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[ted]

Hi. I am building a yacht from MMI plans plus an article in MM Jan/Feb 1997. The article suggests that a standard servo can be modified to act as a winch. The mod consist of removing the mechanical stop and decoupling the feedback servo. I used a Futaba 3003 and it works. I have a motor that rotates in either direction depending on the transmitter stick. However, my problem is that there does not appear to be any way of placing a limit on the amount of movement. Can anyone think of a way of connecting limit switches to what is basically a standard servo?

Ted

[malcolmfrary]

I've been using that system for many years.  Not having limit switches has never been a problem.  When stalled, the motor pulls nearly 0.5 Amps. 
The trick is to look at the sails that you are controlling, and stop telling it to wind in when the sail is fully in, and the same when winding out.  The other trick is to make sure the winch mount is fit for purpose.  All the force applied to the sail ends up being transmitted through the mount, which has to be strong enough to avoid the servo being pulled out by its roots in a sudden gust.
It is posible to make limit switches using the techniques used in the model railway world for traversers involving micro-switches, rectifiers, acuating beads on the control line and considerable butchery to the servo.  Best not to try to fix something that isn't  broken.
If you can find one that fits, you could replace the existing position pot with a ten turn type and leave it mechanically connected to the output gear.  This will run in the middle three and a bit turns and give you a proportional winch.

[ted]

Thanks. I had not thought about a ten turn pot. I must have another look at the servo. But as you say you have managed with the standard modified servo, so perhaps I may try that first. A good tip about the mounting.

Ted