Motor control circuit.

[Diabolical Artificer]

I've a coil winder and need to control a DC motor that drives a carriage back and forth, left to right, this feeds the wire onto the bobbin. Previously this was driven by a stepper motor via a H bridge with PC software, I'm now trying to do the same but with switches, but can't figure out how to do this without using 4PDT push latching sw's but that's no good as the sw shaft is in a different position by about 1/4" in each "state"

How can I do this simply either with transistors or simple sw's or both? One sw will be fixed, the other moveable according to how wide the bobbin is.

Andy.

[jimmc101]

How about a DPDT bistable (latching) relay and use simple microswitches for the limit switches?
If your limit switches are change-over then a single coil type will do the job.
If single throw then a dual coil relay will be required.

Something like this from CPC.

Jim

[Ed_Dinning]

Hi Andy, what type of motor, PM or wound field as different approaches can be used on each. Note also that well rated relays will need to be used, even for a small motor due to the back emf's generated. Forget the use of microswitches, the do not like inductive DC

Ed

[Diabolical Artificer]

Not sure a relay will work as that would need another power source to SW it. My idea was to use my bench supply to vary the voltage thus controlling the motor speed, which isn't ideal but works & then set distance with switches.

Not sure what the motor is, it's a cassette motor I think with a small flywheel on the back.

As I figure it each SW would need to do four things at each end of travel
1) Connect + to + of motor
2) Disconnect - from + of motor
3) Connect - to - of motor
4) Disconnect + from - of motor
& then do the opposite when at the other end.

Of coarse I could do this with one DPDT toggle SW quite easily but that would mean a bit more fettling stops, ehmmm, have to have a think about that one.

Andy.

[wave solder]

Probably to simplify things if only running in one direction would be to put a diode across the motor for braking when the supply is turned off. Would it not need some form of speed control to ramp up gently rather that a sudden start?

[Diabolical Artificer]

A diode is tricky across the motor as the voltage is reversed, my bench PSU seems ok with stopping and starting. The start and stop has to be fast unfortunately.

Here's a sketch of what I have so far, it's the simplest way I can think of implementing it and just needs a bit of metal fab which I can do with pliers, drill & angle grinder + bits out of the "weird & wonderfull odds and sods box" that I've picked up over the years, odd bits from the gutter and metal from scrap domestic electronics.

Andy.

[G6fylneil]

If you use an on-on-on switch it will short out the motor in the off position and reduce the over-run. A proper motor controller would be the best bet. It would provide much more current to accelerate or decelerate the motor. I've used pancake motors that go from zero to 3000rpm. in 3/4 of a turn!

[Mr Moose]

Hello,

You could fit the toggle switch to the moving carriage instead of the frame. You would need flexible wires but the adjustable stops could just be bolts attached to the frame.

You might need to try different switches to find one that is consistent and switches rapidly as any delay could lead to bunching at the ends of the coil.

Yours, Richard

[David G4EBT]

A lot of the DIY coil winders on youtube - some very impressive - seem to use Arduino and the like to control the back and forth traverse. However, whilst most seem to start well with the first couple of layers, even with quite heavy gauge wire, they almost invariably make a coil that's more haphazard than I've made by guiding the wire by hand, running my homebrew coil winder, with a foot speed-controller.

The video at the link below is quite instructive as it addresses the issue of 'bunching' at the ends of the coil and bunching in the middle. Also the need for the wire guide to be as close to the coil as possible. All seems to go well 10 minutes in, with a couple of layers neatly laid down, then at the change of direction at 11.05 mins, the wire has a mind of its own and bunches up. By 11.10, the end result just looks a bonny mess. One of the factors in common with all solenoid coils seems to be the attempt to wind them at too faster speed. The wire guide on many DIY winders also seems to lack precision:

https://www.youtube.com/watch?v=GJcQfJ6JTZg

Maybe that untidy coil doesn't matter electronically.

I suppose what might be undesirable is if a turn on a higher up layer comes into contact with a turn much lower down on the coil, if it's carrying mains voltage, maybe there could be quite a potential difference between the turns, but subjectively, I would have thought that with modern enamelled wire, the breakdown voltage would be way above mains voltage in any event.

Anyway, back the the main point of this thread.

I don't know if you are aware but you can get reversible low voltage DC motor speed controllers which are controlled by a changeover switch. Although it's not really what you are aiming to achieve, maybe stopping the motor at the end of each traverse and switching it to the other direction would provide a simpler solution, with the ability to adjust the speed of the motor down to the desired level. (I've used one to control the speed of a small low voltage circular saw for cutting PCB laminate). EG:

https://www.ebay.co.uk/itm/304784196...0AAOSwjf9j1Nft

I don't know what your plans are for counting turns, but you can get a digital counter display with a 'Hall effect' proximity detector. A small neodymium magnet on the coil winder shaft will trigger the counter with each rev:

https://www.ebay.co.uk/itm/253051965...BoCFPkQAvD_BwE

Some DIY coil winders use a hand 'tally counter' like those that coach drivers use to count passenger on coaches, and trigger it with a cam on the end of the winder shaft. A bit 'clattery' but it works. EG:

https://www.amazon.co.uk/Counter-Cli...63993889&psc=1

Just a few thoughts to consider.

Good luck with the project Andy.

Though for the day:

"The difference between theory and practice in practice is far greater than the difference in theory and practice in theory".

[Diabolical Artificer]

Thanks both, that's a good idea re fitting the SW to the carriage. I got the thing to work but for a test I SW'd the direction by hand, result? A mess. The DC motor is too fast, it'd need either a reduction box or probably something more complex.

I'm trying to stay away from Arduino's, I just haven't the temperament to fiddle about with the damn things. Thanks for all those links David, you've made some very pertinent points about bunching etc. When winding EI tfmr's the turn's have to be bang on, you've only a limited window. I'm going to have to put a lot more thought into this. The coil winder in David's link #1 wouldn't last 5 minutes with big EI bobbins. The one I have is very well engineered, but the control gear, the one from Nut's & Volts is infuriatingly faffy.

At present I've wound half the primary by hand, it's only 2 x 172T of 1mm/18 gauge, it's a big Tektronix 500 series scope tfmr, approx 750VA with many windings, it has to be bang on 100% correct, I may just wind it by hand.

Andy.

[Mark1960]

To put a brake on a dc motor you could just put a resistor in parallel with the motor, it just means you’ll be dissipating power when you drive the motor, but it stops the motor freewheeling when you turn it off.

It might be possible to use a model train speed controller to run the motor at a slower speed.

Do you know anyone with a sewing machine? It might be worth looking at the mechanism used for winding thread on the shuttle as they always seemed to make a neat job of winding thread.