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String Potentiometers

Started by AAnnillo, April 27, 2021, 09:35:16 AM

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AAnnillo

Greetings all.  I hope this finds everyone well and in good spirits.

I'm starting to look at interfacing options for my B727 throttle quadrant and am seeking recommendations for suppliers and types of string potentiometers.   From my initial research, these look like great options for connecting to the reels of each thrust lever in my TQ.

Do you have any recommendations for suppliers and/or types that I should be investigating?

Thank so much.

Antny

mickc

On my previous OEM TQ conversion I used Uni-measure string pots.  Model LX-PA-15-P10K

Best advice I can give is to go for the best quality you can afford, and set them up properly.

Using cheap 3D printed ones will end up giving you endless calibration nightmares.

String alignment is a big issue too, I see many builds where the string is coming out of the pot on an angle, this affects the accuracy and shortens the life of the pot significantly.

kurt-olsson

Mick is 100% correct.

I also would like to add that if possible, using two sprockets can also work very well. Thats what i use in my TQ. I have never needed to recalibrate sofar.

AAnnillo

MickC....THANK YOU!  I had seen that company's string pots in my research and in comparison to others I had seen, agree that they're the best option for my purposes.

Kurt...thank you for your input.
I'm curious to learn more able your two-sprocket approach.  If you (or anyone) can share additional details as to how it was done, I'm all ears (and eyes).

Thank you again.

Antny

kurt-olsson

Nothing fancy really, one sprocket on the regulat potentiometers shaft and another one connecting the chain etc. For example

Reco

I've set up my control's using 2 methods

First method.
Using small 8 tooth sprocket and small 8mm wide chain
I'm using vishay 357 potentiometers
Which have a life cycle of 5 million life.
 I connected the chain to hose clamps and tightened the hose clamps to my rotating control surface.
I made up some small aluminium brackets for the potentiometer to fit into, attached the sprocket to the potentiometer shaft

Second method.
You can replace the 8 tooth sprocket with small GT2 gear from 3d printers and using the GT2 belt drive place the belt drive on the chain
20 tooth GT2 gear may pickup smaller
Movements which will help when you calibrate your control

Regards

Rhys
 

AAnnillo

April 30, 2021, 04:53:03 PM #6 Last Edit: April 30, 2021, 04:53:42 PM by AAnnillo
This is great!!! 
Thank you very much.
I'll start shopping soon and begin the experimenting with the throttle levers.
Speaking of sprockets....
I have the larger OEM sprocket and a 35-pitch 'bicycle' chain ready to go for the trim wheels and am wondering what type of DC motor to use and THEN determine what type (how many teeth) drive sprocket attached to the motor to get and use.  I had been searching for the OEM trim motor and am guessing they're close to impossible to find.

Reco

April 30, 2021, 05:32:01 PM #7 Last Edit: April 30, 2021, 08:09:53 PM by Reco
Regarding sprocket and chain I'm using industrial chain and sprockets  the  smallest available
The sprocket has a 6mm bore hole and I  got 8 and 9 tooth to try.

I had to have the sprockets tapped to screw in a grub screw which secures the sprocket to the potentiometer shaft.
 I looked at string pots but the costs were to high(I'm in New Zealand) so went down the chain and sprocket way

Rhys

AAnnillo

I've ordered three (3) Unimeasure string pots and their mounting brackets.
They should arrive in a month or so then I'll begin the fun experimenting.

Antny

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