Clamp arm stepper motor design — Parallax Forums

# Clamp arm stepper motor design

Posts: 1

Hello there,

I'm new to the forum and would like to ask for advice on a project that's ambitious for me. I would like to build a gripper arm which should consist of Nema 17 motors and a Nema 23 motor. The arm should be able to reliably lift 500g with a total length of 50cm at a good speed. The arm itself will be 3D printed from PETG. Now to my question. For the main axis, on which the entire gripper arm hangs, I chose this motor with 20Nm torque: https://www.oyostepper.de/goods-306-Nema-23-Getriebeschrittmotor-mit-4-1-Planetengetriebe-042-Grad-125Nm-28A-26V-Nema23-Getriebe.html
I need some advice if the power of the engine is sufficient and if the gearbox does not slow it down. Concerns give me the Nema 17 motors (59Ncm), which also bring a little mass.
I hope you can help me.

• Posts: 2,659

That's some serious torque....are you sure that you need it?

Craig

• Posts: 1,166

Torque = force × length
= 2kg × 9.81 N/kg x 0.5m
10Nm if the arm brings 2kg including the 0.5kg pay load as a first estimation.
You will need to design and then recalculate.
I have doubts if a printed arm is strong enough.

• Posts: 2,659

@"Christof Eb." said:
Torque = force × length
= 2kg × 9.81 N/kg x 0.5m
10Nm if the arm brings 2kg including the 0.5kg pay load as a first estimation.
You will need to design and then recalculate.
I have doubts if a printed arm is strong enough.

I had the impression that the motor was only for the gripper. I need to pay more attention to OPs

• Posts: 2,149

20Nm is the maximum torque the gear can handle. The motor only has 1.25Nm so with a gear ratio of 1:4 you get 5Nm. The efficiency is 90% and you need some margin to not to stall the motor so something around 3 to 4Nm is realistic at the output shaft.

• Posts: 2,149

@frank22 said:
The arm should be able to reliably lift 500g with a total length of 50cm at a good speed.

Torque is lever length times force. So 500g * 0.5m gives roughly 2.5Nm which is already near the maximum the geared motor can handle. You need some margin for acceleration, vibrations, friction and so on. So I'd suggest a higher gear ratio or adding a counterweight or weight balancing spring.

Those motors can turn up to 1000 RPM and more if powered correctly. So speed is not an issue. Even with a 1:10 gear you can move >360°/s.