JIMMY WATSON - His mother, Marion, teases her son about his dreams to build a large robot ant with a drawing of her son riding on the ant's back. Then it comes true.

<< CHAPTER 11

CHAPTER 12 - THE ELECTRICAL WIRING CHALLENGE

Jimmy was pleased with progress. The motors were fitted and tested by rigging a temporary DC supply, with no finesse or control, other than unclamping a heavy duty crocodile clasp, accompanied by very large sparks. And that proved to be quite a risky experiment, where the dinobot almost fell off the cycle assembly mounts, to do who knows what damage with each jolt from violent full power torque, to off again, and more sparks.

He thought to himself; "I needed to curb my impatience."

Jimmy vowed not to try that again. His heart could not stand those kind of frights. He was shaking all over when that happened, and perspiring. He needed to have a wash and change his T shirt after that little episode. Liberally applying antiperspirant after showering in his bedroom. Then back downstairs to the workshop.

His father, Tim, had been most helpful in arranging reels of colour coded wires of different capacities along one wall, conveniently below other tools: engineers pliers, side cutters, wire strippers. Jimmy loved the way his Dad was so logical and matter of fact. It filled him with confidence and admiration.

His Dad helped with the heavier cabling. "Okay, Jimmy, today we'll run the power cables from the controllers to the motors." 

Tim unreeled enough red and black cable to run from the left motor to the left speed controller. Jimmy watched closely, as his father threaded the cables along the chassis, under nylon cable ties.

"This is the tricky bit Jimmy."

Tim picked up a cable baring tool with a red handle, carefully measuring the distance from the jaws of the pliers, to the exposed cable.

"Now, we squeeze the handles, and the pvc sleeve is pulled off."

The operation revealed about 20mm of exposed copper cable.

"Wow, I like that tool Dad."

"Thought you might Jimmy." They laughed.

"Now we crimp on end connectors - and note they are different at each end. Brass circles for the motor end. Spade connectors for the speed controllers."

"There are so many different types Dad. A bit confusing isn't it?"

"Sadly, yes. Each brand used a different connector type. But, there are adapters to help us. Check out that large box on the floor, on the left."

Jimmy slid out the box. It had a clear lid and divided compartments. Each of the compartments contained different connectors of varied colours.

"Wow, that's a lot of connectors, Dad."

"Hmmm.... We'll need them and more. Trust me."

"I like these boxes. De Walt. Same as our hand drills."

"They were on offer, down at Screwfix a few years back. I could not resist."

Tim selected connectors that matched the motor and controller.

"Okay, so now a different tool. A crimper. Pass me the one with the yellow handle."

"Thanks son."

Tim squeezed the tool, while the copper cable ends were inside the collars.

"Righto, that's a good electrical connection. Good enough for cars and boats. But for a robot like this, I'd solder the ends, to prevent corrosion creeping in to add resistance to the joints."

Jimmy had a go with the wire strippers and the crimping tools.

Soon, there was a number of cables, neatly installed.

"That is called a wiring harness, Jimmy. This one is a one off. On production lines, for cars, the harnesses are made up on patterns, then wrapped in plastic insulating tape."

"Yes," said Jimmy, I've noticed that on Mum's Camper van."

Jimmy thought about the time and motion study he'd undertaken at school in his statistics class. What seemed useless number crunching, might now be useful. Especially when combined with his ergonomics fascination. The art of matching humans to controls or, in this case, a work station. The layout and precise positioning of robot in the workshop, would determine how quickly and efficiently he could complete a fairly complex wiring task. Where some of the spade connections needed to be soldered, then protected by heat shrink tubing. For insulation, strength and ordered appearance. That might help fault finding further down the line. Debugging. He hated fault finding, but sometimes things went wrong.

Jimmy tightened up the clamps on the two 500w speed controllers. That was satisfying, final alignment. These two aluminium finned boxes were packed with power electronics, to provide infinitely proportional control of power fed to the main drive motors. It meant smooth control of the walking functions: forward, left and right and reverse, left and right - would be possible.

Jimmy built in a number of safeguards. A manual switch to power up the whole shebang. And a wireless switch that also turned on the power from the batteries to the wiring loom, upstream of the manual cut out.

Long ago Jimmy learned the hard way, that the trick with wiring was to first of all draw out a circuit diagram. That way he could think through the logical position of wires and electrical parts, before actually cutting the copper cables. Mistakes were virtually eliminated, this way. And there was always hard reference, with colour coding, that other engineers could understand. Jimmy also used a Dymo Rhino label printer that his Dad had bought for him when they were on special offer from Radio Spares. This was useful where many cables were the same colour, but could be number coded with information labels stuck to the chassis or components.

Soldering was another skill Jimmy had picked up during 'Robot Wars' challenges at school. He bought a number of electric irons. Some small with fine copper tips for working on circuit boards, and others with serious wattage grunt, for thick cables to motors. Crimping was fine for most applications where the copper wire was clean and brand new, a system used in cars and trucks. But with robots that had to work in all weathers. Sometimes it had to be a soldered joint to remain resistance free. The same applied in the nautical world. Even in model boats and 4x4 buggy racing, speed controllers needed to be waterproof.

Having produced a number of circuit diagrams in rough, finally, Jimmy had one that was neat enough to be readable. Including all the components, colours for wires and notes to remind him of any pitfalls.

He was thankful for making that effort now.

"Blinding circuit diagram Jimmy," said Tim.

"Thank's Dad."

"Easy to read."

Tim hugged his son.

"You could teach our lot a thing or two."

...

>> CHAPTER 13

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