HELP with drivetrain decision

alright, so we originally had 4 CIMs driving our chain drive(2 on each side, 2 to a gearbox), but due to weight requirements, we had to remove two of them (so we are left with one on each side. the drivers said there wasn’t much of a difference in driving it, but after seeing the webcasts… the was loads of pushing and shoving, so is losing some weight on another aspect (dunno if we can, but we didn’t have too much time to accomplish that at end of build season) to gain the 2 CIMs going to be beneficiary?? Or is it okay to only aadd one to one side? wouldn’t that make it lopsided? I mean, if we can outpower the other bots… then…but the question, of course, is can we outpower even if we do have 4 CIMs, maybe it’s not a question of pure motor output. Denver regional in about 4 days, we have thursday to make changes… SO… i need some advice, and I’m also wondering what you guys are using to drive your bots.

I would strongly advise you to add the CIMs back and take weight from other parts.

We just got back from Waterloo regional, and our biggest problems were the drive chains that kept falling off (long story). What saved us were the 4 CIMs in 4WD, that allowed us to play powerful defense and push other bots around, even with half the drivetrain disabled.

Unless you have a great shooter, or are very fast with those 2 CIMs alone, I would suggest that you put the CIMs back and make it 4 motor drive.

good luck in Denver.

Putting the chips back in would help a lot, but that is ~10lbs of motors. If that is unreasonable, try putting a smaller sprocket on your transmission (remember the KOP one isn’t 5/8" it’s metric) You won’t go as fast, but it’ll pay for that loss with the additional pushing power and make it easier to aim your robot. All this is sort of pointless though, if you don’t have the traction to harness it. So, if your using, say, the KOP Skyways you aren’t going to be able to push much whether you have two small chips or four small, two large, a pair of FPs, and a 16 speed gearbox.

It all depends on what kind of wheels you are using… The KOP gearboxes with two CIM’s output about 175 foot lbs of pushing power, and unless you have very grippy wheels, that is not your bottleneck. Like Luke said, the KOP skyways won’t do much in the way of traction, no matter what kind of torque is put into them, they will just spin the second you get into a pushing match. I would try getting more traction with your wheels before adding the two motors, you can do this with zip-ties, or some IFI tread, or a little belting screwed to them in place of tread, aswell as any number of other ways.

EDIT I don’t think that adding another CIM to only one side of your robot would make it lopsided, as it would only cause a difference in torque, not speed. It might even be your best bet, once you have ample traction. At pittsburgh, we were able to play a KILLER defense with only one side of our drive train, and we use 2 CIMS in each gearbox, one gearbox to a side. By killer defense, I mean that we were still able to push everybody that we tried to, even having only one functioning gearbox. EDIT

Hope this helped,

well, we do have tank drive LOL the only think we worked on in off season. treads on each side with some sort of polymer pads, they give very good traction.

With the way the game has been played out recently, i would also advise to add the CIM’s back in and take the weight out of other components…eg find anything thats steel and put hole patterns in it.
One of the main items to consider though is that you designed the robot to drive a specific way, basing the position of your motors, gears and even wheels on an ability to generate enough power from the motors. When you suddenly reduce the ability to produce that output by ~50% the design itself changes in varying ways. Eg if you have a 6 wheel drive system, having 2 motors instead of 4 reduces your ability to accelerate out of a jam.
Also by removing the ~10lbs from down low(I’m assuming the drivetrain is based close to the ground) and leaving the weight up higher your CG has just shift upwards by a couple of inches meaning you can tip more easily and and you remove the weight over the wheels altering the overall performance(maneuverability, pushing power etc). Then again as well we designed, an re-designed and re-designed(and a few more in there) for a powerful drive which was one of our top priorities early on.
Then again you might not have an option but I’d advise against using one side with 2 motors and another with 1 as that could lead to more problems than anticipated, but i don’t know how your drive is set up so cannot say it would be totally bad, heck it might even work out ok. Definitely look to remove from other parts, even look at using smaller chain, it might break a little more often, but cutting the chaing size to one 80% will save you that much weight over the entire run. Good luck

If you are using steel sprockets you can save a bunch of weight by going to aluminum. If you have access to water jetting or even the IFI parts are better than hanging on the the kits steel sprockets. If you are using the 8" or 6" wheel chair wheels. You can improve traction with rough top or diamond top belting. Use a lathe to make the rubber part flat and use good glue and screw to hold the belting on. Last year we designed hat like things to go on the kit transmissions that held aluminum sprockets cut the weight of 4 wheel drive by 1/4 or more. Also if you are using the skyway’s use a 1/4" thick donut to keep the chain out of the wheels. The other thing you can do at competition is have the gears in the kit transmission lightened by the machine shop or trailer. If you are doing this in a fix-it window don’t plan so big as to go over the allocated time.

