Let's Make Robots!

Goodwill Goods

So, I went to Goodwill the other day and went straight to the toys sectons.  I found an RC car without the controller for $2.  I bought it, took it home, and ripped its guts out, leaving the motors.  It wasn't until today that I saw fritsl's Toy Challenge.  Four year old challenge accepted :)

I had not thrown the cover out yet, so I put it back on to show you guys the car.  I don't know if you can tell by looking at the picture, but the front wheels are free rolling and have a motor to angle them left and right.  The back wheels are the ones with the motor that drives the car forwards/backwards.  There is also a space underneath for 2 AA batteries.  It currently measures 7.5" x 5" x 4", but that is likely to change.

I am waiting for my robot brains and eyes to arrive in the mail so I can get started and post up something in the robots page.

(9/17/2012)
Here are some pictures of the before and after of the car.  I kept the picture of the receiver board in the attachment section to maintain its dimensions.

Before

After

AttachmentSize
Receiver Board128.95 KB

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Great suggestions from each of you guys.

@birdmun: Just last night I searched online for ready made h-bridges in case I had to use one.  I came across the SN754410, which seems the same as the L293.  Do you think that would do the job?  Oh, and btw I updated the post with two of the pictures embedded.  I left the receiver board picture as an attachment to maintain dimensions.

@MarkusB: As for the receiver IC all it has written on it is the following:

(C)2007
NEW BRIGHT
R288-2    0804

After doing some research on the above it seems that R288-2 is a house marking for New Bright, but many people seem to think it is an RX2c clone.  If it is a RX2c clone, you should be spot on with your guess, based on the datasheet for the RX2c.

@RobotFreak:  The pin configuration for the PT8T9783 that you mentioned is the same as the RX2c, so I think you're right.

@OddBot:  Indeed, I am inexperienced and a double pole, double throw relay is exactly what one of my team members for the IEEE competition suggested we use.  We may end up using something like that for the competition.  Thanks for pointing that one out to me.  I think I am going to go with an h-bridge with this robot and learn as I go.

@Everyone:  Now if I remove this chip, reconnect the 2xAA battery power supply, reconnect the motors, and start sending logic high and low signals to those theoretical h-bridge inputs the motors should react right?

EDIT:  I just connected the receiver board to the 2xAA battery power supply, reconnected the motors, and used another pair of AA batteries to send logic signals from those pins and they are exactly as the datasheet states.

 

If you desolder the chip, you should be Able To Connect To The Pins Labeled Forward, backward, Left, Right, And, Turbo, If You Are So Inclined, To Control The Vehicle With a Microcontroller. Sorry About The Caps, My phone's Text Entry Isn't Behaving.

OK, well that's the plan.  I'll update with my success or failure probably by the end of the week.  I have zero soldering experience, so my next update will likely include a picture of the receiver board with large burn holes and a picture of my attempt to build my own h-bridge with transistors.

As you seem inexperienced with "H" bridges I would suggest that using a double pole, double throw relay might be a better beginners option for you. This simple circuit will let you control a motor using 2 pins. One pin selects direction, the other pin turns the motor on or off. By applying PWM to the on/off pin you can control the speed.

There is a kit that has two of these circuits (one for steering and one for drive) on a PCB with a prototype area for experimenting available from here: http://www.robotshop.com/dagu-mr-basic-dual-2a-motor-controller-board-5.html

The problem is that you don't have the transmitter. Otherwise you could test all pins on the receiver IC for their locigal states (with a multimeter) when you're moving the joysticks on your TX. You would soon figure out which pins representing the 4 inputs of the H-bridge.

I can't see any labeling on the receiver IC (is there any?). Otherwise we could try to find the datasheet for the RX IC and would also be able to figure out where the h-bridge inputs are.

Another possibility would be to redraw the schematic of the whole board, but that's a hack of work...

Just a quick guess and no guarantee that I am right:

Could be a PT8T9783 or a similar RC receiver chip. Here is an example schematic from the datasheet:

If you still have the receiver board, you should just remove the receiver chip and use the board to talk to the motors. I say this because, the receiver board already has an h-bridge on it. It would save you having to add an h-bridge to the toy to control the motors.

There are a couple postings here about reusing toy RC cars as robot bases.

Thanks birdmun.  I have read the term "h-bridge" maybe once or twice since I joined LMR, but I didn't know what it was.  You're comment prompted me to research it.  I knew that reversing the voltage to a DC motor would make it turn in opposite directions, but I never thoought about how I would accomplish that.

I do still have the receiver board, but it is quite intimidating.  I have never dismantled a PCB without leaving it utterly useless.  I usually just take the parts I want and throw it in the garbage.  Plus this board is only 5.5cm x 4cm.  I will search for those posts about reusing RC cars now, but I updated the blog post with a photo of the board.  I think I figured out which transistors make up the H-bridge, but that's about all I figured out.  Any advice on how to proceed would be greatly appreciated.

That will be a bit more difficult to hack in to. The black chip is the receiver chip. Most of the boards I have seen are through hole versions. They are very easy to hack on. I think your best bet is to get an L293 driver and use your preferred microcontroller to drive the inputs to the h-bridge(L293).

Also, you can embed the images in your post by clicking on the little icon that looks like a picture of a tree.