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Topic: Stepper Motor Voltage (Read 1 time) previous topic - next topic

Grumpy_Mike

Quote
Though the overvoltage causes more heat, the intermittent pulsing compensates for that

Yes that's right although the over voltage causes over current and it is the over current that causes over heating.

There are two forms of current chopping. One where you simply put a switched PWM signal into the motor control. The other that actually measures the current through the coil through measuring the voltage across a small resistor in the ground return path. Then when it sees that the current has reached the set value turns off the voltage. This is the better one but harder to implement.

focalist

#6
May 04, 2011, 04:48 pm Last Edit: May 04, 2011, 06:20 pm by focalist Reason: 1
Alpha test of wall/whiteboard plotter :

2n3904's were used to make the stepper controller.. I plan to re-use the darlington arrays salvaged from the printers for the finished version, but I wanted to build the stepper controller from discrete components to help teach myself a bit more.  Tom Igoe's stepper motor reference and the linked info from the Stepper library section of the Playground have been tremendously useful.  Using a two-wire control setup, I'm only using Digital 2-5 to control both steppers.. which is good because I plan to add another axis as well as a print head of sorts.

For this test, the steppers (one rated for 12v, the other 24v) are just being powered by the 9v "Vin" on the Arduino, drawn from a wall wart.

http://www.youtube.com/watch?v=fhtTlr_B-O4

Even underpowered that much, they seem quite up to the job.  They get a bit warm and hum a bit, and I suspect the motion isn't what it could be in terms of smoothness.. but it does work.  I think adding an external 12v supply makes sense, the wall wart isn't a very big one, and on general principles I don't like drawing real power across Arduino board traces...  

When the testing is complete there will be... cake.

MarkT

The key thing to avoid with stepper motors is to avoid over current - older motors would be demagnetized by over current (or even by disassembly), even if only briefly.  In the long term over current will cause overheating too.

For high performance switch-mode drivers are used that provide whatever voltage is needed to overcome back-EMF without exceeding the max current - this means much faster speeds from the motor (and because the controller is switch-mode it doesn't waste power from the high-voltage supply to do this).

However this is more complexity which isn't generally required for low speed use.
[ I won't respond to messages, use the forum please ]

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