RC Power Wheels

[Tom]

Hello,
I just joined the forum and am anxious to see if I have finally found the right place to get some guidance and work through what I think is a pretty cool project.

Long and short. I am working on building a RC car from a Power Wheels car (the child’s toy). Its going to have some other bells and whistles like collision detection, onboard camera, and some streaming onboard stats. The stats will be displayed on a tablet or PC along with the video and possibly a GPS overlay. To facilitate all of this I would like to use a microcontroller.

I am really just getting started and have the idea to use a generic RC system (Tx and Rx) integrated with a microcontroller to handle the drive and steering control. I looked every where (but here) to figure out what the signal was on the output of the receiver, but had no luck. So I bought one and connected it to an o-scope. I thought it was a Manchester coded signal, until I found this site. Thanks very much it saved me money, time, and aggravation.

My question is, has anyone integrated a receiver with a microcontroller? I am not sure how to handle the signal right now or even what it is called other than it resembles a PWM signal.

Thanks in advance,
Tom

[SuperDroid]

Tom,

Thanks for joining!

Radio Control (R/C) is one-way analog communication. If you wanted to stick with this, you would need two transmitters and two receivers to send information back. A more elegant solution, especially since you want to use a microcontroller, would be to start with either an xBee solution, or a simple WiFi setup. This will allow you to send commands and data back and forth from your computer to your robot.

Suggested Reading:

• General information on radio control
• General information on wireless robot control

Suggested Items:

• Arduino Uno (MCU-050-000)

• xBee Shield (MCU-064-000)
• xBee (TE-204-AWI)
• xBee USB Adapter (TE-203-USB)

• WiFi Shield (MCU-063-000)

[Wyldhunt]

Tom,

I agree with everything Jason said. I started out with a very similar idea, and it took me a while to figure out why it was a bad idea for a beginner.

Here is an Instructable on getting an Arduino to work with a RC Receiver:
http://www.instructables.com/id/RC-Control-and-Arduino-A-Complete-Works/

I haven’t looked at it very close, so no guarantees about it working or not.

You’ll notice that it takes a lot of code to make very basic functions work from a RC Receiver…
If you go with WiFi or xBee, you’ll be able to send packets over Tx/Rx without having to decode a bunch of PWM, and you’ll be able to customize exactly what you’re sending/receiving. There won’t be any guessing about what a specific character means.

A few other random notes:
Many RC vehicles pivot the front wheels to turn the car. Skid steering (Turning like a tank) is much preferred in robotics because it is so much easier to control. If you get in to robotics, and decide that you want the car to drive itself and track where it’s at, you’ll run in to problems with normal steering.
What angle are the wheels turned at? How far do I have to drive to turn 90 degrees? How far forward has my robot traveled while trying to turn 90 degrees? How far away from the wall does my robot need to be before it starts its turn?

Also, transmitting video is always a fun thing to do. I recommend that you don’t try to buy a camera and feed it through your robot controller for processing or transmitting. It takes waaay too much processing power to make it viable for most projects. You can get some controllers to work with video, but you’d need that robot controller to be dedicated to only handling the video feed.
It’s easier (And generally cheaper) to buy an IP camera that already has WiFi built in to it. That’ll let you watch it on your phone/PC much easier also.

Even more: Expect to give up on keeping the RC vehicles shell along the way. Once you start trying to fit controllers and sensors and cameras… The shell never fits. At best, you might be able to do some fancy work with a rotary tool and cut holes in the shell as needed… But, I’ve never had very much luck with that.

Good luck
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[Tom]

Thanks for the encouragement and information WYLDHUNT, truly much appreciated. I was probably not clear enough on a few details, so allow me to clarify.

I had planned to have three different communication networks; PC to microcontroller Wi-Fi, RC tx/rx (with wired communication from rx to microcontroller), and separate wireless IP camera.

Since I posted this a few days ago I determined (and you have concurred) that using the RC system was going to be disjointed and clumsy. I am leaning toward using a game controller with USB connection to the PC and then pushing that message to the microcontroller via wi-fi. I should add that I will probably be using a Freescale Tower microcontroller system because I already have one and am somewhat familiar with C language.

Trust me space under the shell won’t be a problem, do a quick web search for Power Wheels cars. The steering is a concern, but not as much because the car is not going to be autonomous. If I did do the steering with the rear wheels I would need to come up with some way to control how the front wheels turn. I have seen some other folks use a linear actuator to control the steering, that is the route I plan at the moment, but we’ll see : )

Thanks again, I’m sure I will have plenty more to ask!

[Tom]

Thanks for the warm welcome and advise Jason. As you can see from my reply to WYLDHUNT, I am moving in the direction you are suggesting. Also thanks for the links to resources, very much appreciated. I am sure I’ll be back with more questions.

I think I should also mention that this is the first forum that actually responded to any of my questions; Hats off!!

[SuperDroid]

That Freescale tower system looks really nice! I will advise that the card edge connectors do not handle well with wheeled robots. I’ve seen them wiggle lose quite often. If you want to stick with that platform be sure that you secure the sides together tightly.

For steering, you may want to take a look at this blog post I made a few weeks ago. You could chain the steering column to a motor and have some limit switches trip when you go all the way one way or the other.

Turning a motor into a linear actuator

[Tom]

Thanks for the information. I had already put a little thought into this and have already purchased a linear actuator with feedback. Here is the link to the site http://www.pololu.com/product/2319 and the part number Concentric LACT4P-12V-5.

I want to use a PID loop to control the steering and drive motor speed, so I decided to go with the linear actuator above and I plan to use a Hall effect switch to get a RPM signal from the drive train.

Any suggestions for some information on a script or other application to pipe the signal from the game controller (USB connection to the PC) to the Wi-Fi port on the PC?

[Author]

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