Fix for weak throttle button (potentiometer)

I’ve snapped my throttle button several times (I may not be the most careful), and I was tired of how delicate it is. So instead of buying another position sensor (https://www.mouser.com/ProductDetail/sensata/9610r34kl20/?qs=y%2bTtbMcwHOnTeiaq7R%2b8pA%3D%3D&countrycode=US&currencycode=USD), I took it apart and and replaced the hollow plastic shaft. First I tried 3D printing it solid, but it was still subject to snapping, so I replaced it with one of the metal longer stand-off’s from the build. Then I put a spring on the outside to replace the one on the inside. Here’s a couple of pics.

Only required a couple of small mods to make it fit, such as widening the hole and grinding the screw head a bit smaller.

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Yeah i just busted my toothpick off yesterday, was so pissed i haven’t wanted to open it and look to see what’s in there. Assuming the toothpick is integral to the sensor because why would it be simple and easy and (heaven forbid!) robust?

Also, where can i find an STL of the current throttle handle? I’m going to redesign this to not be a massive turd.

Fixing it is actually pretty easy. The handle is a hollow tube with the brushes connected at the end on a square block. The block slides up and down the pot housing. The back plate of the pot housing has a very small rod attached to it that goes inside of the hollow tube, with the spring between the rod and the tube.

When I broke mine, I cut off the rod (the spring was lost in the tube’s ejection) and replaced the cavity left in the tube with a solid piece of spring steel rod (landing gear wire from a retired RC plane). The spring now goes on the outside.

Biggest issue I have is the two small flat head screws on the bottom of the pot. I can’t get to them while it is on the board so I have to de-solder the pot to get the back off.

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I don’t know what to expect-- after the stick broke off the throttle was stuck at around 25%, not enough to maintain flight. Had it gotten stuck higher I would have just rode it out until it was dead and then landed.

Yeah, can be a bit scary. But there is always disarming. Nice glide back down.

There does not appear to be anything remaining inside the potentiometer on mine. I see a sort of central “shaft” but nothing on it. Just an empty hole all around. Nothing remains of the stick.

To remove this broken one, I’m assuming desoldering these 3 marked points is all that it needs? I’m going to relocate it in a better design that can actually be stronger than a pasta noodle.

Yeah, those three pads are all that holds it on. Take it slow.

This is what it looks like on the inside. The only part missing is the rod so I placed the screw driver to simulate. I cut off the rod and replaced it and the spring with a steel pin. If I was to lose the tube, I would replace with a standoff as per Jrsimple’s note above.



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@Pdwhite Can you post STL’s of the current throttle handle? The github one is not correct. Would save me lots of time.

I ordered 2 replacement potentiometers and managed to open mine without desoldering it, to see what is left in there. The guts are still in there so it should work if I put something in there that won’t break. BUT-- the overall design of this throttle really sucks. It shouldn’t be able to break like it does, firstly. And secondly, it should be made in a way that resists catching and tangling on things. I’m going to make a trigger-style action where the mechanism is protected and can’t break.

I looked online and there are plenty of prefab RC trigger potentiometers for cheap but I can’t find any info on their rating for compatibility. Would be nice if we could just toss a $10 common part in there instead of this special snowflake toothpick breakable weakling crap.

Does anyone have a measurement for how far the toothpick sticks out of the casing?

My advice: get rid of the top plunger disk or it will catch again and brake off again. Mine broke catching “something”? It snapped at the base. Had to replace the plunger with an original part.


Does anyone have a measurement on how far out the stick sticks?throttle1

Just making an assumption that it sticks out 30mm and change.

So, this is what I’m making. Standard throttle layout, hinged lever moves internals enough to depress stick in pot up to 30mm with a 32.75mm range of motion. Only the stick will be inside, protected, where you can’t break the %^$^& thing.

Top over-the-thumb part will house the pot and a space for the display.

throttle2
throttle3
throttle4

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I have 34.7mm from the top of case to the top of dome.

I thought someone already designed a “traditional” throttle. I’m 10 flight in and like the thumb throttle now. I did snap off the stick after flight 2 but that was because the A lines was on the wrong side. Nothing a little preflight routine didn’t solve…

If you design a new throttle, you are back at the start of the design-protype-test-break-design cycle. Just my thoughts.

I’ve seen people spend years “redesign” or “perfect” systems that were functional, instead of flying. If you would permit me, I would recommend getting it going as originally intended, flying, then modifying.

I can’t fly with a busted throttle that keeps busting.

Printing it up, let’s see how it does.

OpenPPG_throttle_board_batch6_without_pot.STL (53.4 KB) OpenPPG_throttle_board_batch6.STL (61.3 KB)

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Exactly what I did. A small dent in my thumb is not a problem for ten minutes. 40+ flights. No issue.

Quick Story. 1999. PPG Boogie in Md.
New pilot, dropped throttle, and prop whacked it.
Throttle got stuck at about 75% power and he was fast approaching cloud base.
Unable, or too scared to turn off fuel, his instructor put him into a hard turn to avoid going through cloud base.
25 mins later he ran it out of fuel and landed.