Take weight off the top of the bot! Being able to push hard, and being upright thru the whole match, usually count for far more than things like hopper capacity

Okay so think of it as what are the positive and negative affects of adding the CIM back.

1.) more pushing power
2.) more wieght toward bottom of robot
3.) better acceleration
4.) slightly higher top speed

1.) Where do we find the wieght for it
2.) Is the robot a ballerina or a boxer? (meaning does your robot have the right gear ratio’s and traction material to push with) If it is a ballerina then you should probably forget about the CIM.
3.) where do we find the wieght for it???

Find a place with carpet like the field and a wall (or some other immovable object).

Put your robot against the wall (or object).

Try to push the wall.

If your tires break loose, adding more CIMs won’t do anything for you since you already can’t put your power to the ground. Work on traction instead.

If they don’t break loose, then worry about adding more power by adding motors.

A 10 motor drivetrain doesn’t do any good if you can’t put more than 2 motors worth of power to the ground.

IMHO of course…

Don’t be jealous of teams with more motors in their drive trains.

My team built a six motor drive train this year and it wasn’t nearly as impressive as I expected.

For one thing, even in full power we were unable to push most robots sideways. We could only push other teams in head-to-head pushing contests, which didn’t occur very often.

With six motors constantly running we also burnt up a great deal of juice. We were often barely able to climb the ramp at the end of our matches (six motors isn’t very helpful when you barely have any power).

To make matters worse, we often sucked up so much power that the circuit breaker would be tripped and we would die all together (this happened twice).

My advice to you is not to worry about it and leave out the two CIMs. If your using the KOP wheels (or any other kind of skyways) then you shouldn’t have to worry about being pushed sideways, only head-on, which again, doesn’t seem to occur that often.

It really depends on what kind of strategy you wish to pursue.

Actually a lot more went into that problem, the first breaker tripped because it was just old and has been tripped many times in the past. The new one tripped from the crazy current draw, which, if the drivetrain was running properly, wouldn’t happen too often. I have a more than good feeling that we actually killed-over a CIM or two which is causing a whole lot of unecessary resistance. To top it off, the gearing was set with the intention of driver control (7fps, 16fps) rather than sheer chain breaking power.

Sorry for the off topic… But anyways, the amount of power your drivetrain needs revolves around your strategy, or the other way around. With 6 motors (when they did work) I just brute forced my way through other robots, easy enough.
Having two motors doesn’t mean you can’t play defense, it may mean you can’t go around shoving other robots, at least those with more traction and power than your robot’s drivetrain. You still can play defense, you just have to be more clever about it. You can easily prevent 1pt shooters from scoring by just camping in front of the goals, you can try pushing robots sideways, you can throw 3pt shooters off course by hitting the corner of their robot.

Hope this helps.


Our wheels slip whenever we push other robots, and we only have 1 drive motor per side.

Having a multi-speed transmission helps too, and the need for those extra CIMs is lost. Our low gear allows the tires to slip when we push a solid object, so it has enough torque without having to add more CIMs.

yea… thank you guys so much… we were on the number one seed alliance at Denver, but got taken down in the semis…oh well, but the 2 CIMs turned out to be fine. Our tank drive kicked $@#$@#$@# (am I allowed to say that?) and played some major defence. Ha! and to think that we were the last one selected in alliance selection saddens me… i guess it worked out for the best, since we got selected by the top ranked team, and it was the top team not only because they played well in qual rounds, but they were able to find the gem among the many (denver has 49 bots) possible alliance partners. boy, what a great end to our second season. anyways, so i guess someone can lock or delete this thread, since all regionals has ended, i guess this applys to many threads on this forum…

Hey Sunny, I dont know if you noticed, but at least in one match, I watched as we were slid (yep, our tracks were locked, but sliding) by another bot. We measured the coefficient of friction to be over 1 against carpet and the tread plate. In any case, we need to increase our COF. Maybe a different texture on the pads or a softer urethane? Like others have said, if we can increase the COF by 33-50% we will be able to take advantage of additional motors.