Two motors, one axle torque question

So our design just changed to where we have 2 motors on a single axle, before it was one. I already know the stall torque and input/output torque for the single motor. Both motors are also the same rpm, same current, and same stall torque . I was wondering how the stall torque and input torque would be effected by adding the second motor, would it be doubled?

I did find this, but it’s not from the most reliable source and haven’t found any other info on this

The torque on a DC motor is proportional to current flow. Two motors will be able to do twice the work of one. To drive one axle, it is often more economic to use one larger motor than several smaller motors.
Source https://www.physicsforums.com/threads/multiple-motors-to-drive-a-single-axle.743571/

Below is a before and after of the motors on the axle

      M—o—           M—o—M
       —O—           —-O—-
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yes

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Yeah it would double the overall torque, but with that setup you do want to be careful about ease of access. If you ever need to pull that axel off, you’d have to take a motor off, and if the space in between the two motors is small it can also be a little tricky to get the motor off. During a competition this can hurt you if you ever need to fix something really fast.

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Good thing I’m not on the build team :wink:, but seriously, thankyou you @ZackJo and @John_TYler for helping me out and I’ll let my teammates know to be aware of complications of removing the motors.

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@erose My team had a similar way of mounting motors for our puncher last season (we were using cortex), and it was very annoying to maintenance. When you build your design make sure you tighten screws and loctite what you can.

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yup. wish I did that when I was in a similar situation. Looking back…Ugh.

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First, to make an easy access for tightening screws on both motors they could be mounted at 90 or 180 deg angle from each other.

In addition to that, you need to periodically check that axle that connects the motors could be easily moved by hand about 1mm (along its length). If it can’t - that means that it is not aligned and motors waste some of the power on the extra friction. If you cannot get them aligned, then it is better to put each motor on a separate axle and connect them with either chain or gears.

Finally, for the extra credit, you can get the current value from both motors. If one reads larger than the other, it means that one of the motors is doing extra work. In this case you may want to find better matching pair of motors and, maybe, switch to your own PID load balancing algorithm, instead of relying on the V5’s built-in. That would be true for any connected motors - shared axle, geared, or chained. But, in most cases if you get matching motors up to 5% load difference shouldn’t be a problem.

However, doing or just being aware of load balancing will look great during the judges interview! :slight_smile:

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