Stepper Motor Pedal Steel

[b0b]

If someone wants to volunteer to manage such a contest, feel free to start a new topic about it with some rules and a deadline. The Forum can award some sort of plaque or trophy to the winner(s).

[Karlis Abolins]

I don't know about running an actual contest but I have an interest in experimenting with the concept.
I visualize a scenario where the result has the following requirements:
The string should have a scale length of 24 - 25 inches.
A candidate pitch would be the 4th string E on the E9th tuning.
The demo should have the string raise a half step and a full step (F and F#) and the string lower a half step and a full step (D# and D). This should be selectively controlled by software.
The pedal end of the demo should show the full range of up and down for the raises and lowers.

I think that there is room for partial experiments by individuals who are interested in either the string pitch change or the pedal AD process but not necessarily interested in the whole process - virtual (computer animated) pedal and real string setup and vice versa.

My own approach would be phased. I would concentrate on the string side and control it with a virtual pedal to demonstrate proof-of-concept and then develop the pedal. I think I favor a Raspberry Pi for the control center and virtual pedal since I already have one connected to my 3d printer. There is a lot of information available on using the Raspberry Pi in an experimental setting including control of stepper motors.

So, regardless of an official contest, I think I will go ahead with a prototype.

Karlis

[b0b]

Raspberry Pi is a good platform for controller software, and it's only $35.

[Bob Sykes]

This idea is certainly possible and if not practical, it's still a great concept to experiment with.

Something that has not come up on this or previous discussions is noise. Not the kind that I make playing pedal steel, but electrical noise. Steppers, servos and solenoids all generate substantial magnetic fields. Less obvious is the similar noise created by digital electronics. Unfortunately guitar pickups are great at converting this noise into audio. Try holding your smartphone, tablet or even a LED flashlight next to your PSG pickup. Shielding against these magnetic fields can be difficult. I expect the electronics/actuators should be located away from the pickup(s). Possibly at the keyhead?

A conventional changer may not be needed anyway on such a guitar. Motorized tuning keys might work. Sort of like what Gibson did on their 6-strings.

[Dennis Olearchik]

Didn’t Forum member T. Sage Harmos build a proto-type pedal steel with stepper-switches back around 2002/2003? Not to derail this thread but out of curiosity, does anyone still have a Harmos carbon-fiber lap-steel guitar?

[Eric Moon]

It seems like the best way to deal with electrical noise is to pull from the nut. I know Glenn built one of his Moyos that way to experiment with different bridge materials... it moves the servos quite a ways from the pickups.

[Mitchell Smithey]

Tech moves so fast that it’s only a matter of time before this idea plays out. I don’t expect it would play or sound exactly like what we are used to. Our most common tunings and setups are dictated as much by the mechanical limits of the instrument as the musical. We go to great lengths to compensate for those limitations with compensators, tuning temperaments and so on. Imagine not having to deal with all that mechanically....

The pedal steel is the already the whackiest instrument ever invented, lets keep pushing it to the limit!

[Jim Kennedy]

I would think a midi controller and software dedicated exclusively to pedal steel might be an alternative. The physical aspects would remain, while the variations in tunings and copedants would be limitless, handled by software. Add in amp Sims and effects, you could conceivably end up with a light weight rig that would need only a good amp.

[Chance Wilson]

I think Georg said it towards the beginning of this thread. As far as I've ever been able to tell, there's no way to get the variable speed needed, at least not using stepper motors. You could make something to change tunings but for string bending effects, I don't see how it could work.

[James W Smith]

I'm new here, so please don't start the flames yet.... But why not change the pitch without changing the string tension. Pitch shifters are available for electric guitar, so Why couldn't that technology be used for PSG? Something like the Electro-Harmonix Pitch Fork.

[Benjamin Davidson]

Using a digital pitch shift effect wouldnt give the right feel. It would sound digital for one thing, second, isolating each individual strings frequency for pitch shift, without bleed over wouldnt be easily accomplished.

Pulling from the nut would isolate mechanical noise. As far as mimicing the squeeze pedals and levers. I feel a programmed solinoid could be the way to go. A set of solinoids manipulating a keyless tuning system could be programmed to make this work. Calibration would provide its own challenges to such a system.

