Our team used the standard 2010 KoP drive system this year since we were rookies and it worked fairly well, but we want to try something new this year. Does anyone know the advantages and disadvantages of chain vs direst drive vs gears vs belt drives? Trying to get a big picture to try various things (Provided they don’t coast too much).
Coasting isn’t necessarily a problem. Sometimes, being able to coast into a particular location at the end of a match when the power turns off can make a big difference in the match. (OK, so you really meant cost…)
Chain: Easy to run, easy to adjust gear ratios, easy to tension. But, if a critical chain breaks, you could be spinning in circles on the field. If you’re using #25 chain, extra care needs to be taken in alignment of the sprockets.
Direct drive: Chain/belt is still recommended for other wheels, and supporting the non-gearbox end of the axle is highly recommended. If something goes wrong in the gearbox, see what happens if you lose a critical chain. Saves some weight over a chain system, but is tougher to build right.
Belt: See chain. May be slightly tougher to do depending on method of joining belt ends, but is also reliable.
Gear: Heavy, but robust and reliable. If you go this route, you’ll need tight manufacturing tolerances. ±1/4" isn’t going to cut it, you’ll need more like ±0.010" or better for best gear mesh/interface.
In terms of cost, chain/belt is probably the cheapest, followed by direct drive and gear.
I suggest you do a search on the White papers here on CD. I think you will find more information than you can digest between now and kickoff.
Well you have many numerous white paper at your disposal but I will give you a crash course in simple drive systems.
Direct vs. Chain/Belt
- Direct requires more room to incorporate 4 single geared gearboxes
- Direct only has a single speed controlled gear box (Unless you want to mount 4 shifting transmissions :yikes: )
- Chain/Belt reduces space but tensioners and design quality will affect breakdowns
- Chains/Belts do allow you to have multiple non-driven wheels which worked great for this year
- If you were to go with Belts/Chain, Cyber Blue (234) has a white paper that revealed after testing that belts are more tedious to work with but they work better with a drive train
In my honest opinion, go with what the game play will be like. If there will be pushing and shoving, a Chain/Belt drive with 6 or 8 wheels will be optimal. If the game requires fast paced movement and little torque, then a direct driven omni-directional or mecanum wheel system is what you are going for.
Check out this top to see the multiple systems that are available.
Like I said, wait until you know your strategy before deciding on one.
Anyone else want to add? I know there is so much more that can be incorporated.
The “standard” drive, IMO, is #35 chain and sprocket off a gearbox for each side of the drivetrain. I think it’s best to analyze things relative to this, as it is a very solid standard and also happens to be what the kit bot is based off of. It’s also probably the simplest.
The most common deviation from that is direct driving one of the wheels. If you do not have a sprocket reduction or can incorporate that sprocket reduction into your gearbox, you can feed the output of the gearbox directly to a wheel on your drivetrain. This saves the weight of a sprocket / chain run and ensures in the HIGHLY unlikely event of multiple chain failure, you will still be able to move. Generally, this is done in 6 wheel drive setups, direct driving the center wheel. This allows you to bolt 2 sprockets to that driven wheel, chain those to each of the outer wheels, and call it a day.
From there, you can get more creative. A wheel driven by a moving axle is the first part of a live axle drivetrain. While dead axles have the advantage of serving double duty as standoffs that work to structurally reinforce your chassis, occasionally you may see value in using a live axle as it allows you to put your wheel sprocket anywhere on the driveshaft, not necessarily next to the wheel. The most common use of live axles is in cantilevered “west coast” drivetrains; these somewhat complex (relative to the kitbot) drivetrains run the wheels on the outside of the chassis member and the sprockets on the inside, necessitating a live axle.
Moving away from #35 chain is not something to take lightly, as chain is (relatively) easy to work with and allows for some error in design. Moving to timing belt and pulley instead of sprocket and chain is certainly doable, but it requires a lot more planning in advance as you have to order and design around an exact, non-changing belt length (as opposed to roller chain which you can adjust). Gear drives are even more sensitive as idler gears need to be placed in precise points along the drivetrain; they also take a lot of work to reduce weight to an acceptable level. In general, I wouldn’t recommend a team pursue either option without pre season prototype experience.
