JR 180 degree servo conversion

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lightning
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JR 180 degree servo conversion

Post by lightning »

Not totally combat related but I figured there's enough guys around this Forum that SOMEONE might be able to help.
The question is:- What value resistor do I need to put in series with the wires that are connected to each end of the pot wiped resistor surface to fool a JR servo into traveling 180 degrees.
Mechanically they can all do it but the calibration is such that they only travel 45 degrees each side of neutral.
Adjusting end points on the Tx to 150% can get that to 67.5 degrees, but I want 90 at a standard setting.
Any experience out there?
jpmorere
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Post by jpmorere »

The pot is likely 5K and only about 30% of it's travel is normally being used. To double the used pot travel with no other changes, you would need to approximately double the series resistance. All of my numbers here assume a 5K pot.

Probably about 2K ohm would do it, but maybe as high as 5K. I would start with 2K (or 1K on each end) and go higher if that doesn't get you as far as you want to go. You would not just add 5K on one end, maybe 2K on one side and 3K on the other. You need to determine several things. Primarily, the pot's resistance and where along the pot's arc is normal servo center. It is likely offset a bit toward one end. That is the end to which you would add the lower value when adding split resistors. The ratio between the resistors should be about the ratio that the wiper is on the pot at servo neutral. Of course, it would be best to measure the pot and determine it's resistance before adding the resistors in the first place.

J.P.
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lightning
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Post by lightning »

Thanks JP, that gives me somewhere to start.
Maybe I'll "bread-board" some 5K pots at each end and play with them until I get where I need to go, then sub fixed resistors inside the servo case.
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boiler
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Post by boiler »

Keith, you are starting to sound like a good scientist.[;)]
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lightning
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Post by lightning »

JP,
I ended up with 2.2K fixed resistors each side of the servo pot. I then adjusted mid-point and travel using sub-trim and EPA on my transmitter.
ALMOST 180 degrees of movement before I hit the stops.
My 72" Spitfire now has slo-mo retractable landing gear - takes five seconds to retract or extend - much more realistic!
I started with a JR low profile retract servo, but there is no pot, simply two end point contacts for the extremes of travel. I wanted to use the servo speed feature of my JR9303 to slow the gear down, but it would not work with the servo setup as received. I replaced the end point contacts with a standard JR 931 pot, but that reduced the movement to 90 degrees, which is what started the whole question and experimentation process.
Project is now complete and I plan to fly at our club 4-stroke rally this weekend. However no streamers allowed!!
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Post by jpmorere »

Congrats... And nice to know your pad resistor values. This might prove useful for some of us who also like to play with these things from time to time.

J.P.
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