Why are we only allowed one motor per motor controller?

R37. Each power regulating device may control electrical loads per Table 10-2. Unless otherwise noted, each power regulating device shall control one and only one electrical load.

In particular, we cannot control multiple CIM or similar motors with one motor controller.

Why is this? Is it a safety issue, and if so, what in particular? Or is there another reason why we can’t power identical motors in parallel with the same motor controller?

Some of the rules are there because they’re “really good ideas” that help teams to have successful robots. Other rules are there because they help streamline the inspection process or for other “non technical” reasons.

In this case “one motor per controller” is in the “really good idea” category because it means that you also have one breaker per motor. Technically it IS possible to hook up multiple motors, either in parallel or series (hey… its possible) and have them run without anything bursting into flames.

However when you start to load the motors up you also start to draw a LOT of current and that can lead to tripping breakers (or worse if the breakers don’t trip).

For instance a single CIM, at or near stall, will quickly trip a 40A breaker. Two of them would trip it twice as easily. Requiring one controller (and thus one breaker) per motor will help ensure that the motors behave the way they are intended to behave and ensure that your team has a positive experience at the event.

So I wouldn’t say it is a “safety” issue as much as it is a usability issue, particularly when it comes to the CIMS. Multiple lower current motors could probably be connected in parallel to a speed controller without any harm… but then someone would go and hook them up in series and wonder why their stupid motors didn’t work right. It’s much simpler to just have one rule that ensures everything behaves correctly.

Jason

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They have this to insure safety and well being of the robot, now if you were to possibly have a bus of controllers or such designed to do so yes, but each controller is limited to one motor because only one wire comes in therefore one wire comes out equally if two wires come from one this could lead to hazards, breaker tipping or worse an electrical fire

^^ That! As Jason hinted but didn’t quite get to, putting two CIMs on a single motor controller is likely to overload the motor controller, releasing its magic smoke. Much better to trip a breaker or even smoke a $30 CIM than an up-to- $90 motor controller.

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