Recommendation on high torque stepper motor

Other Hardware Motors, Mechanics, Power and CNC
1

I'm interested in buying a high-torque stepper motor. Eventually the goal is to incorporate in a device that will be used to lift the lower part of a human leg below the knee. Based on estimating the weight of a human leg below the knee it should be able to hold a torque of at least around 3 N*m. So far the only motors that I could find within budget (< $50) is here with a corresponding driver here.

  1. Does anyone have any experience with this vendor (Stepper Online). Or can anyone give reasons to or not to purchase this stepper motor? Or is the budget too unreasonable for a decent quality stepper motor with this kind of holding torque?
  2. Could anyone recommend what kind of battery would be needed to power this motor?
2

Overtorqued steppers just fail to low-torque rapid skipping, not a very safe means of support. A standard
DC motor in a current-controlled servo loop can deliver controlled constant torque on overload, and will be
much more efficient anyway.

You are going to need reduction gearing anyway, is your 3Nm estimate is allowing for this?

3

The battery depends entirely on how much time the motor is to be powered on. Remember, the stepper motor will use about the battery current no matter if it is moving or holding in position. So you can compute the ampere hours needed yourself.

Paul

4

MarkT:
Overtorqued steppers just fail to low-torque rapid skipping, not a very safe means of support. A standard
DC motor in a current-controlled servo loop can deliver controlled constant torque on overload, and will be
much more efficient anyway.

You are going to need reduction gearing anyway, is your 3Nm estimate is allowing for this?

Thanks. I'll start seeing what DC motor options there are then. Can you recommend any vendors? And no, the 3Nm estimate doesn't allow for that, so I'll have to take that into account.

5

So is 3Nm the load torque? Why did you think direct drive was a viable option in the first place?
What max rotation speed do you need?
Can you give more information on your requirements, this is the first step.
Does your torque estimate allow for angular acceleration? Have you an estimate of the moment of inertia
involved?

6

Have you considered a DC motor with a worm drive? The worm drive prevents the load from rotating the motor so that the load will stay in position even when the motor is powered off.

The screen-wiper mechanisms in cars use 12v DC motors with worm drives to give a low output speed and high torque

...R