How To Build a Micro Speed Control From a Servo

[Overlander]

The Servo Speed Control.

Servos are pretty cheap, so buy an extra one to experiment with. Here is a link with a picture to help visualize the steps. It is German. Don't worry, I'll talk ya through it....
http://home.t-online.de/home/tfeuchter/Tipps/servo_e.html Thanks again Thorsten:)

1. Disassemble it. Pull all of the gears off the top. (Save them for possible future custom micro drive trains?)

2. Take all the electronic parts out and leave them connected to each other by the wires. Note: Some servos have parts that are rubber glued to the inside of the casing. Just peel it or cut it away with an xacto. Throw the housing/case away.

3. You now have a micro proportional motor and speed control system. Plug it into your receiver and test it! It's cool! O.k, stop that.

4. Note the parts: the circuit board, the motor, and the pot (potentiometer?) The pot is used to find the neutral point between forward and reverse. If you are testing it, and the little motor is still spinning when your transmitter is neutral, just turn the pot slowly either way to find the zero point.

5. Say to yourself, "this pot is too big. I must change it to a micro 5kohm adjustable resistor."

6. Go to Radio shack or other fine electronics supply store and buy a micro 5kohm adjustable resistor. I found one that is 4.8kohms at radio shack that works fine.

7. Un-solder the pot and re-solder the adj resistor on the wires. Take note of the color of the wires. One of them goes in the middle. Your task is to find which one. DON'T CUT THE RED WIRE!! (just kidding. I always wanted to say that.......I watch too many movies.......)

7. Rejoice, for you are done.

It is actually easier than it sounds. The little adjustable resistor does the same job as the pot, but can be mounted in the vehicle where a small screwdriver can be inserted into the middle of it to adjust the zero point. I don't know why, but you have to adjust it all the time. Don't complain, it's supposed to be a servo, not a speed control......


Good Luck!:D ,
-Todd

[tinyrc]

Excellent write-up Overlander! :D

[Overlander]

Thanks, Tiny:cool:

I just wanted to keep this kinda sticky....

[arch2b]

i'm using a pico servo for the speed controller and it doesn't apear to have the large pot to replace with the 5k ohm resistor.

can someone tell me what, if anything must be done to this particular pcb board?
http://mini-zracer.com/albums/album70/t50.sized.jpg

[Overlander]

Arch, the little pico has a pot. It is still in there (based on the pic you posted) under the large white output gear. It has the red wires.

You dont have to do anything to the board itself. You could use the small pot that comes with the servo. The only problem will be mounting it. You might be able to find a way. Also, the shaft of the pot is smoothe, so when you go to adjust it, it might be hard to get your fingers around it. I once used the pot from the servo and just made a little slot on the top of the shaft to put a small jewlers screwdriver in.

The main reason we have been using the adjustable micro resistors is because (besides usually being smaller) they have a small hole that fits a small phillips screwdriver to adjust them with. It does the same thing as the pot.

[arch2b]

thanks for pinting that out. what do i do with the resistor hanging off the back? i plan on replacing the pot with the resisitor as in your instruction.

[Overlander]

Thats a good question:confused:

I have never used a pico for a speed control before and the servos I have used did not have that resistor. I would just take note of where it is connected to the board, then try the micro adjustable per instructions above. Substitute a wire for the hard resistor. If it does not work, put the hard resistor back in.

I dunno..... Let me know what happens. It should not harm the board either way. Just be careful soldering......

[Thorsten]

Hi Overlander & arch2b,
I suggest You to leave the resistor in the circuit. I don't know it exactly, but this resistor maybee a insurance for the IC.
So if the potentiometer is at the end of turning, normaly it have 0 Ohm.
If you put the battery voltage at the IC with a resistor of 0 Ohm, its possible to get some problems ;-).

So if you dissasemble the resisitor you should not turn the potentiometer at the end posistion.

It is no problem to replace this resistor in a SMD package resistor.

best regards

Thorsten

www.mikromodell.de

[killer]

