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Connecting 2 Firgelli L12 Servos to one RC Channel

 

I am a photographer in Alaska and last spring I started building a rc rover with a camera mounted on it to photograph wildlife. I used the Wild Thumper 6wd chasse and controller as the platform. It worked pretty well and I captured a few awesome images, but there were some design issues.  So this spring I am improving upon my design, however, I have ran into a small problem.

In my new design I am using 2 Firgelli L12-50-100-6-R servos to tilt the camera up and down. Now for the problem, when I connect both with a "y" cord to one channel on the RC Receiver, nothing happens.

This is what I have tried to troubleshoot the problem:

-Each L12 servo works flawlessly on its own.

-I connected 2 standard servos to the "y" cord on one channel and they work perfect together.

-I connected 1 L12 and 1 standard servo to the "y" they worked together.

-If both are connected to the "y" and i unplug one, the other starts working and goes right the the position it should be at.

-I have 3 L12 servos and tried every combination of them together, with no luck.

-I tried running power for the servos directly from the Wild Thumper Controller's 5v output and just connecting the white signal wire to the receiver. Didn't work.

-I contacted Firgelli tech support and asked them. They said it should work, no problem. They guy even sent me a video of his quadcopter he built with 4 L12's connected to one channel on the receiver to control the landing gear.  

 

Basically I have tried everything and I have no idea what is going on! haha

 

So if anyone has any thoughts or has any idea what is going on I would love to know!

 

My next question is, if I can't get this to work via a "y" cord directly into the RC Receiver. Is it possible to use the Wild Thumper Control board to relay the signal to 2 outputs. Or to rephrase, can I program the board to receive the signal from the RC receiver in one I/O pins and then just redirect the signal out to 2 different I/O pins (one for each L12 servo). If so, how the heck do I do that! haha

I know it's a roundabout way of doing this but it's the only thing I can think of unless anyone else has any suggestions. 

 

 

Thanks!!! :)

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birdmun's picture

seeming to get nowhere. I am starting to wonder if the resistor on the signal wire might actually be a good plan. If the receiver is the problem, it might be having trouble driving enough current down the signal wires to two servos. 

***Mind you. I am just thinking "out loud" here. I have no degree or advanced knowledge. Only enough information to make me dangerous. :D ***

Duane Degn's picture

I personally haven't had problems with noisy servo wires but I've read several times long wires can act as an antenna and pickup noise which otherwise wouldn't be a problem.

Is there a way to test the servos ganged together without using the Y harness?

How long is the Y harness and the normal servo lead?

Apparently adding a resistor on the line can reduce noise. 4.7K is the value I see most often recommended.

I've also seen long servo wires with a ferrite bead. I'm pretty sure the ferrite bead was there to reduce the noise on the long lead.

I thought noise on the line was a problem induced by motors and such. It's odd noise would be a problem on a workbench.

Do you have three spare servo connections on your WT board? If so, you idea of using the WT to resend the signal could be used. It's just a shame to have to bog down your program with extra tasks that shouldn't be required.

If I do try the resistor. Where along the wire should i put it?

Duane Degn's picture

I've always seen the resistor added near the source of the signal though I don't think it matters.

I have a bunch of hook up wires with resistor in the middle of the wire since it was convenient to add it there. I doubt it matters where you add the resistor.

I just read this from the datasheet for the L12.

"

If the motion of the actuator, or of other servos in your system, seems erratic, place a 1–4Ω resistor in series with the actuator’s red V+ leadwire."

  source: http://www.firgelli.com/Uploads/L12_datasheet.pdf

So should I place the resistor on the red leadwire or the white signal wire?

Duane Degn's picture

I sure looks like they mean the red power wire. I've never seen that suggestion before.

I still think a capacitor between the red and black wire might help.

I've had some servos not work unless I uses a capacitor across the power lines. This was with a setup that could barely supply the required current.

The Y harness is only 6" long and the cord on the servo is 12" so 18" total.

I tried Powering the servos from the WT board and taking both signal wires just helt together and putting them directly on the signal pin on the receiver (so no harness or anyting inbetween) and had the same results.

I do have 3 spare servo conections on my board. Thinking that will be the quickest and easiest solution for now.  I may still try adding a resistor. I read that somewhere as well.

Its just weird. Like I said, the tech support guy at firgelli has 4 on one channel with no issues. He also said they test them 3 at a time on one channel. 

Duane Degn's picture

How about using a level translator type circuit as is often used when going from 3.3V to 5V logic.

I know there are transistor circuits using a 2N2222 that are used for level translating. I think a setup could be used with boost the current of the signal line.

You're sure the "Y' harness is okay?

birdmun's picture

he mentions testing standard servos, and, they worked fine on the Y cable.

Like everyone else, I too still question current draw. Someone mentioned breaking out the power to one, or, both servos. The WT board likely has "servo" connections for most, if not all, of the I/O. Why not just break out the power to the servos, and, power them from the WT board, while using the Y cable to split/combine the signal wires?

Duane Degn's picture

Yes, you're right. I forgot about the Y harness test. Thanks.

I was almost headed to bed but this issue kept coming to my mind. I'm sure I'm not alone in having seen many servo issues cause by power supply problems.