of the bungie from rest to max-extension and then map that curve to your cam. The result would be near perfect.
You could also use an eccentric geared pulley for your belt drives. Allow the motors themselves to have more torque where they need it and less where they don't. It would be less bulky.
You could use a shunt to ,measure loads at the battery. 💜🤓👍