What is the largest and/or heaviest pickup you wind.

[enkindler]

I was trying to do some calculations as to the torque required for halfway decent acceleration on the typical pickup winder. Both for those looking to upgrade existing winders and an idea I have.

Anyways I need to calculate the 'Radius of gyration' and I realized that I don't wind 5 or 6 string bass pickups.

I am pretty sure that 95mm or ~3 3/4" is the widest common string spread for on a 6 string bass but I need the weight.

Does anyone here have a coil from such a beast spooled up who could put it on a scale and tell me the weight. I will pad it by quite a bit so even a kitchen scale would probably be close enough.

Acceleration Time in Seconds = .039 x WK^2 (Final RPM – Initial RPM) / Torque in inch lbs. Where W is the weight in pounds and K is the radius of gyration in feet.

So one half of 95mm is ~ 48mm = 0.15748 feet

70 ounce inches = 4.375 inch pounds

(.39 * (1*0.157^2) * (1000-0))/4.375 = 2.42691

So if my math is correct and if the mass of your shaft,pickup and plate was one pound a 70 ounce inch motor would git 1000 rpm in about two and a half seconds.

Thanks,

enkindler


P.S. I feel dirty doing this type of math in the imperial system (although it is better in the wood shop)

[David King]

I worry you might be over-thinking this one enkindler. The mass to be accelerated is probably less of an issue than the friction to be overcome on a longer coil pulling a wire through the tensioner at very low speeds when DC electric motors tend to have very little torque. Stepper motors are great because they have maximum torque available at lowest RPM but they then fail miserably at high RPMs due to resonance problems and inherent limitations of their own. The best combination of torque and speed in the smallest package is a 3 phase motor with a vector drive aka a 3 phase AC motor or servo motor. Most modern winders will use that motor combination hence the $$$ price tags we see on them.

In regards to your request the last set of 6 string bass coils I wound weighed in at just over 4 ounces per coil. My 1950s sewing machine motor had no problem swinging them.

[jason lollar]

I have made several 18 inch long blade pickups I call "knuckle busters"- sewing machine motor had no problems

[rjb]

I have made several 18 inch long blade pickups I call "knuckle busters"

Just out of curiosity, what are they used for?

[enkindler]

Thank you David for the per coil weight, it fit my assumptions.

Yes, the torque required top pull the wire is another factor, I was only worried about acceleration for this part for two reasons.

One reason is that If I can keep the voltages and amperage of the motor down the component costs are much lower.

The second reason is I would like to keep the motor as small as possible to reduce the rotational mass mostly for safety reasons. The Schatten has that O-ring drive for safety and to protect the motor.

Steppers are fine these days if you are trying to match Schatten levels of performance if you use the type that use rare earth vs the old perm magnets but yes they do loose torque with speed which is an issue.

However I am using BLDC motors, or the type that powers DVD players and hard drives etc... This is basically the same as a three phase induction motor but it also uses rare earth magnets vs a steel induction core. I am using a Nema 34 motor, this means I have no pullies or belts and I have less than 2 mils of run out or end play.

You drive them with three synced pwm sources. With your provided weight I think I can source a motor for cheap enough to make this practical.

I do have a home built 3D printer, pcb mill, cnc router and parts pickers I have built from scratch so this is not my first rodeo.

But we will see I have more design to do before I order parts and find the time to design and mill the PCB to put them on.

The winder is cheap compared to commercial options but finding a good cheap electronic controlled tensioner, that is the problem.

Note, I am not making a winder, I am making a duplicator. As you hand wind it will record the wrap and can recreate it.

My current setup for doing that is expensive but I will be testing lower cost options with this new winder as my 3phase VFD controlled lathe winder doesn't have the positional awareness resolution I need.

Thanks for the info,

enkindler

[CRU JONES]

My whole winder uses 700mA to run. that includes a bit of other stuff to power as well. I wind 8 string p-90's without problem (4"). I like a low power motor as I can get my tension measurements from the motors current draw

....A "knuckle buster" would certainly bust my winder

[David King]

Ah yes these newish smaller motors are pretty cool, I've been looking through the development kits that are available through the usual sources and only wish the kits were cheaper.
Let us know how this transpires.

[enkindler]

Ah yes these newish smaller motors are pretty cool, I've been looking through the development kits that are available through the usual sources and only wish the kits were cheaper.
Let us know how this transpires.

The main issue is that until the past few years the chips that would to sine wave were very expensive and chip manufactures liked to charge a LOT for example boards

The arduino and maker movement is changing that.

I chose the ST STM42 MCU for this, it is ARM based and has 6 dedicated timers for three phase pwm plus additional timers for quadrature feedback. I will have to do some C programming and make the mosfet driver board but I can use their "STM32VLDISCOVERY" board It has a STM32F100 MCU and usb programmer built in for less than $10.

But I will have to write a C program to fit their motor libraries. I have not studied their licences but I'll release my code if it is legal under the MIT licence.

I will start a thread in the winders area once I have something to show and get feedback on. The cost will be a bit much for most though it should be cheaper than the street price for an american standard strat.

I don't really care about the PAF sound, mostly I wind to get a guitar out of the mud and/or to stand out in a particular band's mix.

