Low friction trim-pot?

[stegla]

I need say a 5K or a 10K trimmer that has low friction so that it can be turned by a lightweight pendulum.........any ideas?

The application is for pendulum stability of FF models.

Steve

[MarkusN]

Since this is for a quite limited range of angles and pots have inherent friction through the wiper, maybe a different measuring principle would be better. E.g. an iron core diving into a coil.

As for low friction pots: those used in Tx sticks might work.

[stegla]

maybe a different measuring principle would be better. E.g. an iron core diving into a coil.

Markus...........how might this work? Is it easy to implement?

Also I toyed with the idea of a magnet and hall sensors?

Thanks
Steve

[MarkusN]

I have no experience at all with this. Iron in a coil changes its inductance. You'd have to measure this with an oscillator which changes frequnecy accordingly. But I only know the principles, not the practical circuit design.

Magnet and Hall sensor would also work. Dunno about the linearity of the signal. The same is true about the iron in coil principle, though: not sure if it's linear.

[Gary Warner]

I was also looking for a low torque pot some years ago. I never did find one low enough. I opted for an optical shutter between an LED and a photo sensor. The shutter was on the shaft with a non-round shape and was supported on ball bearings. I adjusted the shape to get the response rate I wanted. My operational range was only 20 degrees.

I toyed with the idea of making my own from the parts of a pot where I could put ball bearings in the shaft and lighten the load on the wiper. I never did get to a working custom pot because the optical sensor was thought to be the least torque resistance.

If interested, it was an AOA sensor vane that needed to send angle of attack info to my micro controller Ic. It worked very well.

[GlowFly]

Look for an optical incremental encoder or a resolver. You may find a low friction item ex-equipment.
--
Steve

[ZAGNUT]

problem with most trimmers is the very low number of cycles they're rated for. the attached data sheet is for something much better IMO although you'll have to look and see if the friction is low enough for you. from playing with them i can say that they are lower friction than all the other pots i have in my radios. can be found at digikey along with a similar one from murata that futaba uses in the 14MZ.



dave

[phil_g]

I need say a 5K or a 10K trimmer that has low friction so that it can be turned by a lightweight pendulum.........any ideas?

The application is for pendulum stability of FF models.

Steve

Use a Hall-effect potentiometer. All solid state, no friction other than the shaft bearing itself. You will probably have to introduce some friction to prevent oscillation! They act just like a normal pot.

In September 2002 EPE (Brit elecronics mag) there was a F/F glider control project called Freebird, which did exacty what you're doing there, in this case it used mercury tilt switches and filtered the output with a pic.

Hall effect pots are a better answer I'm sure.

Cheers
Phil

PS check your PM in a short while Steve

[stegla]

Excellent replies to my question......thanks!

I like the idea of Gary's optical sensor.
I shall investigate position sensors asap
Tilt switches deserve consideration as this system would not be affected by inertia unlike a pendulum.

My interest is FF scale and i've been messing with pendulum ailerons to improve lateral stability in difficult subjects. The pendulum is positioned at an angle of 10degrees from the horizontal as an attempt to minimise inertia problems.

Steve

[bderksen]

How about an accelerometer? Very sensitive, and no inertia and no moving parts.

Cheers
Bill

[stegla]

OK, What I've come up is this...................Remember, I want to acheive pendulum stability (lateral stability)(aileron control) of a FF model

The pendulum weight is a magnet. At either end of the swing is a linear hall-effect device.

North polarity gives a Vcc/2 to Vcc swing. And a south gives Vcc/2 to 0V swing. I propose to use a pic12f683 to read these voltages and to provide the pulse to a servo that will operate the ailerons.

Any comments?

Steve

[Chris T]

I have done this with a hall sensor. Look in the electric flight video forum for micro servo in action. I use the magnet of the actuator to sense the position with one hall sensor. The good thing is, that you don't need an extra magnet and the weight of the hall sensor is really negligible. Resolution is great.

Chris

P.S.: and my prototype routine is running on a pic12f683 :) Interested?

Build thread:
http://www.rcgroups.com/forums/showthread.php?t=757050&page=5


Video:
http://www.rcgroups.com/forums/showthread.php?t=775943#post8598118

[AndyKunz]

OK, What I've come up is this...................Remember, I want to acheive pendulum stability (lateral stability)(aileron control) of a FF model

...

Any comments?

SubTech APC-4, available from www.PandanModelBoats.co.uk

If you leave the input un-connected it will assume level. If you need any customization, e-mail me (I designed it).

Andy

[stegla]

Chris..............nice Hawk..........good luck!
What hall device are you using?

Andy...........your automatic leveller looks perfect for my needs..............I shall buy one if this project falters.

Steve

[Chris T]

Hall sensors from cdrom motors :)