Author Topic: Stepper motor to drive a lathe tailstock  (Read 2752 times)

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Offline peter-h

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Stepper motor to drive a lathe tailstock
« on: April 05, 2022, 03:13:22 pm »
I think a motor like this would do it
https://www.ebay.co.uk/itm/203451317725

but I can't work out whether the controller will accept a simple

- potentiometer for the speed
- toggle switch for velocity

Better still would be a pot with a joystick, spring loaded to centre (zero speed) and push left (to drive in) and push right (to extract).

The people who sell these are not replying to any questions.

Can anyone recommend something off the shelf?

Many thanks in advance.
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Offline ve7xen

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Re: Stepper motor to drive a lathe tailstock
« Reply #1 on: April 05, 2022, 06:36:59 pm »
Motors + drivers like this are almost always step + direction input. You set the direction input either high or low to control motor direction, and then pulse the step input based on the number of steps per rev the driver/motor is configured for.

You will need to add a separate motion control system to plan the motion and generate the driver pulses, especially if you want nice things like acceleration. You could use something like an Arduino with your own code, or running a firmware like GRBL to interpret G-code, or even some simple logic and a 555. Or you can just buy something like this https://www.ebay.com/itm/313508538752?hash=item48fe90a980:g:G3AAAOSwMxRgh6hc

The documentation for this CL57T driver on StepperOnline seems reasonable...
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Online thm_w

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Re: Stepper motor to drive a lathe tailstock
« Reply #2 on: April 05, 2022, 08:52:52 pm »
It explains it to you right in the listing photos: "Pulse/Direction 5V compatible input".
No need to ask the seller, they probably don't have a detailed understanding of this item, as they just dropship.

Here is another pulse gen: https://www.aliexpress.com/item/4001178849568.html

If you just care about direction, speed, and rotation, and not absolute values, this should be easy to setup electrically. You don't need a closed loop unit, but its nice to have.
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Offline langwadt

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Re: Stepper motor to drive a lathe tailstock
« Reply #3 on: April 05, 2022, 08:59:56 pm »
Can anyone recommend something off the shelf?

a cheap battery drill
 

Offline peter-h

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Re: Stepper motor to drive a lathe tailstock
« Reply #4 on: April 05, 2022, 09:20:11 pm »
I am surprised there isn't an integrated fwd/back/speed controller because they exist for 3 phase brushless motors; most of the "inverters" have exactly this function. Unfortunately I would need a gearbox...
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Offline ve7xen

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Re: Stepper motor to drive a lathe tailstock
« Reply #5 on: April 05, 2022, 09:44:43 pm »
I am surprised there isn't an integrated fwd/back/speed controller because they exist for 3 phase brushless motors; most of the "inverters" have exactly this function. Unfortunately I would need a gearbox...

You generally buy a closed-loop stepper because you need precise position control, which the step/direction interface offers. It's not really the kind of motor you buy for non-precision forward/back kind of use. The same vendor also sells geared BLDC kits that might be more suitable for your use case.

You can get an 'analog input' stepper driver, that integrates the pulse generation bit, then you can just hook wire up a DPDT two-way momentary switch and speed pot directly to the driver, but it's a lot less common and probably more expensive than the typical step/direction setup.
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Offline peter-h

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Re: Stepper motor to drive a lathe tailstock
« Reply #6 on: April 06, 2022, 10:56:09 am »
Apparently this will do it (with a pot, or a voltage input; not sure yet)
https://www.micromech.co.uk/Product/100628/rta-andc-94-boxed-stepping-motor-drive

and this motor is recommended although I reckon it must be same as all the others (of a given size)
https://www.micromech.co.uk/Product/101137/sanyo-denki-86mm-18-bipolar-winding-ce
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Online thm_w

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Re: Stepper motor to drive a lathe tailstock
« Reply #7 on: April 06, 2022, 09:20:30 pm »
That is also a step/direction based system.

