Let's Make Robots!

Part 1: Hacking a Tyco (tm) "Rebound" for robot use in 30min.

Cheap 4WD off road chassis for your robot

The chassis of the "Rebound" is perfect for small off road robots. The PCB has a radio receiver and dual "H" bridge. This walkthrough shows you how to make the chassis and PCB microcontroller friendly in 30min.

Thanks goes to Stevek for sending me this great little toy!

 

Step 1: strip off the covers! If it has a good battery then great, go to step 2 otherwise solder heavy duty cable to the power connections. I previously tried a 9V battery clip but the motors lost too much power. I also added a big capacitor to help when the motors start up.

Rebound_power_connections_0.jpg

Solder the cables to a 6x AA battery holder.

Rebound_battery_holder.jpg

Step 2: Desolder and remove the IC.

Rebound_Desolder.jpg

 

Step 3: Fit a 4 pin male header where pins 5,6,7 and 8 used to be.

Rebound_male_header.jpg

 

Step 4: Cut out a small hole in the chassis for the control cable to poke through. I just did a "quick and dirty" with the soldering iron. Then plug in your cable.

Rebound_control_cable.jpg

 

Step 5: Solder 2 power wires for your MCU regulator to what were IC pin 11(ground) and 12 (+7.2V). Your Done!!

Rebound_power_connections.jpg

You can see in the photo below I have re-attached one of the covers to protect the wires and PCB. A small breadboard fits perfectly in the chassis making it perfect for adding an Arduino Nano or a Picaxe IC.

Rebound_ready_to_program.jpg



Interfacing to your MCU:

Now that the chassis is hacked we still need to get it working. Because the "H" bridge circuit is running on the battery voltage (+7.2V in my case) it is necessary to use some NPN transistors to switch the "H" bridge. This prevents your MCU outputs from being damaged. I did try using series resistors of 1K2 and this worked but it may damage your outputs and reduces the current to the transistors in the "H" bridge causing the motors to loose power.

Some picaxe boards have a ULN2803 transistor array built in which is perfect for the job. Arduino users can use such a chip or discrete components as I have done.

Rebound_NPN_transistors.jpg

I found I had a lot of trouble with the Arduino Nano resetting when I tried to drive the motors. I tried various noise filtering but unless I had the USB cable in it would reset when driving both motors. This told me the Nano's onboard regulator wasn't good enough or it's faulty. After making a small regulator PCB everything works perfectly.

Rebound_regulator.jpg

Using the original IC pin numbers - pin 5 and 6 drive one motor, pins 7 and 8 drive the other motor. Grounding a single pin of either motor will drive that motor forward or reverse. Grounding both pins of either motor applies the brakes to that motor. Both pins open circuit turns the motor off and allows it to coast.

Rebound_interface_schematic.jpg

 


 Optional Modifications:

The rebound has a slightly unusual power circuit. Ground is switched by the heavy duty power switch for the "H" bridge. The +V power for the receiver is switched via a A1015 PNP transistor (Q14) with a maximum rating of 150mA. If your MCU and sensors are going to draw more than 150mA then you will need to replace Q14. I used a PN200 with a 500mA rating but as the pin configuration of the two transistors are different I had to cross the base and collector pins over.

Rebound_new_PNP.jpg

 

If you are having trouble with electrical noise from the motors affecting sensors then you may need to add additional capacitors across the motors. I added 220nF monolithic caps just to be sure. Monolithic capacitors have a low ESR (Equivalent Series Resistance)  making them ideal for noise suppression.

 Rebound_noise_suppression.jpg

I also added a second big capacitor on the PCB power connections as I still had the Arduino resetting occasionally when a motor started.

Rebound_extra_big_cap.jpg

 

 Good luck and enjoy!

 

 

 

Comment viewing options

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

I like your hack my friend,it's a good idea to convert them. They are cheap to get when kids loose the remote. I was wondering if on the one I got for a few buck if the pinouts of the chips are the same. I have a TYD031 rx2, 16 pins. Any clues would be appreaciated. Thanks.

