Let's Make Robots!

Motor wiring for Start Here Robot

Hello from a new member!

This is a great site - just what I needed. I just finished building the Start Here robot and... it worked!

Looking at all of the datasheets, I am confused by why the motors work.

I would have expected them to be driven off of digital pins 4-7 from area F (using the diagram at http://letsmakerobots.com/node/75).

They are wired in area G (the 2 A/B pin out areas).  This was the plan but (q1) how did the output get there from pin outs 4-7?  The Picaxe project board data sheet just shows 4 circles there without any description.  I assumed it had to do with replacing the Darlington IC with the Motor IC but I couldn't find any documentation about that on the motor chips data sheet.

(q2) If I had left the Darlington chip in would the digital pin outs (area F) now work?

(q3) Can I use the additional power source (V2) for these area G (A/B) output pins without additional wiring (except for adding the additional V2+/gnd)?


PS I had a few other issues with the motors but solved them myself. In case any other beginners have the same thing, here's what happened.

First, the robot turned to the right because one motor was more powerful than the other. I read elsewhere in here that one of the motors could have been wired backwards so it was really in reverse. Of course, with the programming, this was overcome. But reverse might now be as strong as forward... for what it was worth, I attached a voltage source to each motor and determined that one was wired in the opposite direction and... it fixed that problem.

Second, the robot was a lot slower than Frits' -- I found that there should have been a jumper closing off the 2nd V2 power source. It's in the picture of his robot but my board didn't come that way. Maybe I missed the instruction but, putting that in, speeded up the robot.



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q1 -- so if I took the motor chip out, would the pixaxe be able to control the motors by attaching the motor leads to pins 4-7 (it would seem like I'd need 8 leads - pins 4-7 + and a ground lead???

q2 - yes - my mistake.

Thanks for your fast response!

Not really. The I/O pins on the Picaxe cannot handle that much current. That's why you use a motor driver.

The Darlington chip serves a similar purpose. It can sink a lot of current, much more than the digital I/O pins on the Picaxe can. So you can use it to switch loads that the Picaxe cannot handle by itself.

(Answer to q1) The board runs digital outputs 4-7 through the motor driver and outputs on the A/B pins. You can still access digital pins 4-7, but realize that if you have the motor driver inserted, if you try to use pins 4-7 for something else, you will also turn on one or both motors.  Note that you did not replace the Darlington with the motor driver. You replaced the Darlington with the resistor pack.

(Answer to q2) You should have a resistor pack, or at least a single resistor in the Darlington slot. If nothing is inserted in that slot, Area F will not work. Area E is directly connected to the outputs of the Picaxe chip. Note you can place a single resistor in the IC slot across Area E to Area F if you just need to interface one pin and need some current limiting for protection.

(Answer to q3) Yes. You can separate V1 from V2 by removing the jumper and providing a second power source on V2. When you do this, the L293 motor driver gets its logic voltage from V1, but provides motor voltage from V2. The ground (G) is shared by both V1 and V2. Be sure you connect the grounds of your two power sources together.