:ö: Arch,

if you are going to use the adjustable resistor or what they call "trimmer" ¤ DON'T REMOVE THAT RESISTOR ON YOUR SERVO CIRCUIT BOARD!!! :eek: ¤ , just install it (trimmer) as if the resistor wasn't there, i've tried to removed that before and i can't find the 0 point, just attached one feet of your "5k ohm trimmer" on that resistor then turn the dial on the trimmer, notice that the speed of the motor decreases? if not, try to re-arrange the position of your soldered trimmer feet ti'll you notice that the motor reacts to your dial, one of the outer feet of your trimmer should be soldered on the resistor that is installed on your servo's electronic board..,. move the dial 'till the motor stops spinning, that's the 0 point, (do this while the motor is not yet installed on the truck)... now if you are going to use a "normal resistor" like the one on the thread i've posted on

http://www.tinyrc.com/forums/showthread.php?s=&threadid=9532

this is much easier to install just follow the last instruction properly, and there you can remove that resistor sticking from your servo circuit board, because instead of attaching another 2.2K ohm resistor on the 2.2K ohm resistor of your servo board, replace it with 5.4 k ohm which is also the same value (almost) of 2x 2.2K ohm resistor in series connection ;) , i'll post a pic of the modification i made on my PICO servo 5.4 grams electronic board.

and here are the good points using a normal resistor than the trimmer,

1. you'll do the trimming on your radio (throttle trimmer) rather than twisting the dial installed inside your truck everytime you turn it on.

2. just solder the resistors as instructed (which i find very simple :cool: ) and it's automatically on the 0 point!.

3.you don't have to twist or likely to damage any "dial" on your truck, cause there is none! :p

4.resitors are "smaller" in size compared with the smallest mulit-turn trimmer you can find.

hope this help

-æ

[T_T_52]

Could you post so pictures for instructions.

[arch2b]

killers sc upgrade on a gws pico servo (http://tinyrc.com/forums/showthread.php?s=&postid=91402#post91402)

[sawhit4]

could you replace the servos motor with something more powerful?

[Thorsten]

Hi,
the servoe electronics are designed to use with this motor. So I suggest you to use a motor same size than the original.

Maybe it works with a little larger one. Or just have a look on the ampere of the old and the new motor. You can change the cheap original motor with a better motor with more power and the same amperes

best regards

Thorsten

www.mikromodell.de

[iflyos]

Is it reasonable to replace the servo FETs with better units to increase the board's capacity?

I ask because I have plenty of servos, and plenty of fets, but am low on cash (Just changed jobs)

I need a f/r speed control for my 1/24 scale crawler (right now I am using a forward only GWS Pico from one of my retired slowflyers) and cannot justify buying a Novak Spy right now. (New job is with the local school system, and we only get paid once a month....The wife seems to think buying food is more important than RC, go figure!)

Thanks,

Tim

[Overlander]

Originally posted by iflyos
The wife seems to think buying food is more important than RC, go figure!

That's just CAZY TALK!

[BryceOwen]

I was wondering if anyone knew how much voltage and current the servo board can handle... I have an HPI MMM that I was hoping I could use. I know I won't be able to feed the power the motor requires through the "ESC", but if I knew it's limitations, I can plan around it.

[oldtamiyaphile]

Has anyone over come the problem of limited throttle range?

I mean, it only takes until about 1/4 stick to reach full throttle, makes trucks very jerky to drive. I'd like to be able to reach full throttle at around 3/4 stick. Other than using a TX with EPA (sorry but my good TX stays with my heli and possibly other aircraft), any ideas?

[Thorsten]

Hi,
thats the reason for a good speedcontroler instead of a servocontroler;-)

In a servo you must have a short time of reaction. I think you dont want to wait some seconds until the servo reaches his position.
To do this, the servo controler have a small 0-point and fullspeed at 1/4 stick.

I dont know a solution to modifie the servocontroler.

But I have a little circuit on my website (www.mikromodell.de) . This is a cheap speedcontroler (http://ig.micromotor.org/Tipps/frsmd4_e.html) with "normal" ranges.


best regards

Thorsten

[cheesehead]

the ICS-50 should work if you use enough cells. The voltage cutoff is an annoyance, though.
The Pixie 7p is a better option, with a max. 7 amp draw and all the goodies, including adjustable cutoff. It should work nicely.
I personally think the ICS is a good idea, as with a cheap Li-Ion pack your TTTT will go for a looooooooooooong time

[bluemonster]

So am I to understand that I could use a servo with a larger motor in place as a speed control? I am also building a 1/24 Monster Truck/Rock Crawler, and this would be a very economical and lightweight answer!

I would be running a Speed 300, is that going to kill my servo "speed controller"? I imagine in a rock crawling situation, running 6 volts and a Speed 300, the amps might be a bit much for a servo to handle, or is that guess an incorrect one?

[Overlander]

Yes a 300 sise motor will fry most servo board ESCs. You could try a large 1/4 scale servo but at that cost you might as well buy a standard micro ESC. There are many 1/24th and 1/18th RC models out there these days. Micro ESCs are easy to come by at that size.

IMO, a 300 motor is way too much for a 1/24 rock crawler anyway.