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Metallica Man X wrote:Interesting.
I wonder how well that lid will be able to handle the RPMs....
gary wrote:What speed do you need Harry?, I have successfully driven a Nipkow disk with a stepper at 750 RPM and I wouldn't think doubling that would be a problem. Somewhere on this forum I have an overview of how it is done (I think). You need a decent (not tin-can type) stepper and constant current RL driver. I found that I had to ramp up the speed to overcome resonances etc - no big deal.
harry dalek wrote:i am not sure what you mean about other than tin can types ,the ones that i think of like that are small flat printer types ?.
gary wrote:harry dalek wrote:i am not sure what you mean about other than tin can types ,the ones that i think of like that are small flat printer types ?.
Well, they are commonly found in (modern) printers, yes. The "tin-can" types are those with thin walled, pressed metal enclosures. The stepper you show in the images is a nema type of lowish torque, commonly found in floppy disk drives I think, it may work but the chances of success would be greater with a stepper of, say, 35-50 oz-in torque.
gary wrote:harry dalek wrote:i am not sure what you mean about other than tin can types ,the ones that i think of like that are small flat printer types ?.
Well, they are commonly found in (modern) printers, yes. The "tin-can" types are those with thin walled, pressed metal enclosures. The stepper you show in the images is a nema type of lowish torque, commonly found in floppy disk drives I think, it may work but the chances of success would be greater with a stepper of, say, 35-50 oz-in torque.
gary wrote:As a rule of thumb, if you are using the LR form of controller, you need about 10 times the steppers rated voltage. A lot of these steppers are rated at 2 volts or less (BTW when I say rated it has nothing to do with the breakdown voltage it is the voltage needed to bring the current up to the rated value), so a supply of around 20 volts is best but I am pretty sure I got up to 750 RPM on less than that.
BUT! above all remember that the rated current must not be exceeded (at least for any length of time) and so a series limiting resistor is mandatory - this form of controller is the least efficient (in terms of energy) of all the stepper controller methods, but it is also the easiest and cheapest by a country mile.
It is normal for a stepper to run warm, in fact very warm - the good ones are built to handle that.
Note also that with a bigger stepper the current will go up to a level where the ULN2003's are no longer viable (from memory they are about 1 amp - whereas the stepper I used required 2.5 amps). But don't forget when running in bipolar mode you just need 2 sine wave inputs (90 degrees out of phase).
To power it I used (to compare) a number of methods:
A power amplifier (very good but expensive, also reaching the required voltage can be a problem in some circumstances).
A push pull power transistor amplifier (good but was tricky to get going)
A class A amplifier pair using LM317s believe it or not (I never quite got this going at least to my satisfaction but is a plausible solution but requires hefty output capacitors).
I had intended to experiment until I had a cheap but effective controller that included ramping (essential) but got distracted and I will be more-or-less out of electronics design until I build my new shed which is a few months down the track I fear.
If someone else wants to pick the ball up on that all that is required is two power sine wave generators (and they can be pretty rough sine waves) with a common variable frequency - I was using a PC to generate the sine waves but it should be fairly trivial to use a cheap PIC or other micro controller. I think a simple push-pull amplifier will be the best solution but others may have further ideas - my main criterion was it to be cheap and simple.
PWM rather than LR may also be explored.
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