Sunday, May 25, 2008

Electrical Anatomy of the Stampede

The first thing was to partially disassemble the Stampede and work out how the pieces go together. I'm not planning any major changes to the chassis mechanics. Most R/C modifications are for better speed and performance, which is not the intention here. The chassis is a rectangular plastic tub with shock towers at each end.

Stampede chassis with wheels removed.

Only the rear wheels are powered, and the steering is controlled by a single servo, visible as a black box between the two front shock absorbers. The shocks attach to the black shock tower, which sports two body mount posts above it. The battery normally lies in the well in the chassis center, and connects to the yellow Electronic Speed Control (ESC). You can also see the blue aftermarket bumper (by RPM Racing) that will protect the front suspension from damage (and hopefully prevent a repeat of the broken caster block).

Front Assembly with steering servo (left under shock tower) and radio receiver (right).

Sorry for the slightly blurry picture. The radio receiver has two channels, channel 1 in the bottom slot controls the steering. A servo has a three-wire interface. The black is the ground wire, the red is the 6V power, and the white is the signal line. The receiver gets its power from the ESC, and returns a signal back to the ESC (channel 2) on the white wire, treating it as a servo. The ESC interprets that signal to control the main motor. The steering servo on channel 1 receives its power from the radio receiver, as well as a signal on the white wire.

If I'm going to replace the receiver with the microcontroller, the steering servo still requires a power supply from the ESC. So, the microcontroller must only send a signal on the white wires, and must be connected into the black ground wire. The red power wire must bypass the microcontroller and remain connected to the servo.

The Electronic Speed Control (ESC)

The ESC receives power from the battery (far left) and passes power to the motor. These wires are heavy-gauge to accommodate the high current passing to the main motor. The thinner three-strand wire at the bottom of the image goes to the receiver, powering the receiver and the steering servo, and receiving back a signal on the white wire, as noted previously.

The main drive motor.

The main motor itself is a Titan 550 12-turn. There's not much need for modifications here: except perhaps to gear the system down. The truck's really fast: far too fast for an autonomous system.

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