RC Nitro Flash and RCX

A friend recently gave me a 4589 RC Nitro Flash chassis that had been mishandled. You'll find below a few photos shot as I was taking it apart to repair it.

I intended to use it as a mobile base for robots: RCX can easily generate infra-red remote control commands. You can thus with a single RCX control 5 motors, the three regular ones plus drive and steering of Nitro Flash chassis. Unfortunately, there are two problems that plague this solution:

• The car is very fast, even with small wheels so RCX control is not easy. And since the chassis has neither Technic holes nor female studs below, it is impossible to add reliably an external gear reduction
• Steering coil is rather weak, and with added weight of RCX, it is no longer reliable. With a complete construction, such as a robotic arm with three motors, the steering coil would probably not able to move at all!

RC Nitro Flash internals

	When I got the chassis, the steering neutral position trimming screw had been abused.
	First thing to do: remove the 7 screws...
	...then open the car.
	This image shows the functionnal elements of RC Nitro Flash: Drive motor and gear reduction. Steering coil. Shock sensor. This unit contains a small weight that closes a contact when the car is gently dropped on ground. This is how RC Nitro Flash is started. Drive motor H-bridge. This 4 transistor assembly can run the motor forward or reverse. The motor can also be braked or left free running. Controller. Steering coil H-bridge.
	Drive motor and gear reduction. This 4.5V motor is not efficient, but quite fast and powerful. Some characteristics: No load current: 360 mA Stalled current: 1.5A No load speed: 1500 rpm Stall torque: about 3 N.cm As you can see, this motor can drain your batteries rather fast! Note that this car works very well with NiCd or NiMH rechargeable batteries. You can compare these characteristics to other Lego motors.
	The steering coil contains a permanent ring magnet around a rotating coil. When current flows through this coil, it rotates to align itself (according to current polarity) with permanent magnet and drives the steering arm.
	On this photograph, the steering coil is unscrewed and removed, showing the centering spring and the neutral position trimming screw. The stud of this screw must be inserted in magnet ring notch.

RCX control

Several recent Lego products use an infra-red remote control based on the same protocol. These products include the Bionicle Manas, the Spybotics and the RC Nitro Flash racer. The RCX with firmware version 2 can generate the infra-red remote commands and control these units. Moreover, all 3 IR channels can be used, so the RCX can control up to 6 external motors!

More details on this protocol can be read in this document, synthetized by Rob Doucette from several Lugnet posts (mainly contributed by John Barnes).

Here is a simple test program.