Micro Winch

Marcwolf

Senior Member
Hi Folks.
I have a problem I am trying to solve.
I need to make a 10 turn micro winch. It will not be pulling much so strenght is not an issue. And I have several design possibilities and need some input.

1. Take a 9gram servo and replace its pot with a multiturn unit. Its fiddly, I can do it however I am concerned that multi turn trimpots will not have the durability.

2. Use a 3.5inch diskdrive stepping motor. Easy to get hold of however getting the position of the motor will be messy. 2 ways I can see on this is
a. Micro rotary encoder
b. 'markers' on the pulley wire so that it knows max and min extension and can then 'guesstimate' position from one of those poines. i.e. startup - fully extend pulley and thenback up 3.5 turns - remembering position.


Many thanks
Dave
 

westaust55

Moderator
Hi Folks.
I have a problem I am trying to solve.
I need to make a 10 turn micro winch. It will not be pulling much so strength is not an issue. And I have several design possibilities and need some input.

1. Take a 9gram servo and replace its pot with a multiturn unit. Its fiddly, I can do it however I am concerned that multi turn trimpots will not have the durability.

2. Use a 3.5inch diskdrive stepping motor. Easy to get hold of however getting the position of the motor will be messy. 2 ways I can see on this is
a. Micro rotary encoder
b. 'markers' on the pulley wire so that it knows max and min extension and can then 'guesstimate' position from one of those poines. i.e. startup - fully extend pulley and thenback up 3.5 turns - remembering position.


Many thanks
Dave
Dave,
Thought you had already done the 10 turn trimpot modification method.
http://www.picaxeforum.co.uk/showthread.php?p=93889

Seems to be quite a few doing similar as sail winches for RC boats.
the microservo size may be the issue but others do suggest it has been done in 1/4 size servos.



Here are just a few of what I found I spotted:

http://www.myrc.org/Library/sailwch.htm

Using a BOURNS #3296 10 turn trimpot.
http://crawlcanada.com/forum/archive/index.php/t-3347.html

Have a read at this web document (in particular section 5):
homepage.ntlworld.com/k.partington/eurgle.doc


Putting 10-turn trimpots into quarter-sized servos:
http://newsgroups.derkeiler.com/Archive/Rec/rec.models.rc.water/2005-12/msg00009.html
 

Marcwolf

Senior Member
Hi Westaust

One of the difficulties re using trimpots is that htey have a very limited life approx 200 rotations.

With the articles on 'winch' systems they either use a proper multiturn pot or use gearing in a 4/1 ratio. Both require a much larger area than what a trimpot would take up.

But thinking of it - a length of nicrome wire will have a properly defined resistance so if I was to use THAT instead of some nylon fishing wre (or combine the two) then I can get a variable resistor that could work with a servo

Will have to try that over a few days. I only need to move about 4 inches or so but the winch must be very small.

Thats.. Dave
 

Wrenow

Senior Member
The owner of http://strikemodels.com has found some innovative new servos from a Chinese supplier, including, as I recall, a 6 or 9 turn servo in a standard servo case format (not the larger format of most winch servos). Not sure if he has them in stock yet, or the actual specs, but you can certainly contact him about them. He has found some truly interesting microservos, to - don't know if any are multiturn, though.

Also, can you can unbundle the pt and put it elsewhere in your drivetrain? Like the geared servo adapter sold by http://servocity.com/html/spg425a_standard_rotation.html
You could use a regular multi-turn pot in this case. Not necessarily terribly micro, though.

Cheers,

Wreno
 
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Marcwolf

Senior Member
Hi Folks
After doing some calcs re Nichrome wireI found out there it would not be possible to as I only need a winch that can pull about 4 inches or so.. So using that length as the reisitor would not work that well.

Anyway - I have bitten the bullet so to speak and brough 2 x 10 turn precision 5K pot's.

I'll keep you posted...Again many thanks for all of your advice..
Dave
 

Andrew Cowan

Senior Member
I've used the high quality 10 turn - 5K pots for a servo - they work pretty well. The only downside is that the centre is a bit sloppy if you use the existing electronics of an analogue servo.

A
 

Wrenow

Senior Member
Dave,

You only need a 4" pull? If you have room, a regular old sail winch servo will do well over that. http://servocity.com/html/hs-785hb_3_5_rotations.html The pulley goes 3.5 turns or more, with a 1.456"+ diameter. 3.5*1.456"*3.14159= a tad over 16" of pull. If it is too large, the smaller ones Strike found may work.

Also, if you just fit a larger pulley to your standard servo, you might get there. A 1.5" pulley will pull 4.7+" per revolution. A 2.5" pulley would have a 7.85", so for a servo with a 180 degree throw, would get you there, too. Or, just gearing the output up (there are gears to fit on servo splines available from servocity and other sources). OR, if you need a bit of clutch/release action, a couple of pulleys drive train with rubber belts works nicely to gear up/gear down.

For a similar requirement (I need to rotate a 5" diameter turret in my ship about 270 degrees) requires a little over an 11" pull. A regular sail winch servo with an O-ring belt works just dandy.

The guys for the http://ausbg.org have the same issues I do with rotating turrets in their ships and can probably turn you on to local sources/methods/etc. in OZ.

Cheers,

Wreno
 
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Marcwolf

Senior Member
Hi Wrenow
Ok - I'll explain what I need to do.

This is part of the animatronic ear movements on my wolf costume.

The ear will be an arc of spring metal attached to the top of the skull. The other end will have a wire attached to it that can be pulled down.

The visual effect will be that the wolf will be able to lower and raise his ears.

As such I need a winch to pull the wire, and I need it to be as small as possible (say 9 gram servo size) to fit on the skull.

I do have one of the Hitech winch units and there is no way that that would beable to fit and do the job.

Thanks for the inputs thou - I will definately look at thouse sites.

Dave
 

Andrew Cowan

Senior Member
How about either a 9 gram servo modified for continuous rotation, plus limit switches, or you could use a 9 gram servo modified for continuous rotation with a slipper clutch (such as a belt drive).

A
 

Marcwolf

Senior Member
Hi Andrew

I did consider that - however I want more control than full retract and full extent. I would like to be able to stop it at say 1/4, 1/2, 3/4, and full extension and retraction.

With the continious rotation you have a limited position control.

I have on order 3 5K 10 turn pots and I will be putting the winch pully (which is a sewing machine bobbin) on its shaft and driving the pully with the servo on the other side. The pot is about 22mm diameter but I can use the body of the pot for able guides etcs.

I did consider using NiChrome wire as a sort of linear resistor but the voltage change was too low to measure accurately.

Mny thanks
Dave
 
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