on the white control wire.
Let’s get our hands dirty modifying the HXT900
servos for CR. Literally, you might choose to wear thin
rubber gloves since there’s grease aplenty inside. Be
careful and vigilant. Work in a clean bright area; don’t
get dirt or swarf in the tiny gears which are nice and
greasy. Leave as much silicone grease in place as possible
and don’t bend the brass pot shaft during disassembly.
Don’t break the tiny internal wires on the PCB (printed
circuit board) either.
Both mechanical and electronic modifications are
required. Mechanical stops on the output gear must be cut
away to allow full rotation. Electrically, we replace the small
internal potentiometer (pot) with two fixed resistors. We
need a 50% voltage divider, so any matching resistors from
5K to 100K will work. We’ll briefly remove the
potentiometer to make it rotate 360 degrees, then replace
it to mechanically support the output shaft. Be sure and
check out my videos at www.youtube.com/
watch?v=wfmM3cuihJI and www.youtube.com/
➤ Ready? Take a Deep Breath
and Let’s Roll
1) Disassemble the servo by removing the labels and
four long screws. Remove the top of the case. Carefully pull
the output gear straight off; it’s a tight fit on the pot’s
flatted brass shaft. Remove three white intermediate gears
— noting the location — and set the gears aside. Don’t
remove any grease.
2) Remove the bottom of the case and carefully pull
the PCB out. Cut three wires at the potentiometer. From
the top, push the pot down and out to remove it to work
on (Figure 2). Be aware that
some pots are glued in. I carefully
used a vice to press on the shaft.
Do NOT hammer on the brass
shaft; it will bend. Trust me.
3) Use a hobby knife and
side cutters to remove two plastic
tabs on the underside of the
output gear. Flush cut to the
bottom of the tabs (Figure 3).
Completely remove the tabs or
binding will result.
4) Use cutters to cut/bend
two metal tabs on the pot shaft
38 SERVO 01.2016