OWI-535 Robot Arm Control assembly
There were some issues with assembling this part of the kit and these are the steps taken to overcome them.
Switch "wing" fastening
Page 29 Block 2 shows "switch wings" being attached to the PCB via through holes and screws that threaded into drilled bosses in the plastic housing. There were two problems completing this assembly.
- The screws got progressively harder to drive while they still had about 1/8" (3mm) exposed threads. It is normally a bad idea to continue to drive screws when they force to do so seems excessive. (That can result in broken parts or damaged threads and even broken screws.)
- While investigating this issue by checking hole depth with a small drill bit, it was discovered that one hole had not been drilled to the required depth.
The first step for remediation was to select a drill bit that fit snugly into the holes and mark the required depth with a piece of tape. The hole was carefully drilled to the necessary depth. The screw for that hole was then fully inserted with force that seemed not quite excessive. (In other words, did not require any further techniques.)
The second issue was easily avoided by heating the screws with a soldering iron for about 2 seconds to soften the plastic.
- Start the screws and drive until resistance seemed high (with the threads exposed as above.)
- Touch the soldering iron to the head of the screw for about 2 seconds. (*)
- Drive the screw almost the rest of the way in. Excess force while the screw is hot and the plastic soft would rip the threads out.
- Allow to cool before final tightening of the screws.
Control crossover
Once assembled the controls were connected to the base unit and the unit exercised. It was found that the two left control levers were cross connected and operating either control resulted on movememt from both motors. The control was disassembled and it appeared that slight scratches in the conformal coating on the printed curtcuit allowed a cross connection between the two switch butterflies for these controls. This was remediated by placing a strip of electrical tape across the area where the butterflies were fastened. It was necessary to remove a small patch of electrical tape around the screw holes to provide contact between the butterfly and printed circuit.
With these changes made all motors operated as intended. Some movements resulted in rather loud operation. Motor housings needed to be tightened (close the clamshells) in some cases.