Guitar Pickup Winder

Projects General Guidance
1

I have been thinking about this for a while, and with all the significant evolution of the Arduino and the platforms ready availability its time I put some effort into a project I would like to do. I am a novice with this and am looking for any and all help I can get.

What I don’t really know is what add-on boards and parts, etc. I will need to make the project work.

I want to make a guitar pickup winder that is automated. What I envision is a setup that has two stepper motors, a way to measure resistance, a way to input the desired guitar pickup coil resistance, and LED display to show desired information (desired resistance, actual measured resistance, count the number of revolutions, plus a few others).

Stepper one will control the copper wire moving back and forth to evenly distribute the copper wire around the shell of the pickup as the second stepper rotates the pickup shell to accept the copper wire. Many pickup winders spin incredibly fast and base the amount of revolutions on an approximate calculation of resistance based on the number of windings of copper. My intention is to have the resistance measured on the fly as having the pickup being wound as quickly or slowly as needed to get a fairly accurate resistance measured and auto stop when the desired resistance is met.

42 AWG wire (.003 inch diameter) Spool Copper Wire
Rollers Spaced to keep tension on the wire
Stepper 1 oscillates the last roller to evenly distribute the wire across the pickup
Stepper 2 spins the pickup that pulls the wire

The tricky part will be measuring the resistance of the coil as it spins between stepper 1 and at the end of the wire attached to the pickup. I was thinking of using copper braid that is in contact with the copper wire at stepper 1 as a measuring point and then at the end of the wire on the pickup. (I am sure there will be some resistance in the initial setup that will have to be “zeroed” out prior to starting the coiling process).

Attached is a diagram of what I envision:

pickup winder.jpg
pickup winder.jpg904×698 96.6 KB

2

You probably don't want a stepper motor for the winding motor. You just need an optical or hall/magnetic sensor to count the revolutions.

I'm not sure you need the other stepper motor. I don't think a winch normally has a guide... I think just the cable thickness & tension make it wind-up nicely once you get it started. Or, a bobbin on a sewing machine seems to wind-up neatly by itself without manually guiding it back-and-forth. And, it might get really tricky to get it in-sync with the wire thickness. Maybe you can experiment to see if you really need to guide the back-and-forth movement. (Or, maybe you already know that you do need the 2nd motor.)

The tricky part will be measuring the resistance of the coil as it spins

That's not going to work. Magnet wire is insulated with enamel. You have to scrape the enamel off the ends to make contact and if you scrape it off in the middle of the winding it's going to short-out when you wind it.

However, wire of a known gauge does have a known resistance per foot (or per 1000 ft). You can measure the amount of wire being used (with some kind of rotating pulley gizmo that you can "invent") and calculate the resistance. If you know the resistance you want, you'll know how much wire to use.

A quick search turned-up a chart on Wikipedia that goes down to 40AWG and shows 1049 Ohms per 1000 feet (about 1 Ohm per foot). Obviously, the resistance of 42AWG will be higher.

way to input the desired guitar pickup coil resistance, and LED display to show desired information (desired resistance, actual measured resistance, count the number of revolutions, plus a few others).

If you need to do lots of calculations with lots of variables, I'd consider either using a spreadsheet or interfacing it with a computer (so you can use the keyboard, screen, and calculating/programming capabilities of the computer). Otherwise, it almost sounds like you are building a special-purpose calculator and you'll need a keypad and some function-buttons, and it could get complicated to build and complicated to use.

I'm always trying to keep thins simple, so I'd probably just want to punch-in the number of turns and have it stop automatically when it's done.

P.S.
I don't know that much about guitar pickups, but I think the number of turns and inductance is probably more important than the DC resistance. What's the typical resistance? I'm betting the DC resistance is far-less than the 1 megohm or more input on a guitar amp. As long as the source impedance (pickup) is low compared to the load impedance (amp input), the source impedance makes very little difference. For example, a change from 1k Ohm to 5K wouldn't make any difference (as long as the number of turns and inductance remain the same... In the real world all of these things are going to change together).

If you don't know this already, impedance is a combination of resistance, inductive reactance, and capacitive reactance. You make an inductor by winding a coil (usually around a core) so a pickup is primarily inductive. Inductive & capacitive reactance depends on the inductance/capacitance and frequency, so they can affect the "tone". The input on the amp (or effects pedal, etc.) is primarily resistive, but the amp's input impedance interacts with the pickup's inductance to affect tone..

3

DVDdoug:
I'm not sure you need the other stepper motor. I don't think a winch normally has a guide... I think just the cable thickness & tension make it wind-up nicely once you get it started. Or, a bobbin on a sewing machine seems to wind-up neatly by itself without manually guiding it back-and-forth. And, it might get really tricky to get it in-sync with the wire thickness. Maybe you can experiment to see if you really need to guide the back-and-forth movement. (Or, maybe you already know that you do need the 2nd motor.)

I dont know if I really do, but several examples of DIY pickup winders I see guys manually moving it back and forth.

I figured steppers because I don't care if it takes 4 hours to wind or 20 minutes, and I like the idea of steppers since they can be precisely micro-controlled. Plus I found an example of a somewhat crudely made DIY PIC controlled machine as well that used steppers.

Also, that is a VERY good point about the wire coating, wasn't thinking about that at all. So I guess I will have to settle for an approximate resistance target based on either revolutions and/or approximate length of wire used.

