Manual
Table Of Contents
- Product Features
- Installing the hardware
- Downloading and Installing the software
- Programming a Phidget
- Technical Section
- The PhidgetAdvancedServo software component uses degrees to specify position, velocity, and acceleration. The degree unit is translated into a pulse sent to the servo, but it’s up to the servo to translate this signal into a particular position. This translation varies between servo models and manufacturers so our degree abstraction will not be exactly the same as the servo you are using. Our degree abstraction is based on the HS322-HD servo, which is typically 10.4uS per degree.
- API Section
- We document API calls specific to the 1066. Functions common to all Phidgets are not covered here. This documentation is deliberately generic. For calling conventions in a specific language, refer to that language’s API manual.
- Device Specifications
- Mechanical Drawing
- Product History
1066_0_Product_Manual created: 07/09/09 Page 7
Technical Section
How RC Servo Motors Work
RC Servos are used for positioning
applications. They were originally designed to
control Remote Control airplanes and their low
cost and high torque makes them very useful
as an actuator in prototyping applications.
An RC Servo can be instructed to move to a
desired position by the controller. Internally,
it monitors the current position, and drives
the motor as fast as it can until it reaches the
desired position.
This is a very cheap and simple way to control
a motor. It has some limitations - there is
no way for the controller to know the current
position and speed of the motor. Applications
that want smooth movement suffer from the
aggressive acceleration.
The PhidgetAdvancedServo 1-Motor
The PhidgetAdvancedServo is able to address some of these limitations. Instead of sending
the desired position immediately, the PhidgetAdvancedServo sends a series of progressive
positions according to acceleration and velocity parameters. In most applications, this
dramatically smooths the operation of the servo, and allows reasonably precise control of
position, velocity and acceleration.
The PhidgetAdvancedServo 1-Motor does not use an external supply and is powered through
the USB, giving it an increased efficiency over externally powered modules due to the current
being limited at 450 mA. To prevent the Phidget from resetting due insufficient voltage when
using your own USB cable, make sure it is thick enough to supply a higher current. Also, the
host might shut down the port if the power consumed exceeds what it can provide. A low
power USB bus is limited to 100 mA.
Current Sense
The PhidgetAdvancedServo 1-Motor continuously measures the current consumed by the
connected motor The current roughly corresponds to torque, making it possible to detect
several scenarios.
By monitoring for no current, it’s possible to determine if the servo is not connected. It •
may not be possible to distinguish between a servo at rest and a servo not attached.
Stalled motors can be detected, by monitoring for the maximum current possible with your •
motor.
The position limits of the servo can be programmatically determined by moving the servo •
until it stalls against the internal or external stops.