HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jan 18, 2013, 07:46 PM
Registered User
Brianlon's Avatar
Joined Jan 2013
15 Posts
Help!
Can electric servoless retracs be slowed?

I have recently purchased some eletric servoless retracs and would like to know if I can slow their operation down to an even more scale speed using the servo speed function on my Hitec Aurora??

Any input is appreciated.
Brianlon is offline Find More Posts by Brianlon
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 18, 2013, 07:48 PM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
12,410 Posts
Probably. I'm pretty sure I've heard of this being done with Multiplex EVO transmitters but, of course, that's a totally different radio.

I'd say go ahead and try it. Not much to lose, eh?
C₄H₁₀ is offline Find More Posts by C₄H₁₀
Reply With Quote
Old Jan 18, 2013, 07:58 PM
ancora imparo
jj604's Avatar
Melbourne, Australia
Joined Jul 2005
6,437 Posts
Probably not. You can slow down a servo with a transmitter adjustment since that simply moves the control pulse position more slowly. My DX8 and Evo can both do that. If the servo is moving a mechanical retract it moves more slowly.

But servoless retracts only use the pulse position to tell them when to start operating. They use switches at the end of the travel to terminate movement. They are just a motor running a drive screw at full speed between two limits. To slow them you would have to slow the actual motor speed and that would result in significant power reduction.

You could pulse the actual supply voltage with additional circuitry and slow them that way but that is not what the transmitter servo slow function does.

Try it by all means but I think it will just delay the start of the movement not its actual speed.

John

Quote:
Originally Posted by Brianlon View Post
I have recently purchased some eletric servoless retracs and would like to know if I can slow their operation down to an even more scale speed using the servo speed function on my Hitec Aurora??

Any input is appreciated.
jj604 is offline Find More Posts by jj604
Reply With Quote
Old Jan 18, 2013, 08:31 PM
Registered User
Brianlon's Avatar
Joined Jan 2013
15 Posts
Wow....!

Did not expect replies as fast as that lads!

I will give it a go as soon as I can and report back with the results.

I do see your point regarding the fact they just travel from point to point, where as a servo goes where its told.

Would be a nice feature if manufactures fitted speed pots to the actual undercarriage themselves so you could dial in a speed on them. One for up and one for down.

mmmmmmm.... my patent! lol
Brianlon is offline Find More Posts by Brianlon
Reply With Quote
Old Jan 18, 2013, 08:56 PM
ancora imparo
jj604's Avatar
Melbourne, Australia
Joined Jul 2005
6,437 Posts
It actually wouldn't be hard. Just add a 2A brushed speed controller into each motor lead and control them from a separate channel for the transit speed.
Problem is you would probably have to build the controller since the only commercially available 2A brushed controllers I know about these days are built into the UM receiver bricks.

Pretty simple device though.
Quote:
Originally Posted by Brianlon View Post
Wow....!

Did not expect replies as fast as that lads!

I will give it a go as soon as I can and report back with the results.

I do see your point regarding the fact they just travel from point to point, where as a servo goes where its told.

Would be a nice feature if manufactures fitted speed pots to the actual undercarriage themselves so you could dial in a speed on them. One for up and one for down.

mmmmmmm.... my patent! lol
jj604 is offline Find More Posts by jj604
Reply With Quote
Old Jan 18, 2013, 09:01 PM
ancora imparo
jj604's Avatar
Melbourne, Australia
Joined Jul 2005
6,437 Posts
Looks like TI make an IC that does just about everything in one tiny chip. You could probably add one of these in each motor lead and with a bit of logic signal magic I suspect control the travel speed.

Neato little project.

http://www.ti.com/ww/en/analog/drv8x...drv8837-bt1-en
jj604 is offline Find More Posts by jj604
Reply With Quote
Old Jan 18, 2013, 09:44 PM
Senile Member
Lnagel's Avatar
Moab, Utah, USA
Joined Apr 2003
6,027 Posts
Using that TI integrated circuit, which is essentially a small DC motor speed control, or an aircraft low amperage ESC would not work. They essentially put out a DC voltage that varies in amplitude as the PWM input from the receiver varies in width. The output of those speed controls is incompatible with the input requirements of the gear assembly. The logic in the gear assembly is such that it looks at the length of the incoming PWM pulse from the receiver and decides if its wider than or narrower than 1.5 msec. It then uses that pulse width to determine the polarity of the voltage applied to the motor. Regardless of the length of the input pulse the logic applies a DC voltage of the same amplitude to the motor. As such the speed of the gear motor is always the same and there is no effective way to control it remotely.

The same goes for the servo speed function of a transmitter. What that does is control the rate at which the PWM changes from minimum width to maximum width and vice versa. Unlike a servo, the gear logic doesn't care about the rate at which the PWM changes, it only cares about the absolute width of the pulse as compared to 1.5 msec.

What could be done is to put a potentiometer in series between the gear motor and its power supply. The potentiometer could then be adjusted manually to set the desired gear operating speed.

Larry
Lnagel is online now Find More Posts by Lnagel
Reply With Quote
Old Jan 18, 2013, 10:06 PM
Registered User
Wintr's Avatar
USA, MO, Florissant
Joined Nov 2010
1,704 Posts
Reducing the voltage to the retracts may not be an option, either; depends on the circuitry inside, if it will operate below the nominal range of a standard receiver battery. It will probably run more slowly at 4.8V than at 6V, but I wouldn't expect big changes in speed.
Wintr is offline Find More Posts by Wintr
Reply With Quote
Old Jan 18, 2013, 10:12 PM
ancora imparo
jj604's Avatar
Melbourne, Australia
Joined Jul 2005
6,437 Posts
Sorry, Larry perhaps I wasn't clear. I think that is what I said.

