Spinner design basics: Moi and Bite (combat robot weapons)
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- Опубліковано 29 гру 2024
- In this video we look at the basic theory behind storing and transferring energy from a spinner
Riobotz tutorial: www.riobotz.co...
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This is so well-explained!!!
Thanks for all the videos you have put out Ben, this was really helping in understanding MOI and bite.
Glad to help!
Great job Ben. 👍 This will give us a better understanding of those principles.
I'm certainly interested in the idea of a single-tooth design tutorial, because that looks more difficult to design than a standard bar or disc, due to the issue of symmetry.
This is an excellent video, everything is really well thought out and explained. Some great stuff to consider when designing weapon bars / disks.
I always use singletooth bars for 2 reasons:
1. It's the cheapest option, because it uses the least material.
2. A singletooth bar may have a little bit less MOI but it can be spun twice as fast as a normal bar or disc while still getting the same bite. But doubeling the speed quadruples the kinetic energy.
Point 1 is interesting, if the bars weigh the same they should be using the same amount of material but bars (both single and double tooth) have been cheaper in my experience, because the place I get weapons cut seems to charge more for parts with more holes, so cutting the spaces between the outer ring and the central hub makes the disk cost more
Point 2 is correct, a faster speed does square the energy output and if you are lucky enough to be fighting at a competition that doesn't have a tip speed limit on your weapon then this is the right way to go. However tip speed limits are becoming more and more common, so it will become more of a balancing act.
@@TeamPanicRobotics I guess the place where you get your weapons cut charges you for the time they spent cutting the weapon. "Boring" the laser or waterjet through the material to start a new hole costs a lot of time and is therefore expensive. That's why I connect all the screwholes in the weapon hub with a flower like shape so I end up with only 2 times the laser has to bore through the material. Just like in this picture: forum.roboteers.org/index.php?attachment/720-barspinner-png/
Thats a good idea, I'll have to try that
Thank you for the awesome summary!
Maybe a bit off topic, but i remembee when i was quite young at a science center there being an experiment you could do. It involved rolling cylinders with the same diameter but different moments of inertia (basically denser tubes with a bigger hole through the middle). I remember staying at that experiment for like half an hour trying to figure it out, but not finding the answer. Today i learn.
The UK Robot Hypnodisk did manage to design a blade with maximum MOI and bite in a single blade. The design was a disk weapon with a single tooth sticking out on one side and the opposite tooth sticking up at a 90 degree angle; ring based weapon with only one tooth. Another cool feature that not a lot of people know about (and I think this is an awesome feature that if you can include it, you should) is each tooth had a small section for adding and/or subtracting washers that enabled them to fine tune the balance of the disk.
I strongly disagree that single tooth disks are maximum MOI and bite.
I said this in a different comment:
" The way I see it, a single tooth disk is a contradiction in principles.
You use a disk to get the highest MOI you can, which means wanting the mass of the disk as far out as you possibly can (i.e. having small bite on your teeth so the diameter of the disk can be close to the max diameter of the weapon)
You use a single tooth weapon to get the highest bite you can, meaning big weapon teeth.
A single tooth disk is going to have a greatly deminished MOI when compared to a twin tooth disk because the single tooth has twice the bite, which means the tooth needs to be twice as large, hence the disk needs to be shrunk inwards to accommodate, killing the MOI.
Also the counterbalance in a single tooth disk kills MOI by design, as mentioned in this video, the counterweight needs to be closer to the center of mass, and needs to be heavier then the tooth
So the problem in the design is that it does nothing well, a twin tooth disk has a higher MOI, a single tooth bar will have higher or equal bite without the risk of the disk being hit and a bar will have somewhat similar MOI, with a little less bite and again without the risk of the disk being hit.
I will say though that this is an opinion, I havent done the maths, nor have I run single tooth disks for enough fights to really get a feel for them, mostly because I only run disks in fights where my oponents cant hit back, so I want the highest MOI I can possibly get "
Hypnodisk fought in the old days where a robot built out of a microwave had a chance to make the finals. And roboteers had way less access to precision machining techniques. I very very much doubt that many people in that era considered the MOI or bite of their weapons properly.
Not to say that Hypnodisk isnt a good robot, I love it and it worked well for the time, but if it fought today it would be destroyed unless they did some major upgrades and one of those upgrades would be to remove the single tooth disk and have a dual tooth disk or a single tooth bar
@@TeamPanicRobotics I mean, fair enough, you know more about this stuff then I do, just thought it was an interesting point. although you say the counterweight must be closer to center of mass, hypno's tooth was right on the ring at the outer edge, so only slightly closer and thus only needing to be slightly heavier. Again, I'm just going off what you said in this video.
Although I still stand by that the washer balancing feature is a great idea, you agree on that?
Funny enough, Hypno was likely one of the first precision machined robots. Entire thing was built using CAD.
Yeah the balancing is smart, weapons always get damaged in fights which can unbalance them.
A quick and easy way to rebalance is a good idea
very well said
Fantastic video Ben, much appreciated! Question regarding weapon design and the fight between MOI and bite: you stated that a single tooth weapon has the most bite, but less MOI than the ring weapon due to the large counterweight. Have you tried a ring weapon with a single tooth? In my head, the counterweight would be where the second tooth is but on the inside of the ring and slightly enlarged to balance it. This would keep the weight as far as possible from the center for highest MOI, yet still give you a single tooth to maximize bite.
Likely this has already been thought of, but I can't think of a disadvantage to this design. I must be missing something.
Also, yes to showing us how you design a single tooth weapon! It was the first question in my head watching this video.
The way I see it, a single tooth disk is a contradiction in principles.
You use a disk to get the highest MOI you can, which means wanting the mass of the disk as far out as you possibly can (i.e. having small bite on your teeth so the diameter of the disk can be close to the max diameter of the weapon)
You use a single tooth weapon to get the highest bite you can, meaning big weapon teeth.
A single tooth disk is going to have a greatly deminished MOI when compared to a twin tooth disk because the single tooth has twice the bite, which means the tooth needs to be twice as large, hence the disk needs to be shrunk inwards to accomidate, killing the MOI.
Also the counter balance in an single tooth disk kills MOI by design, as mentioned in this video, the counter weight needs to be closer to the center of mass, and needs to be heavier then the tooth
So the problem in the design is that it does nothing well, a twin tooth disk has a higher MOI, a single tooth bar will have higher or equal bite without the risk of the disk being hit and a bar will have some what similar MOI, with a little less bite and again without the risk of the disk being hit.
I will say though that this is an opinion, I havent done the maths, nor have I run single tooth disks for enough fights to really get a feel for them, mostly because I only run disks in fights where my oponents cant hit back, so I want the highest MOI I can possibly get
@@TeamPanicRobotics that makes a ton of sense and explains what I was missing. Thanks!
UK robot Aftershock has a disc of this kind of design. It certainly looks to hit pretty hard.
This topic looks familiar 🤔 Great video though! The explanation of what MOI is and how it's calculated was something I glossed over in my spinner design videos, probably helps a lot for those who didn't take/can't remember high school physics.
Sorry man, I hadnt seen your videos.
This one was a user suggestion and also one I've been playing with for awhile.
Yeah why MOI and Bite are important was a big part of what I wanted to cover here, people come into combat robots from all sorts of places, so a bunch of things traditionally considered easy (like high school physics or soldering) may not be in their skill set
I'm building my first bot, it's a US plastic ant. I'm building a drum, let me try my best to describe it, I'm sure you'll know what I'm talking about when you get it. Imagine two circles, with a small difference in diameter. It has one tooth. The outside of the weapon draws a spiral line from the outside circle's diameter to the inside circle's diameter over 360°, and then the tooth is just the perpendicular line connecting the two spiral points. It's like Malice's weapon, but filled in and more compact, like Tantrum's drum.
Is this weapon a good balance between MOI and bite, while still being durable in plastic? I feel like an egg beater, or extruded out asymmetrical bar would be better, but being 3D printed, it's probably more fragile? Just curious as to if my train of thought is on track, so to speak lol
Video long time coming im no engineer or mathmetician but all i can say is thnx ?? i guese, this will probably be helpfull in the future when i get into the sport !!
