Converting a Wired Remote Robotic Arm to Arduino Control

Hi All,

Just bought the Arduino Uno and have completed the projects in the "Make" book to get started.
Apart from that, very basic understanding of electronics - so excuse my ignorance please!

I am trying to convert a very cheap ($49 AUD) Robotic Arm kit (see attached image "arm") from wired remote control (see image "remote") to Arduino control (I will worry about the programming latter, just trying to get the wiring in place).

See attached image of the circuit diagram for the remote and arm "circuitdiagram". To keep it simple, I plan on connecting the ribbon cable from the arm to one side of the breadboard using the existing 3V power (this is coming from 4 x D size batteries contained in the arm). On the other side of the breadboard I will connect Arduino. Please see attached "breadboardlayout" for what I had in mind.
The little squares on the board are supposed to be relays of some sort.

My questions are:

  1. Does this seem like a reasonable approach or am I totally on the wrong path?
  2. If this is an acceptable way to proceed, are there such relays available or is there some other form of electronic switching I could use? I know that for the 5 motors I will need to be able to command the switch to be ON positive or ON negative with a rest state in the OFF posititon (or at least be able to command it to OFF). For the light, I merely need to be able to connect it to positive or negative like a switch.
  3. Please advise on the Arduino side of the board. Are resistors required? Will this depend on the relays used? Totally at a loss when it comes to calculating resistance etc. on a circuit like this so, again, please excuse my ignorance.

Thank you for any advise or pointers you can offer!

Dan.

arm.JPG

I have done up the attached breadboard layout using SPST relays as an alternative.
Does this look more realistic?

Does this look more realistic?

No.
Only a very few relays can be switched directly from an Arduino pin. The current limit should be 40mA so if your relay pulls more than that then you need a transistor.

In any event you need a reverse biased diode across each relay coil.

Thank you for your response Grumpy Mike,

O.K. I am trying to learn about Reverse Biased Diode, as I have no idea what that is!

Would this relay suit:

12V SPST Low Cost Reed Relay

Small and light weight.Specifications:- Contact form: SPST normally open- Coil Resistance: 1050ohms- Nom Volts: 12 - Pickup Voltage: 8.4V DC- Rated Current: 11.4mA - Allowable Voltage: 160%- Dropout Voltage: 1.2V DC - Carry Current = 500mA.- Power Consumption (W): 0.1 - Contact Rating: 1A- 12 VOLT

http://www.jaycar.com.au/productView.asp?ID=SY4038&form=CAT2&SUBCATID=979#1

Would you suggest a different approach than what I am trying to do?

Thanks Again!
Dan.

Would this relay suit:

Well it is not the best. It requires 12V to drive it, do you have 12V?
If so then you will also need a transistor and diode. Look at the first diagram here and replace the motor with your relay coil.

http://www.thebox.myzen.co.uk/Workshop/Motors_1.html

You might use relays like below to control the motors. You would need two relays for each motor.

reversemotor.jpg

Someone has done what you're looking to do. I've done this before following these instructions and code. The motor controller used in this example has 4 outputs, so you'll need another of some kind for the 5th, since the arm has 5 motors. But this will get you started at least.

Thank you Zoomkat and Allanonmage,

Appreciate your feedback! The relay shields available at my local store don't seem as good, so I will order one in and try that.

Out of interest, being that the motors are only 3V - would there be any advantage / disadvantage to using MOSFETS instead of relay shield such as in this video:

Dan.

If the motors need to be bi-directional you would need 5 H-BRIDGE circuits to do it, but using DPDT relays you can do it with 5 relays but then you wouldn't have speed control using PWM.

PWM CONTROLLED H-BRIDGE

Unfortunately 3V is too low a motor voltage to use an L293 chip.

but using DPDT relays you can do it with 5 relays but then you wouldn't have speed control using PWM.

The motors also would always go to the end of their travel with no stopping in between.