Actuators and Motor

Description and Function

Elcano uses linear servos (actuators) to control steering and brake hardware. An electric bicycle hub motor drives the rear wheel.

Parts and Materials

  1. 2in linear servo (braking)
  2. 4in or 6" linear servo (steering)
  3. servo mounts
  4. linkage hardware to connect servos to brakes and steering
  5. electric bike conversion kit
  6. power subsystems (batteries, connectors, wiring) for servos and motor

Detailed bill of materials: https://github.com/elcano/elcano/blob/master/Documentation/Elcano_BOM.xls

Steering System

There are two main steering signals:

1. Signal Out is a 1 to 2 ms pulse sent from the Arduino to control the steering actuator.

2. Signal In is a 5 V analog feedback signal that gives the pointing angle of the wheel. This is covered under Sensors.

The linear steering actuator on the Catrikes https://www.servocity.com/motors-actuators/linear-actuators/heavy-duty-linear-actuators has 25 lb. thrust with either a 4 or 6 throw.

The brake system is essentially the same as the steering system. The same actuator with 2 throw is used to pull both brake cables. The Catrikes have disk brakes on both front wheels and no brake on the rear. This actuator is expensive, and too many of the brake actuators have failed. The failure rate on steering actuators is lower.

The steering actuator is powered by 12V DC. It produces 5V DC which can be used by other equipment. Steering is controlled by sending a pulse to the actuator. A pulse width of approximately 1 ms will cause the actuator to fully extend (right turn on Catrike). A pulse of about 2 ms will fully retract the actuator. A pulse of 1.5 ms will keep the vehicle pointed straight ahead. There is some variation in these voltages; thus the Catrikes have a mechanical adjustment for fine-tuning the position for going straight. Typically there are about 30 pulses per second; the exact rate does not matter. At 12V, servo operating speed is 56mm/s with no load or 35 mm/s at maximum load.

The actuator interfaces to the Arduino over a three wire servo connector that is standard for RC planes and cars. The three wires are Signal Out, Ground, and Power. The power wire is not used since both the actuator and Arduino have their own sources of power. The actuator is fused for 5 Amps and has blown fuses. Be careful not to drive it beyond physical limits.

Assembly and Configuration

Links and Resources

Other linear servos: https://www.servocity.com/servos/heavy-duty-linear-servos

-- JosephBreithaupt - 2017-05-05

Topic revision: r2 - 2017-12-21 - TylerCFolsom
 
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