Newbie question on Potentiometers

[matta757]

Hi everyone,

First off, let me say how excited I was to find this forum and I am hoping that maybe someone from this wealth of knowledge can help me out with this question.

I am building a 757/767 throttle stand. Currently, I am using the Saitek Proflight Throttle Quandrant (2) to use the speed breaks, throttles and flaps. However, since I am building with wood and the throttles are quite heavy, I was looking for an alternative and more stable way to complete the setup. I saw some posts on here about "sliding pots" and did some research on potentiometers and feel that these are probably the way to go.

So I was wondering if anyone can offer me advice on what kinds to get, how to setup and program them, and also if it would be possible to use them for the thrust reversers inside my wood throttles. Also, should a slide pot be used for the speed brakes and flaps as well, or is there a better type?

Again, this is all uncharted territory for me, so any help you can offer would be amazing. I have posted pictures of my in-progress throttle stand (currently with the Saitek throttles) as a reference. Thank you in advance!

Regards,

Matt

http://www.mycockpit.org/photopost/data/500/thumbs/throttle31.JPG ('http://www.mycockpit.org/photopost/data/500/throttle31.JPG') http://www.mycockpit.org/photopost/data/500/thumbs/throttle21.JPG ('http://www.mycockpit.org/photopost/data/500/throttle21.JPG') http://www.mycockpit.org/photopost/data/500/thumbs/throttle11.JPG ('http://www.mycockpit.org/photopost/data/500/throttle11.JPG')

[jmig]

Welcome Matt. Nice throttle, good work. You can use either rotating or sliding pots with the same results. The secret is to get as much movement as possible.

Sliding pots are often used with GA Cessna style throttles. I used them in my throttles (which are old Suncom throttles) my home made control stick and rudders.

I have also used the regular pots. Using gears or long moment arms, you can 180 to 270 degree of rotation on a pot. This is as good as a slider.

I would do a search on the forums for pots. You will find most of your questions answered two or three times. Also, check Mike's Flight Deck. Mike has a lot of good basic info on pots and all things simulator.

You noticed I haven't really answered your questions. That is because there is no one perfect solution. It depends on what you have and room in which you have to work. I would recommend looking at pictures of throttle construction from different sites and reading on the pros and cons of different pots before settling on a solution.

[matta757]

Hey John,

Thanks for the advice. Will definitely be doing some research.

Does anyone have a place they would recommend buying pots from?

Thanks,

Matt

[jmig]

Hey John,

Thanks for the advice. Will definitely be doing some research.

Does anyone have a place they would recommend buying pots from?

Thanks,

Matt

If you want inexpensive pots and switches but not always the exact specs you want, you might try All Electronics. When I want something to spec and want to know exactly want it is, I buy from Mousers. They have a good selection of 65 and 100 mm slide pots. Just make sure they are liner and not audio.

John

[matta757]

Hey John,

Thanks again for the reply! Does Mouser's carry rotary pots? I keep getting confused with the terms "linear" and "rotary". A rotary pot can still be linear, correct? Also, if I was going to go with rotary pots, where might I be able to find plastic gear mechanisms to attach to the pots and the throttles?

Regards,

Matt

[matta757]

Ok so doing some research, I have been finding some rotary pots that look pretty good (Vishay Spectrol 249), but I am curious what would be considered a good rotational life span? The 249 says 25,000 cycles, is that acceptable for a throttle setup?

Thanks,

Matt

[jmig]

Yes Mouser sells rotary pots. Their print catalog is about two inches thick. If it is electronic, they probably have it in stock.

Ok, there are rotary and slide (linear pots) both types of potentiometers can be set up to have a linear (equal change for distance) curve or a logarithmic (the more you move the sliders the greater the slope of the curve) or audio pots. Audio pots are what is used as volume controls.

In sound (I think this is right) every 10 points increase in decibels is a doubling of the loudness or volume. So the pot is set to give that type of curve. We want an equal change for the distance of movement or a linear progression.

Most rotary pots have about 270 degrees of turn. A linear pot can come in three different lengths. You want to use the longest possible to get the most resolution of the 1000 or so steps MSFS gives you.

A Google search on potentiometers will give you a lot of information on the construction and materials of pots. The best and most expensive are the wire wrapped, then the ceramic pots. Finally you have the lowly carbon pots, which are what most of us use. They will vary in life. I don't remember the life cycles but I have never worried about them. I change things so often, it doesn't matter. :roll:

I hope this helps?