Dual speed four CIM or single speed six mini CIM Drivetrain

Dual speed 4 CIM drivetrain or single speed 6 mini CIM drivetrain? Which would you run? Why? Experience with each? Other considerations?

I recognize that one is not objectively better than the other, and that all drive trains are game dependent. I also know that there are other options that exist.

Walter

Mini CIM always. We will never use CIM motors on our robot ever again. Mini CIM motors are specifically designed for FRC use and are a superior motor.

I would go with 6 MiniCIMs over 4 CIMs in any skid steer set-up. Reason: same peak power, more heat capacity and brush surface, therefore the MiniCIMs will heat up more slowly, maintaining peak power longer. Motor power falls off rapidly as the windings heat up, and windings get hot much faster than magnets and cases do.

Depending on the game and driver experience, I might pick a two speed set up over a single speed.

Also, the 6 motor set up costs more and uses two additional power circuits.

Since you already know about other options, I won’t mention 775s. :rolleyes:

I think the additional motor controllers, wiring, and weight mean that I personally prefer the 4CIM setup. That being said, the primary drawback of using the 4CIM arrangement is that you cut out a lot of space in the middle of the robot, so it often means that you need to either split the electronics board in half or make a board that’s smaller or differently located.

We managed to get around the “interior space robbing” issue with this geabox concept. It started as a two-CIM design that we morphed into a three-miniCIM design the following year.

https://www.chiefdelphi.com/media/photos/45777

I wouldn’t say that’s the primary drawback of a 4 CIM setup vs 6 mini CIMs. If it were just an issue of packaging, more top teams would find a way to keep using 4 CIMs.

I’m also in the camp of 6 mini-CIMs based on some of the test data discussed last offseason and comments from other teams on the benefits of such a setup. It seems to handle the rigors of a 2 minute match better.

I concur with most that packaging is not the reason to select one over the other, unless you have some stringent robot requirements. 6 minis will spread the heat load out when things are working properly, and give you 67% vs 50% power if you lose a motor, and that’s even ignoring the bearing vs bushing and other improvements made to the miniCim relative to the CIM.

The reason we continue to use 4 CIMs vs 6 minis is simple: $$. We don’t have particularly deep pockets, we’re heavily invested in 2 motor COTS gearboxes, and we’re still building up our inventory of SRX and SPX controllers to levels where we could consider 6 motor drivetrains and have enough left to develop manipulators.

Edit: I missed dual speed originally, and don’t see that anyone addressed it. Why would this be one or the other? Going to single speed 3 mini-CIM is a very straightforward, low-impact change yielding a definite but relatively minor effect. Going to dual speed is more complex in terms of mechanical systems, controls/programming, and driving, but with a potentially more significant impact on robot performance, especially for robots which are near the weight limits which have trouble accelerating on a gearbox optimized for relatively high speed. If you somehow evaluate the cost of doing these two things as being equal, I would have to recommend the shifting gearbox, especially if you can make a shifting gearbox pre-season and give your mechanical team time to learn about it, your programmers time make it work, and give your driver(s) practice time on your system.