[Bobby D. Jones]

About 50 years ago in 1970 when I built my steel guitar. I worked in the light bulb industry. There was a electrical engineer and a mechanical engineer both figured on simplifying the mechanics of a steel guitar. They studied servo units, Air pistons, eletro magnetic pulls. They even studied air pistons and Selonoid valves for movement. They came back with some ideas to move the pitch, But could only do it at one speed, Could not vary the speed of the pitch changes for each song. With modern computer controls it may be possible to vary the speed of pitch movement. Maybe by the use of the song's timing placed in a computer program to control a varied speed of pitch change for each song.

Like a wheel there may be limits to change to the original design.

[Glenn Demichele]

For fun, I built a one string unit using a linear solenoid. It took a lot of current! Although I could get the pitch to bend fine, I started thinking about the pedals and there’s something about the pedal feel that would be difficult to replicate. The Feel of the mechanical linkage to the string is lost, and it would be a pain to build tactile feedback into the pedals.

[Karlis Abolins]

Re-visiting the use of stepper motors and electronic controls rather than mechanical controls, I have come to the conclusion that it is not feasible at this time. My research leads me to conclude that a stepper motor than can accommodate static torque of 30+ pounds would be prohibitively large, expensive, and noisy. It would be impossible to mount 10 or 20 such motors on a pedal steel.
I don't have enough knowledge of the other electro-mechanical devices mentioned in this thread to judge whether they would be feasible, but my guess is that we are not ready to go that route.
It appears that old-fashioned mechanical linkage is and will continue to be the best choice for pedal steel control.
The possibility of using electronic (software, midi, etc.) means of pitch change suffers from the same issues in that the control pedals and levers and their interfaces with the software suffer from technical insufficiency.
The use of midi with pedal steel is complicated by the lack of midi support for instruments that have more than 6 strings. The industry leader in analog to midi implementation, Roland, has excellent products that convert analog pitch to midi via segregated pickups but their interface to the midi control box has only 6 pins for input.
As a side issue, midi pedal steel using the Roland products lends it self to use on a 6 string pedal steel such as the steels made by Jim Flynn, Jimmie Hudson, and others.

Karlis

[Ian Worley]

https://www.youtube.com/watch?v=fSQ9Dg65EFo

[Karlis Abolins]

Ian, What a timely link! I had just posted that stepper motors were not an option when you posted the link to the servo bender guitar. The counter-force mechanism is ingenious. It is also applicable to a stepper motor implementation. Instead of having the stepper motor pulling against the whole of the 30 pound static torque of the string, it can be helped by a spring that reduces the static torque to near zero. Thus a small, fast, and quiet (and relatively inexpensive) stepper motor could be attached to each string.
I had resigned myself to giving up on this project but now I am re-energized.

Karlis

[Ian Worley]

I posted a link to that earlier in this thread, it was actually a link to a different conversation from about five years ago. If I were designing something like this for a psg, I would use a mechanical changer like what we have now. There would be no static tension on the servo at rest, it would only experience resistance when a pull was activated.

Even with a pull-release type changer setup the mechanical tension balance between the strings and return springs could be separate from whatever means you used to activate a change.

There is a mechanical advantage in a typical all-pull changer that reduces the effort needed to activate a pull by 50% or more, a crude illustration of this below.



much less than the typical ~30# string tension on a psg.

[Karlis Abolins]

An all-pull changer would require two servos or stepper motors per string whereas a pull release (or constant pull for a better name) requires only one. In my mind the constant pull scenario requires that the device knows where neutral is. Your point that the stepper or servo on an all-pull implementation would be at rest unless engaged may or may not be significant. A constant pull mechanism clearly would require to be active the whole time. I don't know if stepper motors are rated for 100% duty cycle. That is an important avenue of inquiry.

[Karlis Abolins]

The ball screw drive combined with a stepper motor is quite an elegant solution. The only issue I see (and found mentioned) is contamination of the screw with foreign matter causing degradation of performance.

[Bobby D. Jones]

It may be that we would have to go back too some of the first pedals being attached through the key head pulling down in the middle of the string span of the key head.
There is a physics rule about pulling sideways in the middle of a lines span. Working with the white water rafters they would run a rope from a stuck raft and a tree, Then attach a line in the middle of the rope and pull at 90 degrees to the main line. They said the got like a 7 to 1 mechanical advantage. They could pull a stuck raft out of places that could not be moved any other way with just Man/Woman Power on a river.

[b0b]

Would such a guitar make robot-like noises as you pushed the pedals?