servos

sorry for the stupid question, but how do i controll a 12v servo? I’m not sure which wire goes to what. it’s not responding to my program .thanks.

What kind of servo is it?
What kind of connector does it have?
Are you sure it is 12 volts?
What are you using to operate the servo?
What is the code you are trying to operate it?

Please give more information as it is impossible to help you with out key information.

it’s got a female PWM calbe, (yellow red and black)
I’m using the 2004 RC. It turns out the guy we have setting the servos up hasn’t tried any code yet, because he doesnt know how to wire it. I’m not sure either.
U dunno what kind it is, it’s GWS brand.
I’m told it’s 12 volts, I didn’t buy them.

The servo that you are connecting is not legal on a 2005 FIRST robot. You are only allowed to use are the Hitec HS-322HD servos which were included in the kit. You can purchase these from IFI.

They plug directly into the PWM outputs of your RC.

Regards,

Mike

i know, but I’m not going to put them on our robot.

The correct servos run on 6 to 7.2 volts. You will have a hard time getting a 12volt servo to work plugging it in directly. They may work with the pwm signals, but power and ground will have to come from the main fuse system. I have never tried this. Best bet is to talk to a Tech at IFI.

R/C airplane servos like we use are designed for four- or five-cell NiCad packs, with four being the most common number of cells used. Most standard servos will probably be “fried” if connected to a 12v source. Do 12v servos exist, and if so, what are they normally used for?

sorry… a non related servo question.

can you get feedback from a servo, so it can tell the controller at what degree it is rotated at, say if you have it on an arm that moves, and want to use it as a sensor?

also, if the above situation does not work, can you use that servo, along with another motor, to move the arm by degrees? What I mean is, you tell the servo to whatever degree you want it, and when it reaches that degree, you have the other motor cut off as well?

Why I am asking exactly is because I want to know how to easily do feedback on swerve drive. And I dont like potentiometers at all.

I imagine the sensor that provides feedback in a servo is a potentiometer. What exactly don’t you like about them? The idea of using a servo as a sensor is certainly going to be a lot more work. Only way I can think of doing it is to measure current flowing to the servo and cut off when the current drops off.

we are currently remote controlling a go-cart, and are using a servo to run the gas. however, we cannot make the servo (an appropriate hitec) run with the 2004 brain. we have tried running it through pwm outs, and through the ttl port the camera uses ( we were getting rather desperate).
can someone explain what we are doing wrong, and how to make it work?

Let me see if I can answer a couple of questions at once.

Normal hobby servos usually work by having their own internal feedback. You are feeding them a Pulse Width Modulated signal (PWM). they use this signal to determine where to position them selves, much like having a built in feedback pot, which in fact some actually have. So, if you try to get feedback from them, you will have to add a device to create/re-create the position feedback signal from inside, that could be a potentiometer (sorry), an encoder or the like. If you are going to use that signal for position control, then you might as well use a motor to drive the “axis of motion” and use a pot to encode the actual position. As you can see, you would be re-inventing the wheel.
The advantage of using a motor to drive an axis is that you can choose the motor size, power and speed to meet the requirements of what you are trying to achieve. As for the go-kart throttle being driven by a servo, the servo may not have the torque you need to move the throttle. I don’t know if I would try to add a motor to a throttle connection, but maybe a servo rated to do the work you are asking it to do on the voltage provided by the RC. Remember, the RC only puts out 6-7.2 vdc. That may not be enough to drive the servo the way you have it installed.

Read Gregs responce below. He may have called it correctly. It’s always the simple things we overlook. :cool:

Do you have a backup battery connected? On the 2004/2005 robot controllers, servos receive power from the backup battery.

Thank you!

I think that we overlooked the backup battery. I believe that the servo is strong enough, because we had it hooked up with an Airtronics reciever for model vehicles (It ran on 6 volts) and it worked fine :slight_smile: . The only reason that we are switching to the first brain is so we can set up an auto mode that allows it to avoid obstacles.

Thanx from 306:D

Yep, it was the Backup battery, sure made us feel stupid :slight_smile:

Once again, thank you for your help :slight_smile: