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Stepper motors

Difficulty setting up to run smoothly

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Steve Pavey23/07/2021 21:05:45
351 forum posts
40 photos

I've spent the last few months putting a laser cnc together and have just got to the stage of testing the stepper motors.

The Y axis (Nema 17, 2 amp) one works perfectly - smooth, quiet and cool - so at least I know I can wire one up correctly.
The Z axis (Nema 23, 3 amp) one is smooth and quiet, but gets pretty hot - too hot to comfortably touch after about ten minutes. If I set the current lower then it doesn't rotate.
The X axis motor (Nema 23, 2.3 amp series, or 4.2 amp parallel) is very noisy, especially when starting and stopping, and it also seems to randomly make its own mind up on which direction it goes in. I have tried every current setting, and, since this one has 8 wires, I have also tried both series and parallel wiring configurations.

The motor drivers are DM542's and the controller is a Ruida 6445G. The testing so far has been with the arrow keys on the controller (not ready for g-code yet, and the laser tube isn't installed).

The Z axis motor is not going to be used much, unlike a cnc router or mill its only used to set the bed height at the start of a job, but it will be sitting there getting hot because of the holding torque, so I'd like to sort it out if possible.
The X axis motor is more of a problem as it will be constantly on the move, so it would be nice if it was reasonably quiet, and important that it moves in the direction its told to!
Any ideas?

Martin Kyte23/07/2021 21:34:24
avatar
2536 forum posts
45 photos

Have a look at SW4. Should be set to OFF for standstill current reduction.

It's section 7 in the data sheet just after Dynamic Current Setting.

regards Martin

Keith Petley23/07/2021 22:35:24
13 forum posts

Check that the X motor coils are wired correctly. Sounds like one pair may be wired so that they oppose each other rather than work together. Try just one winding out of each pair and see if it improves things - then add the second winding of each pair.

Keith

Steve Pavey23/07/2021 22:52:09
351 forum posts
40 photos

Martin - I’m pretty sure that I have got sw4 set correctly but I will check to make sure.
Keith - Also worth me checking this again, but I hadn’t thought of just using one set of coils - I’ll try that tomorrow morning. Fortunately it’s connected up with Wago terminals, so very easy to change.

Ronald Morrison24/07/2021 12:08:06
70 forum posts
4 photos

The power of the stepper motors is a product of voltage and amperage while the heating is just amperage. If possible increase the voltage and the amperage requirement will go down.

Andrew Tinsley24/07/2021 13:15:51
1461 forum posts

Ronald, if you increase the voltage the current will increase and thus make things even worse!

Andrew.

John Haine24/07/2021 13:57:10
4106 forum posts
241 photos

No, the driver regulates the current irrespective of voltage. Are the currents you quote the ones given on the motors? If so they are the maximum not the recommended operating level. As as been suggested check the sense of the windings in series or parallel. I use the same drivers on my CNC mill at currents of around 1 amp for X and y and 2 amps for z iirc.

Steve Pavey24/07/2021 18:11:27
351 forum posts
40 photos

I’ve had another play about this afternoon. First I removed the Z stepper (the one that was overheating) - I’ll sort it out later.
next to the X axis, and I tried Keith’s suggestion of just wiring one coil from each pair, but it made no difference - still the same vibration on starting and stopping, and still the random choice of direction at each start. I then swopped to a 4 wire Nema17 motor, (same as on the working Y axis) and the vibration problem is still there. Then a swop of the X and Y motor leads, and the problem is transferred from the X to the Y motor, so it looks to me as though the problem lies with the motor driver.
I can’t see the reply now, but yesterday the first response suggested that the DM542 was not the best - maybe the next step is to buy a new driver for the problem axis.

Re the overheating Z motor, there is no provision for adjusting voltage. The dip switch settings adjust the current and the microstepping, except for sw4 as mentioned. Clearly it’s overheating because the holding current is too high, but changing the current setting either results in a motor that doesn’t spin, or doesn’t affect the overheating. Maybe two new drivers are needed.

Steve Pavey24/07/2021 18:17:53
351 forum posts
40 photos
Posted by John Haine on 24/07/2021 13:57:10:

No, the driver regulates the current irrespective of voltage. Are the currents you quote the ones given on the motors? If so they are the maximum not the recommended operating level. As as been suggested check the sense of the windings in series or parallel. I use the same drivers on my CNC mill at currents of around 1 amp for X and y and 2 amps for z iirc.

John - I’ve just digested your post. I set the current as suggested on the datasheet. Maybe I need to have another go at trying lower current settings. I have also been wondering about the polarity of each of the four windings, and whether the datasheet shows the correct colour codes. I’m not sure how I can test for this.

John Haine24/07/2021 20:33:53
4106 forum posts
241 photos

Have you checked the axes for friction?

