Quote:
Originally posted by VanWEric
Last year we had a nice little black box that we could plug into a victor and control the motors from a little pot on the box. THe person who made it is no longer on our team, and i was wondering if anyone knows how to make one.
Thanks
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Oh, sure! That's called a "servo simulator", used in radio control modeling all the time...
The Victors look like a standard RC servo (that's "radio control", not "robot controller") to the controller. It requires a 1ms to 2ms positive going 5v pulse, repeated somewhere in the 15ms - 20ms range. In reality it shouldn't be more often than about 15ms, yet it has to be more frequent than whatever timeout value the Victor's "I've lost the Robot Controller so I must shut down" watchdog timer is set to.
1.5 ms corresponds to "127" or the center "off" position of the Victor, and the 1ms and 2ms times correspond to the two full on directions. (I'm assuming 0 generates 1ms and 255 generates 2ms, but I've never bothered to verify that. Doesn't matter, though. One's full on in one direction, and the other is full on the other way.)
You can make that with a simple 555 circuit. Piece of cake... Here's a link to Ahmet Onat's page, which includes both the circuit and servo theory.
**
BE CAREFUL THOUGH*** Ahmet's diagram has the leads
in the wrong order for the Victors!!!
Victors use the "Futaba standard" for wiring order (Black, Red, White), where Black is Ground, Red is +5VDC, and White (or other color) is the pulse signal... Ahmet's diagram OTOH has the white signal lead in the MIDDLE for diagram simplicity, which is the WRONG ORDER for the Victors! Make sure it is in "SIGNAL, +5, GROUND" order on your connector!!! If you look closely at a Victor's case, you'll see it is marked "W R B" for White, Red, and Black respectively.
Here's Ahmet's page:
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http://www.geocities.com/BourbonStre...rvobasics.html
A couple of notes on part selection:
Transistor - If you need a part number for the "small signal NPN transistor", use whatever you can find, like a 2N2222, or a 2N3904.
Potentiometer - Make
SURE you use a LINEAR TAPER pot, and NOT an "audio taper". The first has a resistance vs shaft_angle graph that's a straight line of constant slope from one end to the other. An "audio taper" pot has a
logarithmic resistance vs shaft_angle graph. That means the center of the pot is NOT "the middle value", and the Victor will not be off in that position. You can tell you have an audio pot if the motor will want to run almost full on in one direction for all but a small pot angle on one end.
BTW, you will
not be able to use the CH Flightstick or other PC joystick for this circuit, because (1) they are the wrong resistance value, and (2) they don't bring all three connections of the pot to the connector.
Disclaimer: Verify your connections BEFORE powering it up. I disavow any damage to your Victors caused by improper wiring...
- Keith