|Jan 18, 2014, 12:33 PM|
Down-geared slow speed modified Parkzone micro linear servo
Thanks to all the experience and examples I found here on this forum I am studying some micro retracts for my UMX P51.
I was disappointed by the excessive speed of the retracts so I tried a way to have slower, more realistic undercarriage movements and came out with this solution - that I think is cooler than the retracts themselves and of more general use for other projects too (bomb doors opening? :-))
Take whatever linear servo. I used one of the oldest 1.5 g Parkzone ones.
Pull away the spur from the worm. Put a Didel 60/12 spur at its place.
Put a Didel 40/12 spur on your choice of axle and "bearing".
Find the right place on the servo motor housing to glue the added gear. I had to use a 0.5 mm spacer.
REVERSE THE MOTOR WIRES!!! I didn't do it at first and almost destroyed the thing. Of course putting one more gear in the train reverses the train direction!
Enjoy a slower and stronger servo movement! :-)
maths: original servo gearing pinion 8 teeth spur 32 teeth so 1:4
new geartrain: 8 teeth to 40 teeth so 1:5 and then 12 teeth to 60 teeth so 1:5 again. If I am not wrong this gives a 1:25 total reduction ratio that should make the servo more than 6 times slower and its pull more than 6 times stronger.
The two gears from Didel cost more than the servo but are excellent stuff
sorry for the poor quality..
|Jan 18, 2014, 01:34 PM|
does any force on the wheel transfer to the servo when up or down, or is it a full lock in both positions?
nice servo mod too btw, its fun to build different mechanics from servos and see them work
|Jan 18, 2014, 01:39 PM|
It's full lock in both positions.. new one will have a 92° movement instead of 90° to push the wheel a little further against the fuselage. And it will be larger and heavier because it has to take the place of the original Parkzone mounts. This one has a 10 x 10 mm footprint and is 6.6 mm high. weights less than the original mount.
|Jan 18, 2014, 03:48 PM|
I like it!
That is some really cool servo hacking. With the slower speed you'll also get more power too, and that may come in handy with retracts. If the jack screw can take the 'strain' you don't need to bother with a locking mechanism on the retracts.
Retracts on a UMX P51 is also really cool! Too bad the wings are too thin to properly bury the wheels, but even folded flat against the wing would look great. Provided the retracts aren't too heavy. If I'm seeing your weights properly, the retract mechanism weighs less than the stock plastic gear clip. That's amazing! So you're really only stuck with the weight of the extra retract servo.
I've long wanted to put retracts on my UMX corsair (complete with the 90 rotation). If the aileron control could be re-routed to use a single servo, then the spare aileron servo could be re-used for retracts with no weigh penalty. Another project for another day (or lifetime)...
Since I've jumped on the Devo/Deviation transmitter combo, I can set the speed the servo moves directly in the transmitter. So no more mucking about with un-realistic servo speeds or slow speed servo circuits (or modified servos). Just program a switch to drop the gear at what ever speed I want.
|Jan 18, 2014, 04:07 PM|
Thanks for posting this.
Can you please post links to the sources.
I'm interested in gearing the servo down to something wry slow like 7-10 rpm for a mechanical simulated machine gun noise maker
|Jan 19, 2014, 12:20 AM|
They also have 0.5 module spur gears but most for 2mm shaft(check page #1,2,3...):
Homefly also carry many small gears(Didel &WES-Technik) much easier to deal with than BidProduct and Didel
|Jan 19, 2014, 12:12 PM|
yeah I would like to find a cheaper alternative but it doesn't seem easy using readily available components. mod .5 gear is way too big, .3 already is big..
One possible source of suitable gears could be watches - but the classic one-dollar-chinese alarm clock I opened didn't had any suitable gear inside.
Since we are playing with a servo we could use not only gears but other less precise trasmission/reduction systems like pulley and belt.. but we would have to make our own parts anyway.
I don't think it would be possible to cut mod .2 gears on on my CNC router - the smaller router bits I use have a 0.3 diameter and are a pain to work with, they break just at watching at them.. and probably neither a lasercutter could cut such small teeth.. Epilot's opinion on this matter would be the most precious for his knowledge and direct experience..
This Japanese guy makes amazing small 2ch IR models, some with belt transmission. At the end of the video he shows how he made it.
and he started to cut his own mod .2 and mod .15 gears. I strongly suggest to explore his videos on youtube..
|Jan 19, 2014, 12:16 PM|
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