Steve Pavey24/07/2021 20:57:10
351 forum posts
40 photos

Only the Y axis is connected up at the moment (and that’s the one that’s working fine). Being a laser cnc there is very little load on the motors though, even with all the pulleys and toothed belts fitted.

Edited By Steve Pavey on 24/07/2021 20:58:25

John Haine25/07/2021 09:35:40
4106 forum posts
241 photos

Actually I'm using the 2M542 drivers which are very similar. I have 6 of them, 4 on the mill (XYZA) and 2 on lathe, and found they behave exactly as expected.

The odd behaviour of the motor that can't make up its mind may hold a clue. One cause of that may be that the pulse and direction signals going to its driver have the wrong timing. If the active edge of pulse changes state at the same time as the direction the driver may get confused about which direction it should go in. The controller should have the ability to change this as a configuration option, or the driver. Look in the manual for the position of the jumpers J1 and J3. Does the controller work in "pulse/direction" or "CW/CCW" modes?

Ronald Morrison25/07/2021 14:18:31
70 forum posts
4 photos
Posted by Andrew Tinsley on 24/07/2021 13:15:51:

Ronald, if you increase the voltage the current will increase and thus make things even worse!

Andrew.

The driver I use allows me to change the amount of current which it regulates. By increasing the voltage I was able to reduce the current and still get the same power to the motor. That reduced the heating of the motor and the heating of the driver chip which was cutting out due to overheating.

Steve Pavey25/07/2021 14:59:13
351 forum posts
40 photos

John - thanks, I will have a look at the jumpers. I recall seeing a setting on the Ruida setup menu to change from Pul/dir to cw/ccw mode, and also to change from leading to trailing edge. I assume that these controller settings have to match the jumper settings?

I’m still a bit puzzled by the talk of changing the voltage - I can’t see how this is done without changing the power supply (mines a 24v Meanwell model).

John Haine25/07/2021 16:56:08
4106 forum posts
241 photos

No need to change voltage! 24v should be fine.

Steve Pavey25/07/2021 22:15:14
351 forum posts
40 photos

A small bit of progress - in a fit of frustration at my own inability (!) I decided to remove the wiring to the steppers and drivers completely and start from scratch. The result is now three steppers that run smoothly and don’t seem to get hot. I have no idea what I rectified by rewiring which is slightly annoying, but I’m pretty sure it was a daft mistake on my part.

But I still have problems with the X axis motor not knowing which way to turn, and it hasn’t been solved by substituting a different stepper motor. I have checked the jumpers in the driver - actually no jumpers are fitted to the pins, so it is set to Pul/Dir and active on leading edge. I configured the Ruida controller with these same settings.

I did wonder if the datasheet for the motor has incorrect colours described for the 8 wires, although when I substituted a four wire stepper it exhibited the same behaviour. Another possibility might be some sort of electrical interference, although the cable to the this stepper is the only one that is shielded.

Martin Connelly26/07/2021 08:16:53
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1853 forum posts
197 photos

There is a possibility that the voltages being supplied to the enable, pulse and direction connections on the driver board are not going high enough. Some time back TTL chips used 0 and 5 volt signals. When newer technology was introduced (CMOS I think) the voltages were changed to 0 and 3.6 volts. Some computer parallel port were only supplying the 3.6v levels and caused problems with equipment that was expecting 5v. There is a possibility of something similar happening here and the voltage being supplied is not quite enough to switch the state of the direction circuit 100% of the time.

There is also the possibility that the voltage levels are not being pulled down to 0v completely as well. What would be ideal is using an oscilloscope to look at the voltage levels and add a pull up or pull down resistor if this was the case. Another option is to add a chip between the transmitter and receiver to clean up the signals. A digital voltmeter on the direction line should be sufficient to see what is happening to the voltages since the direction voltage is not usually pulsing unlike the step signals.

Some details here may be slightly out since I am writing this from memory but it is what I think needs looking at.

Martin C

John Haine26/07/2021 09:10:16
4106 forum posts
241 photos

I can't find the documentation for the controller Steve is using online but there is a connection diagram showing the interface to the stepper drivers with a +5V line, which implies that it's using standard 5V levels. Actually the original CMOS levels were 0 and 5V (or Vcc at any rate, usually 5V), it was TTL that had a 5V supply but the logic levels were a bit lower because of using bipolar transistors. Later CMOS reduced the supply to 3.6V to reduce power consumption and that led to the problem with the PC parallel port. However the controller Steve is using is a dedicated design not using a PC. Still worth checking the logic levels in the documentation though.

John Haine26/07/2021 09:26:41
4106 forum posts
241 photos

Try changing the pulse signal to trailing edge active on the controller. It may be that if the edges on pulse and direction are coincident it can't make up its mind.

John Haine26/07/2021 10:08:46
4106 forum posts
241 photos

Driver data sheet says that direction signal needs to be stable at least 5 microseconds before active pulse edge.

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