360 Degree servo speed reduction method?

[Smokin' Beaver]

I've just modified a 9 gram Tower Pro servo to continuous rotation - no problems there,
But can anyone tell me how to slow it down?

I can put a 15 ohm res. in series with the drive motor and get a speed reduction but am looking for other, more reliable ideas


cheers - Phil

nb. a servo slower will not work - tried that.
Increasing the resistance of the rheostat resistors does not appear to work either.

[Gary Warner]

Are you still using a servo drive pulse? If not, you can isolate the motor and use and brushed ESC to change the motor speed. If you are still using the drive pules you can adjust the pot for your off point and then use a transmitter with a very low travel volume setting, though it will be touchy.

[Smokin' Beaver]

Thanks Gary,

I simply disconnected the rheostat & substituted a pair of 2k2 1/4W resistors and on the final drive gear, I removed the mechanical stop block.
So I presume I am still controlling it by 'drive pulse' control, based on the following criteria,

I have it hooked to the 'gear' function on my JRX2610 trx and it returns a forward/reverse response dependent on that switches position.

I'd be happy to use my servo slower, but it looks like it needs the feedback loop to work, this would require the rheostat to be functional again I presume.
My problem is the rheostat will not rotate 360+ degrees.

As you say, I might have to go to an ESC which gives me sufficient drive current to maintain torque in the motor.


Phil

[Odysis]

Phil,
A couple of quick ideas off the top of my head...
1) You could hook the pot to a torque rod on the landing gear itself, or
2) Put a couple of small switches in the gear bay that indicated full up or full down, and have them change the resistance passed to the controller cct.
3) Replace the current pot with a multi-turn pot. Trying to find one small enough / the right form factor may not be possible...

[MetroGTi]

How about adding a gear reduction to the servo output. You could probably use the gears from a motor gearbox.

[Smokin' Beaver]

Ah - sorry forgot to mention, the application is for a gun turret rotating continuously forward & reverse with occasional stops.

I'd posted a similar question in the radios/rx & servo forum & explained some of the details there

Also the application is for a miniature video camera within the turret = limited space of 45mm vertical clearance into the fuselage
unfortunately that puts gearbox additions out of the equation.

To add clarity, attached is a pic of the model - a Guillow's B-17, 45" span (not a big plane) the turret goes into the upper position (maybe underneath also later).

Thanks for some great ideas though!

Cheers - Phil

[Odysis]

Actually, just had a quick thoughty...

You've replaced the pot with a couple of equal value resistors, right? So the servo control cct thinks it's always in the centre position? Servo motor voltage is roughly proportional to the angular error, so if you just commanded a 10* change instead of a 30* one, it should spin slower.

I.e. change the throws on your Tx for the gear channel to 10% instead of 100. Quick, easy, see what happens. May work, may fail miserably. But it requires very little work, and it's all reversable.

Odysis

[Smokin' Beaver]

Mate...you are a legend!!!
I did as you said to 10% and got a substantially reduced rate of travel.
In the end I found 21% got me what I wanted.
When I went below 8% it started reversing and conversely, when I got to 22% I got dead stop.
All exactly what I was chasing.

If you were in Perth, I buy you a carton & come round & drink it with you!

So if ever you do turn up in this neck of the woods PM me for my contact details - there's always a dozen coldy's in the fridge with your name on them.
..I will of course drink the other dozen with you ;)


Cheers - Phil

[Odysis]

Dude, I was based in Bullsbrook last year - timing!
Good to know it worked as you'd like though. Looks like an awesome plane you got there

[Smokin' Beaver]

Hmmm...Bullsbrook, Sale....you seem to be hanging out around RAAF bases a bit?

Well next time you're at Bullsbrook, give Chequers a miss & call me instead!

And the planes a blast mate, it was built for purpose - video footage.
I've got a fair bit of footage from the onboard video and I'm slowly compiling footage for a bit of a home-movie.
Nothing flash, but it's my entry level into AP video fun.
The rotating turret is an extra 'cool' factor.
I'm also doing a tow-glider for stern attack footage from a Me109 (but that's all secret stuff ;))

fwiw the build log is here;
http://www.rcgroups.com/forums/showthread.php?t=696805
go to the end to see some starter videos. cheesy but fun to create.
It actually provides enormous incentive to get up before dawn for the calm winds when you have an extra 'reason' to go flying.

Anyhow thanks again O-man

Phil

[Odysis]

Hmmm...Bullsbrook, Sale....you seem to be hanging out around RAAF bases a bit?
:rolleyes:

I remember the winds over there... Early morning would be the only time to fly! Beautiful corner of the world you've got over there though. Good times at the Cott :D

I'm having a read through the build at the moment, nice work

[Scott McKie]

Hi Beaver,
Did you ever get the servo speed reduction thing for your forward turret worked out? If you didn't, I know of a small circuit kit that does exactly that and it's variable. It's normally used for slowing down retract servo speed but would work perfectly here. Anyway, let me know if you want it and I'll look up the site where you can get it.
Scott McKie USA -- scotsman7@comcast.net

[Smokin' Beaver]

Hi Scott,
Thanks - Yes I did, in post #7, Odysis suggested a method which did the job.
I'm limited with the mixing options I have on my trx but this method worked well.
I have a 3-pos switch but it's locked into flaps control & I can't mix it to another channel so for/stop/rev was not possible.
So what I have is forward/reverse & if I wish to go forward/stop I just trim it down.
Pretty easy in the end and it's just for video work anyway.
When the footage is all collected, it will become a stationary turret again.

phil

[TMorita]

A servo slower designed for retractable landing gear would also work.

Toshi

[harrymc]

A servo slower designed for retractable landing gear would also work.

Toshi

Where would I get one of these?

[Smokin' Beaver]

http://www.dionysusdesign.com/product_info.php?products_id=164

or Google 'servo slower'

[mike50]

A servo slower designed for retractable landing gear would also work.

Toshi
These devices will not work for this application. They just slow down the rate of change of the servo signal as it switches from one extreme to the other. This application requires that the servo signal change only a tiny bit (from the "stopped" position) and stay at that tiny change. To go in the opposite direction you need a tiny change in the other direction.

Mike

[Scott McKie]

Hi Guys,
I have just sent the PDF on the "GoSlow" to Smokin Beaver. You can find it by going to google, type in "servo retract speed controller", and look for C. Brent Dane's "GoSLow" site. You can download the PDF from there. If that is not successful, contact me directly at scotsman7@comcast.net, and I'll email the attachment to you.
I have built one of these and it works great.
Scott