Model Boat Mayhem

Please login or register.

Login with username, password and session length.
Pages: [1]   Go Down

Author Topic: Reversing a Servo  (Read 496 times)

Buccaneer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 284
  • Location: Ringwood Hants
Reversing a Servo
« on: December 15, 2019, 01:04:23 PM »

I have five boats with a single prop and rudder which all run off the same programme on my transmitter. My latest however is similar build but the Servo needs to be reversed to operate the rudder correctly. I can do this on the transmitter and run it off a different programme but it would be more convenient, and less prone to possible errors, if I could run them all off the same programme. I know I can buy a Servo Reverser from Action but if I simply change over the Red and Black leads into the Servo would this have the same effect? My theory says this is simply a DC Motor so will now run in reverse. Have I got this all wrong and would I build in problems? Any comments from those with more knowledge than me would be welcome.

John
Logged

grasshopper

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 745
  • Location: Lincolnshire!
    • A1 Hobbies Ltd.
Re: Reversing a Servo
« Reply #1 on: December 15, 2019, 01:38:30 PM »

Don’t do it!


The power supply into the servo also supplies an internal circuit board whose components won’t like reversed voltages!
Logged

DaveM

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 475
  • Why on earth do I do this?
  • Location: Nottingham
Re: Reversing a Servo
« Reply #2 on: December 15, 2019, 02:35:38 PM »

John
No. One of these will do the job for less than a fiver https://www.componentshop.co.uk/catalogsearch/result/?q=servo+reverser
DaveM
Logged

Buccaneer

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 284
  • Location: Ringwood Hants
Re: Reversing a Servo
« Reply #3 on: December 15, 2019, 03:50:55 PM »

Thank you both. Life is never quite as easy or obvious as it seems!
John
Logged

Ken G121

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 80
  • Model Boat Mayhem is Great!
  • Location: East yorkshire
Re: Reversing a Servo
« Reply #4 on: December 15, 2019, 07:06:39 PM »

I could be wrong but I thought Hitec servos turned the opposite way to Futaba, perhaps someone with more experience can confirm this. Personally I use cheap servo reverses from e bay but if my thinking is right then perhaps change of servo type is an option
Cheers. Ken

Logged

TailUK

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,662
  • Location: East Midlands
Re: Reversing a Servo
« Reply #5 on: December 15, 2019, 08:18:07 PM »

I've probably got this wrong but don't you get the same effect if you physically turn the servo through 180 degrees.  I've been trying to visualise it but it's too late in the evening.
Logged
No human society has ever functioned without models to capture, explain,disseminate,
persuade, sell, reinforce and analyse all kinds of ideas, values, concepts and situations.

grasshopper

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 745
  • Location: Lincolnshire!
    • A1 Hobbies Ltd.
Re: Reversing a Servo
« Reply #6 on: December 15, 2019, 10:10:48 PM »

I've probably got this wrong but don't you get the same effect if you physically turn the servo through 180 degrees.  I've been trying to visualise it but it's too late in the evening.


Your approach won't change the rotation of the output shaft unless you mean turning it upside down?
Logged

TailUK

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,662
  • Location: East Midlands
Re: Reversing a Servo
« Reply #7 on: December 15, 2019, 10:58:05 PM »


Your approach won't change the rotation of the output shaft unless you mean turning it upside down?





I knew it was one or the other.
Logged
No human society has ever functioned without models to capture, explain,disseminate,
persuade, sell, reinforce and analyse all kinds of ideas, values, concepts and situations.

Ralph

  • Shipmate
  • *
  • Offline Offline
  • Posts: 15
  • Model Boat Mayhem is Great!
  • Location: Perthshire
Re: Reversing a Servo
« Reply #8 on: December 15, 2019, 11:49:01 PM »

To reverse operation of a servo you need to open it up and firstly swap round the leads connected to the motor (on some servos the motor is directly soldered to the circuit board which makes life difficult).  Secondly you also need to swap over the outer wires connected to the pot - the pot measures the travel on the servo so you need to change the wires here as well, otherwise the servo will turn straight to one of the end stops and sit there with the electronics still trying to drive the motor and everything get hot.


Ralph
Logged

Umi_Ryuzuki

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,147
  • Location: PDX, OR USA
    • Models and Miniatures
Re: Reversing a Servo
« Reply #9 on: December 16, 2019, 05:26:01 AM »

To reverse operation of a servo you need to open it up and firstly swap round the leads connected to the motor (on some servos the motor is directly soldered to the circuit board which makes life difficult).  Secondly you also need to swap over the outer wires connected to the pot - the pot measures the travel on the servo so you need to change the wires here as well, otherwise the servo will turn straight to one of the end stops and sit there with the electronics still trying to drive the motor and everything get hot.


Ralph
Yes this, exactly.  :-))

roycv

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,395
  • Location: S.W. Herts
Re: Reversing a Servo
« Reply #10 on: December 16, 2019, 09:21:01 AM »

Hi I agree it works well, you do need a very narrow diameter soldering iron bit to do the soldering. 

If you wanted to extend the throw of the servo you can use a 1K ohm resistor at each end of the pot and this will almost double the throw of the servo arm.  I used to do this before we had servo extenders available (Flytron).
regards
Roy
Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,606
  • Location: Blackpool, Lancs, UK
Re: Reversing a Servo
« Reply #11 on: December 16, 2019, 09:43:33 AM »

To reverse operation of a servo you need to open it up and firstly swap round the leads connected to the motor (on some servos the motor is directly soldered to the circuit board which makes life difficult).  Secondly you also need to swap over the outer wires connected to the pot - the pot measures the travel on the servo so you need to change the wires here as well, otherwise the servo will turn straight to one of the end stops and sit there with the electronics still trying to drive the motor and everything get hot.


Ralph
For anybody at the level of thinking that just reversing the power leads will do the job, a servo reverser is the simple reliable answer.  Certainly cheaper than going through the rebuilding procedure where any error will result in a dead servo, and the need to buy a new one plus the reverser that was wanted in the first place.
The Futaba confusion was brought about by Futaba, who thought that going their own way with the pulse length logic generated by their transmitters was a good idea, probably with the intention of locking users into their system, when just relying on having an excellent system would have worked.
Someone like servo city might have a reversed servo in their list of goods.
Logged
"With the right tool, you can break anything" - Garfield

DaveM

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 475
  • Why on earth do I do this?
  • Location: Nottingham
Re: Reversing a Servo
« Reply #12 on: December 16, 2019, 11:28:08 AM »

When servos were almost the size of fag packets and had nice discrete motors and feedback pots with accessible contacts this was a feasible operation. I remember regularly having to change Black label Futaba FD16M servos to Red Label (opposite rotation) when I worked in Pegasus model shop in the 70s. These days the internals of a servo reveal an almost fully-integrated electronic/mechanical lump once you manage to open it up. When you can obtain a signal reverser for less than the cost of a servo - BangGood has one for £1.35 incl free shipping - it makes no sense to go down the DIY route. As Malcolm says, you will likely end up having to buy a new servo as well as the reverser you could/should have bought in the first place.
https://www.banggood.com/Servo-Signal-Reverser-Compatible-for-all-servo-p-939127.html?cur_warehouse=CN
DaveM
Logged

chas

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 394
  • now in los montesinos Spain.
Re: Reversing a Servo
« Reply #13 on: December 16, 2019, 04:07:34 PM »

Whilst I agree with all who've said just get a servo reverser, there is another simple option. IF you can re site the servo a little so that the pushrod will connect properly to the opposite servo arm, it will give the result you want. I.e. if the pushrod is connected to right of the servo connect it to the left or vice versa.
Turning the tiller arm through 180 degrees will also do what you want, again you'll have to re mount the servo so it lines up properly.
  To be frank, getting a reverser is probably simpler, things like this are best sorted whilst building and planning the layout but I'm sure there isn't a modeller among us who gets it right all the time. Me? I'm lazy, I just flick the servo reverse switch on my transmitter.
Chas

Logged
Pages: [1]   Go Up