My idea of using a brushed controller was to put it only in the motor leads not the retract servo supply. Driven from a separate channel to control the effective voltage to the motor, how is that different in principle from a pot in the motor supply? Advantage is that if it is a proper controller and not just a variable resistance it supplies time sliced full voltage rather than reduced voltage to the motor and keeps the torque up. It acts only as a speed controller in the motor supply circuit and has nothing to do with the logic of the servo retract function.

The gear channel pulse width controls when the servo retracts and extends as normal, the other controls the speed of the motor.

Agree the TI chip driven by an external pulse source is not straightforward. On further reading, they don't in fact respond to a standard RC PPM pulse width but are a simple bi-directional controller driven by steering logic which would need to be switched at the correct intervals to alter the speed.

It may not all work in practice but it would be fun to try.

UPDATE: But it won't work on thinking about it a bit more since the retract is supplying a bidirectional voltage to the motor and any motor controller will only work in one direction - oh well, that's the big advantage of a pot. A resistor doesn't care which way the current flows.
Quote:
Originally Posted by Lnagel View Post
Using that TI integrated circuit, which is essentially a small DC motor speed control, or an aircraft low amperage ESC would not work. They essentially put out a DC voltage that varies in amplitude as the PWM input from the receiver varies in width. The output of those speed controls is incompatible with the input requirements of the gear assembly. The logic in the gear assembly is such that it looks at the length of the incoming PWM pulse from the receiver and decides if its wider than or narrower than 1.5 msec. It then uses that pulse width to determine the polarity of the voltage applied to the motor. Regardless of the length of the input pulse the logic applies a DC voltage of the same amplitude to the motor. As such the speed of the gear motor is always the same and there is no effective way to control it remotely.

The same goes for the servo speed function of a transmitter. What that does is control the rate at which the PWM changes from minimum width to maximum width and vice versa. Unlike a servo, the gear logic doesn't care about the rate at which the PWM changes, it only cares about the absolute width of the pulse as compared to 1.5 msec.

What could be done is to put a potentiometer in series between the gear motor and its power supply. The potentiometer could then be adjusted manually to set the desired gear operating speed.

Larry
jj604 is offline Find More Posts by jj604
Last edited by jj604; Jan 18, 2013 at 10:59 PM.
Reply With Quote
Old Jan 19, 2013, 08:31 AM
Senile Member
Lnagel's Avatar
Moab, Utah, USA
Joined Apr 2003
6,027 Posts
Quote:
Originally Posted by jj604 View Post
UPDATE: But it won't work on thinking about it a bit more since the retract is supplying a bidirectional voltage to the motor and any motor controller will only work in one direction - oh well, that's the big advantage of a pot. A resistor doesn't care which way the current flows.
Besides the fact that a pot wouldn't require an additional channel that may or may not be available.

Larry
Lnagel is online now Find More Posts by Lnagel
Reply With Quote
Old Jan 19, 2013, 08:34 AM
Wake up, feel pulse, be happy!
C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
12,410 Posts
A servo board can be used as a small forward/reverse brushed ESC provided you freeze the feedback pot in an appropriate neutral position, or else replace it with a resistor of an adequate value.
C₄H₁₀ is offline Find More Posts by C₄H₁₀
Reply With Quote
Old Jan 19, 2013, 10:10 PM
Life begins at transition
Australia, VIC, Sale
Joined May 2007
3,593 Posts
Could place a pair of diodes antiparallel between the control coard and the motor?
It'll reduce the speed, but also the torque unfortunately.

Maybe replace the motor with a lower kv one?
Odysis is offline Find More Posts by Odysis
Reply With Quote
Old Jan 20, 2013, 11:39 AM
Registered User
Canada
Joined Nov 2000
6,985 Posts
Change the gear ratio... Likely genuinely tricky to do, I suspect... but at least you won't risk under powering it :-).
Bare is online now Find More Posts by Bare
Reply With Quote
Old Jan 20, 2013, 12:56 PM
Registered User
manuel v's Avatar
Mexico, BC, Mexicali
Joined Aug 2004
5,197 Posts
This device works fine with standard servos, I've not tried it on a retract servo less

http://www.hobbyking.com/hobbyking/s...Regulator.html
manuel v is online now Find More Posts by manuel v
Reply With Quote
Old Jan 20, 2013, 01:11 PM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
13,199 Posts
Quote:
Originally Posted by manuel v View Post
This device works fine with standard servos, I've not tried it on a retract servo less

http://www.hobbyking.com/hobbyking/s...Regulator.html
You cannot slow a genuine 'retract servo', they are not like standard servos, they do not have proportional control to stop at any position but drive to one end or the other.

I have one of those Turnigy servo slows, works a treat on standard servos though.

The servoless retract problem sound like a thread is needed in the - DIY Electronics forum - there's some real wizards in there.
eflightray is online now Find More Posts by eflightray
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Bixler v1.1 EPO 1400mm Can wings be transported separately????? Ron Christensen Electric Sailplanes 4 Feb 09, 2013 03:24 PM
Discussion Can a finning-fast electric jet can Frequent Mileage Arizona Electric Festival 3 Jan 18, 2013 04:50 AM
Discussion If there's even one life that can be saved..... BE77 Pilot Life, The Universe, and Politics 22 Jan 17, 2013 06:22 PM
Question Connecting Cells in Parallel: Can This Be Done? AEMontoya DIY Electronics 3 Jan 09, 2013 10:39 PM
Discussion Mounting wheels to servoless retracs Condre' HobbyKing 9 Oct 17, 2011 03:14 PM