Linear Servo

A linear servo acts the same as a standard servo but in a linear movement instead of rotational. There are two sizes of linear servos with two different speed and torque values.

Linear Servo Specifications (Click to Open)

Control Specs

Function	Value
Control Signal	PWM
Frequency	50 Hz
Motor Voltage	6VDC
Signal Voltage	5VDC
Wire Length	340mm
Connector	2.54mm Dupont 3-Pin Female
Operating Temperature	-10˚C ~+50˚C
Storage Temperature	-10˚C ~+50˚C

Mechanical Specs

Function	50mm 50N	50mm 200N	140mm 50N	140mm 200N
Stroke Length	50mm	50mm	140mm	140mm
Gear Ratio	63:1	150:1	63:1	150:1
No Load Speed	13mm/s	6mm/s	13mm/s	6mm/s
No Load Current	150mA	150mA	150mA	150mA
Max Efficiency Point Load	30N	75N	30N	75N
Max Efficiency Point Speed	11mm/s	5mm/s	11mm/s	5mm/s
Max Efficiency Point Current	360mA	360mA	360mA	360mA
Peak Power Point Load	66N	170N	66N	170N
Peak Power Point Speed	8mm/s	3.3mm/s	8mm/s	3.3mm/s
Peak Power Point Current	560mA	560mA	560mA	560mA
Max Force Load	95N	190N	95N	190N
Max Force Speed	5mm/s	2.5mm/s	5mm/s	2.5mm/s
Max Force Current	850mA	820mA	850mA	820mA
Stall Torque	150N	325N	150N	325N
Stall Current	1A	1A	1A	1A
Max Static Force	100N	190N	100N	190N
Weight	65g	65g	96g	96g
Stroke Repeatablility	±0.5mm	±0.5mm	±0.5mm	±0.5mm
Max Side Load	10N	10N	10N	10N

Programming

Programming the Linear Servo is similar to the standard servo however, the pulse width range must change. A standard servo operates with a range of 500µs to 2500µs. A linear servo has a rough range of ~800µs to 2200µs. We say rough range as every linear servo is a bit different (tolearnces).

JavaC++

//import the Servo Library
import com.studica.frc.Servo;

//Create the Servo Object
private Servo servo;

//Constuct a new instance
servo = new Servo(port);

/**
 * Modify the Pulse Width Range
 *
 * Parameters:
 *     - max: The max PWM pulse width in ms (2.1 in example)
 *     - deadbandMax: The high end of the deadband range pulse width in ms (2.1 in example)
 *     - center: The center pulse width in ms (1.5 in example)
 *     - deadbandMin: The low end of the deadband range pulse width in ms (0.95 in example)
 *     - min: The minimum pulse width in ms (0.9 in example)
 */
servo.setBounds(2.1, 2.1, 1.5, 0.95, 0.9);

//Can then use this mutator to set the linear servo position
servo.setPosition(position); //Range 0 - 1, 0 being fully retracted and 1 being fully extended

The mutator method will allow you to set the distance travel of the linear servo.

Calibration

To calibrate the linear servo and find the correct pulse width range for the bounds function a trial and error test is required.

1. Start with the linear servo fully retracted.

2. Set the minimum pulse width range to as low as possible (0.8) is a good starting point. Make sure the deadbandMin is the same as the min value for calibration. This can be adjusted later at your own descreation.

3. Start moving the linear servo with servo.setPosition(0.2); If the servo does not move increase the min number and repeat. If it does move, go to the next step.

4. Set the servo.setPosition(0); The servo should fully retract. If it does not lower or raise the min pulse value until it does. When complete repeat step 3 and 4 to ensure repeatablility.

5. Set the max pulse width range to around 1.9. Make sure the deadbandMax is the same value.

6. Move the linear servo with servo.setPosition(1); The servo will move as far as it can. Using a ruler verify if the linear servo has fully extended 50mm or 140mm based on the servo. If it has not slowly increase the max and deadbandMax until it does.

7. Verify that the servo will fully retract and extend without issue by using servo.setPosition(0); and servo.setPosition(1); If not repeat the steps above.

Note

Going outside the bounds of the linear servo will produce weird results. A slow and proper calibration will yield the best results.