Let's Make Robots!

Question about ground (first robot) and dual H bridge

Hi everybody,

I finally built my first robot, loosely based on the start here tutorial and obviously I have tons of question.

This is the motor driver I am using : http://www.geekonfire.com/wiki/index.php?title=Dual_H-Bridge_Motor_Driver

and in the examples the ground of the motor driver is not connected to the arduino's ground.

Is it correct ? Or should I anywway connect both grounds together ?

Also I have a question about the batteries,

I am sorry about that I read a lot about on the forum and I am just more and more confused.

Currently the arduino is powered with 6x1.5v (9v) and the motors with 4x1.5v, which is a lot of batteries I think.

Can I connect both the arduino and the motor driver on the 6x1.5v pack ? I my dual H bridge good enough to handle that ?

Thank you


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Thank you I understand better how to connect them together now, I have yet to experiment all these ideas.

I wonder if I can also power the motor driver directly from the arduino, instead of the other way around, as Maxhirez suggested.I tried to connect the arduino's 5v pin  to the vms and both ground together, but the results were not so good.

I have a bug, I am not sure why it's happeining, I think I connected the servo straight to the 6v battery(I plugged it to the vms and grnd)  and now it is acting weird, whit another servo it seems to work fine. I will have more experimentation to make to be sure of what is going on anyway.

@Oddbot, I was refering to the first example concerning 2 dc motors connected to the motor driver unit.And the robot has been working quite well until know without connecting the grounds together.I will use 7.2v Nimh, I found out they are standard rechargeable betteries and should be easy to find.

I have some of these and will buy some more (6 should be fine) : http://dx.com/p/gp-1-2v-2700mah-ni-mh-rechargeable-aa-batteries-2-pack-41118

Not sure it is the best place to ask, but I'd like to add a camera to the robot, if possible something cheap to begin with, I would be glad if you could share some link to tutorials concerning cameras and transmission to the computer....

Thank you so much 





I wonder if I can power the motor driver directly from the Arduino...

Remember that your h-bridge actually needs two power sources, logic line and motor. What this unit does is split them from a rail into the two sources and regulate them with the option to send the 5v regulated line out to something else. The Arduino does something similar, which means if you send 5v to the motor control unit it will be trying to drop the power down from that. Conventional wisdom is that this shouldn't work, but we've been surprised before. See http://letsmakerobots.com/node/34894. You will most likely get very unsatisfactory results-motors generate noise that micro controllers don't like back into the circuit, and at that point, beginners usually begin questioning their programming, when separating the power sources is usually all it takes.

With this unit you can run the 6v into VMS and Gnd and power the Arduino from the 5v out directly into the Arduino Vin without too much trouble. It simplifies the signal path. Yes, do ground the Arduino to the driver.

I am not sure what example you are refering to but if you do not link the grounds then the signals from your Arduino have no return path. You need to connect the grounds or it will not work.

You should be able to power it all from 6xAA batteries. The motor controller is rated at 35V according to their specifications. I recommend using NiMh batteries as they can deliver more current and being rechargeable they are cheaper in the long run.

The NiMh batteries will give you 7.2V which is slightly less than the recommended 7.5V for the Arduino but it will still work fine and your Arduino's regulator will not get so hot.