Motor Sizing

Help & Support Robot Parts
1

I am going to start a first DIY toy car project, and my input parameters in the sizing calculator seem to make sense to me (except I am not sure whether I want/need 6V or 9V or 12V, so let’s go with 9V for now):

Total mass: 1kg
Number of drive motors: 4
Radius of drive wheel: 0.05m
Robot Velocity: 5 m/s
Maximum incline: 30deg
Supply voltage: 9V
Desired acceleration: 5 m/s2
Desired operating time: 1h
Total efficiency: 65%

This gives me the following results, but I need help interpreting this:

Angular Velocity: 955.41 rev/min
Torque: 1.9417 kgf-cm
Total Power: 19.048 W
Maximum current: 2.1165 A
Battery Pack 8.4658 Ah

Basically, what is not clear to me at all from above is what are the specs of the motors that I am looking for?

Does this straightforwardly translate into motors where the specs say (for each of the four motors) that at maximum efficiency I get

  1. torque of about 2kgf-cm / about 0.2Nm / about 28oz-in
  2. speed of about 1000rpm
  3. about 20W
  4. current of about 2.5A

??
What about torque stall / current stall??

Next question then of course: does such a thing exist? Unfortunately, it doesn’t seem to be possible to filter your DC Brushed Motors by these specs, so it’s quite hard to go from the results to the calculator to a choice of motors (and then from there to a choice of matching motor controllers).

PS: Yes, I realize that 1kg is maybe a bit heavy for my velocity and acceleration “requirements”, but first of all I want to make sure I understand how to go from the calculation results to specs that I can use to narrow down my choices of motors (and then motor controllers). I can then still lower the weight of the vehicle and/or my velocity and acceleration requirements.

Thanks in advance and sorry for the long question…

2

The specs provided are per motor, so each motor should have at least the specs provided:

]~1000rpm/:m]
]9V nominal/:m]
]28oz-in continuous torque/:m]The acceleration is really high, and the wheels are really small.
Normally 9V is not used often - you might consider 6V or 12V. You won’t find many at 9V nominal.

The tool cannot provide stall torque - this is the value for the motor when the shaft is prevented from rotating. The continuous torque is often 1/4 to 1/3 stall.
Given that most DC motors rotate at ~5,000 to 10,000 rpm, you’d be looking for a 10:1 gear ratio.
We do apologize for the search and are working to improve it.

3

Ok, thanks a lot for that. I didn’t realize that my acceleration is really too high. Fair enough, I can adjust that down a bit as well as the weight. So is there a 12V motor that gives me about 14 oz-in torque at 1000rpm - or 150 oz-in at 100rpm - it’s a more or less linear inverse relationship, right? Is there such a thing? Thanks again!

4

Keep in mind that gravity is 9.81m/s^2, so 5m/s is 1/2 gravity or “half a G”.
Your RPM is high because of your wheel diameter.