high speed stepper

[Mariss Freimanis]

Low inductance and low current current equals tiny motors (NEMA 17).

Mariss

[pminmo]

Originally Posted by jseiler Indeed. I've ordered a small desktop cnc with .1" lead screws. Not expecting whip as the largest possible unsupported length would be less than 14". I'm very limited by the choice of control box, limited to 5-8K pps (don't ask ). This means that 1000rpm = 100 ipm on this particular machine. Lets pretend I can get 120 ipm or 2 ips. 2 in/sec * 200 steps/rev * 10 rev/inch * 2 pulses/step = 8000 pulses/sec. The x axis (one containing z carriage) is the only one that needs high speed and high acceleration. The Y axis can be slower and have low acceleration (due to the application). The Y axis is the one with the highest load as it needs to move both the x axis gantry and the z axis. Force is limiting to my acceleration. Acceleration is limiting my ultimate speed because of the short gantry. I won't be sure how much everything weights and how much screw friction I have until I get the machine. Once I get everything spinning and working right, I'l likely ditch the slow control system and get something with a lot more current and pps capability. Still, any suggestions on low inductance, low current motors would be appreciated. John

Usually people want rpms to traverse long spans, then mechanics become a serious factor.

FYI, I'm getting around over 14xx rpm on a small machine similar in dimension with a keling KL23H51-24-8B running unipolar at 42V. Leadscrew is 12tpi acme. Quarter step, Allegro SLA7078. Over 120 ipm reliably. Their 282oz in motor has lower inductance and coil voltage rating.

[jseiler]

Ok, thanks guys. Now for the followup question:

I am limited to 2A drive current. Am I better off using half coil or parrallel on this motor (bipolar drive)?

http://www.kelinginc.net/KL23H256-21-8B.pdf

[pminmo]

I would think you would get more power at 2A with parallel even though its only 66% of the rated current. You are doubling the number of coil turns at the same current.

[jseiler]

At low speed, I definately agree, but I don't have any torque issues there. At high speed though? Hmmm. I've not had much luck finding information about torque speed curves running half coil. Is it exactly the same as running unipolar? If so, I can compare pretty reasonably (unipolar vs scaled down bipolar).

John

[jeffs555]

I am limited to 2A drive current. Am I better off using half coil or parrallel on this motor (bipolar drive)?

You are doubling the number of coil turns at the same current.

Going from half coil to parallel does not change the number of turns. The coils are wound with the two wires in parallel (ie bifilar), and connecting the the two coils in parallel is equivalent to just increasing the wire size. The only effect is to decrease the resistance of the coil.

For the same current, bipolar half coil, bipolar parallel, and unipolar will all have the same torque vs speed characteristics. If you use the unipolar current, you can use the unipolar curves for all three connections. The motors would run cooler with the parallel connection because of the lower I^2 R losses.

[pminmo]

Jeff's right and wrong, but the result he is correct.

I wasn't thinking...(too much grey hair) The current is split between the two windings, so the effective result is the same. So 2A thru half coil should produce the same magnetic effect as 1A through two windings (bifilar). However you would have a net effect of a lower coil voltage so the parallel winding should still be better as inductance would be the same.

[jseiler]

Got it. I think it finally sunk in. Thanks guys.