I’ll leave discussion about 4wd, 6wd, mecanum, swerve, etc. out of this post because it’s not what you asked about, but I do want to leave a note: When in doubt, 6wd.
We have been looking at incorporating the 6wd, so thanks for reiterating it for me. I was actually going to post another thread on the wheels but since you brought it up, what wheels are good for what? plus they’re expensive…
A six wheel drive can be done one of two ways (well, these are the two most basic ways to do it).
The most common and in my opinion best way is to use 6 high traction wheels, with the center wheel mounted a small amount lower than the others (1/8" or so). AndyMark Plactions are a good combination of strength, weight, and price; my team was satisfied with these wheels last year. You can also buy AM’s Performance line, which are aluminium instead of plastic, but at a higher cost. IFI also sells wheels that work pretty well.
Optionally, you can buy omni wheels and use them for the outer four wheels in your six wheel drivetrain. This makes turning easier but also makes it easier for opponents to spin you. Omni wheels also have less traction in the forward direction than a normal wheel.
what about the mechanum wheels? how well do those fit into the eqn?
4 motors, independently controlled. Chain, belt, gear, or direct. Arrange the wheels so that you can turn and strafe (there is a wrong way to do this!)
Well I think everyone would agree that mecanum wheels would can be either directly driven or chain/belt driven depending on how you mount the gearboxes. It’s really the same concept as a 4 wheel drive but the programing is slightly different need being that you would like the bot to strafe.
If you use a chain drive or a belt drive, or even geared drive with mecanum wheels, you are taking away the advantage, that is strafing. To strafe, the wheels in parallel (assuming the wheels are aligned correctly) turn in the opposite direction. When you mount mecanum wheels with a chain and sprocket, belt and pulley, or gear drive setup, the parallel wheels cannot rotate in opposite directions.
So, if you are planning to create a mecanum DT in which the parallel wheels are chained or belted, you should probably use a regular center drop plaction wheel setup.
I hope this helps!
Not necessarily. The key is 4 independent motors. Chain routing can run 1 motor/gearbox to 1 wheel, which is exactly what you’d be doing with a mecanum drive.
I saw at least one 2010 mecanum bot with exactly that setup.
We were definitely looking into mechanum for the strafing ability. So the key is 4 independent motors huh? If thats the case we have a problem. We have 4 Jags and all show that they are working with their light. however, one of them is giving the signal that it is working but it doesn’t turn the motor. The others turn the motor, but extremely slowly. The battery is fully charged, so that’s not the problem. is there too little power going to each one? Is there something we are over looking?
Look at the Dashboard. Does it indicate that your software is indeed giving a full throttle PWM command ?
I’m not sure about the Jags, so I’ll leave that to the experts. But I’d check connections if you haven’t already, and see if you can get some voltage readings on the inputs/outputs.
The key to mecanums is independently powering each wheel. Quick controls explanation follows; coding it is left as an exercise for the team.
–Front/back: all wheels forward/reverse
–Strafe (side/side): Front wheels forward, back wheels reverse/front backward, back forward, depending which way you’re going
–Diagonal: Wheels not on diagonal powered the same way (Annoying physics here).
–Anything in between: various combinations of the above.
–Turning: Same as a 2WD, 4WD, 6WD, etc… It behaves like a 4WD when turning, though it doesn’t bounce as much as a “sticky” 4WD does.
Oh, and the other thing about mecanums: you want their footprint to look like an O, but when the wheels are viewed from the top, they’ll look like an X. This is normal.
Ether has posted a whitepaper on the physics behind mecanum drive at http://www.chiefdelphi.com/media/papers/2390
Ok. I’ll take a look at that sometime in the next few days. Ether: No, I believe we are getting just over 1/2 PWM on each, including the one that isn’t working right. Would we need to change the sensitivity on the analog output relative to the joystick?
By this, I meant one independent motor/gearbox driving 2 parallel wheels. I knew what I was talking about, I just did not convey it specific enough.
What programming language are you using? Can you post your code?
You mean something like the Nonadrive, but with mecanums instead of omnis?
Nonadrive: Really good drive system, but you darn well better know what you’re getting into about 3 years before you even think about trying it.