~ ANSWERED ~ If this is a repeat, my apologies - 4 servos all turning at once with one potentiometer...This is NOT the way the project is to work. Please help

Question

Hello all, I am working on a project with 4 servos, and 4 potentiometers. I will include my coding momentarily. Here is my dilemma. As the title states: "4 servos all turning at once with one potentiometer...This is NOT the way the project is to work." The project is to turn each servo unit with its own potentiometer (dial style). I have compiled my coding and it all comes out ok, I then upload it with no issue. I then attempt to turn the pot and all 4 turn, and if I may add, with quite a bit of jitterness. Can you please take a moment, look at the code and advise where you think the problem is. This code was the KNOB example from the Arduino UNO example library. I removed the name of the person as I have continued to add to the program. You will see the things I have added as I have notated them. Thanks in advance, Anna Now the code: #include <Servo.h> Servo myservo0; // create servo object to control a servo Servo myservo1; // i added Servo myservo2; // i added Servo myservo3; // i added int potpin0 = 0; // analog pin used to connect the potentiometer (i added the zero to the potpin before the equal sign) int val0; // variable to read the value from the analog pin int potpin1 = 1; // i added int val1; // i added int potpin2 = 2; // i added int val2; // i added int potpin3 = 3; // i added int val3; // i added void setup() { myservo0.attach(3); // attaches the servo on pin 3 to the servo object --- I changed it to 3 from previously 9 - Anna myservo1.attach(5); // i added myservo2.attach(6); // i added myservo3.attach(9); // i added } void loop() { val0 = analogRead(potpin0); // reads the value of the potentiometer (value between 0 and 1023) val0 = map(val0, 0, 1023, 0, 179); // scale it to use it with the servo (value between 0 and 180) myservo0.write(val0); // sets the servo position according to the scaled value delay(15); // waits for the servo to get there val1 = analogRead(potpin1); // i added val1 = map(val1, 0, 1023, 0, 179); // i added myservo1.write(val1); // i added delay(15); val2 = analogRead(potpin2); // i added val2 = map(val2, 0, 1023, 0, 179); // i added myservo2.write(val2); // i added delay(15); val3 = analogRead(potpin3); // i added val3 = map(val3, 0, 1023, 0, 179); // i added myservo3.write(val3); // i added delay(15); } Message was edited by: Annasta Brandon
My project question was answered, now on to part 2... 

 http://www.element14.com/community/thread/24030

mcb1 · Accepted Answer

Annasta

From your message above, it appears the problem has been resolved, and you now have a few minor wiring concerns.?

If you have followed your excellent drawing, and you seem to want this to be the final method of connections, can I make some suggestions.

1. The power for each of the servos, could go onto the power rail, eliminating two jumpers per servo (total 8)

2. The power for the pots can go onto the 5v power rail eliminating two jumpers per pot (total 8)

3. The 4x ground wire you have connected between the pot side and the servo side, can be a single wire from the second ground pin on the Arduino to the servo ground rail.

This ensures that any noise is sent to the Arduino ground and not mixed into the pot information to cause extra jitter.

The end game is to get the body of the capacitor as close to the servo motor as possible, but if the size prevents that and you need wires added onto them, then so be it.

Generally you try to remove as many joints as possible, hence the suggestion above which removes 16 extra joints.

Your capacitors can still go across the servo power rail just next to the wires going off to the servo, although I suggested you should only need 1 at 1000uF.

Generally breadboards are not designed as permanent wiring, and it should work without resorting to rubber cement.

You may find that if the component/wires are not shiny, they don't make good contact, and plugging them in and pulling them out a few times tends to improve their contact with the breadboard.

So can you please modify the first message to include ANSWERED and give Chris ( http://www.element14.com/community/message/76244#76244 ) and John (http://www.element14.com/community/message/76250#76250 ) the points for solving the problem.

Thanks

Mark

e14 Contributor · Answer

Anna, Mark's final question is the one the one that I'm still not clear on. Bill, servo 'standards' are really quite loose and there is no completely accepted standard. Most are close enough to be interoperable. The two biggest radio manufacturers have 1500uS and 1520uS as their defined centre point. Even this is not always true, as some specialised type have a shorter mid point e.g. 760uS so that the updates can be faster. This would be the case for a tail servo for a helicopter where the gyro needs to update quickly to give a good tail control. Normal update rate is about 50Hz but most digital servos will accept faster than this. Analog ones will burn out. As far as I know, all servos will give a change of output position of about 90 degrees for a change of input pulse of 1000uS. This is subject to manufacturing tolerances. Due to manufacturing tolerances it is not possible for this travel to be at the ends of the internal feedback pot so that they will travel beyond + and - 45 degrees of neutral if the input signal extends beyond the + and - 500uS of the nominal neutral. Exactly how much depends on the individual servo. I do not see any advantage in trying to use this extended range as if the servo motion is being converted into a linear motion by say a push rod, then beyond+/- 45 degrees the motion becomes very non linear. Radio control sets will use a little of this extended travel to allow trimming of the centre position to compensate for manufacturing tolerances in the servo and in the model setup. I have just tested a random sample of the 40 odd servos of various makes and types that I have and they all conform to these numbers. (judged by eye) In practise the difference between 1500 and 1520 neutral is unimportant as some form of trimming is usually needed. However there may be strange ones out there, some early ones I beleive had a neutral of about 1300uS. For anyone not sure the difference between analog and digital servos it is in the processing and drive of the motor, not the form of the input signal. (Other than the rate as mentioned above) Chris

mcb1 · Answer

Annasta I think the servo library documentation gave a hint as to what pins to use, and I believe they were the ones handling PWM. re capacitors The general rule with any power supply is you have 1000uF per amp. Assumming your power supply has some capacitors, then 1000uF should help. You place them between the 5v of the servo supply and ground as close to the servo as you can. You may get a way with 4 x 470uF across the 5v and gnd at each servo, and it will work. Do you have access to any capacitors. (They need to be greater than 5volts).? Your drawing shows the final configuration with 4 pots installed. I don't suppose you've tried it with all 4 connected.? Mark

e14 Contributor · Answer

you have: int potpin3 = 3; // i added ... myservo0.attach(3); // attaches the servo on pin 3 to the servo object --- I changed it to 3 from previously 9 - Anna both apparently attached to pin 3.

~ ANSWERED ~ If this is a repeat, my apologies - 4 servos all turning at once with one potentiometer...This is NOT the way the project is to work. Please help

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