Hacked Servo & H-Bridge Question

BrianmcmBrianmcm Posts: 33
edited 2004-10-16 - 22:18:11 in Robotics
I assembled the H-Bridge that is shown on Bob Blick's website. It uses 2, TP120's and 2, TP125's. Also hacked an Airtronics servo, taking the pot out and replacing it with 2, 3.3k resistors. Then I added wires to the from the servo motor to the inputs on the H-Bridge. I connected a 12 vdc motor to the bridge, 5 vdc to the servo,·and and the control wire from the servo to a BS2.· When I gave a Pulsout command of 1100 the 12-volt motor rotated one direction, a Pulsout command of 700 rotated in the other direction. My question is 3-fold. First, I never found a value for the Pulsout to hold the motor. In fact Pulsout of 796, motor rotated one direction, Pulsout of 795, motor rotated in the other direction. Even with a hacked servo isn't there a value that will "hold" the motor? Second, Pulsout values from 796 up to the upper limit, the motor speed was constant. Is this right or should I see a difference in speed depending on the value? Third, and this kind of ties in with the second question, when I gave a Pulsout command that spun the motor in the opposite direction, i.e. 795, again the speed was constant no matter the value, but the speed was half of what it was in the other direction. Is this due to the nature of the H-Bridge or something else?
Any information would be greatly appreiciated.
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