astronomerroyal
New Member
Context:
I have built a machine that drags a (20lb, say) camera up some rails and just need to pick a suitable stepper motor. This is something that engineers must do frequently, but I can't work out a basic set of guidelines (other than torque requirements). I've browsed manufacturers' specs and the variety is wild and bewildering.
Desired specs:
Size: NEMA-23
Drive voltage: 12v battery
Current: I have some IRFZ20 MOSFETs for a simple driver so current not an issue(?)
Torque > 120 Oz-in. I have a 180:1 gearbox installed so massive torques aren't necessary.
max RPM @ 12v: ideally >100, but not critical.
Unipolar - I'm doing the switching from a uC. I know how to do basic full- half-stepping etc.
What I have
Currently I'm using this (cheap) stepper, and am not entirely impressed by it;
https://lib.store.yahoo.net/lib/webtronics/57BYGH207.pdf
and was thinking of replacing it with a motor from rows 4 to 6 of this selection,
**broken link removed**
but don't know how to pick one, and whether I could achieve those currents (>1Amp) with a constant 12 voltage (as opposed to a fancy constant current-type driver).
---------------------------------
The following just reflects tidbits of my understanding, please speak up if I'm horribly wrong,
Inductance: for a given voltage, a low inductance motor allows you to drive it at higher RPM, because the current in each coil can rise faster towards it's final value.
Reactance: By adding a resistor, and cranking up the voltage - provided one respects the max current rating - the overall impedance (resistance and reactance) becomes more resistive and less inductive -> higher rpm possible.
Voltage: the current and resistance ratings of steppers sometimes suggest they're rated for v.low voltages ~few volts. Fancy drivers achieve high rpm by exceeding this voltage during the current-rise time, then dropping it once current approaches max value.
I have built a machine that drags a (20lb, say) camera up some rails and just need to pick a suitable stepper motor. This is something that engineers must do frequently, but I can't work out a basic set of guidelines (other than torque requirements). I've browsed manufacturers' specs and the variety is wild and bewildering.
Desired specs:
Size: NEMA-23
Drive voltage: 12v battery
Current: I have some IRFZ20 MOSFETs for a simple driver so current not an issue(?)
Torque > 120 Oz-in. I have a 180:1 gearbox installed so massive torques aren't necessary.
max RPM @ 12v: ideally >100, but not critical.
Unipolar - I'm doing the switching from a uC. I know how to do basic full- half-stepping etc.
What I have
Currently I'm using this (cheap) stepper, and am not entirely impressed by it;
https://lib.store.yahoo.net/lib/webtronics/57BYGH207.pdf
and was thinking of replacing it with a motor from rows 4 to 6 of this selection,
**broken link removed**
but don't know how to pick one, and whether I could achieve those currents (>1Amp) with a constant 12 voltage (as opposed to a fancy constant current-type driver).
---------------------------------
The following just reflects tidbits of my understanding, please speak up if I'm horribly wrong,
Inductance: for a given voltage, a low inductance motor allows you to drive it at higher RPM, because the current in each coil can rise faster towards it's final value.
Reactance: By adding a resistor, and cranking up the voltage - provided one respects the max current rating - the overall impedance (resistance and reactance) becomes more resistive and less inductive -> higher rpm possible.
Voltage: the current and resistance ratings of steppers sometimes suggest they're rated for v.low voltages ~few volts. Fancy drivers achieve high rpm by exceeding this voltage during the current-rise time, then dropping it once current approaches max value.
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