DFRobot 4WD Arduino Mobile Platform Review

Hi Scott, I found your post about the DFRobot very helpful. I'm thinking about getting one soon and this was full of great info. I'm still a newbie so I have a couple of questions...

In your post, you say "The Motor Shield has a max current of 1.2 amps per motor. I did some testing and couldn’t get the motors to pull more than 700mA so I should be OK, but it is something to consider."

Can you elaborate on that? Specifically, 1) do you want each motor to pull more than 700mA and if so why? 2) Why is it something to consider? 3) Is the lower amperage affecting the bot''s ability to carry a heavier load or move faster?

One other question... what is the possibility of using stronger motors?

Thanks for your insight!

Hey Doug, I'm glad you found the post helpful!

I'm a newbie to much of this myself, but I think I can answer your question: Basically, the less amperage the motors pull the better. Ideally you want to remain as far below the current limit of the motor shield as possible. As you start to get closer to the 1.2A peak (and 600mA operating) limit, you run the risk of burning out the motor driver chips on the shield. I mentioned it as something to consider because although it appears to be working well for me, I am getting close to the current limit of the motor shield and your mileage may vary.

There's definitely a relationship between motor speed and voltage. Basically the higher the voltage the faster the motors spin, but the trade off is that the motors draw a proportionately larger amount of current. Push it too far, and the motor shield simply won''t be able to handle it and the driver chips on board will burn out.

As I said, I'm a bit of a newbie myself so I can't offer anything more scientific than that. I discovered what worked best for me by basically piling some weight on the base, and powering the motors with my variable voltage power supply. I checked to see if it could carry the weight, and use a multimeter to check how much amperage was being pulled by the motors at different voltages.

If your interested, I'll be posting over the next few weeks / months about the build of my robot here:

Pedro2 build log

i was wondering what code you used to make one side go slower then the other i am trying to do the same with a tank style, at current it rips the treads off...

any ideas on how to keep the wheels on? mine keep falling off.....smoothing out any jitter has helped and not letting the robot yaw too much helps but fed up with the wheels coming off.

I would think that weight may be an issue with turn, I've got stationary turns and moving turns working as a tank ie opposite direction for stationary or slow dow one side speed up the other for moving turns. But I am using newer solarbotics standard motor with 6.5 V to the motor driver.

I would also advise on suppressor caps on the motors, they will also add some life to the motors. I''d be aiming at 6- 7.5 Volts for the voltage to the motors. Some drivers will drop some and so the voltage at the motors is less than suppplied.

Have fun with Pedro!

Dave

Hi Scott, great article. What are you using for power? I''m having a heck of a time getting these motors to work on battery power.

Great post. I''ve built pretty much the same thing, DFrobot 4wd, Arduino UNO, and Adafruit motor shield. I get movement and turning, I''m just trying to fine tune my code for more control.

What i have noticed is that when i define my 4 motors independently like this:

#define motors
AF_DCMotor motorRF(1, MOTOR12_1KHZ);
AF_DCMotor motorLF(2, MOTOR12_1KHZ);
AF_DCMotor motorRR(3, MOTOR12_1KHZ);
AF_DCMotor motorLR(4, MOTOR12_1KHZ);
...

I seem to get delays when i change the motors speeds

motorRF.setSpeed(255);
motorLF.setSpeed(255);
motorRR.setSpeed(255);
motorLR.setSpeed(255);

The delays are slight. I would say about 500ms between the time motor 1st and motor 4th spin up. In your setup do you see a similar delay, or have you done something to sync the motor starts.

I''m looking to put encoders on my wheels and worry that navigation tracking will be off if I end up dragging an encode wheel.

appreciate any help or referrals to information.

Chris

yessir! Thank you for the tip about the caps on the motors. Was just assembling my chassis today and the soldering iron is warming up. Now, I hope I have a few of those laying around. Also, thanks for the heads up about turning this chassis. Saved me the effort!

What is the dimensions of the motor enclosure, I know the overall dimensions of the kit but im planning on using a SBC mini2440 for my robot. how high is the secondary "shelf" off of this motor enclosure top surface? Your site has been a big help. Thanks!