Make Your Own Giant Servo -- Episode 442

Are you looking to move the load to known positions with a servo? It sounds like you want to move something that continuously rotates. How long is the lever arm of your design? 2-3lbs could be lifted by a tiny motor if it's only 1cm out, but things get much harder (i.e. more expensive) if you need to move something at a large radius. I wouldn't worry about specific motors/parts at this point. Right now, defining your objectives in detail will determine what parts/design can satisfy your goals. So:

• What is the maximum weight of any object that you intend to move? (Keep in mind the mass of the arm/wheel itself)
• What is the maximum distance of load from the axis of rotation?
• What is the maximum speed you need to rotate? (Does acceleration matter? Does is need to change directions at all or infrequently? How accurately does the RPM need to be kept?
• Budget?

Thank you for responding,

I do not actually need it to be as large as your project was but the principal is the same as where you used water, I won't be using water but it will only be about 2 - 3 lbs so a lot lighter. As for speed, Yours was only doing half rotations so I am not sure how to figure the RPMs on that but the speed I am looking for I would say 120 - 180 RPMs (or 120 - 180 of the arm going to its down most position per minute) if that makes sense. So from the research I have been doing, i think I would need an electric motor obviously, a power supply (I'm assuming I will need an AC to DC converter), speed controller, and a body to hold it together but I can manage a body myself. A problem I have found is that I do not know what speed controllers and power supplies will work with any given motor. Sorry in advance as I am not that familiar with working in this area so that's why I am looking for help and advise.

Hi Scott,

My design is actually quite terrible and the software was never properly finished, so I don't recommend using it for anything. Do you have more specifics for your build? How much does your water actually weigh? How fast is "faster?"

I can recommend different off-the-shelf servos or other actuators that may be what you need.

Cheers,

DJ

Hello, i am currently doing research on building a mechanism similar to what you built in the vid. I am new to all this stuff but I could use something just like it for a purpose like when you did the test of it pulling up the container of water only a bit faster and would only need to hold a couple pounds really and I don't think I would need it as large. I dont know how to build this or the names of the parts i would need so any help would be greatly appreciated.

okay so before watching this video, I tried to do this using a PID controller sketch and the Arduino. Failed miserably. What I am trying to do is control a dc motor using a potentiometer but also having a potentiometer on the motor to get the current position of the motor.(like seen in this video)

Here is my setup.

12v Wiper motor.(12DC motor with Gearbox)

10K pot connected to arduino (pin A0)

A motor driver (BTS7960) connected to arduino (pin 5 and 6)

10K pot connected to arduino (pin A1)

I tried to get a set up like this video (https://www.youtube.com/watch?v=3pYWLF8qw-g&t=753s)

just without the radio controlled components.

He was using the pid library from the arduino example libraries.

Here is my code:

#include <PID_v1.h>

#include <PID_v1.h>  //PID loop from http://playground.arduino.cc/Code/PIDLibrary

#define PIN_INPUT A0

#define PIN_SETPOINT A1

double Pk1 = 1.0;  //speed it gets there

double Ik1 = 0;

double Dk1 = 1;

int deadZoneX = 50;

double Setpoint1, Input1, Output1, Output1a;    // PID variables

PID PID1(&Input1, &Output1, &Setpoint1, Pk1, Ik1 , Dk1, DIRECT);    // PID Setup

void setup() {

  pinMode(PIN_INPUT, INPUT);

  pinMode(PIN_SETPOINT, INPUT);

  pinMode(5,OUTPUT);

  pinMode(6,OUTPUT);

  Serial.begin(115200);// Start the serial monitor.

  //initialize the variables.

int curPos = analogRead(PIN_INPUT);

int comPos = analogRead(PIN_SETPOINT);

Input1 = map(curPos, 0,900,-255,255);    

Setpoint1 = map(comPos, 0,900,-255,255);

  PID1.SetMode(AUTOMATIC);              // Turn on the PID and set limits.

  PID1.SetOutputLimits(-255, 255);

}

void loop() {

int curPos = analogRead(PIN_INPUT);

int comPos = analogRead(PIN_SETPOINT);

Input1 = map(curPos, 0,900,-255,255);    

Setpoint1 = map(comPos, 0,900,-255,255);

      PID1.Compute();

      Serial.print("Current Position: ");

      Serial.print(Input1);

      Serial.print("     ");

      Serial.print("Commanded Position: ");

      Serial.print(Setpoint1);

      Serial.println(" ");

      Serial.println(Output1);

      Serial.println("");

      Serial.println(Output1a);   

      Serial.println(" ");

      Serial.println(curPos);

      Serial.println(comPos);

      if (Output1 > deadZoneX) {

        analogWrite(5, Output1);

        analogWrite(6, 0);

      }

      else if (Output1 < deadZoneX) {

        Output1a = abs(Output1);

        analogWrite(5, 0);

        analogWrite(6, Output1a);

      }

      delay(20);

  }

If you start with the data sheet for the DRV8871 and mash that up with a analogue input example for the arduino you'd soon be able to recreate what DJ has done.

hey MAN where is circuit diagram?

crikey mate, you come with some CRAZY! ideas!

I recall 'Scrapheap Challenge' converting some cars to R/C control a while back.

But why not think big ?

Liebherr 9800 excavator controlled via Lego Technic control:

https://www.youtube.com/watch?v=njgDC-HTKrM

next stop: build an RC car scale t othe servo meaning 1:1 sacle to a real car, but its constructed like an rc car and works exactly the same....wow that would be a grave for some dollaridoos...and possibly lethal o nthe streets...