Can I use two of MX-64 actuators for a differantial drive mobile base?

Hello Dear Roboticists,

I’m planning to build a ~50 kg (with max load) mobile base with differential drive traction system like turtlebot3.

Can I use MX-64 for wheels and, how much max. translational velocity my robot can have with a diameter of 20 cm wheels?

I roughly calculated 60 cm/sec but I have no idea about RPM value of the motor when lifting a weight.

I’m a software guy and I have no idea about selecting a motor:
http://emanual.robotis.com/docs/en/dxl/mx/mx-64-2/

@cosmicog
Hi,

According to your wheel diameter of 20cm and platform weight of 50Kg, total required torque should be (0.2m / 2) x 50Kg x 9.8N/Kg = 49Nm.
Dividing this by 2 for left and right wheels, you’ll need about 25Nm actuator.

Also, please note that the Radial Load of MX64 is about 40N at 10mm away from the horn which means your platform could be too heavy for DYNAMIXEL if you are directly connecting wheels to DYNAMIXEL.

Thank you

1 Like

Thanks a lot for the answer, The MX-64 page says;

  • Stall Torque: 6.0 [Nm] (at 12 [V], 4.1 [A])

So I cannot use this motor because 6Nm is way lower than 25Nm. (Or stall torque is something different?)

If, I can use the MX-64, how can I connect wheels correctly in order to reduce the load?

EDIT: I was just thinking that if turtlebot3 can carry 30 kilograms with two of XM430-W210s, 2 x MX-64 could take care of 50 kilograms. We also have 3 omni support wheels.

For more information about the stall torque for DYNAMIXEL, please refer to note below the Performance Graph.
One of the reasons that MX-64 does not fit to your application is because of the wheel size.
TurtleBot3 wheel diameter is about 6.5cm while yours is 20cm which requires about 3 times more torque to move the same weight platform.
Another reason is the Radial Load which could damage the DYNAMIXEL for long term use when heavily loaded.
You should consider connecting wheel axle to DYNAMIXEL with belt and pulley or chain so that DYNAMIXEL output horn should not affected directly by the platform weight.

1 Like

Thanks for the detailed answer. We could change the wheels but then, We would lose max speed. I was confused about all these parameters but the performance diagram helped a lot. I’ll use these motors for another project in the future :+1:t2:

Sure, please feel free to let us know if you need further assistant for applying DYNAMIXEL on your project. Have fun!! :smiley: