Let's Make Robots!

RC car

As some of you may already know, I'm building an RC car which will ignore user input and prevent a crash when necessary. It'll run on an arduino platform. I'm waiting for my parts ATM and doing whatever I can on the chassis I already had (making a motor mount, making a deck to put the electronics on, fitting in a battery...).

All pics can be found here.


UPDATE May 5th, 2011

I just finished a 5V regulator to power my Arduino UNO board. Of course I kinda forgot Arduino accepts a voltage of 6-12 V. Stupid me. Going to mount the motor the the chassis and maybe cut out the deck.


UPDATE May 7th, 2011

Got the motor mounted, and tested it... Boy this thing is LOUD and powerful!

My mailorder arrived, trying some things out with the arduino. Love that thing already :D I'm still waiting for my other mailorder with 20 transistors and 2mm pin sockets for my H-bridge and my 2nd xBee. Will keep you guys up to date!

PS: I know the servo doesn't work with PWM, made a mistake.


UPDATE May 12th, 2011

Cut out the new deck and it rocks! There's just enought space between the base and the deck to fit the battery between them. Also, I've mounted the servo and tested the steering. I'm still waiting for those transistors :( 

Update 2: mounted the Sharp IR sensors, pictures are still here.


UPDATE May 22nd, 2011

Got my transistors and soldered toghetter my H-bridge... Now I only need to solder a 5V regulator and som pin headers to make all the connections to my µC. I'll keep you guys updated.


UPDATE May 26th, 2011

I completed the PCB which holds the H-bridge and a 5V-regulator. There is a problem with the H-bridge though... I use the BD911 and BD912 transistors in my H-bridge and they are not repsonding as I expected them too. More info in the fourth vid.

Datasheets on the transistors can be found here. Can anyone confirm that I should feed 5V to the base to make these things switch on/off?


UPDATE July 19th, 2011

Since I couldn't get the H-bridge to work, I just tested the system with one transistor and a potentiometer (see pic). I found out that I will need a transistor to drive every transistor in the H-bridge. Too bad all radioshack-like shops in the neighbourhood are closed for vacation at the moment. Seems this project will take a lot longer than expected. I was happy to see the wheels finally spinning though :)


UPDATE March 20th, 2012

Alright, this has been some time! I kind of lost my eye on this project for a few months, but now I'm back on it! I've just finished soldering up the motorcontroller (pic below) and am now going to start figuring out how xBees work and communicate, so that will take a while to complete. At the moment, I'm kind of doing two projects at the same time, so it can be another while before I update this.

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Check here


I did the same thing long time ago without using any microcontroller :-)

It was a fun and simple project. Looking forward to what you are going to do !

That car of yours look very nice! But this project is more a way into arduino for me so I wont go brainless on this one ;)

What is the deck made out of?  I spent some time looking into materials last night, and I came to the conclusion that there are a lot of options.

my preferred material was triplex because of its high stifness at low thickness. But I didn't have that so I used some scrap wood... I think it was the back side of an ikea closet one time

how did you calculate the torque for the propultion motor?

I see no use in calculating the torque. But if you want, I think it would be something like this: power=voltage*current. 'angular velocity'=2*pi*rpm. Torque=power/(angular velocity)

That should be about right :) if you can measure your voltage, current and rotations per minute, you can calculate the torque produced using the three formulas above. I cant measure my rpm's so I have no Idea about the torque.

it's so heavy that it does not move forward very fast and check this site out it shows how to build a r/c circuit for cars http://www.botskool.com/tutorials/electronics/general-electronics/building-rf-remote-control

Do you have the car posted here on LMR or do you have a picture of the motor? It really seems not that much...

my comps bust

It sounds like you are sending your PNP transistors the wrong voltage to turn them on. Or you are not "fully saturating" them to turn them on fully. Can you post a schematic of your h-bridge?

Your BD911 transistors are NPN, and the BD912 are the complementary PNP. The difference is that an NPN needs a positive voltage bias at the base to turn on, and the PNP needs a negative voltage bias at the base to turn on.

So you will typically see your NPN transistors at the "top" of the h-bridge with their collectors connected to the battery and their emitters connected to the motor leads. The PNP transistors will be at the "bottom" of the h-bridge with their emitters connected to the motor leads and their collectors connected to ground.

To turn on the motor in one direction, you need to send a positive voltage to the base of one NPN, and a low voltage (logic low) to the base of the PNP that is diagonally across from the NPN you are turning on.

If you are already doing this, then the issue is that you are partially turning on the PNPs, instead of fully turning them on. What value resistors do you have at the base of the transistors? You may need to adjust them to get the PNP fully turned on.

Oh, one more thing. There is a voltage drop from the collector to the emitter (Vce) of each transistor. So you feed 7.2V in at the top of the NPNs, but it is going to drop 1V to 3V (depending on how much current you are running through it). The PNP transistor diagonally across from the NPN provides the current a path to ground through the motor. When the PNP transistor is fully turned on (saturated), the voltage at its emitter will not be 0V, it will be between 1V and 3V (again depending on the amount of current). So the voltage difference supplied to the motor is going to be significantly less than 7.2V.

Try turning on your h-bridge as I described above (logic high to the NPN base, logic low to the PNP base) and measure the voltage you get across the motor. If your motor is pulling less than 5A, you should get a decent amount of voltage. If you are closer to 10A, you may have to use a higher voltage battery to supply your h-bridge.