Driving 4 Hacked Servos from Basic Stamp


I'm currently trying to build a little robot with 4 hacked servos My problem is just that when i try to drive 4 servos it stalls. I have no problem driving 2 servos like others do, and i have even tryed to make a paralell coupling of the servos with 2 servos on each dataline but with no luck

Yesterday i tryed to make a driving circuit with a BC547 and connect it like this:

Base i coupled to the dataline with a 2,4K resistor Collector is connected to a 2,4K resistor to +5v and Emitter is connected to ground

i connect the signal line from the servo to the collector pin of the transistor ( hoping it would work ) but it didnt :-(

What am i doing wrong ??? can anyone help please !!

Thanks in advance /Thomas Krogstrup

Reply to
Thomas Krogstrup
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Is the Stamp resetting when the servos attempt to activate? If so, you may have one of two things going on. First, your power supply may not be adequate to run all four. Try more batteries. Second, it may be the start up load is too great. In this case, get some large capacitors, like 2200uF or greater, and put one next to each servo.

The Stamp is too slow to really run 4 servos and do object detection, etc. You might want to think about a PWM controller to run them independently.


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Reply to
Jonathan Peakall

On a similar theme as below, if the additional servos are pulling too much current through your voltage regulator, it may get too hot and go in to thermal shut-down.

Reply to
Geoffrey Swales

To prevent an excessive voltage drop from the power supply to the servos, run each servo from its own Stamp pin, and do the pulsout to each pin in the usual method. You do not need a driver for this, though you may consider a 330 ohm (or so) resistor between the Stamp pin and the servo signal wire, as a precaution.

(The idea with the above is that the servo is only really on when it's getting a pulse...this applies to standard servos, anyway, and not the newer digital servos. By pulsing each servo in turn you avoid "doubling up" on the current demands.)

No doubt the problem is coming from brown-out. You don't specify, but it sounds like you're running the servos from the same power source as the Stamp. This is common in some Parallax-produced boards (like the Board of Education), and is acceptable for two servos. It's not for four servos. You're FAR better off connecting the servos to their own unregulated battery supply. A simple four-cell holder is sufficient. A set of four ni-cads or NIHM will produce 4.8 volts; alkalines will provide 6 volts.

Be sure to tie the ground of the Stamp and its electronics to the ground for the servo battery pack, or it won't work properly.

-- Gordon Robots for Less at Budget Robotics:

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Thomas Krogstrup wrote:

Reply to
Gordon McComb

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