Model Boat Mayhem - Forum

Please login or register.

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

Author Topic: Turning a Servo into a Motor  (Read 2100 times)

Tug-Kenny

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 7,680
  • Location: Newport. S Wales
Turning a Servo into a Motor
« on: March 22, 2012, 12:14:13 PM »


I have decided to use servos to control the Crane on my latest boat. Whilst doing this 'Mod' I though I would share with you the secrets of getting it right.

I wanted a small motor which would continuously run either clockwise or anticlockwise with a bit of thrust, to be controlled by the Radio.  The servos I'm using are Futaba's 1003 and they come apart by removing 4 long screws.

The top was then removed to show the gear arrangement.  These were slid of their shafts and laid out on the bench in order and attention was given to the other end.  The cover was pulled off to reveal a tiny circuit board and the rear of the motor.

This circuit board does not lift off easy as there is a potentiometer underneath it which is secured by a tiny Phillips screw which is in-accessible.  (soldered in after fitting  hmphh)

By de-soldering the three legs of the Pot, I removed the circuit board. I then unscrewed the Pot and put it aside.

Now to make the system run continuously we have to substitute two resistors into the vacant Potentiometer holes.  The stated value of the Pot is 5k but in reality it goes to decimal places ! so a good meter is essential.  The reason for the Pot is to centralise the servo in the middle of it's travel so it's vital that the value of the resistors is correct.

Please note that Not all resistors are the value it says on the tin !!  So, with this in mind I fitted one resistor valued at 2500 ohms to one side and the salvaged Pot to the other and connected it up to the R/X  on channel One to utilise the self centring position and switched on the radio.

By adjusting the Pot I could get the servo motor to stop it's rotation exactly on the centre position. I removed the pot and measured the Exact value and substituted a fixed resistor in it's place. This was actually different on other servos that I did and the value was down to decimal points to achieve dead centre of the stopping position.  What we didn't want was to have a servo motor creeping when we though we had stopped it.

I enclose the pictures of my Modification. You will notice that I had to use two resistors on one side to get the correct value.

Hope this is of help.

cheers

Ken


Logged
Despite the high cost of living   .......... It remains popular

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,564
  • Location: Blackpool, Lancs, UK
Re: Turning a Servo into a Motor
« Reply #1 on: March 22, 2012, 05:55:43 PM »

I've always just used the pot to set the centre off.  Using a different value might give a wider deadband. 
More recently I've removed the servo electronics and fitted one of Actions Pico controllers.  Only downside to that is that the new board doesn't fit fully into the case and pokes out of one side.
Logged
"With the right tool, you can break anything" - Garfield

Corposant

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,613
  • Location: Hampshire UK
Re: Turning a Servo into a Motor
« Reply #2 on: March 22, 2012, 07:46:48 PM »

Ken

Well done! When I tried to do that, if I got the motor to stop when the tx lever returned to centre from one direction, then the motor crept when coming from the other. Such was the tightness of the deadband - so I gave up!

Mike
Logged

Tug-Kenny

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 7,680
  • Location: Newport. S Wales
Re: Turning a Servo into a Motor
« Reply #3 on: March 22, 2012, 08:40:18 PM »


Accuracy is everything, I've found. I used the self centring lever of the T/X so that at least one parameter was constant. I fine tune by using the extra centring lever adjuster and try to get it to not move left or right within two clicks each side of centre.

However ....

Upon testing today I've found a flaw.  When you switch on the set up, the servo judders a fraction and starts revolving minutely until you joggle the direction control.

Now this might be OK unless you forget at the lake and find it's started to turn unnoticed and and moves something it shouldn't like a crane pulley. !! 

Funny you should mention leaving the pot in the circuit Malcolm, as I played around with this idea and found it worked as it should but it was ultra sensitive compared against the fixed resistor idea.  Any vibrations might alter it's position.

I was trying to save costs of 3 pico controllers but obviously, this is the way to go.  I assume they reverse, although it doesn't say so.

Also in the above description I forgot to mention that one of the gear wheels has a stopper block built in and THIS has to filed off to allow the wheel to travel 360 degrees.

Overall I'm not happy about using these on my crane but I'll give it a try to see how it works out.

ken




 
Logged
Despite the high cost of living   .......... It remains popular

Corposant

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,613
  • Location: Hampshire UK
Re: Turning a Servo into a Motor
« Reply #4 on: March 22, 2012, 09:56:04 PM »

Ken

It looks as though Action's P52A should fit the bill - a call to Dave M should be fruitful, as always. I used P44's in my application - too bulky to fit in the servo housing. I only kept the servo housings because I had already fitted them with winding drums and mounted them under the winch.

You're right to get things working reliably on the bench - you won't be able see the motor creeping when it's in the middle of the lake!

Mike
Logged

Tug-Kenny

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 7,680
  • Location: Newport. S Wales
Re: Turning a Servo into a Motor
« Reply #5 on: March 22, 2012, 10:00:25 PM »


Hey Mike.  The more I think about it, the less I like my idea.

I have plenty of room as I'm still in the design stage so I'll probably just use the motors with their associated gearing in a cut down servo box.  These can then be controlled by a decent speed controller.

Thanks for the advice

ken

Logged
Despite the high cost of living   .......... It remains popular

barriew

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,006
  • Location: Thaxted, Essex
Re: Turning a Servo into a Motor
« Reply #6 on: March 23, 2012, 08:13:50 AM »

Kenny

I can confirm the Pico controller will work with a servo motor - and it does reverse. I used one in a very small model to be the propulsion. I started using the servo controller with pot, but found it wasn't accurate enough to give a reliable "off".

Barrie
Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,564
  • Location: Blackpool, Lancs, UK
Re: Turning a Servo into a Motor
« Reply #7 on: March 23, 2012, 10:33:45 AM »

Heres a couple of shots of my versions.
"winch" is the early version with the original electronics.  It did have the problem of a narrow deadband.
"winch2" is the update, with the Action Pico poking out of the side.  Repeated disassembly and reassembly revealed that the drum started to catch the line, the black band on the drum is a sliver of heatshrink which stops the problem. 
The case is a potting box from Maplin, who will probably read this and cease selling it, going off previous form.
Logged
"With the right tool, you can break anything" - Garfield

Corposant

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,613
  • Location: Hampshire UK
Re: Turning a Servo into a Motor
« Reply #8 on: March 23, 2012, 10:52:25 AM »

Ken

From Barrie's and Malcolm's (and my!) responses, it seems everyone has the same trouble! There are several websites with articles saying how easy it is to modify a servo thus but I think they mostly relate to use in robots.

My very first post on the forum was on this subject, right at the beginning of my puffer build - October 2008!!

Mike
Logged

Tug-Kenny

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 7,680
  • Location: Newport. S Wales
Re: Turning a Servo into a Motor
« Reply #9 on: March 23, 2012, 11:21:27 AM »


I have communicated with ACTion and the P52 is discontinued. It has been superseded by the P68 so we are up to normal speed controller thinking now.

The only reason I chose Servos is their powerful low speed rotation.  Back to the drawing board

ken
Logged
Despite the high cost of living   .......... It remains popular
Pages: [1]   Go Up