https://cnc-steuerung.com/media/pdf/99/92/4d/CSD94_Manual.pdf

Although the way  they've described the enable input is slightly confusing:

Quote
ENABLE INPUT (RUN operation mode): When this signal is ON, motor rotate in the direction set
by DIRECTION signal. When this signal is OFF the motor stops and after adjustment it keeps the
load blocked with the torque at 50% of the set value (automatic current reduction). The maximum
delay at enabling or disabling is lower than 1.5 millisec. In case a revolution time lower than 20
millisec is needed. command circuit has to be realized very carefully and thus it is suggested to
contact RTA.

« Last Edit: April 06, 2022, 09:22:47 pm by thm_w »
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Offline ve7xen

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Re: Stepper motor to drive a lathe tailstock
« Reply #8 on: April 06, 2022, 11:52:16 pm »
It looks like RTA does produce analog input stepper drives, but you would need the ADW series for that. There is also the popular-with-hobbyists brand Leadshine DM805-AI.
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Offline peter-h

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Re: Stepper motor to drive a lathe tailstock
« Reply #9 on: April 07, 2022, 11:14:07 am »
You are quite right. Only the ADW does analog input. So I got duff advice from Micromech...

The ADW96 ought to do what I want: https://www.rta.it/uploads/ADW_eng%205.pdf
0-5V or 0-10V but I can't find the voltage for the direction signal... can't be that complicated.

And it looks like almost any stepping motor will work with this, so the choice is going to be based on the guesstimated holding and driving torque.
« Last Edit: April 07, 2022, 11:41:41 am by peter-h »
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Offline ve7xen

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Re: Stepper motor to drive a lathe tailstock
« Reply #10 on: April 07, 2022, 06:38:04 pm »
I'd think the inputs are optocouplers with internally-commoned anodes. Common should generally connect to 5V and then ground the inputs. But this could be a different setup.

Best to get a proper manual to confirm the wiring and also you will need to know the dip switch configuration to enable the appropriate analog input mode, current limit, etc, and that the mode will function as you want, before you purchase. It also claims to have an internal logic supply for the pot / inputs which would be useful for your application, but I don't see this in the pinout.

And yeah, stepper motors are commodity parts, such a drive should work with any two-phase/bipolar stepper motor, though you would want to size it appropriately for the maximum motor current, so you can set an appropriate current limit in the controller.
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Offline peter-h

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Re: Stepper motor to drive a lathe tailstock
« Reply #11 on: April 07, 2022, 07:36:05 pm »
ISTM that if you want to run at some high RPM, you need to choose a motor with a low enough inductance to get the current to build up fast enough to produce the required torque, and/or use a high enough voltage.

My plan is to run this at the bottom voltage which is 24V.

One can get say an 86mm stepper with an inductance of 2.7mH, or more, all the way to 10x that.
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Online thm_w

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Re: Stepper motor to drive a lathe tailstock
« Reply #12 on: April 07, 2022, 10:13:57 pm »
The ADW96 ought to do what I want: https://www.rta.it/uploads/ADW_eng%205.pdf
0-5V or 0-10V but I can't find the voltage for the direction signal... can't be that complicated.

In the datasheet I linked:

Quote
STEP INPUT (STEP operation mode): Step is performed on ON-OFF transition of this signal. Suggested duty-cycle: 50%. Max. frequency: 60 KHz with square wave signal supplied from a source with voltage between 3.5 and 13 Volt. In any case STEP signal half period has to be higher than 8 ╬╝sec.

direction would be the same voltage.
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Offline peter-h

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Re: Stepper motor to drive a lathe tailstock
« Reply #13 on: April 08, 2022, 02:40:08 pm »
I found out a couple of things:

The motor inductance is very relevant. Sanyo motors, say 3mH, have much less than most others, so develop a given torque at a much lower voltage. A lot of the chinese motors are 30mH.