I do have a huge interest in emperical data as it would allow me to sculpt those sounds. Getting repeatable winding into the hands of others is the best way I can think to move forward with that goal.

enkindler

PS: I do want to know if those "knucklebusters" Mr Loller was talking about were for. Myabe a piano or electrified Autoharp or what?

[Mark Hammer]

I also eagerly await Jason's reply, but for now I'm guessing for some sort of normally acoustic keyboard, like piano or even harpsichord. I know the piano player in my old band had a Lesage acoustic upright with pickups in it, and what I gather was one pickup per group of strings.

[copperheadroads]

I also eagerly await Jason's reply, but for now I'm guessing for some sort of normally acoustic keyboard, like piano or even harpsichord. I know the piano player in my old band had a Lesage acoustic upright with pickups in it, and what I gather was one pickup per group of strings.

I'm very curious as well .......Maybe it's a pickup for an Autoharp

[Steve Conner]

couldn't resist! I'd much rather induct anyway.

FWIW I think enkindler greatly underestimates the time and effort needed to make a working brushless DC drive with a favourable torque characteristic for coil winding. To give one tiny example of the many issues you'll face: The RC model motors are sensorless, and the controller derives its timing signals from the motor's back EMF: that's not at all conducive to smooth acceleration from rest, because back EMF is zero at rest.

And, permanent magnet brushed DC motors don't have "low torque at low speeds": the torque is always proportional to the current. You put 1 amp through the motor, you get so many ounce-inches of torque, irrespective of the RPM.

If you must make your own controller, Microchip have several application notes with example code for their higher-end PIC processors. I've seen hobbyists make 3-phase motor drives based on it. I suspect it is using the proverbial Cray to crack a nut, though.

[enkindler]

couldn't resist! I'd much rather induct anyway.

FWIW I think enkindler greatly underestimates the time and effort needed to make a working brushless DC drive with a favourable torque characteristic for coil winding. To give one tiny example of the many issues you'll face: The RC model motors are sensorless, and the controller derives its timing signals from the motor's back EMF: that's not at all conducive to smooth acceleration from rest, because back EMF is zero at rest.

And, permanent magnet brushed DC motors don't have "low torque at low speeds": the torque is always proportional to the current. You put 1 amp through the motor, you get so many ounce-inches of torque, irrespective of the RPM.

If you must make your own controller, Microchip have several application notes with example code for their higher-end PIC processors. I've seen hobbyists make 3-phase motor drives based on it. I suspect it is using the proverbial Cray to crack a nut, though.

Actually it is quite easy...mostly because other people have done the hard work and if you look above I note that I'm not running sensorless. And yes sensorless is hard at low RPM but with any of the latest generation of MCU it si not as hard as you claim due to their hardware support. They actually tie ADIC for back EMF control of linked PWM timers, the STM 32 has 6 dedicated 16 bit PWM timers.

ST has a library for their MCU's you can google "STM32 FOC PMSM SDK v3.0" they also have a GUI called "MC Workbench" that will help you configure the C headers and it also provides a freeRTOS example app if you use the performance line.

I already have it controlling a BLDC motor with an encoder that I have but it is a 10,000 RPM NASA surplus motor and would be way too expensive.

I am looking at using Hall sensor motors for cost on the project but really it is only a $70 up charge to use a 200 PPR encoder.

I may bump up to the STMF4 MCU from their STMF100 value line to use freeRTOS because it is nicer.

I do agree if I had to write the code for the current control and feedback it would be much harder but you should go look at it, it is quite trivial if you take advantage of the chip vendors offerings.

I have ordered the parts

[jason lollar]

usually used on pianos, i use to have a clip of an uprite running through a marshall stack - very odd sounding. I dont know if I still have that or not

[enkindler]

Actually it is quite easy...mostly because other people have done the hard work and if you look above I note that I'm not running sensorless. And yes sensorless is hard at low RPM but with any of the latest generation of MCU it si not as hard as you claim due to their hardware support. They actually tie ADIC for back EMF control of linked PWM timers, the STM 32 has 6 dedicated 16 bit PWM timers.

ST has a library for their MCU's you can google "STM32 FOC PMSM SDK v3.0" they also have a GUI called "MC Workbench" that will help you configure the C headers and it also provides a freeRTOS example app if you use the performance line.

I already have it controlling a BLDC motor with an encoder that I have but it is a 10,000 RPM NASA surplus motor and would be way too expensive.

I am looking at using Hall sensor motors for cost on the project but really it is only a $70 up charge to use a 200 PPR encoder.

I may bump up to the STMF4 MCU from their STMF100 value line to use freeRTOS because it is nicer.

I do agree if I had to write the code for the current control and feedback it would be much harder but you should go look at it, it is quite trivial if you take advantage of the chip vendors offerings.

I have ordered the parts

Sorry about the bad grammar and spelling, the site was having issues and I started doing edits and it submitted in the middle of them.

I do wish we had nice round spools like your HUGE inductor the challenge of tracking and placing a wire that is 2.5 mills thick on a bobbin at speed is painful especially with the commercial spools having tolerances. Luckily pickups really are not that sensitive to differences but it still bothers me.