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MasterSnow
01-22-2004, 05:24 PM
Hi,

My team and I are trying to hook the main robot controller to the edubot. We have been successful so far, but the edubot servo motors do not respond to the joystick, even though we are recieveing a response from the controller through our OI. The system works with some other servos that we had. One thing we had to do was convert the 4 wire connection of the edubot servos to a 3 connection pwm cable so that they would plug in. Is the orange wire on the edubot servos important? It looks like it just runs to the battery, but this is the only conclusion we can come to. Anyone have any ideas on how to make this work?

MasterSnow :confused:

DanL
01-22-2004, 07:16 PM
I'm confused.

First of all, are you connecting the Edubot to the RC, or the Edubot's servos?

If the latter, the 4-pin servos that came with the Edubot are modified servos. They've been modified so that they act as variable speed motors instead of servos. If it says "IFI Robotics: Multi-Speed Motor," you're looking at the modified servo. If this is the case, it sounds like you're trying to use these guys as normal servos, which won't work.

You'll need to wait for one of the RC guys for details on exactly what that 4th wire does (I'm sure its somewhere in the IFI docs). All I know is the 3-wire servos that came with the Edu kit are normal servos, and the 4-wire servos are the IFI modified servos.

MasterSnow
01-22-2004, 07:24 PM
hi,


To clarify a bit, I am setting the Robot controller on top of the edubot and hooking the 4 wire servos to it to act as motors, not as a typical servo. However, the RC does not seem to work with these 4 wire servos.

MasterSnow

DanL
01-22-2004, 09:33 PM
A thought just occured to me:

Rather than finding the specs for the modified servos themselves, check the PWM pinouts for the 4-port EDU PWM's (page 8 (http://www.innovationfirst.com/FIRSTRobotics/pdfs/EDU-RC-2004_Ref_Guide_2004-Jan-14.pdf))

Indeed, like you said, the 4th pin is a +battery pin - same as the middle pin in a 3-pin PWM connection.

Now, there are a few questions. First, do the two +battery pins supply the same voltage. You can check this out with a multimeter while attaching the multispeed servo to the edubot.
Second, whats the current draw on those modified servos? I'd say just splice that 4th wire to the other +battery, but if the current draw is too big, you run the risk of frying your RC (the breaker description is vague, but it sounds like the built-in breakers only protect the additional battery, not necessarily the PWM ports themselves).

I'd say measure the current draw on the modified servos when attached to the RC - both under straining and free conditions. The safest bet is to attach that 4th wire to an external battery of the appropriate voltage, but if you're feelin' lucky and you tested the current draw, splice it to the center pin of the 3-pin PWM connector.

...we really need one of those electronics people in here