2 motors with different speeds in one Gearbox

What is the rule for using motors with different free speeds on the same initial reduction, how close should they be? Should anything else be considered? Thanks.

If they are within 10% free speed, you should be ok, however also take into account some motors do NOT like being run slowly - most of your 550 and FP motors have an extreme dislike for it and may smoke.

You should be more concerned with matching the torque curves than free speed. If not close, one motor will work against the othe, and reduce power. :slight_smile: :slight_smile:

If you gear to match free speeds, both motors will be producing torque in the same direction over the full range of voltage.

If you gear to match stall torques, then above a certain speed one of the motors will be acting as a generator and will absorb power from the other motor.
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An old thread goes into more detail:
http://www.chiefdelphi.com/forums/showthread.php?p=24193#post24193

Excellent point.
And there are lots of options now to match CIMs with other motors that are legal this season and vice versa.

When using mismatched motors, at some point in the speed range, one or the other motor will be backdriven by the other. As a mechanical guy, I have to ask the question to the electrical guys: What is the effect on typical motor drivers (such as the Jags) of having a motor being back driven and acting like a generator when the driver is trying to turn it the other way?

I suspect the short term effect isn’t catastrophic, as under-geared robots get pushed backwards quite often. But, I suspect that having this happen continuously, as might happen in a mismatched motor system, might cause something to overheat and fail.

Anyone know?

We did have some issues running a CIM FP Andymark Shifter (any series) over a repeated use of time. The FP finally gave out after 4 tournaments though.

There is nothing all that magical in this.

For motors with similar power ratings (e.g.250W BB + 340W CIM), the variations between matching stall torques or matching free speeds is not that big of a difference (~5:1 for stall torque, ~4:1 for free speeds). It is not that big of a deal, really.

For my tastes, in high power applications (which is why you want the extra motor isn’t it?), I prefer to have the smaller sized (and in the case I discussed power as well) motor do less of the work (so that it will have to dissipate less heat which, because it is smaller is more critical – heat transfer is a Area X DeltaT thing – for the same heat to dissipate the less Area the more DeltaT)

In other cases, I only need the more power in one or other of the speed ranges. For drive trains, I think most folks add motors for more torque at low speeds. To that end, I tend to match stall torques. If I give up some speed on the high end, Que Sera, Sera…
Good luck.

Joe J.

*circa 2002:

The internet never forgets :slight_smile:

Sorry Joe, I couldn’t resist!
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More specifically speaking, since I am unable to get my hands on more FP 0673’s is it viable to put one FP 0673 and one RS550 into the same gearbox at a overall reduction between 5~8

Two different motors do NOT fight. They simply distribute the load and run at a speed according their own characteristics, and you should gear them appropriately to run them at similar speeds, so that one is not doing the brunt of the work (why have two motors?).

If the 2 motors are geared the same, the 0673 will be working harder (and generating more waste heat) than the 550.

0673 & 550.png


0673 & 550.png

Not much. Every time a robot is pushed by hand this happens. It has never damaged any Victor or Jag that I’ve ever seen.