unmod servo oscilations
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Posts: 46,084
Hi there!
About a week ago, I started my hobby robotic project using a Basic Stamp 2e.
I'm "redesiging" a RC toy car using a Basic Stamp 2e and a bunch of sensors.
One of those sensors is to sweep the area in front of the car (radar
principle). To make this sweep, I am using an unmodofied servo with an
IRrange sensor mounted on top. The servo shows some remarkable behaviour.
using a standard program as listed below, I can rotate the sensor to any
desired angle (within the range of the servo). But before the servo is
reaching this final position, heavy oscilations take place. It can even take
several seconds (e.g. 10-20 sec!) before the servo is settled. The
oscilations (before settling) demand high current (op to 0.5 Amp) of the
power supply. This current demand was sometimes even high enough to draw the
powersupply of the BS2e up to a reset state. In other experiments, I used a
seperate power supply (not connected to power supply of BS2e) but the same
large currents and oscilations showed up.
In "control system engineering" terms the servo seems to be "too stiff".
This means that the servo controller electronics are reacting to heavy on
the servo errors (pot deflection or possibly pot noise). The servo
electronics will then react in full power, overshooting the desired position
etc.
the elec. connection of the servo is pretty standard and simple as well:
servo:
BS2e pin0 ----[noparse][[/noparse] orange (signal)]
[noparse][[/noparse] red (supply) ]
supply 6V
BS2e GND ----[noparse][[/noparse] brown ]
GND supply (GND connected to BS2e
GND)
Does anyone has any experience with these kinds of problems? All ideas are
very welcome!
Thank you very much in advance,
greetings,
Matthijs Boerlage
'example BS2e/BS2 program for servoangle:
low 0
loop:
pulsout 0,750 ': vary this value to obtain different angles: bS2e: 1500/2
micro sec
pause 20
goto loop
'end of example
About a week ago, I started my hobby robotic project using a Basic Stamp 2e.
I'm "redesiging" a RC toy car using a Basic Stamp 2e and a bunch of sensors.
One of those sensors is to sweep the area in front of the car (radar
principle). To make this sweep, I am using an unmodofied servo with an
IRrange sensor mounted on top. The servo shows some remarkable behaviour.
using a standard program as listed below, I can rotate the sensor to any
desired angle (within the range of the servo). But before the servo is
reaching this final position, heavy oscilations take place. It can even take
several seconds (e.g. 10-20 sec!) before the servo is settled. The
oscilations (before settling) demand high current (op to 0.5 Amp) of the
power supply. This current demand was sometimes even high enough to draw the
powersupply of the BS2e up to a reset state. In other experiments, I used a
seperate power supply (not connected to power supply of BS2e) but the same
large currents and oscilations showed up.
In "control system engineering" terms the servo seems to be "too stiff".
This means that the servo controller electronics are reacting to heavy on
the servo errors (pot deflection or possibly pot noise). The servo
electronics will then react in full power, overshooting the desired position
etc.
the elec. connection of the servo is pretty standard and simple as well:
servo:
BS2e pin0 ----[noparse][[/noparse] orange (signal)]
[noparse][[/noparse] red (supply) ]
supply 6V
BS2e GND ----[noparse][[/noparse] brown ]
GND supply (GND connected to BS2e
GND)
Does anyone has any experience with these kinds of problems? All ideas are
very welcome!
Thank you very much in advance,
greetings,
Matthijs Boerlage
'example BS2e/BS2 program for servoangle:
low 0
loop:
pulsout 0,750 ': vary this value to obtain different angles: bS2e: 1500/2
micro sec
pause 20
goto loop
'end of example
Comments
servos that do not have ball bearings oscillate as you
describe. Usually when my occured was the servo
returning to the center position or stopping close to
full deflection. In some cases my connection for the
signal wire was dirty, in others the servo was just
cheap. The worst servos I have seen with this problem
are towerhobby brand servos. Myself and two other club
members have had oscillation problems with them.
Usually the pot is dirty or signal wire connection is
dirty, dirty connectors were a major problem with
servo extension wires. The pins were not gold plated
but tin and corroded quickly even when connected, many
an airplane crashed due to that problem.
Good luck check out my website www.stoneflyers.com
within the next week for information on GPS guided
model airplane project, currently has GPS guided
truck.
Matt Klarich
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