Stepper motor ampage question

[m_c]

For a lather spindle, a stepper really isn't good. The torque will drop of far too fast, and I'd think you'll struggle to get even those shallow depths of cuts.

For cheapness I'd suggest finding a suitable basic DC motor, and combine it with a basic speed controller. Gear it with a suitable poly belt to get spindle speed within a suitable range, and you'll have a far more capable spindle.

[Fivetide]

For a lather spindle, a stepper really isn't good. The torque will drop of far too fast, and I'd think you'll struggle to get even those shallow depths of cuts.

For cheapness I'd suggest finding a suitable basic DC motor, and combine it with a basic speed controller. Gear it with a suitable poly belt to get spindle speed within a suitable range, and you'll have a far more capable spindle.

m_c what about a high-bred I believe they are much better at high rpm in keeping good torque? My mate has the original motor in bits he seems to think it can be salvaged, it may become a combination of DC and stepper motor like you say with a PWM. I want the flexibility of simple spindle work and carving, its all theoretical at the moment until I get it full assembled and tested - I'll let you know the results :)

[m_c]

It depends what you mean by hybrid. Pretty much all stepper motors you buy now are technically hybrid motors (most square motors are hybrid), and they are far better than conventional (typically round) stepper motors.

A quick search of eBay has thrown up the likes of this - https://www.ebay.co.uk/itm/200W-220V...e/253850778051
And they also sell a 500W version with a basic speed controller - https://www.ebay.co.uk/itm/500W-220V...d/253982275690

To give you some reference figures, using the speed torque curve of a leadshine nema 23 motor (http://leadshine.com/productdetail.a...S&model=57HS22 - one of the first motors I found that has the needed data), at 2000RPM depending on configuration/supply voltage it's only producing 0.4 to 0.7Nm, which works out at 80 to 150W of mechanical power. To get that relies on driving the motor at 68VDC. Drop the voltage, and the torque will drop of far quicker.

At that point costs are verging in to the same as buying a small single phase motor, or even three phase and cheap VFD. A quick ebay search shows a 1/2HP 3 phase motor can be had for £62, and a suitable VFD for £45. It will likely cost you more than that to get a suitable 68VDC power supply and suitable stepper drive.
The only thing with using a standard induction motor, is they are far larger than a similar power DC motor.

[Fivetide]

m_c I ment closed loop stepper sorry

- Closed-loop vector control technology ensures the high torque output, while ensuring that the motor does not lose step.
- With overvoltage, overcurrent, tracking error or over-error, and other protection features.
- Closed-loop driver can significantly improve the high-speed performance of the motor, increasing the effective torque of the motor by more than 30%; Effectively reduce the motor heating and motor vibration, the output current of the driver becomes larger or smaller as the load and speed increase or decrease; It can improve the processing speed and accuracy of the machine and reduce the energy consumption of the machine.

[m_c]

I suspected you really meant closed loop. Yes, they will offer more performance for a given size, and will recover more gracefully depending on settings (I forgot to mention, one big issue with using a stepper for a spindle, is if you do stall it, it will probably remain stalled until you stop/restart it).

If you want to run some comparisons, find the relevant speed/torque curves, then run the figures through the calc here - http://wentec.com/unipower/calculators/power_torque.asp

One thing I should of mentioned in my last post about DC/Induction motors, is the rated power is only at full rated speed. So if it's 200W at 4000RPM, it will only deliver 100W at 2000RPM.
With an AC motor and VFD, you do have the possibility of running the motor above it's rated speed, however you enter a power constant stage. I.e. if the motor produces 1Nm at it's rated speed of 1500RPM (works out to 160W), if you were to double it's speed to 3000RPM, you would only get 0.5Nm (which is still 160W)