RPM and torque conversion

Electromechanical Motors, Actuators, Solenoids and Drivers
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1

Hi,

I have a technical question about DC motor. The motor it is rated for 3000RPM and 110mNm. I need a motor for 5RPM and 60Nm. If I look at the power it would be okay, but :

  1. Is there a problem to go over the rated torque with a lower RPM?
  2. Would I have the right RPM on load?
  3. If I use a gearbox, would it reduce the speed variation if my load varies?

Motor in question : https://www.digikey.ca/en/products/detail/crouzet/89850007/6137262

Thank you!

2

Hello Hoola , Thank you for contacting us at Digi-key Forum

  1. Is there a problem to go over the rated torque with a lower RPM? yes you can damage the motor.

  2. Would I have the right RPM on load? well you have to add a gear to get the speed you want. this would be one solution.

If I use a gearbox, would it reduce the speed variation if my load varies? your torque if used at or higher will handle the load.

You may want to order a custom part.

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3

Hi Hoola,

Thanks for your inquiry. What is your application?

RPM correlates with speed & power. It could be safe to run a lower torque motor through a gear reduction box to get the torque you need without burning out the motor.

Gearing and motor torque would be fairly proportional, as example if you gear down by 1/2, then physical motor power output (after gearing) increase by about 2x, but of course at much lower RPM -as long as this is the RPM you need it should be okay.

You’d have to calculate the gearing you would need for a specified RPM, and assess if the motor torque is sufficient based on your gearing ration.

A lower gearing will provide slower RPM, more power to load, and thus more power will provide more load stability when the load fluctuates. Using a gear reduction box will also always increase motor resolution and create greater control of the output rotation with MUCH higher load stability.

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4

In the case I mention, 3000RPM and I want 5RPM. So, I need a 600 ratio. For the 110mNm it would give me a 66 000mNm or 66Nm. This ratio seems huge for the motor size. I think it would be a custom gearbox as Robert mention?

5

A custom gear box, or find a whole different motor/reduction box. Below are some other options somewhat similar:
https://www.digikey.com/en/products/filter/motors-ac-dc/178?s=N4IgjCBcpgzALFUBjKAzAhgGwM4FMAaEAeygG0QAmMABkoA4B2EIyygTgFYx2WrYa7AGyUQAXSIAHAC5QQAZWkAnAJYA7AOYgAvkR4MkIVJEy5CJclUaxOQoXwgSQMuYtWad27UA

We could special order something from Crouzet, but we would need the orderable part number. They may be able to provide you with what that part number would be:
https://www.crouzet.com/contact-us/

6

Page 9 of the datasheet for the motor in question contains relevant information, in the form of a torque-speed curve:

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This shows that the unloaded speed of the motor with nominal voltage applied will be approximately 4000 RPM. With 110mNm of load torque (66Nm after a 600:1 step down ratio, before losses) the motor speed drops to approximately 3000RPM, and will draw approximately 4A of current.

Actual speed will vary depending on the amount of torque delivered and any variations in the supply voltage to the motor.

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