One can do this whole thing with a 100 quid chinese PLC... if you know how to program a PLC.

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Offline langwadt

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Re: Stepper motor to drive a lathe tailstock
« Reply #14 on: April 08, 2022, 06:49:05 pm »
I found out a couple of things:

The motor inductance is very relevant. Sanyo motors, say 3mH, have much less than most others, so develop a given torque at a much lower voltage. A lot of the chinese motors are 30mH.

Everything equal, lower inductance implies fewer turns of wire, so requiring higher current to develop the same magnetic field and thus torque.  Physics rarely gives you free lunch.
 
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Online thm_w

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Re: Stepper motor to drive a lathe tailstock
« Reply #15 on: April 08, 2022, 08:42:01 pm »
The motor inductance is very relevant. Sanyo motors, say 3mH, have much less than most others, so develop a given torque at a much lower voltage. A lot of the chinese motors are 30mH.

Its not necessarily a "cheap vs expensive" tradeoff as you imply. Even expensive brands have both low and high inductance motors (2-50mH), depending on your application.
Here is a $10 2.5mH nema23: https://www.aliexpress.com/item/1005003030339932.html

https://blog.moonsindustries.com/2019/10/24/what-are-the-important-parameters-for-stepper-motor-selection/
https://www.motioncontroltips.com/faq-inductance-phase-imbalance-degrade-performance-can-drives-help/
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Offline ve7xen

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Re: Stepper motor to drive a lathe tailstock
« Reply #16 on: April 08, 2022, 09:25:11 pm »
One can do this whole thing with a 100 quid chinese PLC... if you know how to program a PLC.

DM805-AI is about 85 quid and will do what you want out of the box.

Do you need to run at high RPM in this application? What is the target RPM?

Quote
One can get say an 86mm stepper with an inductance of 2.7mH, or more, all the way to 10x that.

Sure, the 86mm just describes the mounting dimensions so there's a huge variety of sizes, not to even mention the variety of torque curves / current ratings available within a size class.

I think a PMDC gearmotor would be the more 'usual' way to do this, as someone mentioned, basically a drill motor.
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Offline peter-h

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Re: Stepper motor to drive a lathe tailstock
« Reply #17 on: April 08, 2022, 09:49:23 pm »
Target RPM is zero to about 50.

Torque, I have guessed at about 1NM. So I chose that size, 86mm, because it should be big enough, and there is room.

It is for driving the tailstock of a bench-top lathe. It is a repetitive operation which is tedious if you are doing thousands of them. Normally you turn a wheel by hand.

I have now ordered 1 x DOUBLE SHAFT STEPPING MOTOR 103-H8221-6211, but due to a mixup I ordered the wrong controller (digital input only), not the RTA ADW96 (or 06 for the open-PCB version) which I am now trying to get. I am getting this straight from Italy because the UK disti is not replying with prices.

I don't want to do PLC programming. Done enough C lately :) and have never played with PLCs.


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Offline NorthGuy

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Re: Stepper motor to drive a lathe tailstock
« Reply #18 on: April 17, 2022, 01:50:32 pm »
Target RPM is zero to about 50.

At such speeds, the inductance won't matter much. The driver must be able to increase the current in the winding from zero to the rated current during the step. If your motor has 200 steps/revolution, at 50 rpm, this is 60 ms per step. Use the supply voltage (minus I*R, minus back EMF) and the motor inductance to calculate whether 60 ms is enough to attain the desired current. Give it some margin because if it's right on the edge then you'll get current of triangular waveform (or worse, depending on the driver) instead of a nice sine wave which you could get with fine microstepping.
 

Offline peter-h

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Re: Stepper motor to drive a lathe tailstock
« Reply #19 on: May 10, 2022, 12:51:44 pm »
I got it running using the ADW06
https://www.rta-store.com/en/product/141757-azionamento-open-frame-adw-06-v-with-intelligent-speed-controller--adw6v
and the MSH34196
https://www.rta-store.com/en/product/141831-motore-passo-passo-103-h8221-6211-msh34196

Took a bit of trial and error and getting data sheets on the dipswitches which are not openly published...

