Saturday, 3 August 2019

Powerful car jack linear actuator

Creating a powerful linear actuator by attaching a car jack to a motor is nothing new, but a lot of the demonstrations that I've seen neglect the fact that the point where the motor needs to mount to the jack (at the end of the threaded rod), will have movement both vertically and horizontally towards/from the middle of the jack. This makes it difficult to mount the motor in a fixed position.


So while this isn't a project in itself - it's a small part of a bigger project I'm currently working on, I thought I'd share my solution to this problem in case it is of use other others attempting something similar.


I found the best method is to focus on mounting the motor in relation to the threaded rod, rather than the jack, or the other frame/other parts of the project, as this is the only bit where the position remains relative.

The frame supporting the motor in line with the jack
(Jack body not illustrated)
This frame (yellow) goes around the middle of the jack, and hooks at the end over the threaded rod (green).

At the other end, the motor (red) is attached to the rod in order to turn it and mounted securely to the frame, allowing it to move with the rise and fall of the jack.


The downside to this mechanism is that the torque of the motor will cause the whole frame to rotate. This can be overcome by building the frame as close to the jack body as possible, to minimise the amount of rotation.


In addition, springs are mounted from the underside of the elevated surface to the frame, to add additional support and reduce vibration.

Electronically, the motor is driven by a H-bridge controller. Reed switches are mounted to the base - one on the base itself, another positioned in an elevated position to line up with the frame at it's highest point. Corresponding magnets are mounted on the frame, which line up with the reed switches to create a high level limit and low limit.

Control is currently provided by an Arduino with a single button input - each button press will either raise or lower the platform.

Code is below:

#define R_EN 13
#define L_EN 12
#define R_PWM 11
#define L_PWM 10

#define MAIN_SWITCH 4
#define LIMIT_LOW 7
#define LIMIT_HIGH 8


void setup() {
  pinMode(R_EN, OUTPUT);
  pinMode(L_EN, OUTPUT);
  digitalWrite(R_EN, HIGH);
  digitalWrite(L_EN, HIGH);

  pinMode(MAIN_SWITCH, INPUT);
  pinMode(LIMIT_LOW, INPUT);
  pinMode(LIMIT_HIGH, INPUT);


}

void loop() {
  if (digitalRead(MAIN_SWITCH)==HIGH) {
    runProcess();
    
  } 

}
void runProcess() {
  if (digitalRead(LIMIT_LOW) == HIGH) {
    while (digitalRead(LIMIT_HIGH) != HIGH) {
      lift();
    }
    freeze();
    return;
  }
  if (digitalRead(LIMIT_HIGH) == HIGH) {
    while (digitalRead(LIMIT_LOW) != HIGH) {
      lower();
    }
    freeze();
    return;
  }
}
void freeze() {
  analogWrite(L_PWM,0);
  analogWrite(R_PWM,0);
}
void lower() {
  if (digitalRead(LIMIT_LOW) == HIGH) {
    freeze();
  } else {
    analogWrite(R_PWM,0);
    analogWrite(L_PWM,255);
  }
}
void lift() {
  if (digitalRead(LIMIT_HIGH) == HIGH) {
    freeze();
  } else {
    analogWrite(L_PWM,0);
    analogWrite(R_PWM,255);
  }
}


Demo Video 

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