Digital.Complex: Servo Conversion Tutorial for MRCG's - Digital.Complex

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Servo Conversion Tutorial for MRCG's

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Posted 17 June 2009 - 11:56 AM

Hi everyone, here's a quick and simple servo conversion tutorial that should be especially useful for MRCG and MRCG1.1 owners.

As you may know, the Mini-Z ASF 2.4GHz electronics package has 5 wires coming out of its servo control circuitry that go to the Mini-Z servo motor and servo potentiometer. Meanwhile, all hobby-grade servos have 3 wires, so at first glance it seems like an impossible problem to use them with the ASF PCB. But in fact, hobby-grade servos have 3 wires going into an internal control PCB, which then has 5 wires coming out of it to the internal servo motor and servo potentiometer! So to make a hobby-grade servo work with the ASF PCB, we simply have to take the control PCB out of the servo casing, and hook up the servo motor and potentiometer directly to the ASF PCB.

There is a catch, however. Different servos have different specs for their motors and potentiometers, so in order to work properly with the ASF electronics, the servo must have motor and pot specs at least similar to the ones that the ASF PCB was designed for (the Mini-Z servo motor and pot). We've tested a number of servos against the ASF PCB, and so far have found that the Futaba S3114 works the best. So for that reason, we'll be working on it in this short tutorial.

What you'll need:

- Futaba S3114
- Kyosho Mini-Z ASF 2.4GHz electronics set
- Small screwdriver (jewelers' type is best)
- Soldering iron (the finer the tip, the better!)
- Tweezers
- Helping Hands (they come in handy!)

Let's begin. Here's the servo; just take out two screws holding the bottom of the case to the top, and you can pop off the bottom of the servo casing. (Before taking this photo we had already stripped out the internal control PCB and wires, please accept our apologies for this inaccuracy.)

Posted Image

Once you have it apart, cut or unsolder the internal control PCB from the servo motor and potentiometer. Once you're done and have cleaned everything up it should look like this. You can clearly see the + and - terminals of the motor, and all three prongs of the potentiometer.

Posted Image

Now onto the ASF PCB. If you bought yours new, then it will probably come with a Mini-Z servo motor and potentiometer attached to the wires. If you took yours out of a Mini-Z, you'll probably have them attached too. In any case, you don't want those two items hanging on the wires anymore, so unsolder them. You should end up with 5 free wires like such (hopefully, not looking as abused -- this ASF board has seen a lot of time on the bench).

Posted Image

And now the fun part. Solder those 5 wires to the servo motor and pot respectively, like the following picture. Make sure you have the colors and orientation done correctly, or your servo probably will not function properly! (It is actually possible to do this wrong and have the servo running perfectly well, but in reverse. If you're lucky enough to do that, just reverse the servo control via your radio transmitter.) If you have Helping Hands to use, you'll be really glad you brought them along, as these wires often don't like to cooperate. When you're all done you'll have the wires soldered on like so:

Posted Image

Again, make sure you have the right color wire in the right place! You should also try and keep the black and red wires as close to the motor as possible: it's a tight fit back there, so this makes it easier to pop the back of the servo casing back on. Once you've made sure your connections are secure, go ahead and reinstall the back of the servo casing and casing screws.

Now a check: the Futaba S3114 potentiometer is more "sensitive" (for lack of a better word) than the standard Mini-Z potentiometer, so when you first turn this thing on and try it out, turn your steering travel/dual rate down to about 20%. This should still produce quite a bit of servo travel from lock to lock, but in our experience it's plenty safe for you to now install the servo in an MRCG, MRCG1.1 or other micro RC. Proceed to tune your steering system to your liking. Good luck and have fun!

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