gearbox calculator

[apalrd]

Originally Posted by 1683cadder

oh lol, I finally got how to use JVN. But the question still remains. If you are using two different motors in a gearbox, then how do you factor that into the calculations?

There are a couple ways to do this.

I use JVN's Old design calculator for this, since it was written in the olde days before the CIM was the king of drivetrain motors and people mixed all kinds of things to drive. It's available here. I also have a version Here which includes battery voltage modeling, useful for some advanced simulation but not necessary for the basics.

To calculate the contribution of a motor, it's easiest to start with the speed and calculate the torque. Since the speed of each motor is the same (or tied through a fixed gear ratio), we can use it to calculate the torque contribution of each motor. You don't have to do this at free speed.

The JVN Old Calculator method (Acceptable for basic modeling, not quite ideal) basically creates a single 'super-motor' which you specify a free speed and gear ratio for each input motor and it calculates the sum torque for use as an assumed single motor. This is good enough when you match to free speeds. You can match free speeds and get moderately good results. IF free speeds are matched perfectly, then each motor will always be running at the same % operating point, and produce it's share of torque. For example, say we have a motor (Motor A) which produces 4 units of torque at 5 units speed. Another motor (Motor B) produces 1 unit of torque at 10 units speed. We gear motor B 2:1 relative to motor A such that they are spinning at the same speed when mixed, and the torque output at the mixed point will force motor A to produce 2x the power and torque of motor B, while consuming 2x the current.

It's also possible to design for non free speed matching. In that case, you could force the 'weaker' motor to produce more than it's share of power at your design speed. This can be useful sometimes.