Model Boat Mayhem

Please login or register.

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

Author Topic: servos  (Read 3243 times)

elvis

  • Guest
servos
« on: November 15, 2009, 08:43:56 pm »

hi all.
how easy is it to convert a servo to full rotation.
like a sail winch but with smaller servos.
thanks
Logged

BarryM

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,704
  • Location: West Lothian
Re: servos
« Reply #1 on: November 15, 2009, 08:52:05 pm »

Elvis,

As you are back in the building try the 'Search' facility on this forum and you will find plenty of info of how 'tis done.

Barry M
Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 6,027
  • Location: Blackpool, Lancs, UK
Re: servos
« Reply #2 on: November 16, 2009, 11:03:54 am »

Just in case the search doesn't turn one up --
The position sensing pot needs to be disconnected from the drive gear (resiting so that it can be easily adjusted is probably best) and the output gear needs to have its end stop lug removed.  This after making sure that the gear has a full ring of teeth.  The only real downside is that without modifying the electronics, the deadband is very narrow, and an unstable battery supply can cause unexpected creeping.
Logged
"With the right tool, you can break anything" - Garfield

Martin (Admin)

  • Administrator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 24,052
  • Location: Peterborough, UK
    • Model Boat Mayhem
Re: servos
« Reply #3 on: November 16, 2009, 01:31:45 pm »

Logged
"This is my firm opinion, but what do I know?!" -  Visit the Mayhem FaceBook Groups!  &  Giant Models

elvis

  • Guest
Re: servos
« Reply #4 on: November 16, 2009, 04:52:56 pm »

hi all.
thanks
for your help.
just need to finish a couple of bulldozer of and need to use servos as drive motors.
thanks
elvis
Logged

funtimefrankie

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,259
  • Location: Birkdale, Lancashire. twixt the Mersey & the Ribble
Re: servos
« Reply #5 on: November 17, 2009, 10:16:34 am »

If you keep the pot connected, electrically but out side the box, so to speak, does that mean that the sero will go round and round but always return to the same place when the transmitter is released and centered?
Logged

Corposant

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,627
  • Location: Hampshire UK
Re: servos
« Reply #6 on: November 17, 2009, 11:21:48 am »

No, the motor slows as the transmitter lever approaches the centre position and then stops when it gets there. If the lever movement is continued in the same direction the motor movement is reversed. The creeping problem caused by the very narrow deadband, mentioned by Malcolm, is a real pain. I modified two servos like this but have decided to by-pass their electronics and use FLJ's P44 units. In other words, I'm only going to use the servo's as sources of geared motors. The disadvantage is that there will be no speed control. My application is operating a winch on a boat.

Mike
Logged

funtimefrankie

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 1,259
  • Location: Birkdale, Lancashire. twixt the Mersey & the Ribble
Re: servos
« Reply #7 on: November 17, 2009, 11:37:51 am »

I was wanting to move Shottel drives through 360 degrees but return to straight ahead.
Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 6,027
  • Location: Blackpool, Lancs, UK
Re: servos
« Reply #8 on: November 17, 2009, 11:49:24 am »

No, the motor slows as the transmitter lever approaches the centre position and then stops when it gets there. If the lever movement is continued in the same direction the motor movement is reversed. The creeping problem caused by the very narrow deadband, mentioned by Malcolm, is a real pain. I modified two servos like this but have decided to by-pass their electronics and use FLJ's P44 units. In other words, I'm only going to use the servo's as sources of geared motors. The disadvantage is that there will be no speed control. My application is operating a winch on a boat.

Mike

To explain it from a slightly different view - the electronics compares the position pot to the required position given from the control stick, usually via the radio.  If there is a difference, it drives the motor to correct this difference, the bigger the difference, the harder the drive, and vice-versa, so that the motor drive is reduced the nearer correct it is.  If the motor drives the pot, a new position is taken up.  If not, there is a de facto speed controller.
In the elder days, the same chip was used for both functions,the difference being the component values that set the deadband.  The datasheets for the ZN409 were fairly comprehensive, but could cause sore brains.  They did it for me, anyway.

Just been warned about Frankies post - the best bet there would probably be to gear up the output of a standard, out of the box, servo from 90 to 360 or more degrees.  This would have the disadvantage of being a bit (!) fiddly around reverse, but would leave the setup capable of returning to dead ahead while having the lever give some indication as to which way the drive was pointing.
Logged
"With the right tool, you can break anything" - Garfield
Pages: [1]   Go Up
 

Page created in 0.015 seconds with 17 queries.