Rotary Motor recommendation

Help & Support Robot Parts
1

Hi,

I would like to buy a small rotary motor to drive wheels at specific relatively low speeds (depending on current).
However, I would like it, if somehow given external torque (i.e. through gravity for rotation) the motor could rotate at a higher speed.
Also, if it’s possible to have a brake mode, such that at this state reasonable external force could not rotate the shaft, that could be great.

Could you suggest any appropriate product?

Thanks

2

Hello @ljaybar and welcome to the forum,

I would like to buy a small rotary motor to drive wheels at specific relatively low speeds

Could you be more specific about the speed? torque? This guide can help you get an estimate of the torque the motors would need:

I would like it, if somehow given external torque (i.e. through gravity for rotation) the motor could rotate at a higher speed

Does the speed need to vary depending on the torque, or could a potentiometer be used to control the speed? If you want to use a potentiometer/joystick to control the speed you will also need an Analog Voltage DC Controller.

Also, if it’s possible to have a brake mode, such that at this state reasonable external force could not rotate the shaft, that could be great.

Yes, you can use electromagnetic brakes on your motors and use a motor controller that has power outputs for them, for example the Sabertooth controllers.

1 Like
3

Hi,

Thank you very much for the reply.

Thanks for the recommendations so far. I’ll try to be more specific.

The rotary motor itself should turn at max 10 km/h.
I am okay with the speed being determined by the voltage input (so controlling the speed through the amount of voltage supplied,

And what I meant with external force was, that if the motor is at 4 kmh for example, and now the wheels are riding down a slope, the motor will not be like the first gear of a car and maintain 4 kmh but rather be like higher gears and let gravity increase the speed.

With the brakes, that’s a nice idea, if you could recommend parts for the motor (with/without brakes and appropriate controllers, I would really appreciate that!

Best

4

The rotary motor itself should turn at max 10 km/h.

In order to calculate the speed, you would have to take into account the wheel radius and the weight of the robot, this is why I suggested using this tool:

I am okay with the speed being determined by the voltage input (so controlling the speed through the amount of voltage supplied

Good because that is exactly what a motor controller does, varies the voltage supplied with pulse width modulation.

And what I meant with external force was, that if the motor is at 4 kmh for example, and now the wheels are riding down a slope, the motor will not be like the first gear of a car and maintain 4 kmh but rather be like higher gears and let gravity increase the speed.

You could achieve something similar by measuring the current draw on the motors (some motor controllers already include this function), as the torque is related to the current draw (the higher the needed torque to maintain a certain speed the higher the current draw) you could use this information to increase/decrease the speed.

5

Hi,

Thanks for the reply. I used the tool and these are the specs:

23.885 rev/m

torque: 0.0083538 Nm

Total power: 0.020885 W

Current: 0.0041769

Battery Pack: 0.0041769

Is there any recommended rotary motor for these specs? (that will not resist external torque too much, and can brake?

Thanks a lot,

6

Hello @ljaybar,

As the torque needed is not high you have lots of options so I recommend checking the DC motors comparison list:
https://www.robotshop.com/en/compare-dc-motors.html

Check if the speed and torque specifications match your requirements (and take into account that that speed is without load and that you can decrease the speed with the motor controller). If you don’t want it to withstand a lot of torque then choose one without gear reduction.

7

Hi,

Thanks very much for your help with this!

One last stupid question. How do I know if it has gear-reduction? Should I naturally assume it doesn’t if nothing is stated?

Thanks

8

If it says gearbox, or if it mentions a gear ratio like 10:1 or 50:1, or if it has a high torque it probably has a gear reduction.