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Old 24th May 2018, 2:27 pm   #1
retailer
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Default Another DIY Coil Winder

Posts pop up every now and again about coil winders both diy and commercial - the most common being the Douglas/Avo winders, having long wanted a coil winder I gave up waiting for one to come up at a good price and decided to go the DIY route. Now that I have come to the pointy end of the project here is a bit of info for those that are interested.

My winder is built in 2 parts each with it's own 18M2+ picaxe, - a variable speed motor unit with counter that will operate in 3 modes, the 18M2+ chip running at 4Mhz and a stepper operated traverse unit that has 2 modes, the picaxe chip running at 32Mhz.

The motor unit will operate as:-
1.) a simple hand turned winder with counter, usefull for doing heavy gauge wire with a small number of turns.
2.) a powered variable speed, hand fed winder with counter - stop start is with either a panel mount toggle switch or foot switch,
3.) as in 2 but the number of turns can be set with a 4 digit thumb wheel switch, the motor will then continue until the number of turns are reached.

Front panel controls are quite simple - toggle motor 0N/0FF, momentary on push to start the wind for a preset number of turns that have been set on a 4 digit thumb wheel switch. The 12v motor belt drives a spindle that has a 1/2" chuck on one end, speed is controlled by PWM type speed controller, the picaxe turns this on or off via a relay, there is dynamic braking applied to the motor by shorting the motor connections when the drive to the motor stops. The turns counter is a separate CMOS 925C 4 digit led board, the picaxe sends a count pulse for each revolution of the spindle. The count pulse comes from a photo transistor and disc with slot.

The traverse unit has the now usual stepper motor traverse, the traverse travel per turn is set with a 3 digit thumb wheel switch, with 1 step being a tad under .02mm or approx .0009 inches (9 tenths of a thou), a toggle switch on the front panel selects whether the traverse stops at the end of each layer or not - this is to allow for the addition of insulation between layers if needed. Setting the traverse travel to 000 will prevent the traverse from operating in the event you want to hand guide the wire. The actual stepper driver is one of the readily available units featuring a TB6600 chip these are quite cheap I think around AU$8 each (about the same cost as a picaxe chip) and have the ability to current limit and microstep if needed.

Front panel of the traverse unit is also quite simple - left and right jog push buttons to aid setting the travel limits of the wire carrier, a toggle switch to select either full auto or stop at end of each layer for insulation and a resume push button to continue once the insulation has been added. The traverse limits are set by adjusting the position left and right micoswitches.

Once a transformer bobbin has been set up in the chuck the traverse travel limits are set using the jog buttons and adjusting the position of the micro switches. The wire being wound is accurately measured and using .02mm per step the number of traverse steps per spindle revolution is set with the thumb wheel switch. Pressing both left and right jog buttons together then sets the traverse amount and also the initial direction of traverse so in practice the winding can start from either end of the bobbin, also if the last layer to be wound does not have enough turns to fill the bobbin the traverse distance can be reset for the last layer to space out the turns to take up the full width of the bobbin.

The actual winder does look like a bit of a bitsa this if just me being a bit of a scrooge and wanting to spend as little as possible, I did use a lathe to screw cut the 24tpi lead screw as I wanted to a limit the backlash as much as possible, presently it is very good the wire carrier changes direction within 2 steps of the stepper motor, I guess only time will tell if it wears well or not. If not then I'll have go the route of a commercial ball screw as used in 3D printers and routers.

The wire carrier/tensioner is an unashamed copy of an AVO/DOUGLAS type and was just straight forward machining job, the wire reel spindle runs on sealed ball races and has a static brake to apply a small amount of adjustable drag to the spindle and an overrun brake to stop the wire reel once winding stops.

The first tests are here on youtube https://youtu.be/xRtlDay8yBg

I tried it up to around 900rpm and the results were very encouraging - I do need to do some work on the wire carrier as the wire tends to fall off the pulleys at the extreme ends of traverse travel - perhaps add some guides/eyelets or increase the size of the pulleys and increase the distance between the wire carrier and traverse unit to decrease the angle between the wire and pulley.
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Old 24th May 2018, 11:27 pm   #2
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Default Re: Another DIY Coil Winder

Great work!

I love seeing the DIY versions of coil winding machines. Every iteration gives me more clues on how to approach the subject myself. It is my desire to construct one that will do wave winding competently as well as the 'vanilla' stuff.
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Old 25th May 2018, 3:00 am   #3
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Default Re: Another DIY Coil Winder

Yes I had a bit of a look at wave winders and possibly incorporating it, they all seem to have circular cams for the wire traverse, so the wire guide travel is not a linear function. This would be doable with a micro controlled stepper however it would probably involve floating point maths with trig functions which the picaxe does not have, while trig functions like sine can be very closely approximated as the sum of a series it would probably complicate things too much for me . A simpler way to do this with a picaxe would be to have a lookup table to step through which would give the displacement of the traverse for each rev of the spindle, the displacement would then have a multiplication factor applied for different wind widths. If your maths is not great like mine I believe that even drawing a cam on paper, marking it off the degrees of rotation and them just measuring the displacement produced by the cam would probably be accurate enough. I don't however have a need for wave winding so I did not really go into it.
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Old 29th May 2018, 10:36 am   #4
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Default Re: Another DIY Coil Winder

When wave winding, should the wave be faster or slower than the rotation and by how much?
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Old 29th May 2018, 4:35 pm   #5
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Default Re: Another DIY Coil Winder

I did a trial run to see if wave winding was possible and with my current setup and it is not - to trigger the turns count and traverse I have a single slot in a disc that cuts the light between a led and photo transistor - my attempt at wave winding forced the traverse mechanism to make large movements in the order of 6-8mm at each revolution of the spindle, while I did eventually manage to get a wave wound coil I had to play around with the spindle speed and once I synch'd the traverse stepping with the spindle speed it worked after a fashion- however the spindle speed control is an open loop type (PWM) so any slight drag on the wire causes the spindle speed to vary with obvious results.

