6 CIM Drivetrains... What's Your Experience?

Actually, mine would probably be “hey yall, watch this!”. I could never imagine an FRC robot being able to push a robot with tank drive that could only go forwards and back sideways? If one exists I hope I’m on their alliance, not the other way around!

Has anyone adapted one of the gearbox/drive train calculators to account for a combination of different motors in a gearbox? With the miniCIM and Vex/Andymak having gearboxes for other motors with outputs made to mount where a CIM would, I’m wondering how to enter that. Or do I just write “2 2/3” for the number of motors if I have 2 CIMs & a miniCIM in one box?

I don’t recall seeing any of the calculators adapted; however, I do recall two things on this topic (1) Paul Copioli designed the mini-CIM to be used in combination at 1:1 gearing with a CIM in a drivetrain, and selected its free-speed and stall torque with that in mind, and (2) Ether did some analysis last year aimed at answering your question above. Maybe he or Paul will see this thread.

Mini-CIMs have a higher peak efficiency than CIMs because their commutators are the same size, while the mini-CIM has a shorter armature. This difference allows the mini-CIM to operate in combination with a CIM without overheating, unless the loading is very high and prolonged.

See the presentation and associated spreadsheet by Paul Coipoli: http://www.fightingpi.org/Resources/Business/MSC%20Seminars/2013%20State%20Seminars.shtml

Last year my team used 6 CIMs and it was pretty awesome. We had huge torque and a pretty decent speed. Throughout the entire regional and an off-season event this past November we didn’t lose any pushing fights (possibly one at the regional, can’t remember).

However, use caution when having such high torque. In the last match we played at the off-season event I shattered our middle wheel on one side when I hit another robot, knocking the chain off and leaving our poor robot limping from side to side. We didn’t realize until we disassembled it before this build season that all of the six wheels were cracked; that one wheel just gave first.

tl;dr: It’s a load of fun to push around whoever you want, but be aware that it is in fact possible to push too far.

Speaking from experience, because a tank drive is inherently designed not to go sideways, you pretty much end up in a deadlock with no way to escape if you get shoved into from the side (I think it’s referred to as a t-bone, but not sure). It’s difficult to break until the defender lets up a bit either unintentionally or to avoid a penalty/ref call.

Both my analysis and Paul’s are in this thread. See posts 1, 5, 13, 14, 15, 18, 19, 22, and 24

And that is exactly what we want, if that one person is a great shooter, and have the only ball?? sounds like a win to me? But thats me and our team doesn’t have experience in much else so if we can do that then it works for me!

This may apply alot less this year because there are no obstacles to go over? last year running over those Frisbees at high speed wasn’t great for wheels.

We tested out our gear driven single-speed 6 CIM 8WD for the first time last night and loved it - http://youtu.be/pQ6TMzGwV6U We’ll be running a similarly designed drive this season with a 2 speed shifter incorporated.

Note that this frame is larger because we plan to use it as a test bed robot for seasons to come and it will double as a T-shirt shooter drive base.

With 6 CIM drive, I assume you are anticipating XXXXXL T-shirts

Once we throw on the 6 T-shirt barrel shooter, 2nd battery, large air tank and compressor, it starts to weigh a decent amount. This also just gave us a chance to try out 6 CIM motors in the drive as no one on the team had tried it yet.

Ether, do you have a ‘drag race’ spreadsheet lying around (i.e. multiple d(t) scenarios on a single graph) with the proper modeling? I may have to cobble one together if not. I’ve poked through your acceleration models, but haven’t found the time to make them more user-intuitive in a spreadsheet.

Such a spreadsheet could help a team make the decision of whether 6 CIM acceleration is worth it or not in a few different situations:

  • Robot attempting to ‘turn a corner’ around defense (i.e. get ahead of a defensive bot by 0.8-1.0 ‘robot lengths’ in order to be able to turn in front of the defender and zoom away towards the goal)
  • Robot attempting to beat a defending robot to a specific spot with N number of seconds to spare in order to get a shot off quickly

It would also help the drivers understand the limitations & strengths of the robot so they can make smarter decisions when defending or being defended. The driver coaches could setup specific scenarios to help give the drivers better practice.

Back in early December I posted a large text file which lists the “time to distance” for a range of model parameters:

Would that be useful if I updated it for 6 CIMs?

Also, I don’t know if you’ve seen it yet, but in mid December I modified the source to get the parameters from the OS environment (instead of being hard coded) and added a “ready to run” compiled executable attachment. It’s at the bottom of the list.


The executable gets its input from the OS environment, which the user can edit in the script that runs the executable. The user can generate a variety of CSV files for various values of the parameters. In Excel these CSVs can be combined to get a single graph if desired.

If there’s enough interest, I was thinking of integrating it with gnuplot so that graphing would be more seamless.

back in my day, 4 CIMS were enough and we had enough pushing force to push at least 2 robots at a time.

Uphill in both directions?

Last year we had 4 CIMS and teams made threads about us pushing them.:slight_smile:
In 2010, we ran 2 CIMS and 2 FP with AM Planetaries for Breakaway. It is our best pushing robot, still.
However, for this season, we will bite…and go with a 3 motor per transmission setup.

Since we’re going there… I remember when only TWO drill motors were enough - and when they weren’t we learned to shift the provided drill planetary transmission…

Yes. Both ways - and we LIKED it!

  • Mr. Van
    Coach, Robodox

We built a 6CIM 2 Speed with a PTO last year and the results we’re amazing in terms of pushing power and acceleration. It’s biggest draw back was the voltage drop, was as low as 6V in some cases, luckily we foresaw this potential problem and added current sensors on each trans to monitor and adjust for this


Yup, in 2012, we had 2 CIMS on each side and could push two alliance partners up onto the bridge uphill at once. Definitely lived up to it’s namesake, Panzer.