Question: Motor Power Basics

[blackskydave]

We are building a small linear actuator using stepper motors. We have tried the following combinations to drive an 7/8" ACME thresded rod and nut and find them all underpowered. The device is a lever system to lift 500 lbs.


(All NEMA 34 frames)
640 oz stepper motor with 12/1 gear reduction (8 wire, wired bipolar serial)
1200 oz stepper motor mounter direst (w/o reduction) 4 wire
1800 ox stepper motor with 3/1 gear reduction (8 wire, wired bipolar)

Power supplies we have tried are 24V5A, 48V5A and 48V7.8A

range of motor RPM is 0-30, maybe 45

We have a number of drivers from Keling and Anaheim Auto (5A to 10A). and can't seem to get enough power no matter the step options set (1/2 step thru to 1/64 step).

An amp meter placed between the power supply and the volt input to the driver reads, generally, something between .8 and 1.8A. Stalling the motor provides the higher (1.8A) reading.

By all our math and torque calculations any of the above combinations should work. We are thinking of going to 80V to see if that makes a difference. Any suggestions would be helpful.

[justfx]

Sounds like the drives are not set up correctly. Most drives require a specific resistor to set the maximum current of the drive. Seems like yours is set @ 1.8 amps.

Stick w/ the 48v 7.8a power supply - that should be sufficient. An 80v supply would only increase the top speed of the motors.

[blackskydave]

What do you mean "drives", we have the driver board set at 5A. Is that what you mean or is there something else you suggest we do?
Thanks for your reply.

[TOTALLYRC]

Originally Posted by blackskydave We are building a small linear actuator using stepper motors. We have tried the following combinations to drive an 7/8" ACME thresded rod and nut and find them all underpowered. The device is a lever system to lift 500 lbs. (All NEMA 34 frames) 640 oz stepper motor with 12/1 gear reduction (8 wire, wired bipolar serial) 1200 oz stepper motor mounter direst (w/o reduction) 4 wire 1800 ox stepper motor with 3/1 gear reduction (8 wire, wired bipolar) Power supplies we have tried are 24V5A, 48V5A and 48V7.8A range of motor RPM is 0-30, maybe 45 We have a number of drivers from Keling and Anaheim Auto (5A to 10A). and can't seem to get enough power no matter the step options set (1/2 step thru to 1/64 step). An amp meter placed between the power supply and the volt input to the driver reads, generally, something between .8 and 1.8A. Stalling the motor provides the higher (1.8A) reading. By all our math and torque calculations any of the above combinations should work. We are thinking of going to 80V to see if that makes a difference. Any suggestions would be helpful.

Originally Posted by blackskydave What do you mean "drives", we have the driver board set at 5A. Is that what you mean or is there something else you suggest we do? Thanks for your reply.

To get the max power verify that the stepper motor drive is set to max amps or at least the max amps that the motor(s) are capable of handling.

Make sure that the motor is wired bipolar parallel. I suspect that even the 4 wire motor is wired serial and that will kill the low speed power. Remember that the torque ratings are holding torque and the torque will drop off as soon as you move the motor. If you are using a 7/8" x 6tpi acme rod you will not have enough torque.

500lbs on the end of a 1ft lever is 500 ftlbs = 96000 oz in.

1 = 46,080 oz in
2 = 7200 oz in
3 = 32,400 oz in.

If my math is correct but I am to tired to double check.

Based on the holding torque of the motors times the gear ratios times the 6tpi acme screw. Plus the acme screw if about 50-60 % efficent so you will need even more power to make this work. Plus if you need to do this at any speed you will need even more power or gear reduction.
Mike