# 4-Wheeled Mobile Robot, Motor-Torque, RPM Calculation

I want the torque, rpm of every motor to be used considering certain factors, in a 4 wheeled robot as you see in the picture below.

Here are the factors affecting motor specifications that I Had taken into account::::

2. Wheel Mass = 0.25KG
3. Wheel outer Diameter = 0.1 m
4. Number of Wheels = 4
5. Friction Coefficient = 0.4 (hard plastic on dry plywood)
6. Drive system efficiency = 70% (this is actually from brushed dc motor averages)
7. Transmission = Direct coupling
8. Floor maximum slope = 10 degrees
9. Load holding while the motor is stopped = Yes
10. Required robot velocity = 24 m/s
11. Required robot Acceleration = 8.8 m/s^(2)
12. Number of motors = 4
13. Type of wheel = Omni wheel/Normal wheel (not sure how you calculate for omni wheels as they have rollers on them)
14. Type of Motor = Brushed DC motor

From online motor sizing tools, I am getting a total torque requirement of 6 nM for the entire system. However, this answer varies from other online resources and my own personal math that I had done. I also tried to take into the type of wheel to be used as a factor but the I am unsure of the math involving Omni wheels and their load.

Can someone shed some light on Getting the torque and rpm for motors in this system, on normal wheels and on Omni wheels if possible?

If anyone has any papers or did similar math for getting these values, kindly share your workings if possible, it will be of great help. Also I apologize if this is a wrong stack exchange to post as it can be considered a borderline Physics question.

• Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer.
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Commented Oct 31, 2021 at 18:15

Hope this still helps you, you can try here:

https://www.societyofrobots.com/RMF_calculator.shtml

https://www.orientalmotor.com/motor-sizing/index.html

https://www.maxongroup.de/medias/sys_master/8819062800414.pdf?attachment=true

(Page 23, Sorry it is in german but it has everything for estimations.)

Load holding when the motor stops: I think without brakes you will need self-locking gears.

You should use rolling resistance instead of friction. https://www.engineeringtoolbox.com/rolling-friction-resistance-d_1303.html