Arduino Forum

Using Arduino => Motors, Mechanics, Power and CNC => Topic started by: Asa Herring on Mar 04, 2012, 02:26 am

Title: Do I Have the Right Sized Motor?
Post by: Asa Herring on Mar 04, 2012, 02:26 am
(http://asaherring.com/Reef/Tower/RobotAssembly.jpg)
This is a rendering of my 2 axis plankton feeder. I has another wheel, like to white one shown here, at the other end of the 8 foot rail.

I have a stepper motor that was given to me but I don't think that it is working at its best. It is not running as well as the last time that I tested it. When I take the wire off and turn it manually, the drag is not constant as it makes a full rotation.

The motor was being tested in the assembly without having to move the carriage. It just has to drive wire around the two wheels that are 8 feet apart. There is very little drag on the system. The other wheel spins freely, even under a side load.

That being said, when I run the assembly, it does not running well. It is slow and chatters. Given the same amount of power from the driver, should I go with a motor that is bigger or smaller?

The motor that I now have is a 57BYG084/1.8 Step Angle/12V/4 phase/0.6A per/100ohm(500VDC)/20ohm per/Class B/25mH Inductance per/Rotor inertia 38g.cm2/holding torque 6Kg.cm

It is powered by an Arduino Mega 2560 with a Rugged Stepper Motor Driver. It does not have a micro-step mode.The spec.(s) on the driver say that it has a Peak DC current per phase of 2.8A. I am running it at 30V from a printer adapter. It supplies 0.83A which could be part of the problem as well. ? Would a 30V 5A adapter improve the situation and be safe to use?

I am wondering if I should buy the same motor or go with a different size, either bigger or smaller?


I use this code for MaxRPM:
int maxRPM = 150; // Top running speed of main stepper

instead of 300

and it still chatters and can barely turns the cable. Besides the potentially ailing motor, do you think that a bigger or smaller motor would perform better, powered by the Rugged Stepper Motor Driver, should I just buy the same thing new?
Title: Re: Do I Have the Right Sized Motor?
Post by: MarkT on Mar 05, 2012, 01:41 am
I have to say that a 2-axis plankton feeder sounds amazing, every home should have one(!)

I'm wondering if you have resonance problems - mechanical oscillation can cause a stepper to mis-step, and its common to need to damp-down oscillations to control this (micro stepping helps prevent oscillations starting when the step frequency is close to the resonant frequency).  Your large system probably has some low-frequency resonances?  Could these be damped (more friction?).  Of course this then means you might need more torque.
Title: Re: Do I Have the Right Sized Motor?
Post by: Asa Herring on Mar 05, 2012, 02:27 am
LOL I didn't want to take up peoples time explaining what it was. This won't help much but I am making a small plankton farm that will fit in my garage. For What? To feed my corals and fish in a sale water reef tank.

Tank you for another thing to considerate. It sounds like that might have a lot to do with it.

Now back to the questions.
Would a 5A adapter help things.
And should I buy the same sized motor, go bigger or go smaller? 
Title: Re: Do I Have the Right Sized Motor?
Post by: jwatte on Mar 05, 2012, 03:45 am
If your motor wants 0.6A per winding, and your power supply is rated at 0.8A, then you will get significant power sag when you step more than one winding at a time (which you will.)
I would try with a stronger power supply first. If that doesn't solve it, then try to adjust acceleration parameters of the stepper motion -- start and stop slower, run faster in the middle.
If that still doesn't work, I'd try for a bigger motor. Bigger is always better! (OK, I lived in Texas for a few years, I'm irreparably damaged :-)