Hi All.

I am making a DIY camera slider for my partner's birthday, motorizing it based on instructions on the JuicedLink website.

I bought a Hitec HS-5645MG Digital Servo from Servo City and a Custom Electronics Digital Servo Driver from Phils Hobby Shop.

I put them together with a 4.8V battery pack today, and although the servo runs (powered through the driver), it turns on automatically and the driver doesn't control its speed at all, nor does it turn the servo on or off. Basically it seems like the Driver is completely non-functional, apart from routing power into the servo.

Is there something I can do to make the driver work, or does it sound like there's something wrong with it?

Thanks for any help!
Rebecca.

If you have access to an oscilloscope, check the servo driver output. The signal should appear as described in the following thread, post #6 and #7:

http://www.rctech.net/forum/radio-el...controler.html

I don't have any tools like that unfortunately.

I am wondering if I need some kind of converter, or extra piece of kit to make the driver control the servo's speed?

Okay, let's start simply:

Does the servo output arm position move in response to changing the position of the pot on the servo driver?

Can you provide a link to the instructions on the JuicedLink website?

Thanks for your reply.

No, the servo just comes on immediately when it is plugged into the driver (which in turn is plugged into the battery pack). It then doesn't change speed at all or respond when the driver is clicked to "off". Bassically, the driver seems to have no effect at all.

I was told that I can't post links on this forum, but I'll give it a shot: juicedlink.com/diy-cookbook/8ft-slider Scroll down to "motorizing the slider" for the instructions, which aren't detailed.

Many thanks for your help!
Rebecca.

Thanks for the link.

First, try the driver on a known good servo. If you don't have one, is there a race track near you? You might have one of the racers try it on a known good servo. That way you'll know if the problem is in the driver or the servo.

It's also possible that the servo's internal potentiometer (normally used for position feedback) is not adjusted correctly. Is it adjustable externally? If so, then set the knob on the driver to its midpoint, and then adjust the servo's potentiometer. At some point, the servo will stop and reverse direction. You need to set the servo potentiometer to the point where the servo stops.

If the servo needs to be opened to get at its potentiometer, then you'll need to consider if this will void any warranty.

When you purchased the servo, did you choose the continuous rotation option? A standard RC servo will only move back and forth some. It appears you need a servo to run in one direction continuously, takes a special type of servo.

yes she needs a 360 degree servo if that what is needed
Futaba makes some but there pricey.

Thanks everyone for the help.

Howrdcano, I will see who I can find on Monday to give me a hand testing the servo and driver. Someone else recommended I get an auto electician to test the driver for me too, so I'll try that when the weekend is over. It seems to me that the servo is working fine, but the driver isn't doing anything except passing power from the battery. But I could be very wrong...

Dave, yes - I paid extra to get a continuous rotation servo, and it is working as it should in that regard. It just can't be controlled at all, except for the little servo knob (sorry, don't know the correct term) that changes the direction.

On the piece of paper that came with the driver it has two subheadings. One is "Operation". The other is "speed control operation" and says this: "Simply plug a speed controller into the servo Driver to operate your electric motor. HOWEVER, if your speed controller has a BEC (Battery Eliminator Circuit, DO NOT plug your 4.8 volt battery into the servo driver. This will allow the speed controller to power the servo driver".

I'm sorry to say that I have no idea what the above means? Does it mean I need an extra piece of kit to make the servo driver control the servo speed? It was not mentioned by the guy who made this set-up first...

Rebecca.

Howardcano, thanks for your advice! I just fiddled with the servo and driver for a bit and managed to get the driver to control the speed. The only problem now is that the driver is "off" when it is pointed to the middle (there's no click, which makes it hard to judge), and the click at the beginning of the driver still does nothing. If I used the other half of the driver, the servo reverses direction.

Still, as long as I can control the speed of the servo, I'm fairly content.

Thanks so much for all your advice! If you have any idea how I can set up the servo and driver so it clicks on and off, that would be wonderful.

Rebecca.

Since the knob on the driver has no detent, it certainly can be difficult to exactly find neutral. You could rig a switch to simply remove power to get it to stop.

I think you'll want the ability to go both forward and reverse, depending on how the camera is set up and what effect you are after.

As I understand it, the 'click' position all the way counterclockwise(?) on the driver is to automatically sweep the servo back and forth, which will be of no use to you.

Good to hear you are making progress. Yes that is how I would expect it to work, center no rotate, then go in each direction as you move from center. Think loosening and tightening a sail winch for example, one application that a continuous rotation RC servo is intended for. All the stuff about a speed control BEC can be ignored, it’s a different way to power the controller and servo that doesn’t apply in your situation.


For better stop and overall control, this is a little speculative on my part, but something like this more advanced tester may provide what you are looking for.

HFP-25 Digital Servo Field Programmer and Tester

HFP-25 Manual

Looking at the manual at the very end for the manual test mode it appears the M button would provide center (Middle?), which would be stop for you. It appears the readout could be used for a speed reference, might be helpful. Perhaps contact Servo City and discuss your application, they can probably confirm if this would be worthwhile to accomplish what you are after, or may have other suggestions.

It has a lot of programming capability, if you do decide to try it or something similar please advise, we can help translate the RC terminology for you. Seems it could provide a lot of control possibilities, top speed, repeat speeds, make center-stop less sensitive, etc, which may be useful in your application.

Thanks very much for the advice. The programmer is a little expensive for me to bother with at the moment given all the cost of all the parts I've already had to buy for this project, so I will just try and work it as it is for the moment and see how I go.

I wonder if an RC shop here in New Zealand would have such a programmer that they could help me tweak the servo with, just a bit...

I've accepted the fact that off is in the middle, and very sensitive. The only thing that's not great is how small a turn is needed to get the servo on its slowest rotation (a hair's width of a turn, if that).

Thanks again everyone. It's nice to be able to draw on such advice when I have no clue about these things myself. The thought of having to send the driver back to the States was a little stressful!

Servo programmers are likely to be far more common in flight RC, look for an airplane oriented shop, or perhaps better yet an airplane club flying field.

To make center wider and easier to hit, turn up the dead band width. Playing with EPA should adjust how sensitive it is as you turn it, how quickly it builds speed for a given knob turn.

If you can, reduce the servo's loop gain. That will make the speed easier to adjust with the driver. (I'm not familiar with the particular servo you are using; it's possible that the adjustment could be called EPA, as Dave mentioned. The concepts are related.)

The driver circuit can also be modified to do the same thing (by reducing the variation of its output pulse width), but that will take a certain level of experience with electronics which you might not have. If you have the schematic for the driver available, then we could suggest some changes.

Part of the advantage of digital servos is that the loop gain can be set very high, since, unlike analog servos, it is not dependent on the frame rate. So using an analog servo could make the speed adjustment less critical. But that's probably not an option, given the cost, and your location.