2 cim vs 1 cim

[ckpash88]

I cant seem to find the answer to this question.

Do you believe we can get away with using 1 cim motor per tough box mini. We plan on making a light robot and we think that taking two motors out would save on weight. Our thoughts is that we aren't going over any obstacles so we should be able to get away with it.

Do you agree?

Thanks,
Team 5637

[Ginger Power]

Originally Posted by ckpash88

I cant seem to find the answer to this question.

Do you believe we can get away with using 1 cim motor per tough box mini. We plan on making a light robot and we think that taking two motors out would save on weight. Our thoughts is that we aren't going over any obstacles so we should be able to get away with it.

Do you agree?

Thanks,
Team 5637

Assuming you mean to use these toughbox mini's on your drivetrain, use 2 per toughbox. In my rookie year, we used 2 cims to power our drivetrain and we quickly added 2 more when we got to the competition. It's worth putting power into your drivetrain, and having weight down low is never a bad thing.

[FrankJ]

The top of my head answer is no. Yes the robot will move with 1 cim per side. Unless you gear down or use omni wheels on one end, it will not turn from a stand still very well. You will have issues playing defense or with defense.

[efoote868]

Originally Posted by ckpash88

I cant seem to find the answer to this question.

Do you believe we can get away with using 1 cim motor per tough box mini. We plan on making a light robot and we think that taking two motors out would save on weight. Our thoughts is that we aren't going over any obstacles so we should be able to get away with it.

Do you agree?

Thanks,
Team 5637

The amount of weight saved is negligible compared to the amount of power you'd be taking out of your drive train. I'd recommend that you keep the motor.

Take a look at Ether's drivetrain acceleration model, and compare your results between a 2 cim vs 4 cim (+6 lbs) robot.
https://www.chiefdelphi.com/media/papers/2868?

[mrnoble]

I vaguely remember thinking this would be a wise decision in one of my team's early competitions. It was not wise. You will lose significant acceleration, and everyone else on the field will outrun you. More importantly, the teams chasing you will catch you and push you, and they will win the pushing matches. You will regret the choice, unless your team goals do not include being competitive.

[ckpash88]

Sounds like we will being going with 4 motors. Thanks for the quick responses

[mrnoble]

Best of luck. You will not regret this decision.

[logank013]

I'm not sure if this is exactly what you are looking for but this is a paper our team did at the end of 2014. It is comparing 2 CIMs (1 per side), 4 CIMs (2 per side), 4 CIMS + 2 Mini CIMS (2 CIMS and 1 mini CIM per side), and 6 CIMs (3 per side). I think it's worth checking out for drive train decisions, even if it's not exactly what you're looking for.

[MichaelBick]

If your robot is light, the weight of 2 extra CIMs shouldn't be an issue.

[rich2202]

Originally Posted by logank013

I'm not sure if this is exactly what you are looking for but this is a paper our team did at the end of 2014. It is comparing 2 CIMs (1 per side), 4 CIMs (2 per side), 4 CIMS + 2 Mini CIMS (2 CIMS and 1 mini CIM per side), and 6 CIMs (3 per side). I think it's worth checking out for drive train decisions, even if it's not exactly what you're looking for.

Interesting. Any guess how 6 mini-CIMs would perform?

[Oblarg]

Originally Posted by ckpash88

I cant seem to find the answer to this question.

Do you believe we can get away with using 1 cim motor per tough box mini. We plan on making a light robot and we think that taking two motors out would save on weight. Our thoughts is that we aren't going over any obstacles so we should be able to get away with it.

Do you agree?

Thanks,
Team 5637

Never, ever make a drive with only one CIM per side.

Your acceleration will be bad, and you will trip the 40 amp drive breakers repeatedly as you inevitably stall your motors.

[cj3958]

Yes you could theoretically do this. It is probably not a good idea for several reasons. The first is that you probably don't need to save weight. This year especially, unless you have 12 moving actuators and you make everything out of steel you probably won't be too close to the 120 lb limit. If you want to just be lighter so you accelerate faster, removing the motor is not the way to go. Drive train motors put more energy into moving than they take out, so removing them will not help you accelerate faster. If you really need to weight savings, I would recommend using 2-3 775pro's per side. They have approximately the same power output, but they are a lot lighter. The downside is that they COULD overheat, but they probably wont. You can use a CIM-ile from vexpro as your first stage, and from there it will fit right on to the toughbox. I would only do that once you find out you need the weight though.

TL;DR
You can, but you shouldn't(most likely). Better option would be to use 775pro's, but the best option is to simply use more CIMs.

[RoboChair]

Originally Posted by cj3958

TL;DR
You can, but you shouldn't(most likely). Better option would be to use 775pro's, but the best option is to simply use more CIMs.

Please don't put 775pros in the drivetrain unless you REALLY know what you are doing with them. I have in my 12 years of FRC only heard of 1 CIM in a drivetrain that got smoked. CIMs are the closest I have seen to indestructible motors that you can buy, they just won't die.

[efoote868]

Originally Posted by cj3958

The downside is that they COULD overheat, but they probably wont.

In a drivetrain, a 775pro WILL overheat.
Stall them for more than 3 seconds, and they're no longer motors. Run them for more than 90 seconds at peak power, and they're no longer motors.

See actual test results here: http://motors.vex.com/775pro

[jwfoss]

Originally Posted by Oblarg

Never, ever make a drive with only one CIM per side.

It was absolutely okay in 2009.