Nicely done Ben, helps a lot for when I come to designing by own bugs weapon.
I have two designs in mind sofar that are essentially a dual action saw blade with 4 teeth (two are cutting and thinner, two are fatter and for energy transfer) the idea is for the the cutting teeth to open armour and for the wider teeth to rip armour away and/or for the ability to transfer bigger hits. ( Think pussy cats blade from robotwars)
My second weapon will be much like your disk but rather than the closed wheel/disk design I'm going to remove a section of the outer ring to create a gap and then add that material to the end of the blade to create a side ways dull axe like frount and a mounting point at the end of the blade for the option of a small sharper cutting/weight adjustment piece that will be highly likely sacrificial.
All I need now if for my friends brother to finish with the Lazer cutter, hopefully some time this year.
While those sound interesting, the KIS principle applies here: Keep It Simple.
These weapons spin at super high speeds, and often come to a full stop during a hit.
This makes it impossible to predict how exactly your weapon contacts your opponent and how it transfers the energy, so you are much better to keep the weapon simple and only try to get it to do one thing (because that way you can guarantee it will, at some point)
The dual action saw blade is a great example here, lets say by chance, the fatter teeth hit first and the blade stops.
In this case the thin teeth are useless, and the weight/shape is better to be a 2 tooth design to maximize bite.
But if the thin teeth hit first and the blade stops, you might get stuck. (you have teeth capable of medium-big bite that also cut, if they get too big a bite they will embed and stop)
The point being, if you want a weapon that does two things, design two weapon options and switch them out based on your opponent. Especially if its one of your first designs in a weight class
@@TeamPanicRobotics Thanks for the feedback, ill take it into consideration and make some alterations, i still think that the later design would be a great idea but ive probably made it sound more intricate than it really is, the idea of the end part of the blade being modular is to essentially offer different options for types of armour so the utility would be easy way of having multiple types of cutting teeth on the same spinning bar.
I really think I want to make this as it makes the bot seam different to most other spinning bots, sort of like a character building element as much as a practical one.
I think you could be right about the other blade, i hadn't thought about the usual types of armour that bugs are made up of, had it been relatively thin metal or PLA i dont really see an issue.
But your comment made me think about the usual types of metals that the blade is going to come into contact with is highly likely going to either stop the blade rather than CUT, and be more susceptible to breaking at the joints rather than CRACKING and breaking the panel outright.
Not to mention, I don't think i would have anywhere near the skills needed to make a blade that precise enough that it allowed for my to hit the weight limit and also be stable when spun at a high speed in this design.
Could you do a list of weapon shapes that do and don’t work, with examples of them on bots and moments where they demonstrate
I’m wanting to gather info that I cannot gather due to lack of knowledge for the shape
Shape isnt that important,
What is important is where the mass is sitting (changes the MOI), how deep the tooth is (changes the bite) and how may teeth you have (changes the bite)
Two different shapes that have mass in roughly the same place, with the same number or simarly deep teeth will have very similar performance
So dont worry about shape worry about MOI and Bite
Would these principles also apply to something like a thwackbot or a full body spinner?
Yes, anything spinning
Which you prefer most MOI or bite
Neither.
The whole point of this video is that you need a balance between MOI and bite to make an effective weapon.
If you optimise for one too much your weapon becomes very ineffective
You are smart
The "idea" is good sure but disc robust and a kind of heavy is gonna a lote more energie, is like hit other with disc with 3kg is better than a blade with 1kg, i use a disc full aluminium 7075 20mm with steel teth of couse without "holes" and i never gonna change that, riobotz use the same ideia, drumm full aluminiun with teth steel and this is why they have a good impact, minitaur have the dame build as touro compete in robogames, he is just a replica because they dont use touro anymore, soo the idea is not exactly like that, i never get hit in the disc with horizontal spinner and dont hit the teath before..
I'm in 10th grade high School and I was never taught this
I was teased mercilessly in the 6th Form in school in both Greek Language and Physics whenever a lower-case omega appeared on the blackboard.
I couldn't possibly explain why, but there's a clue in my nickname, which was Eleanor 'WatermEleanor' Peterson.