stepper motor's detent torque decreased

Whelzorn

I have 2 stepper motors that are exactly the same. I ran one of them for about 3 minutes at the voltage it specifies (12v) (and the power supply gave more than enough current), under quite a bit of load, but the stepper could handle it without much problem. It is the only one out of the two I had run, and the detent torque on the one I had running for 3 minutes is less than the one I hadn't run at all. (detent torque·[noparse][[/noparse]I think]·is the amount of force required to turn the shaft without any power applied to the motor). Is this normal/ok? I'm hoping it's not that the coils are being ruined under that much force...
BTW I was running the motor in unipolar mode if it matters.

Thanks,
Justin W.

Post Edited (Whelzorn) : 2/23/2005 5:01:35 PM GMT

kelvin james

You are right about detent torque, it is only the physical makeup of the the motor that determines this, with no power applied.
It can be useful to judge if the motor will hold a load while the coils are turned off, thus saving power and reducing the heat generated by the motor after it reaches it's position. I can't see this changing by use, unless heat is a factor reducing friction from the bearings, or the magnetism. If the motor is overloaded, it simply will not turn, and there is nothing there to damage. I'll do a test with mine to see if there is any difference after the motor has been run. I still think there is nothing to be concerned about.
kelvin

Whelzorn

ok, thanks alot, I will try my other stepper to see if it's just the initial running that affects the detent torque, mabe after that it will stay the same... i will wait for your results too.

thanks again,
Justin

Jonathan Allison

Justin, since you have your stepper motor(s) working would you be interested in taking a look at these schematics to see if I have this wired right pls?

No one seems to be able to help me. Some people are saying PIN 10 goes to + of you power source, others say it goes to -, parallax documentation is saying -, I don't really know what else the problem could be.



Thanks

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Johnny

Jonathan Allison

PS - In the above image, please don't go by the power source wire colors, I'm sick of moving them around, just go by the signs (+ or -)

thansk

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Johnny

SteveW

The black (common) wire of your stepper needs to go to the + of your supply (same as pin 10 on the buffer chip)
The -ve terminal of your supply needs to go to the system ground - which should also be connected to VSS on the stamp and pin 9 on the buffer chip.

All the buffer chip can do is connect selected ones of its output pins to pin 9, grounding them. It's up to you to put your load beween the output pin and the supply. The buffer chip can only 'pull down' - it can't drive any current out of its pins.

(At the moment, all you're doing is attaching all of your stepper wires to the same place - ground. No voltage from ground to ground, so no current flows anywhere, and nothing happens to your motor. )

Is there a good intro guide to transistors on the web / in a Parallax book? This honestly isn't as hard as you're making it [noparse]:)[/noparse]


Steve

RickB

Justin: Many years ago I worked on Apple II computers. One of the problems I had to contend with was the 5 1/4 floppy drives overshooting the intended position when moving to a new track. The positioner was a spiral track in a plastic circular disk attatched to a stepper motor. This was only a problem after a lot of use. According to an engineer at Shugart, the magnets in the motors became demagnetized over time. The greater the current, the sooner the problem showed up. It may be that Apple used to much current to overcome the inertia of that goofy positioner. The only recourse was to replace the drive. You may have run it at to high a current. The process is not reversable by mere mortals.

Rick

kelvin james

I checked my motors, since i have 1.8 degree steppers, it is very difficult to see any variance.
Unless you have a use for detent torque, it is a non issue. When you have the coils 'powered' and are not getting the same holding torque, then you might have some concern.

kelvin