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Stepper motor voltage

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(@andydowns)
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@davee @inq Thank you both for the further information.

The application is to open extractor blast gates in a woodworking workshop. I have six blast gates and intend to operate them with an ESP and stepper motor on each. The idea is that a remote will open one gate and close the rest and then start the extractor.

I'm not quite sure what torque I need and could optimise the gate opening/closing with delayed starting of the extractor to reduce the required torque.

I have played around with the voltage and current this afternoon. I thought that from what @inq post said, a 'skipping' problem I am having might be resolved by increasing the voltage, but it didn't seem to make any difference. The motor appeared functioned the same (unloaded) between 12V and 18V but starting skipping more after that, so I've set it back to 12V.

I think I'll carry on the software development and get a prototype built using the A4988 to try it out. If the torque is insufficient, I'll try the DRV8825 driver.

I'm reading through the posts on @inq original post and am learning from some of it. Some of it is currently above my head, but there is lots of good stuff.

Each time I post, I learn something. What more could I ask.

Thanks.

 


   
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byron
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@andydowns

The question of the automation of blast gates has come up a couple of times before I think, though I don't recall what / if anything came to fruition.  Its something that I thought I may have a go at for my small home workshop, but its been low down on my list of potential projects, and right now its still rather at the bottom of my list.

However I did see some good stuff on youtube of those who have done this, and I see I saved a link to one that I though might be a good idea.  I linked it because I thought the idea of using a linear activator could be the way to go for driving the blast gate ( though I had in mind to somehow link it to my existing blast gates rather than the spiffing ones the chappie in the video makes )

So not saying stepper motors would not be good for the task, but in case you did not come across this particular video in any youtube perusing on the subject of blast gates you might have undertaken, I give this link in case you find it food for thought.

Do let us know on how your project progresses and I may well add a link to it to my my list of interesting projects for me to do, though with some measure of doubt that I will actually get around to being productive enough to actually do it. 😎 


   
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Ron
 Ron
(@zander)
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@andydowns FYI @byron I haven't seen a stepper used for woodworking blast gates, but I have seen a lot of pneumatic systems. The pneumatic solution has the advantage of being able to make a positive closure without causing any damage while a stepper has enough torque that if it were to overshoot you could unless you are using a guillotine style gate. If I was building a woodworking shop again, I would use air activated and guillotine style gates. With the guillotine styyle, there is a quick visual check possible that the non guillotine don't offer.

First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
My personal scorecard is now 1 PC hardware fix (circa 1982), 1 open source fix (at age 82), and 2 zero day bugs in a major OS.


   
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(@andydowns)
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@byron Thanks for the link, I saw the video when I did a little poking around for ideas. I do like the linear actuator idea, but they are a bit expensive. I.e. £23 each and I have currently have six gates with another to be installed later this year. I also initially considered servos, but would have to extend the travel with levers to achieve the required travel. This still isn’t ruled out, but decided to go the stepper motor route for now.

My design retrofits to my existing gates with very minor modification. They work fine and I didn’t want to build more gates.

I started to build a crude prototype last night which seems to work very well. I’ll finish that today and will make the decision on this approach.

I had thought about putting a system design thought process and running progress in the forum’s projects section, along with access to 3D parts, circuit, pcb design, etc, when it’s finished, but I wasn’t sure anyone would be interested. Most I’ve seen so far are robot related.


   
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(@andydowns)
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@zander I had considered pneumatics as well as hydraulics (very briefly), but decided against it.
The blast gates I have are the guillotine type and my design has limit switches that will prevent overloading by trying to push the gate beyond its travel. I also have a plan to add error checking to the soft to detect errors. This is yet to be implemented, but I’m fairly confident it will work.

Another draw to stepper motors is that it is something I wanted to learn about. My mind isn’t set on this approach yet, but it is looking very promising so far.


   
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Inq
 Inq
(@inq)
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Posted by: @andydowns

The blast gates I have are the guillotine type and my design has limit switches that will prevent overloading by trying to push the gate beyond its travel. I also have a plan to add error checking to the soft to detect errors. This is yet to be implemented, but I’m fairly confident it will work.

Another draw to stepper motors is that it is something I wanted to learn about. My mind isn’t set on this approach yet, but it is looking very promising so far.

I don't know anything about blast gates.  I did YT to see what they were.  Anyway... I do know that steppers skip steps, so your limit switches are redundant.  You can set the current as discussed above to "just enough" to close it.  If obstructed, it'll stop, chatter (skipping) the few steps and stop trying.  Since it has no way of knowing it skipped the steps (unless encoded steppers are used) it thinks it has reached the desired command.

Although cheaper, servos are opposite... they'll keep driving till they reach the desired location and either burn up or break gears until it reaches the commanded location.

Although, I don't need blast gates, I'd be interested if you do a project thread.  Actually you'll find more other projects than robots... some mine.  I was more discouraged at the lack of robot projects.

VBR,

Inq

 

3 lines of code = InqPortal = Complete IoT, App, Web Server w/ GUI Admin Client, WiFi Manager, Drag & Drop File Manager, OTA, Performance Metrics, Web Socket Comms, Easy App API, All running on ESP8266...
Even usable on ESP-01S - Quickest Start Guide


   
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Ron
 Ron
(@zander)
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@inq @andydowns I think the limit switch will still be needed, since if the gate is not in position vacuum will be lost so the light that is normally associated with a gate will indicate manual intervention is needed. (All lights off except the one that is currently being used)

I am sure Andy already knows this, but the vacuum motor must be OFF before the last gate is closed otherwise you can easily suck the piping flat.

And before Dave jumps in, be sure to ground EVERYTHING. My brother had an explosion and fire in his shop because he cut corners. I only had (grounded) plastic at the ends that had to move as some of my machines were on wheels (small shop)

I am assuming from what Andy has said so far that this is a profession system withh the heavy duty walls, large radius bends and a 3 phase motor to draw the vacuum. Mine was similar to the picture.

Screenshot 2024 07 10 at 08.03.46

 

First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
My personal scorecard is now 1 PC hardware fix (circa 1982), 1 open source fix (at age 82), and 2 zero day bugs in a major OS.


   
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(@andydowns)
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@zander @inq

I will start a project thread and explain further, but for the sake of this thread…

I was originally going to calculate the number of steps required for the required 90mm travel and then use a for then loop to travel the right distance, but I then discovered that the motors skip steps which would result in the gate either not being fully open or fully closed.

Since then I’ve changed the software to a while loop that looks for the limit switch to close to stop the travel at the right point. i.e. two limit switches. There will be a status led with five (currently) statuses, but driven a slightly different way from the software.

The error detection will be by counting the expected steps for the distance and then reporting an error if it thinks it’s gone too far. The error detection will light a red led and stop function for manual intervention. I’ll probably also add a calibration function to check for both switches on boot up.

My workshop is not a professional setup, but I would describe as a well setup home workshop. I am retired and it is just for fun.

Apologies for the fast pan, it’s the only way I could get the video file small enough, also the state of the workshop. I always have too many projects on the go. 😊

It has two extraction/vacuum systems, one high vacuum low flow, and one low vacuum high flow. The blast gates are on the low pressure system, so closing all the gates isn’t a problem for short periods.

IMG 9276
IMG 9275

I have pondered many times about the explosion risk, and would have liked an all metal earthed system with large radii, but alas it was well beyond my budget. Fingers crossed.  

This post was modified 6 days ago by AndyDowns

   
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byron
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Posted by: @andydowns

I have pondered many times about the explosion risk, and would have liked an all metal earthed system with large radii, but alas it was well beyond my budget. Fingers crossed.

For plastic ducting, with the risk of a static charge buildup, I think the idea is just to run an earthed copper wire inside the tubing, and that should be quite cheap to do.  In my workshop (similar to yours in a log cabin type shed) I just have the flexible dust hose draped over hooks, and its not as nice as your neat tubing... and admittedly I also do not have the said earthing copper wire either though thus far I've not been crossing any of my extremities.   My main danger in the wshop at the mo is tripping over all the offcuts that clutter the workshop but kept just in case they prove useful 😀. 

Good to read you are going to do a project write up. 👍 

This post was modified 5 days ago by byron

   
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(@davee)
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Hi @andydowns,

  Thanks for the additional information - an impressive project!

  @Inq, who obviously has a lot of experience, has provided a lot of valuable information, particularly when his previous posts are included.

-----------

I do not want to slow down your progress, but as I would like you to have a reliable system as a reward for your endeavours, I am somewhat concerned with your comments:

  • "I then discovered that the motors skip steps which would result in the gate either not being fully open or fully closed." and "a 'skipping' problem I am having might be resolved by increasing the voltage, but it didn't seem to make any difference. The motor appeared functioned the same (unloaded) between 12V and 18V but starting skipping more after that, so I've set it back to 12V."
  • " but I then discovered that the motors skip steps which would result in the gate either not being fully open or fully closed."

Stepper motors, when driven correctly, are very reliable. Applications like 3D printers, and until recently, disc drives for computers both require the motor to do exactly what it is told, never missing a step, to function as required.

Obviously, limit switches and other methods of checking the motor is doing what is expected can be a useful feature, but I would expect such checking mechanisms to normally just report "All's well", as the counting approach should usually be sufficient, whilst the motor remains powered.

The simplest reason that a motor skips, is when the mechanical load exceeds the available motor torque; and of course torque is a function of both the motor design, and the coil current. In addition, the motor torque tends to reduce as the stepping rate increases, so stepping too fast can also cause issues.

Your first comment above, reporting that increasing the voltage above 18V caused it to skip, seems particularly bizarre, suggesting something 'basic' needs fixing. Intuitively, I would have expected the motor torque to stay the same (if the system is being used well within its limits) or increase (if the system was being used a bit beyond its limits), when the voltage was increased, suggesting performance should stay the same or improve, not worsen. Perhaps others have experienced this particular symptom, and can comment more specifically than I can, but it doesn't 'feel right'.

As a start, things I would attempt to check are:

  • Electrical wiring. Stepper motors tend to be driven with high speed, high current pulses. Such pulses can confuse digital circuits, if some of the electrical energy inadvertently gets transferred from one place to another.   As stepper motors usually have a separate power supply from the computer control system, particular care is needed to ensure the grounding between the parts is well implemented, including the physical layout etc. , to minimise the chance of 'spikes' from the motor side, which includes half of the driver chip, do not 'contaminate' the computer control side, which includes the other half of the driver chip.
    •  
  • If stepper motors are moved in complete steps or half steps, they tend to 'cog', due to being rapidly accelerated and decelerated from one position to the next position. This effect can be accentuated by any additional mass attached to the shaft, which will increase the effective inertia of the rotor and attached shaft, etc. (Microstepping, discussed below, might help if this is an issue.)
    •  
  • Is the mechanical load too high for the motor, at the present current level? I don't know about the mechanics of the blast gates, but are they mechanically stiff and/or are there certain intermediate positions between open and closed, at which the load increases, maybe due to leverage or the air flow/pressure on the gate?
    •  
  • Does stepping slower, affect the skipping?
    •  
  • I don't know if you are using 'microstepping', in which the drive to the motor is changed in small fractions of a step, but I suggest you try a few experiments using different fractions of a step, to see if it affects the skipping problem.  (More recent 3D printers use microstepping to greatly reduce the amount of noise they make, as well as improving print quality, by reducing the amount of vibration.) I am not suggesting microstepping is essential for your application, though I would not expect it to be harmful, and it might be helpful, but rather that it might help to diagnose the issues.

I am sorry, these suggestions are rather vague, but I hope they are helpful. Of course, you may prefer to stay with your workaround for now, whilst you develop the rest of the system.

Best wishes and good luck, Dave


   
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Ron
 Ron
(@zander)
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@andydowns If the plastic pipe is PVC then no problems, PVC is anti-static and has a very high resistance to current flow. For the flex plastic hose, ground the wound spring part of the hose and you are good to go.

If the pipe is NOT PVC then wrap the pipe in braided copper. Putting it inside leads to jams and does a poor job of grounding.

Good luck.

First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
My personal scorecard is now 1 PC hardware fix (circa 1982), 1 open source fix (at age 82), and 2 zero day bugs in a major OS.


   
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byron
(@byron)
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Posted by: @zander

@andydowns If the plastic pipe is PVC then no problems, PVC is anti-static and has a very high resistance to current flow. For the flex plastic hose, ground the wound spring part of the hose and you are good to go.

If the pipe is NOT PVC then wrap the pipe in braided copper. Putting it inside leads to jams and does a poor job of grounding.

Good luck.

Ha, read this in a final peruse around just before my bed time, which got me thinking where I got the inside the pipe thought from.  Just what I don't need as now I may be going to dream of blasted pipe explosions.  Anyway this is from a quote from a woodworking forum with some links should anyone be daft enough to want to wade through them.   Whether the opinion has any merits I don't venture an opinion as I'm not going to be doing any grounding in my shop.

So I quote:

"An Electrician did a video about installing an extraction system and he specifically said not to put the wire on the outside as it won't do anything (has to go inside)."

Ok end quote, and bloody heck is that the time 😮 

 


   
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(@andydowns)
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@davee Yes, this has been troubling me too. I thought of the exact same two examples you gave, which made me think I am missing something as they should be reliable. I have never heard my 3D printer or PC drive of any sort miss a beat.

Thanks for your suggestions, I will keep returning to this until all possible avenues have been exhausted. I will, however stay with the current scheme to keep the project moving along. 

I did try a few experiments with current and step frequency when I first tried the motors, but all gave inconclusive results. I think I will try out your suggestions that I can, presently, and then repeat the results and publish them for public perusal.

I haven't tried micro stepping as yet, but intend doing so at some point. If this might give an indication of problem area, I'll try it sooner than later.

Something else I noticed yesterday was wining coming from the motor when powered up but not moving. I varied the current limiter on the bench power supply and it did change the frequency of the hum. 🤔


   
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(@andydowns)
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@byron I've watched these exact same videos when I was trying to work this out myself. 😁

The company I used to work for was owned by a company that designed and developed intrinsically safe products. I'm still in contact with one of the engineers, also retired, and will sound him out about this.


   
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Ron
 Ron
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@byron @andydowns I have seen some mentions of inside the pipe. Some are straight down the middle, some drill holes and weave the wire in and out. As a former electrician, I can see no benefit to not just winding around the outside. Down the middle will do almost no good, and the in and out weave is just too much work for no apparent benefit. I will add however, apply some tape to make sure the wire or much better braid like solder wick or more cost effective common braided cables that you remove the insulation from and partially unwind so it can be flattened. I would tape it maybe every 6". As far as winding around the pipe, a 12" pitch 'feels' about right. If at the end of a run you have flexible plastic hose, the flex part is often steel so make sure the pipe ground wire connects to that and then to ground. SOME plastic flex pipe use plastic for the helix, do NOT use that!!!!! I see you have some metal flex hose in some cases, that is excellent, just connect the plastic pipe ground braid to it and then to ground. Try to avoid putting screws through either the plastic or metal or flex as they collect debris, use cable clamps instead.

I never did this as I went with an Oneida system and used the heavy gauge large radius pipe after I saw what happened to my brothers shop. Remember things like fine saw dust, flour, other fines can build up static charges from rubbing up against other fine particles. At some point it will discharge, 99%+ with no damage BUT eventually you may experience the 1% so give the excess charge an easy path to ground.

This post was modified 5 days ago 3 times by Ron

First computer 1959. Retired from my own computer company 2004.
Hardware - Expert in 1401, and 360, fairly knowledge in PC plus numerous MPU's and MCU's
Major Languages - Machine language, 360 Macro Assembler, Intel Assembler, PL/I and PL1, Pascal, Basic, C plus numerous job control and scripting languages.
My personal scorecard is now 1 PC hardware fix (circa 1982), 1 open source fix (at age 82), and 2 zero day bugs in a major OS.


   
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