Korel

 

I realize that your post is several months old, but I wondered if you found anything out about this chip. My son has a large RC car with a lost remote and it has sentimental value (given to him by my late MIL) so I am trying to make use of it. I have done some Arduino based robotics, so I am sure I can make it work if I can get some info on that chip.

Sorry, I have no more information. My car did not have a transmitter so I just removed the receiver IC. It might be worth using a couple of Xbee modules if you want to go robotic or just adapt the car to use standard RC controls.

I probably would go xBee as that is what I have recent familiarity with. If I knew the pinout of that TYD031 (I was replying to the post that mentioned that), then I could remove the IC and work with the existing board.

Why use xBee if RF Link 434 Mhz cost 1/10th  of the price?

Because Xbee can do a lot more, it has built in error checking to ensure you get accurate data. If you want accurate data transmission with the cheap radio modules then you will need to write your own code for error checking and retransmission.

The 2.5GHz bandwidth also allows much faster data transfer rates. With 433MHz then you will be limited to maybe 4800 baud if you have a clean signal. Far less with error checking and re-transmission.

It has better range if you buy the more expensive modules.

Oh, thanks, that explains the price. 

I've done the same thing you did with the 4700uF cap, and it solved the arduino restart issues I was having  ;)
great hack!!! waiting for a video ;)

You can do this hack and leave the on-board RF receiver chip in place also. That way you still have remote control over the car.

OR, if you want to get really fancy, you can use the RF chip outputs as inputs to your micro-controller!

I have a rebound hacked up that requires me to press a button on the controller to enable "autonomous" mode. Without it pressed down the micro-controller will not run the motors. Its great as a dead-man switch for if the car goes to far away. The real bonus is that it was an UNUSED pin on the controller/receiver, the PDF for the chip refers to it as "Turbo" enable :D

explorer

http://www.hellspark.com/dm/ebench/sx/dave/explorer.sxb

 My favorite rebound is my web enabled one.http://www.hellspark.com/vcar/ I did it back in 98 when the original (non-super) rebound came out :D It is at my work so the batteries are dead right now (long weekend) but I charge it first thing Monday morning.Its a simple parallel port to optoisolator hack, but the software side of upkeep has been an interesting ongoing challenge.

nerdy details below for explorer/protobot (these are old like the picture).

 The right side is my logic "power supply" A 9v battery(its on the top left) feeds into a black switch connected to a IRFU pnp mosfet (for reverse battery protection) then through an auto resetting 800ma circuit breaker (its orange in the picture) for over-current protection then into a 5v regulator then into a 5.6v Zener diode (for over voltage protection) and finally into a few bulk caps with tantalum voodoo caps everywhere to eliminate socket-board noise. I experiment on this thing, so I wanted a robust and safe power supply :D

 On the left is an IR emitter driven by the Parallax/Ubicom SX28AC. Underneath it all is a Tyco toy rc/car that i am(was) driving with IXDN404 chips (center) pressed into h bridge duty, they sucked raw 6v power from the 4AAs visible on the extreme right of the pic (currently disconnected, note the black wire just hanging there), and boy did it suck, i sucked many a AA battery down playing around :D. On the front of the car frame are 2 IR detectors that are wired with those red/black/white wires you see in the middle of the pic. Later i replaced the 2 IR detectors with 1 and added 2 IR emitters that i switch on and off to detect left and right. Since the detectors are more expensive i figured i'd add emitters. Now i have a spare IR detector, maybe i'll add rear detection at some point :D

I later bypassed the IXDN chips and interfaced the SX chip directly to the RF receiver chip from the toy car so that i can control it via a remote control as well. I also used an unused pin/channel (turbo!) on the receiver/transmitter) to enable "micro controller" control over the car. That way i can throw a switch on the transmitter and the car can take off, if it gets out of range it losses the "turbo" signal and just stops.
This acted very strangely until i remembered to create a common ground between the raw motor power supply and the 5v regulated one.

When it is time to program i just pulled the SX out and plug it in to the programmer.

 

 

 

 

 

In my case the car was an old one with no remote or battery. I did have a quick look for the datasheet of the receiver chip with no luck so please post it if you have it.