Servo Controller Power Issues....

[John Gutmann]

Ok well I have a thread made for the current project of mine here:

http://www.chiefdelphi.com/forums/sh...056#post614056

Basically what I am trying to do is control this Servo controller.

AS for the actual circuitry, the servo power and control power are seperate but the grounds are connected on the PCB. So when I am sending commands to it I have power on the servo lines then I will jump it to the control lines so I only need on battery pack, and the controller will accept the commands just like it should but it won't move the servo like it should. Now when I do this but with a battery pack on the control power and ground and a battery pack on the servo power and ground it will work. I am just wondering why it only works with 2 seperate sources of power. Any insight would be helpful

Thanks,
John

[sciguy125]

In an ideal world, you should be able to power the controller and servos with only one battery. What kind of battery are you using? When you use a single supply, are the servos doing anything, or just sitting there? Also, try putting a capacitor across the supply. Maybe 0.1uF, exact size isn't that important though.

[John Gutmann]

The servo is just sitting there, it will go to it's defualt position sometimes. As in after the first command is received all servos go to 127 as a default position. and after that it doesn't move at all. RIght Now when I send the commands it has the yellow LED on, meaning there is a position error, which doesn't make sense because I am using the mode that accepts all positions. It is even saying position error after I just send the first byte in the packet. Which doesn't make much sense, but when I do get it to go past there the servo just sits there, sometimes holding the default position sometimes without doing anything (free to turn by hand).

For both supplies I am using a 4 Cell non rechargable AA packs. This means there is 6 volts from each pack, Both packs have brand new batteries in them, and the control circuitry can have from 16 volts as an input so that is no problem either.

I can't think or figure out any reason it isn't working.

[Al Skierkiewicz]

John,
While AA batteries are capable of supplying some high currents, it is not without some other problems. By using two battery packs you do not draw down the board power below the critical 5 volts at which point the electronics cease to function. You do not specify how many servos you are using , but you need to keep in mind that even servos are in stall when they aren't moving (starting). Try going to a C cell pack and I think you will have better luck. You can use a smaller pack for the board power, like AAA or some lithium cells since it is max 10 ma and stay with the AA pack for servos if that works. You are likely getting position errors, since the micro thinks it sent commands but the servo hasn't moved.

[John Gutmann]

Well it shouldn't thinking the servo move when itididn't because the micro onboard doesn't get feedback from the servo. As for power issues I am using one servo and it isn't driving anything. I measured the voltage when it was trying to turn the servo and it was still +5 volts. I even tryed to connect the VEX battery pack and that didn't even work.

Ok right now I just tryed it and I have my vex battery hooked up to control power, and servo power, and common ground. When I send commands it will do one of 2 things:

1.) The servo will move to the default position (127) and it will not move no what position command I set it.

2.) The servo will "jump' to some position, but the controller will read a position error. And if I do get the servo to hold a position if I put a tiny amount of stress on the horn it will indicate a position error.

-John

[Al Skierkiewicz]

John,
According to the manual, he Yellow LED indicates that the internal processor has determined that the position you have sent is out of range for the mode selected. The controller indicates it is capable of sending two different protocols to the servo outputs so this might be part of the problem. Remember that when a motor is asked to move, it produces a high current demand on the power supply, even for a short period of time. This might be related or it might not, but it is possible to draw the power down below 5 volts for long enough to upset the controller. The fact that you can move a servo once powered might be that it is just disabled, i.e. not recognizing the data it is receiving.

[John Gutmann]

If it didn't recognize the data the LED would be red. But I took out my multimeter out once AGAIN, and hooked it up to the battery to look at voltage. And this time I did notice the voltage getting below 5 volts. I could barely see it though because the display is so fast. I guess I would have been able to see it better with something that would record and graph it. I am guessing this is the problem. I guess it also explains why it resets when I turn the servo. Because I am stalling the motor and cause a big current draw. I was figuring this was the problem yesterday, but I didn't see any proof of with on my multimeter. Thanks for taking to time to look at the manual and help me out.

When I get better batteries I will report back.

-John

[6600gt]

Originally Posted by sparksandtabs

If it didn't recognize the data the LED would be red. But I took out my multimeter out once AGAIN, and hooked it up to the battery to look at voltage. And this time I did notice the voltage getting below 5 volts. I could barely see it though because the display is so fast. I guess I would have been able to see it better with something that would record and graph it. I am guessing this is the problem. I guess it also explains why it resets when I turn the servo. Because I am stalling the motor and cause a big current draw. I was figuring this was the problem yesterday, but I didn't see any proof of with on my multimeter. Thanks for taking to time to look at the manual and help me out.

When I get better batteries I will report back.

-John

Either get a FIRST type 7.2V battery pack or get 6 rechargeable batteries at 1.2V each. How much current can the board output to the servos?

[John Gutmann]

The board doesn't power the servos, as I said they provide a signal. And in my opinion a FRC 7.2 volt battery is a big no. I already what I WANT to use and what I can use. Right now while I am at college I can use nothing becuase I have nothing here to use. When I get home I have old RC car batteries and VEX batteries at my highschool. I would like to use a 8.4 volt RC car battery because those cells are bigger then AAs. But as for the actual project I go the code working. I think I have a dead servo, I have no idea how it died, but I need to gear down the vex bot and then it will work fine. The servos right now just don't have enough power to carry a laptop. let alone enough power for running at under 6 volts.

The program I wrote on my computer work though. All I need to do is plug the serial cable in and type 4 things and it will move forward. I will get pictures and videos and a nice little presentation all put together once I get it all working together. The best part about this project is I can take my laptop to ANY FRC robot and have their robto running off any computer in the world in a matter of minutes. *In theory* *yet to be tested*

Look out for more on this project!

-John