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Making a servo winch

From the beginning of RC rock crawling there has been a need of a winch, whether it is to winch the suspension down or to pull a crawler up an impossible rock face. As many of you know this aspect of radio control was born from home brewed chassis and some of the most ingenuitive people out there. And thats all it took for some of the founders of rccrawler.com to figure out how to make a standard steering servo into a functional winch.

 

 

 

 

 

 

 

 

I could tell everyone how to do it from my experience, but I thought it was better to hear it from Grizzly4x4 or Chris Ladd for some of you that may know him better. Chris taught us how to do it before many had ever heard of RC rock crawling, this is the write up taken from right here in October of 2005. Sure a few things may have changed, like the servos we use, and changing out the control boards in some cases, but rest assured this method will work now just as it did six years ago.

 

 

Grizzly4x4:

“ Hopefully this will get put up on the tech article page soon but for now I am posting it cuz I’ve had so many people ask me about it. Sorry it took so long. Once this is on the tech page I may delete this thread but ask any questions you have.

 

With scale crawlers being as cool as they are it is only natural to have a winch to get you through those tough spots. I have used several different servos and found that the Hobbico CS-70MG makes a great winch, it is cheap and plenty strong enough to pick up a 6.5lb rig. Another great servo to use is a Hitec HS-645MG or HS-525MG.

Before we begin let’s make sure you realize that you will need a radio with a three position switch to run the winch. My favorite is the Traxxas TQ3 with the 3rd channel modified for a 3-way toggle.

 

Begin by removing the servo horn, then the four screws on the back, and then remove the front cover. Lift out the center brass gear first and then remove the aluminum output gear. On the CS-70 (and some of the Hitecs) there is a small plastic insert in the backside of the output gear. I use a small allen wrench inserted through the screw hole to push the insert out. On the 525MG there is just a flat plastic piece that sits over the bushing. This is used to turn the pot in the servo to help it find center, we want the servo to turn forever (or at least until we center the winch control switch) so this piece is the first to go.

 

Next remove the pin in the front side of the output gear. I grab it with a pair of pliers and use a twisting/pulling method to get the pin out. An alternative is to cut it flush with a rotary tool; this method fine but just remember it can never go back to being a regular servo again unless you buy a new gear.

 

Now plug the servo into your receiver along with power, either from an RX pack or an ESC/battery. Set the winch control switch to the center position and turn on the radio (and the ESC). If you are lucky the servo motor will not be spinning but most likely it will be. Grab the pot adjuster (the needle nose plies in the picture are just for clarity purposes) and turn it until you find the point where the servo stops. It will be touchy but it’s there somewhere. Once you have found the “off” position, flip the switch on the radio to make sure the servo turns when you want it to. Skippy told me that a dab of CA will help keep the adjuster from drifting. I have not tried this before but it sounds like a good idea to me.

 

 

Now replace the gears, then the cover and tighten the cover screws. If you did not glue the adjuster pot in place be careful not to bump it or you will have to readjust it.

 

For a drum I just use a couple of round servo horns. If you use fishing line for your “cable”, string it through a couple holes and tie it off. Be sure to use a good strong line, I tried the stuff that came on one of my fishing reels and it broke all the time. I have had good luck with yellow twine from the hardware store. You can’t have as much line on your drum but it has never broken. To use the twine drill a hole in one of the servo horns close to the center. Pass the twine though as shown in the picture and tie a knot to secure it. Put this horn on the output of the servo, as this will be the one that takes the force when you are winching. Lay the second horn on top of the first so that there is a gap between the two and then install the servo horn screw. Your servo horn screw will just barely grab a couple threads when you install it so don’t over tighten it. If you can find a longer one use it, I used a spare from one of my Hitec 5945MG servos and it worked great; otherwise be sure and tighten the screw every once in a while. The outer horn will spin but that is ok, it is only there to hold the rolls of “cable”, remember, the inner horn takes the load.

 

After all this, check the servo to make sure the pot is still centered. If it drifts then use the 3rd channel trim screw on your radio to re-center it. The trim is located in the lower left corner of the radio on the backside, right next to one of the case screws. For a hook I use a small picture hanging hook, they work OK but they bend sometimes and don’t look very scale but they are cheap and easy to find. If you have the time and desire then make one yourself.

 

That’s it! Now install your winch and go tackle those impossible obstacles. Happy crawling.”

 

 

To check out the original thread go here:

http://www.rccrawler.com/forum/showthread.php?t=17970

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