A thing to try would be to modify the disc that cuts the light beam and increase the number of slots to possibly 18 or even 36 - 36 slots would give a traverse step every for 10 deg of spindle revolution, as long as the spindle was run slow enough so the stepper could keep up it should work.
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Old 29th May 2018, 6:08 pm   #6
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Default Re: Another DIY Coil Winder

Quote:
Originally Posted by retailer View Post
Yes I had a bit of a look at wave winders and possibly incorporating it, they all seem to have circular cams for the wire traverse, so the wire guide travel is not a linear function.
Really, to make a mechanism move back and forth with a steady speed motion the cam should be 'heat-shaped', but the simple 'Gingery' hand-powered wave-winder, one of which I made, uses a circular 'penny washer' offset on a brass bush for a close approximation to a heart-shaped cam.

As the shaft on which the bush & cam is mounted, the 'cam follower' moves the wire back and forth to the desired extent according to how you set the simple drive mechanism to make the waves as the coil rotates. Pic 1 shows one of my cams. (the wider the coil winding, the greater must be the extent of the offset).

For anyone who hasn't seen one of these simple but ingenious little winders in use there's a video here, which makes clear how it works. I built mine from scrap:

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

Some years ago there was an article in Model Engineering Workshop magazine of a coil winder built using Lego for some of the components. There was an accompanying five page article on heart-shaped cams showing how to draw the shape. You see heart-shaped cams in all sorts of mechanisms - the bobbin winder on old Singer sewing machines for example, and on record player turntables such as the one in the second pic below (A Garrard AT6).

Pics 3,4 & 5 are of the Heart-Shaped Cam article in M.E.W. magazine. I'm not sure how clear they'll come out, but hopefully, they'll be legible. I'll attach the remaining two pages in another post.
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Old 29th May 2018, 6:09 pm   #7
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Default Re: Another DIY Coil Winder

Here are the remaining two pages of the heart-shaped cam article from M.E.W. magazine some years back.

Hope it's of interest.
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Old 29th May 2018, 8:44 pm   #8
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Default Re: Another DIY Coil Winder

Hi David,

I recently read the "Model Engineering Workshop magazine" article.

I was wondering about the linearity of the traverse though as the arm driven by the cam traces out an arc, and I suppose it would be difficult to compensate for because the traverse is necessarily adjustable.

I love the ingenuity and intricacy of these sorts of mechanisms - I recently looked into making a braiding machine to make my own braided wire, and was fascinated by the vintage machines that I came across in my research that were developed by the textile industry.

Not only were the machines functional, but they were also works of art... not unlike vintage radios in this respect!
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Old 30th May 2018, 2:50 pm   #9
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Default Re: Another DIY Coil Winder

While looking for info about coil winders I did come across your youtube video David - and watched it a few times but as wave winding was not on the list of things to build into my winder I promptly forgot about it , I've just gone back and had another look at your video and noticed that the video that follows is also a universal or wave winder that is micro controlled, it looks to have a stepper driving the winding spindle and what looks like a servo driving the traverse, the type used in model cars and planes, I've not had any experience with servos but believe they need a continual stream of pulses to hold their position with their positioning being governed by the width of the pulses, quite a clever way to operate and position the traverse with software. The Gingery type winder is very popular probably due to it's simplicity and the very credible results it achieves. Not sure if you have seen it but there is a pdf book available on the internet archive called "Coil Winding" put out by the Stevens Co. that built (and possibly still do) all manner of coil winders, they go into a lot of detail about "universal" type windings and how they should be built up to be self supporting.
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Old 1st Jun 2018, 6:18 am   #10
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Default Re: Another DIY Coil Winder

Looked at your video, nice job. Are you using switches to reverse the motor that drives the bobbin L/R/bobbin length winding?

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Old 2nd Jun 2018, 2:43 am   #11
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Default Re: Another DIY Coil Winder

Yes I'm using microswitches seemed like the easiest way rather than setting a start and end point by software, I think I'm going to have to add a fine adjustment to the microswitches, just playing around/testing it I can see that when winding up to a bobbin cheek the traverse reverse point needs to reasonably accurately set to prevent gaps or extra buildup next to the cheeks. I can slow down and even stop the motor as the traverse approaches one of the bobbin cheeks and turn the spindle by hand - the traverse will still operate, once I wind on a few turns and check for correct wire placement and the traverse has changed direction I can restart the motor. Having a fine adjustment means I could easily make a small correction at this time if needed.
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