4

I figured steppers because I don't care if it takes 4 hours to wind or 20 minutes,

That's a design decision and it's up to you! A stepper (or servo) would be appropriate for the back-and-forth movement. Rotating the winder with a stepper would mean that you don't need a mechanism to count the rotations because the software can count the steps. On the other hand, you don't need the 1.8 degree precision of a stepper, a DC motor is easier to power, and it will run faster.

So I guess I will have to settle for an approximate resistance target based on either revolutions and/or approximate length of wire used.

It would be the length of wire used. The number of rotations doesn't affect resistance except as it relates to the length of wire used. If you measure the length accurately, the resistance calculation should be very-accurate. It would be less accurate if you try to estimate the length from the number of turns, but you might be able to get close enough.

Or if you are willing to take the time, you can wind-on a little extra wire, measure the resistance, then pull-off several turns cut wire and take another resistance measurement, and repeat 'til you hit the target resistance.

OK.. I've got a CRAZY IDEA!

If you can figure-out a way to make connections to both ends of the wire while it's spinning.... The resistance from end-to-end isn't going to change but the inductance is going to increase as you add turns. So, you could measure the inductance while you wind.

You'd have to figure-out how to measure inductance. It would require a high-frequency oscillator and measuring current and/or voltage get the inductive reactance and calculate the inductance.

And, you might have to re-spool the supply reel onto a larger (non-magnetic) spool, to minimize the inductance of the supply spool.

5

rbarr110:
So I guess I will have to settle for an approximate resistance target based on either revolutions and/or approximate length of wire used.

It has been explained to you that the resistance of the pickup is neither critical nor in fact, relevant at all. It plays almost no part in the performance of the instrument.

Question now is - whatever makes you believe it is?

rbarr110:
I don't know if I really do, but several examples of DIY pickup winders I see guys manually moving it back and forth.

Do they also show them stopping the winder and unwinding the wire when it fails to complete an even winding layer?

You need the winder to guide the wire a quite precise angle back from the current position so that the turns are tight together, and to move back to the opposite slant the moment the layer reaches the end. This is a non-trivial task and will require steppers and precise calibration of the wire diameter against the length of the bobbin (a task traditionally performed by choosing substitutable gear sets on the winder). If the settings are correct and there are no faults in the bobbin or wire, this can result in a low failure rate.

And you need to control the winding speed so that the wire does not start vibrating (resonating).

6

This project appealed to me a couple of years ago. I put quite a bit of effort into it but it was not an essential project so I decided to move on after not eventually getting it to work correctly. The problem I encountered, and did not resolve, was in changing the left/right direction of the wind. When the end of a layer of wind would come about and a direction change was initiated, the winding wire would want to linger at the end and build up additional layers there. After enough pull in direction change, it would move in the opposite direction but by that time the device pulling the wire would be significantly away from the end. When the wire finally 'obeyed' and did move, it would move way over to it's intended position, skipping over most of the wind from the previous 'end' to it's new position. After only a few iterations of layers, it was a mess of hills and valleys. I used these motors. - Scotty

7

Paul__B:
It has been explained to you that the resistance of the pickup is neither critical nor in fact, relevant at all. It plays almost no part in the performance of the instrument.

Question now is - whatever makes you believe it is?

Yes, it is impedance. In my head when I hear OHMS my brain automatically goes to resistance, and that is all. The impedance, pending desired sound, typically ranges from 5k ohm to 12k ohm.

Paul__B:

rbarr110:
I don't know if I really do, but several examples of DIY pickup winders I see guys manually moving it back and forth.

Do they also show them stopping the winder and unwinding the wire when it fails to complete an even winding layer?

No, I have never seen anyone unwind them if it fails. I have seen failed attempts but it typically came from people trying to wind them really fast. When you do it manually people dont like sitting for much more than 20 minutes to manually guide/wind the pickup. Part of the reason why I want to go automated and if I am not sitting there the whole time I really dont care how long it takes.

scottyjr:
The problem I encountered, and did not resolve, was in changing the left/right direction of the wind. When the end of a layer of wind would come about and a direction change was initiated, the winding wire would want to linger at the end and build up additional layers there. After enough pull in direction change, it would move in the opposite direction but by that time the device pulling the wire would be significantly away from the end. When the wire finally 'obeyed' and did move, it would move way over to it's intended position, skipping over most of the wind from the previous 'end' to it's new position. After only a few iterations of layers, it was a mess of hills and valleys. I used these motors. - Scotty

I am somewhat concerned about this as well. How fast was the winding being done? Perhaps the design should have a stepper that moves the entire winding assembly (pickup bobbin and DC motor) back and forth rather than the copper wire?

8

How fast was the winding being done?

It wasn't very fast; perhaps 75RPM.

Perhaps the design should have a stepper that moves the entire winding assembly (pickup bobbin and DC motor) back and forth rather than the copper wire?

What would be the difference?

At the time I was thinking that having a piece to guide the wire onto the spool, located very close to the spool might eliminate the lag in changing direction but that would require having that position change relative to the ever increasing diameter of the spool winding. That was more work than I was willing to put into it.

  • Scotty
9

scottyjr:

Perhaps the design should have a stepper that moves the entire winding assembly (pickup bobbin and DC motor) back and forth rather than the copper wire?

What would be the difference?

The problem you had is the wire not changing direction when needed, perhaps, if the wire does not move but the substrate it is being applied to does there is no lag in wire movement. So when the bobbin makes one revolution, the stepper slides the bobbin over one wire diameter. There would have to be some input required to determine when the stepper should start back the other way, but is doable.