Push/pull controls

[Kerbo]

The nut would slide back or forward as you TURN the control. The nylon rod turns as you turn the control moving the nut to one of it's extremes. So you can slide the nut back and forth by pull/pushing the control and rotating the control also moves the nut but much more slowly giving you a fine adjustment.

Why would the nut slide and the control rod not move in/out when you turn it? The only way I can see this working is if the force to move the control rod in/out is greater than the force required to move the pot. Are you relying on the friction of the control rod bushing, where it goes through the MIP?

[Ronson2k9]

Okey...

The nut will not rotate as it is attached to the pot control arm (drill a small hole in the side of the nut for the control arm). The control knob is secured to the nylon rod via set screw and or glue to keep the rod and control knob as one solid structure. So when you turn the knob the rob turns too. That means the nut on the pot has to move. It will move if you pull on the rod or if you turn the rod the nut doesn't turn only the rod.

The pot is secured in the guard which is itself secured to the MIP.

So..

Pot + guard attached to MIP (so that you can if needed remove the pot later)
Nut attached to pot so nut can't turn. This will cause the nut to move should you turn the rod.

The guard is there to help prevent the nut from turning. Just a bit bigger then the outer diameter of the nut so the nut can slide but not turn. If using UHMW that will make that even more so as it's super slippery plastic.

Rod can turn or slide either way the nut moves the pot. Either incrementally or directly.

Hope that helps

[Kerbo]

So when you turn the knob the rob turns too. That means the nut on the pot has to move.

Why would the nut have to move?

When you turn the rod it is just as likely the rod will slide in/out (and the nut not slide) as it is the nut will move (and the rod not slide). There has to be some force stopping the rod from sliding to get the nut to move the pot when you turn the rod. That force is my confusion.

Think of holding a bolt with a nut threaded on it in your hands. The nut is in your left hand and the bolt is in your right hand. Now turn the bolt with your right hand. Does only your left hand get pushed? No, because the force against each hand as the nut travels on the bolt is the same (all else being equal).

If you are planning on the friction required to slide the rod through its mount being great enough to overcome the force of the nut sliding the pot (thus causing the nut to slide and not the rod when the rod is turned) that is fine. I am just trying to get your design clear in my head.

Sorry for being so dense!

[Ronson2k9]

Yep your right I hadn't thought of that. Okay.. So to get the nut moving we need to keep the rod from moving during the rotation.. Working on it.. Remember the button on top of the knob.. We know that's to keep the rod from moving when not pushed in. So that must release something in the cable to allow it to slide freely.

What could I use to keep friction high when rotating but low when push pulling that could be activated by a push button. Non of them simple options.

- Separating the rotation from the push pull via CAM.

- Spring loaded release.

- Electro magnet (always on until you push the button to turn it off)

- Turnbuckle. Rod has threads going in opposite directions. If you have a nut at both ends turning will bring then together or spread them apart. Like a wood clamp where the turning brings the end together.. Trying to think of what kind of thread that is.

Wood clamps keep coming to mind for a solution to this though.. I'm still working on one perhaps you have some thoughts..??

[Kerbo]

I don't have any bright ideas yet. We need to know how a real one works because some bright engineer already figured this out.

[Ronson2k9]

I dare say they aren't going to give their engineering drawings for a shot at duplicating their controls. Cutting open one to find out how it works probably not a good option. I would use it first.. hehe..

Difficulty is that the hole thing has to move.

Okay is possible to route two pots through the same control. 1 could be for the push pull and one could be for the fine tune. 2 50k's for instance. The only problem with that would be in order to have the full movement of the control the turning pot would need to be fully engaged (turned).

I think I have it .. Worm Gear...

Beauty of this is you can rotate to get a movement and you can push pull to do the same movement. The resistance to being pulled is greater then being turned (theoretically). Or if resistance is still pushing the control out. We could use the two pot method in this case it perhaps is a bit easier to set up.

Essentially what the nut on the rod is - is a worm gear. If you think of the nut as a gear.

It would be cool to have the linear pot cancel out the the rotating pot when getting close to either end. Reduced the amount the rotating pot effects the total output voltage.

Probably what we could be looking at here is a rack mount throttle group with PC board and 3 sets of pots.

The linear one would change from having nut to a simple bushing to allow the rod to turn but not pull through.. The worm gear would be prevented from moving laterally but be allowed to turn. So the driving gear would have a hole with a key way to get it to turn.

Or we could work it so the button turns off the rotating pot as it's (push button to pull/push control). That brings about a possibly different thinking all together. Both pots work independent of each other. Then you would need a form of memory so that one can act on the others last position. Doing in logic what I've been trying to do physically.

I'm pretty sure you could put both pots in series and have a cumulative effect on voltage. The control wouldn't be that accurate in as much as you have two positions and combined they equal the output. So those two positions would change from time to time to equal the same output making for inaccuracy when using the control. Weather or not that inaccuracy is a problem depends on the amount of fine tuning that is permitted that is the percentage of change due to turning. If it's not very much then it's not so much a problem. Hold on a sec that would happen in the real control too. As you could fine tune back to a position you had first slid too. That being the case the actual control must move when turning. Otherwise it would get out of 'tune' when you did that over time?

Any thoughts now??

PS: We could just forget the whole fine tune thing and go for the straight push pull only.. Eliminating nearly all this stuff.. and about half if not more the cost of construction.

[Ronson2k9]

Rethink.. Again:

That bushing moving the pot and the screw action moving the control got me thinking again. What if the nut didn't move the pot but a bushing did. Then the nut could hold the rod till you turned it. We would need to change the amount of hold preventing the nut from sliding when you want to pull/push the control. Or provide enough constant resistance so that you still slide the control including the nut..

I'm thinking UHMW again this time though you want to make it as resistant as possible. Working at from the other direction. You still want it slide but under force. A bit more engineering involved yet.. I'm getting closer though.

The nuts job is to allow the turning of the rod to move the pot.. That's all it does. So we need a way to add resistance to the push pull to stop the from moving the nut... Need to separate off the resistance to turn the rod from the resistance to pull/push the rod. So one can be greater then the other slightly.

New drawings will be on the way I think I've got it licked this time.

[Kerbo]

Someone mentioned the button on the mixture knob locks the control in place. Does this then allow fine tuning by turning? I've always been an armchair pilot so have no idea how the real stuff works.

[Ronson2k9]

I think it would be pretty easy to grab the knob with your fingers and pushing in with your thumb release the control then push or pull. I think it stays locked as a natural course and is released when pushing the button..

That said I think I found a solution to the friction problem that keeps the design pretty much the way it is now.

We need a tube to go around the threaded rod that is free floating rotation wise at the contact with the control knob. So long as the threaded rod is able to turn within that tube the tube can then be acted upon for friction purposes.

I got new drawings on the way.

[Kerbo]

I got new drawings on the way.

Sweet!

What software are you using for the drawing and rendering? If you mentioned it I apologize for missing that.