pic: Drivetrain Prototype

First drivetrain I’ve ever actually caded so if you find any problems that i didn’t catch due to lack of experience please point them out. One of the ideas that’s been thrown around by a few guys on my team.
Wheels: 4x Innovation FIRST Stickies
Motors: 4x CIMs going to 2 p80 transmissions (Gear ratio TBD)
Sheet: 1/8" Aluminum
Spacers: 1" x 1" w/ 1/8" wall
Weighs ~30 lbs without chain

If anyone has any tips that would be great. This is just a preliminary cad to see how the drivetrain would go together so not everything is to full detail.


What’s the diameter of the wheels?

And what is the effective wheel base?

A lot of robotics in '09 were wide based, so this stance might be alright. But some teams took this design even further and turned it into a 6WD.

And also, you have a lot of supports, or spacers, running along the top of the chassis, it might also be benefitial to put some support along the bottom.

  • Sunny

Make sure you add some cross supports to the bottom of the two plates. Right now if that thing takes a hit it’s going to bend inward.

Your sprockets look large, if you reduce the size of the sprockets both off the gearbox and on the wheel you can save some weight (and space) and keep the same ratio.

I’m not particularly qualified to talk about drive chassis durability, so I don’t have much to add.

However, I think I can save you some weight on this, or another drive train that you build. Having a pair of sprockets with built in hubs is heavy, and having those extra couple of inches of steel shaft is heavier. What you could do is take an AM hub and attach a pair of sprockets to it, spacing the sprockets with bits of plastic. Then just run enough shaft to cantilever the sprockets and hub.

A top down view would look like = ]: () : ()

Where = is shaft, : are spacers, () are sprockets, and ] is the hub. Spaces are only there to prevent them from being turned into smilies.

Does that make sense? :slight_smile:

You could save a bit more weight without losing much strength by changing all the X patterns into pairs of triangles. Your machinist will also thank you for doing that; fewer cuts means fewer opportunities for something to go haywire and less time before you get the plate back.

Also, I might ramp up the plate thickness a bit around high-stress areas–mounting points and axle attachment areas–or put a flange on, like you would do for sheet metal.

i would recommend against dually P80s. our team has used them in the past and found that they are hard to assemble, as well as grease migrating towards the motors and out of the planetary part of the gearbox. two single P80s would be better in my opinion.

Two single p80’s per side? Or two total?

Also, we have never had issues with our p80’s, though is the first year we have used them.

I would shy away from the p80’s simply for the fact that the planetary transmissions are less efficient by design and arguably more fragile than standard toughboxes. You can easily buy all the parts necessary for direct drive from andymark as well and direct driving one wheel and chaining to the other would be the most reliable and lightest weight solution.

yup, as long as it’s properly tensioned 35 chain.

I’m not sure why, but we always use 25 chain

25 chain is lighter, but less forgiving than 35 chain.

Yeah, thats probably why. We also invest a lot of time in tensioning our chains perfectly, so we can get away with it.

The issue is reliability, you can tension 25 chain properly, but then it stretches and falls off, with 35 chain, some stretching is more acceptable and doesn’t need to be adjusted as much. If weight is your focus, and you have no issues getting things tensioned properly, than timing belts may be a better option as they don’t stretch (depending on the material), but they aren’t always as strong or reliable either.

I have never seen a properly tensioned #25 chain break or fall off. Team 254 has been using 25 chain for years with no reliability issues.

I agree with Nick here. I’ve seen many people complain about reliability of 25 chain, yet I have yet to see my team have any problems with it. There has to be something you aren’t doing properly.

I would say for a team that is designing everything in CAD and understands the need for tensioning, 25 chain should absolutely be used. We have only ever used 25 chain and this past year used timing belt. The belt worked flawlessly but does require even more planning beforehand. I would definitely put emphasis on really determining what size of belt you need for the given power. All things considered, 25 chain isnt much heavier than belt and probably easier for you guys so I’d say stick with that but move to direct driving one of the wheels and a spur gear transmission ala toughbox

If you’re using 1/8" aluminum without flanges, you might as well leave it unpocketed.

Hold the phone here. Why are you using 4 CIMs? I can see using 4 CIMs for Mecanum wheel, besides you have to use 1 CIM per mecanum wheel. This years limit on CIM Motors was only 5. You are using up most of them and not leaving yourself more for other things. If you used only 2 CIM Motors, one for each side, you would give yourself 3 CIM Motors to play around with on the rest of the robot.

Only using 2 CIM motors in a drive train will have a noticeable performance drop on regular carpet, as the robot will accelerate slower and in most cases will be torque limited (which means it’ll lose almost every pushing match). Make Mark Leon happy and do the math. The numbers won’t lie.

In 2009, the FRP flooring and acetal wheels had a much lower coefficient of friction, thus making a 2-CIM drivetrain not only feasible, but much better than a 4-CIM drivetrain at maximizing the potential use of each motor.

Edit: If you really want to have three CIMs for elsewhere on the robot, use CIM+FP combo for each gearbox. It’ll provide better performance than a lone CIM would, and depending on how it’s utilized (here’s where math comes back in) might just very well be able to pull off a friction limited drivetrain, especially if it’s use in conjunction with a shifting transmission.

As 254’s 2004 & 2010 robots and 1114’s 2010 robot (among others) demonstrated, just because there are 4 CIMs in the drivetrain doesn’t necessarily mean that they can’t also be used for other functions…