The Yard Rover Project

I wanted to drive it around by remote control. So I decided to use my R/C transmitter and receiver that I had.

I needed some way to drive the motors from the 1-2ms pulses coming form the R/C receiver. I went to my junk box and came out with some R/C servo chips that had purchased earlier. I don't remember the part number, but it was a Signetics part. (I think it was a NE544 or something like that. I wired them up on proto-boards per the spec sheet. So I basically ended up with the same circuit you find in any R/C servo. But I needed to beef-up the drive current.

I built drivers with 2N3055 power transistors. Actually I made a darlington configuration with the addition of a smaller transistor. I didn't know if I would get interference from motor noise so I isolated the driver transistors with optoisolaters. I didn't worry about having a reverse. I only had the forward direction. I mounted the R/C receiver, the servo control chips and the transistor circuit to the robot base. I hooked the motor drivers to the proto-board with jumper clips. And I wired up a 7.2V ni-cad pack that I had. I used jumper clips for the battery too.

I propped it up so the wheels weren't touching the ground. I pushed the stick forward and the motors began to turn. (And there was no smoke or sparks. :-) I pushed it further and the motors turned faster. So far, so good. I took it off the blocks. I drove it around on the side walk and it worked fairly well. So I tried driving through the grass and it barely moved.

"More power" I thought. So I tracked down my 12V ni-cad packs. I wired one up and turn it on. Worked much better this time. It could drive through the grass but still slowed down. It was also slower than I originally thought. Something big in a small space always seems faster than it really is.

So, I might as well add another battery. I wired up another 12V ni-cad to give me a total of 24V. It was REAL peppy now! It didn't even think about slowing down in the grass. And it ran well on the sidewalk. So I ran it up and down the side walk a few times. It was coming back down the side walk at full speed when... it came to an abrupt halt and flipped over on it's top. I may add, that was quite a surprise!

I checked it out and found out that one of the jumper clips vibrated off and shorted something out. It apparently had shorted the motor leads together which caused dynamic braking to occur. And with a dead short they braked REAL hard. Since both wheels stopped the momentum caused the whole thing to flip over forward.

I assumed all the electronics were fried so it got parked back in the garage for a later day.

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