Interesting that the slower the stepper motor runs the more current the whole thing draws.

All kinds of quirks on the controller config e.g. not easy to do it so you can change fwd/rev with just the DIR switch, without tripping some sort of overcurrent protection. There is a ramp but is quite fast and barely noticeable, and it doesn't get applied when you change direction. I think one needs to build a circuit to generate the required analog input, to get it to do exactly what you want.

The torque of this motor is immense.
« Last Edit: May 10, 2022, 01:18:21 pm by peter-h »
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Offline eugene

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Re: Stepper motor to drive a lathe tailstock
« Reply #20 on: May 10, 2022, 05:27:05 pm »
I wouldn't try to flip the direction switch while the motor is moving. I regularly use the cruise control on my car, but I still come to a complete stop before putting the transmission into reverse.

Whether the controller has digital or analog inputs, you still need to generate the motion profiles somehow. This could be done by a human twisting knobs and flipping switches, but if you want automation then, well, it will require more. But, automation is a rabbit hole with no end. Digital inputs allow precise positioning. That means that if each part is chucked into the lathe at exactly the same spot, then you could program the tailstock to go to a specified position and stop. That sounds dangerous to me, but some controllers can be told to run the motor at a specified torque. That means you could program the motor to advance until the tailstock is tight and then stop. This is basically what you do when you turn the knob by hand.

I once help some students with a project where an automated vice would close to a programmable point by monitoring the current of a DC motor. It ended up working, but it was trickier than you might guess at first. Like I said, automation is a rabbit hole.
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Offline peter-h

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Re: Stepper motor to drive a lathe tailstock
« Reply #21 on: May 10, 2022, 06:22:41 pm »
If I drive the analog input "manually" then I can achieve bidirectional motion with "instant" direction changes, with the acceleration/deceleration being controlled by the ramp slope and not by the controller itself.

It is surprising that this controller implements a ramp on start/stop but does not implement it when you flip the DIR input. I can see what they did; it is easier.

The comparison with a car holds only to a point, and similarly this motor can be reversed while moving if it is running slow enough. The ability to reverse it is related to the maximum motor current (dipswitch config) which is not surprising because more current is needed if reversing at a higher rpm. What I found is that because the max rpm is so low (about 50-100) the drive has enough power (when set to 6A max) to reverse the motor instantly, so I don't need to build any external circuitry. I am running at 24V and at 48V or so there would be much more power still.

In fact if you set the current too low, the motor does not run, which sort of surprises me.

This isn't moving the whole tailstock; it is just turning the middle bit which feeds the drill in/out. I will post a pic when it is done.

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Offline peter-h

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Re: Stepper motor to drive a lathe tailstock
« Reply #22 on: May 18, 2022, 10:26:59 am »
One funny thing I found, with this dual shaft motor, is that if you turn it by hand, it generates enough EMF to light up the LEDs on the controller board :)

It may not do the controller much good...

So I have to add some switching to the two motor coils to stop this.
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Online thm_w

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Re: Stepper motor to drive a lathe tailstock
« Reply #23 on: May 18, 2022, 09:33:49 pm »
One funny thing I found, with this dual shaft motor, is that if you turn it by hand, it generates enough EMF to light up the LEDs on the controller board :)

It may not do the controller much good...

So I have to add some switching to the two motor coils to stop this.

Unless you really crank it, or shut it off when its running at high speed, the voltage should not exceed regular supply voltage.
Considering your driver is rated for ~75V it should be fine.

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Offline peter-h

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Re: Stepper motor to drive a lathe tailstock
« Reply #24 on: May 29, 2022, 07:57:51 am »
Getting there





I will post pics later of the finished thing.
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