I know several FRC and Vex teams have paired different motors with different specs, but they usually run at the same rpm. Theoretically it would be valid to run a 393 and 269 on the exact same shaft or mechanism and not have any problems, but I’ve known some teams who do this with their drive systems and constantly strip the internal gears in the 269s; my brother just switched his drive (both front and back) to a 3:2 sprocket ratio and just had the same problem. (Note: both the 393 and 269 ratios were 3:2 on the drive system and the internal gearings were in their original configurations)
I was speaking to an engineer and he said that it might be risky because even though the motors run at the same rpm, the speed the motors run at, when under load, would spike differently on a chart. Thus one motor would pretty much be dragging the next one along. But since some of the best teams like to pair different motor types, I wanted to know if there were any risks involved in coupling a 269 and 393.
In general, there is no risk in coupling motors of different types together. Ideally you gear them so their speeds are matched (the simplest way to do this is to gear them together at free speed) but this isn’t necessary…
As it was originally explained to me: “There is no magic… sometimes one motor may drag a bit, sometimes the other may drag a bit, but overall the motors will both contribute if your gearing is close to matched.”
The one caveat I’ll add is this… if you are using a system with LOTS of motors matched together you could end up in a situation where one motor is instantaneously being backdriven by multiple other motors (i.e. one motor is taking the shock load of 6 others!) This can be a problem, because the motors are not designed to handle this “above and beyond” load.