Subject:
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Re: strange TS-53 servo problem
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sat, 4 Dec 1999 22:47:40 GMT
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Viewed:
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862 times
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Hi ... It sounds as though you are obtaing the power for your servo
from the HandyBoard's motor output pins ... and if so, this is the
source of your problem. The HB does NOT control motor speed by
varying the DC level ... it uses PWM to reduce the average DC level
sent to the motors ... and your servo requires a +5V DC source for
its power. As a general rule the servo should NOT get its +5v from
the same source that powers your microcontroller because the high
load imposed by the servo under mechanical load may cause your power
source to sag and possible cause a reset. Try using 3 AA or C cells
to power your servo, but be certain that the negative end of your
batteries is connected to the HandyBoard's ground ... otherwise your
servo will still be erratic. If you are using the HB's expansion
board, then it supplies the required +5V directly to the servos
by using the large diodes to drop the voltage to a value that is
okay for the servos (they like from 4.8 to 6.0V for their power).
Good luck,
- Nick -
Kah Mun wrote:
>
> Since the output ports for the motors of the handyboard supplies
> 11V, i connected a 5V regulator to power my servo. i have a capacitor between
> the driver's + and - terminals. I looked at the control signal on the
> oscilloscope. The duration of the pulse is correct, the period of the signal is
> a about 20ms. the servo just buzzes.
>
> one thing i noticed: whenever the ground lead of the oscilloscope
> is connected to the negative terminal of the motor driver port, the servo
> spins only in one direction regardless of the duration of the control
> signal's pulse. i measured the voltage of the negative terminal with
> respect to ground, it is 1.03V.
>
> do i have a grounding problem in addition to the servo problem?
>
> here's the code i used: basically the i keep sending a 0.2ms pulse till the
> stop button is pressed. then a 2.4ms pulse till the button is pressed. then the
> servo is turned off.
>
> void main()
> {
> fd(1);
> servo_a7_init(1); /* activates PortA bit7 that gives the control signal */
>
> while (stop_button()==0)
> {servo_a7_pulse = 400; /* a pulse with duration 0.2ms */
> sleep(0.0198);
> }
>
> while (stop_button()==0)
> {servo_a7_pulse=4840; /* a pulse with duration 2.4ms */
> sleep(0.0176);
> }
>
> ao();
> servo_a7_init(0); /* disables port A bit7 */
>
> }
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Message is in Reply To:
 | | strange TS-53 servo problem
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| Since the output ports for the motors of the handyboard supplies 11V, i connected a 5V regulator to power my servo. i have a capacitor between the driver's + and - terminals. I looked at the control signal on the oscilloscope. The duration of the (...) (25 years ago, 4-Dec-99, to lugnet.robotics.handyboard)
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