our servo jitters and buzzes when it should be holding still

The provided documentation does not directly address why a servo jitters or buzzes when it should be holding still.

However, the documentation notes that every pair of servo ports (0-1, 2-3, and 4-5) shares a 2 amp limit, and exceeding this limit can cause power issues; plugging servos into every other port is recommended to avoid overloading a pair . Additionally, if you want to stop a servo from actively holding its position, you can use setPwmDisable() to turn off the PWM signal, which causes REV Smart Robot Servos and goBILDA servos to stop holding their position entirely .

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SDK Servos

Game Manual 0·CC BY-NC 4.0

The SDK offers several methods of controlling and communicating with servos, as well as a couple of hidden methods that can be easily accessed.

Servos are controlled via a PWM signal. PWM signal is one where the signal turns on for a number of microseconds, then off for a number of microseconds. Servos are controlled by sending variable length pulses every 20 ms, with the length of the pulses dictating what angle the servo should move to (or with CR servos, what speed it should move at). This length of the pulse, expressed in microseconds, is called the PWM pulse width. By default, the sdk generates signals from 600 to 2400 microseconds (with SDK 0 being 600 microseconds, and SDK 1 being 2400 microseconds). However, the expansion hub can actually generate between 500 and 2500 microseconds if the range is set manually.

Open Game Manual 0

Servo Usage Tips

Game Manual 0·CC BY-NC 4.0

goBILDA 6V Servo Power Injector — A Servo Power Injector (SPI) is a device made by goBILDA that boosts the voltage that the Expansion Hub provides to a servo. The Control/Expansion Hub's output for servos is 5V at 6 amps, and the SPI boosts the voltage to 6V and up to 24 amps total output. It works similarly to the original REV Servo Power Module, but with significant improvements to maximum output power and overcurrent handling to prevent failure.

Open Game Manual 0

SDK Servos > Hidden Methods

Game Manual 0·CC BY-NC 4.0

All REV hub servos are instances of ServoImplEx, which exposes some more methods to the user, such as setting the servo PWM range.

Note: There is no downside to using ServoImplEx, in order to convert a Servo to a ServoImplEx the user simply just needs to cast the Servo returned by the hardwareMap to a ServoImplEx.

Tips:

You can use setPwmRange() to increase the servo range to a maximum of 500 to 2500 microseconds. This changes the SDK mapping, with 0 becoming the minimum microseconds and 1 becoming the maximum microseconds. Increasing the range to 500-2500 can give more range when controlling servos that use 500-2500 PWM Range, such as goBILDA servos and REV Smart Robot Servo
setPwmDisable() and setPwmEnable() can be used to turn on and off the PWM signal to a servo. On some servos, this will cause the servo to de-energize and "turn off" with no holding power. Other servos may stay on and hold their position. Behavior will vary from servo manufacturer to servo manufacturer. It will also disable 5V power if the servo is the only one in its group of ports.

Tip: Both REV Smart Robot Servos and goBILDA servos will stop holding their position when setPwmDisable is called, regardless of if the 5v power is still on or not.

Open Game Manual 0

Choosing a Servo > Servo Range

Game Manual 0·CC BY-NC 4.0

The angle over which a non-continuous servo can rotate while retaining position feedback is called the range. When choosing a servo, it is important to make sure you have enough range for the movement you need.

By default, the FTC control system outputs 600-2400 microsecond signals. However, this range can be expanded to 500-2500 microseconds. When choosing a servo, it is important to make sure that its range will be usable for your application inside of 500-2500 microseconds.

Note: The default 600-2400 range of the FTC control system when selecting the "Servo" configuration limits the range of many servos to less than the advertised range. Make sure you select the "Full Range Servo" configuration instead to get the full 500-2500 range.

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Reading and Writing to Hardware > Examples of Using Common Hardware Components > Servo

Game Manual 0·CC BY-NC 4.0


Servo relicServo = hardwareMap.get(Servo.class, "Release Servo");

After instantiating a Servo, there are two main functions that can be called: setPosition() and getPosition().:


releaseServo.setPosition(0.75);
telemetry.addData("Release Servo Target", releaseServo.getPosition());

setPosition() sets the position of the servo. The SDK will use a built-in control loop with the servo's potentiometer to drive the servo to that position and hold that position. setPosition() takes in a double between 0 and 1, where 0 is the servo's lower limit of rotation and 1 is the servo's upper limit of rotation. Everything between is directly proportional, so 0.5 is the middle, 0.75 is 3/4 the way up, etc.

getPosition() does not return the servo's current position, rather its current target position. If a variable for the servo's current target position is stored properly, this function should never be needed.

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SDK Servos > General Explanation > 5V Power

Game Manual 0·CC BY-NC 4.0

All servos require a minimum of 5V to operate, and so the expansion hub generates 5V to power the servos. The 5V power is shared between pairs of ports (0-1, 2-3, 4-5). By default, this 5V power is OFF, and doesn't provide power. However, doing any servo operation, such as setting the position of a servo, will turn ON the 5V power to both shared ports. Calling disable PWM seems to turn OFF shared power, however if another servo is used or is active the 5V power will remain ON instead.

(Figure: An example of servo PWM waves. NOTE: Servo angles are arbitrarily selected and will not be accurate to all servos)

Warning: Every pair of two ports, (0-1, 2-3, 4-5) share the SAME 2 amp limitation, so care should be taken that pairs of servos do not pull more than 2 amps. Putting servos in every other port is recommended when possible.

Open Game Manual 0