2 cim vs 1 cim
 

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

Re: 2 cim vs 1 cim
 

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.

Re: 2 cim vs 1 cim
 

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.

Re: 2 cim vs 1 cim
 

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?

Re: 2 cim vs 1 cim
 

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.

Re: 2 cim vs 1 cim
 

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

Re: 2 cim vs 1 cim
 

Best of luck. You will not regret this decision.

Re: 2 cim vs 1 cim
 

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.

Re: 2 cim vs 1 cim
 

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

Re: 2 cim vs 1 cim
 

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

Re: 2 cim vs 1 cim
 

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.

Re: 2 cim vs 1 cim
 

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.

Re: 2 cim vs 1 cim
 

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.

Re: 2 cim vs 1 cim
 

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

Re: 2 cim vs 1 cim
 

It was absolutely okay in 2009.

Re: 2 cim vs 1 cim
 

Well, yes - we used nothing but BaneBots motors on our drive that year. But that's pretty clearly an aberration.

Re: 2 cim vs 1 cim
 

33 ran 6 mini-CIMs going around 13.5ft/s single speed in 2016. It worked great.

Cheers, Bryan

Re: 2 cim vs 1 cim
 

Your drivetrain is THE most important system on your robot. Don't rob from it.

Re: 2 cim vs 1 cim
 

Swamps off season robot used 6 minicim drive geared around 9 FPS and while the performance was respectable, it would brown out frequently at the end of the matches.

Re: 2 cim vs 1 cim
 

We used only 1 per side in 2015. It was perfectly fine also.:)

However, for this year and years like 2013 and 14, I would never run just 1 per side.
Driving is an important aspect of this year's game. At the very least, it needs adequate power in all situations before even thinking about added weight issues with functions of the robot.

Re: 2 cim vs 1 cim
 

I am not so sure about the statement above that I have put in bold.

The facts you refenced are sound but it doesn't follow that 775Pros are the wrong answer.

I believe a lot of top level teams will have great success this year using the 775Pros in their drivetrain. This year weight is probably not the huge driver that it is in many years so I don't suppose it will be as common as it would have been if teams were fighting for every gram.

Even so, I would not make blanket statements predicting failure when I don't think the data necessarily support this conclusion.

FWIW, you will have much less margin for error when it comes to overheating your drive motors but that does not mean that good teams with sound engineering can't find a way to make it work.

Dr. Joe J.

Re: 2 cim vs 1 cim
 

Our team has used the 1 775 and 2 CIM setup per side for several years now, where recently we've swapped out the 775 for the Pro version.
We actually have an AM Supershifter setup where we modified one side of the transmission plates to add the 775pro.
In the past we've gotten away with the 1 AM Planetary 1 CIM setup and it was fine also, back when the no. of CIMS that could be used were much less and we needed them for other functions of our robot.
We have tried running 775-550 with Planetary combo before. That didnt turn out well. The drive sounded nice, but stalled out very quickly.

Re: 2 cim vs 1 cim
 

Yes, and very few teams are top-level. Top level teams know how to handle the tradeoffs of the various motors. Mid-level teams can experiment in the offseason.

Most teams are lower-level and have plenty enough on their plate just to get a robot functional. For those teams, an all-CIM drivetrain is dead simple obvious, and is the correct solution for 99.5% of the time. It's appropriate to make blanket statements for the benefit of those teams, rather than to make every single team do a detailed analysis.

Re: 2 cim vs 1 cim
 

And 2015. But those were games where speed was less desirable than manuverability while dragging around large game pieces.

Re: 2 cim vs 1 cim
 

The OP is from an inexperienced team asking if they could use 1 cim in their drivetrain for weight savings. Teams using 775Pros in their drivetrain should know enough that 1 cim isn't a good idea, and will likely be aware of all the 775pro dangers.

I suppose I could've included all those caveats, but the last thing I want is a young team smoking motors on the field.

Re: 2 cim vs 1 cim
 

I see you haven't seen Bomb Squad's 2016 drivetrain. If i recall correctly they ran dual 775 pros per wheel.

Re: 2 cim vs 1 cim
 

Maybe someone from Bomb Squad would care to comment on their drive train from 2016. Did you run with all 775 pros, how many and did you burn any of them out?

But as far as drive trains go, Bomb Squad's are about 12 years experience more advanced than the majority of teams, and I'm consistently amazed at their level of performance on the field.


I'll modify my original statement:
Without CAREFUL consideration, using a 775pro in your drivetrain is VERY LIKELY to overheat and become a fancy paperweight. I STRONGLY urge you to stick with cims and mini cims.

Re: 2 cim vs 1 cim
 

We just had one per wheel. Committing 10 motors (4 drive, 4 steer, 2 tank) to the drive train is a lot to begin with. We would have been ALL drive train if we went for 2 775s per wheel. :)

We lost a few (<5 between practice and competition robots according to my memory). We theorize it had more to do with the impact from the defenses than stalling. The brush holders were breaking rather than melting/disintegrating. Just a theory, though.

And thanks for the kind words. We sure like our swerves here in Mountain Home. :)