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[tigertiger]

"Servo modified for continuous rotation for use as a winch"

On another thread Malcolmfray said he did this.

Malcolmfray or anybody else tell us how please?

[HS93 (RIP)]

this may be what you are after But you just leave the pot on the outside to set the neutral   Peter

http://www.uoguelph.ca/~antoon/gadgets/servos/servomod.html

[tigertiger]

Thanks HS93

I think this site is talking about rotating 360 degrees only, to turn that camera.

However, I am thinking of contious rotation to wind in an anchor.

TT

[malcolmfrary]

The output gear has a lump on its shoulder that acts as a stop against the internal moulding of the case to limit travel to 270deg, which is the limit of a normal pot.  This can be cut off.  As has been suggested, the pot can be relocated with the spindle poking out of the side to "tune" the centre off.  When stalled, the entire device will not take more than 1/2 amp, and if the stall is at a low speed setting, the duty cycle will be so narrow that problems are very unlikely.
It is not generally appreciated that when the servo is approaching parity (when it has nearly got to where the stick says it should be), the motor is slowed to prevent overshoot and hunting.  This allows use as a proportional speed control as well.

[Telstar]

Hi tigertiger
One thing that bothers me about using a modified servo for continuous rotation is stopping it at the correct position.
It is fine if, as in the listed site, the movement has no 'endpoint' ie can go round and round  but what happens when your anchor is fully wound in, how does the winch know to stop. 
So far I have had no success fitting limit switches to controle servo electronics, once the position pot has been disabled I am very wary of the servo loosing control and turning continuously. I do recall in the early days of sailing Radio Marblehead  yachts a mate built a sail winch from a modified Futaba Mammoth servo. When water got in, the winch wound in and managed to bend the mast before pulling the whole thing through the deck. I have modified servos ,cutting off the end stop as in the article but I fitted a 10 turn pot in place of the single turn one normally fitted, to give a servo with 7 to 8 turns rotation and still positional control

Cheers Tom

[malcolmfrary]

The trick is to watch, and when the anchor gets where it is going, stop.  On a scale model, make sure the servo is securely fitted.  A normal servo can generate a lot of force, but if the model has taken on enough water to have a bad effect, the anchor winch will be the least of you worries.
The limit switch problem is the same one that pops up in model railways at stations where you want a train to stop automatically, but be driveable out.  The answer in this case is to have the servo mounted on a hinge, so that when it winds up it moves one end, operating the switch.  The switch would be in the motor circuit with a rectifier connected acrossit so that when winding in the motor gets stopped, but is allowed to drive when the wich need to wind out. 
Telstar's use of a multi-turn prop is another very valid approach.

[HS93 (RIP)]

If its an anchor winch you could probably use the method I have used in the past. If you use a round servo disk and instead of a self taper use a short length of stud sand the top of the servo disk flatplace the drum on top and a washer on top of that use a spring on the stud then a nut you can adjust the amount of slip and when it comes in . this works well in fact I have been using the same system for over 10 years on my Kitchen blinds they are vertical and instead of a drum I use a toothed belt gear . this is used every day to open and close as the window if to far to stretch to I have done away with the circuit board and just use a switch on two AA batteries that last about five years. Peter

[Martin (Admin)]

Have a look at:

http://www.modelboatmayhem.co.uk/forum/index.php?topic=276.0

http://www.modelboatmayhem.co.uk/forum/index.php?topic=2485.0

http://www.modelboatmayhem.co.uk/forum/index.php?topic=1502.0[/b][/color]

[Telstar]

Thanks Malcom
 your Diode across the switch acted as the proverbial kick in the pants.  I (you) have just solved a ongoing thing I am working on.  I needed to stop a fast spinnecker hoist at the correct point (easy with a limit switch) but was struggling to downhaul.
Easy fit a diode
Thanks Tom

[malcolmfrary]

Just make it a nice knobbly one, 1N5401 seems to ring a bell from somewhere.

[Martin (Admin)]

FYI:  How to make a servo winch - https://youtu.be/nRfOCV_xu2s