Let's Make Robots!
tc  

My robot is a hacked RC car controled by an Arduino Duemilanove.   It has no sensors,  but I have left room on my chasis so I can add some more later when I feel more comfortable around Arduino.  Most of the time on this project was spent dealing with Arduino code and the motor shield.  

The chasis is a $7 RC car that I bought at Walmart.  Cheap enough, as I would soon find out.  After I stripped everything but the plastic frame,  I added a plexiglass flat top that I could place my arduino board and batteries.  

A sid view of the chasis

I had to trouble shoot a lot in the begining.  A good view of the control panel is shown here,  with the 9volt battery with an old modem connection tip,  the arduino with motor sheild,  and simple breadboard.  The breadboard shows when the shield has the brake command and which direction the motor is going.  

The plexiglass control panel attached to the upside down chasis

  Currently,  it can run fine off the floor,  but when placed on anything but wood, it does what I call stuttering, and doesn't move.  It even does it occasionally on wood as well.    This is after I soldered every wire from the motor to the board,  so I have ruled out a bad connection.   I believe that my problems (outlined in the video)  are due to not enough voltage to the motors,  but I am not sure how to add more voltage without overloading the arduino,  which maxes at 12v.  

 

I have fixed the stuttering problem,  thank to birdmun, by adding  4AA batterys to the motor shield.  Apparently,  the arduino can take multible voltage inputs of over 12v, which I did not know.   But now the cheapness of my RC chasis has sunk in.  Now the plastic cover that hold the motor and the gears does not properly latch, and the gears are not meshing correctly.  I have hit a dead end with this particular chasis, and I now plan to move on to a robot completely designed and built by myself.  

 

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Thanks birdmun! I had looked at some other robots and thought that might be it. But, do you know how I would add those 4 AAs? I can't take away the 9v, since the micro controller needs it. Woul I have to plug it into the vin pin on the motor shield, or would I set up something that connect the AAs to the motor but doesn't complete the circuit until a singal comes from the arduino? The only way I could think to do that is with some AOI logic gates.
birdmun's picture

You just need a minimum of, I believe, 7v to meet the voltage drop out of the voltage regulator on the arduino board. 6 AA alkaline batteries would give you 9v. 6 AA rechareables would give you 7.2v. Either option would be enough to give your robot power.

I can't speak to how to hook things up to the motor shield, because I am not very well versed in the arduino universe. I do believe I have heard mention of some shields having a jumper that allows one to connect an external source for the motors. If that is the case, you could keep your 9v and add a set of 4 AA batteries to power your motors.

birdmun's picture

Honestly, you should swap your 9v out for 4 to 6 AA batteries. 9v batteries are fine for powering your uC, but, they can't supply the current really required to move motors, and, if they can manage to move the motors, they won't be able to move them for long.

I would guess what is happening is, the freewheel current for your motor is pretty low. Low enough that the 9v can drive it. When you actually put a load on the motor, the 9v can't supply the current and the motor stalls out.

Thanks for bringing that to my attention!  I changed the settings,  you should be able to see it now.  

GeneralGeek's picture

Looks good, but I can't watch the video due to privacy settings... can you change it to public please?