Printed from www.nzmeccano.com
I started building this model as soon as I downloaded the instructions for the kit.
I learned very quickly that even a 1950's 10 set wouldn't be enough to build this one. So there's a few modern bits of zinc standing in from vintage green where I ran out!
Since I didn't have the geared motors and controller from the kit, I had to improvise with what I had. 2 PDUs and a modern triflat motor with a gearbox took the places of the intended motors. The slewing PDU wouldn't fit in the operator's cab and had to be mounted on top.
Also, a standard 133 tooth 3.5" gear took the place of the custom 121 tooth 3.125" gear in the kit. A 3" pulley on top of it provided the wall to keep the plastic spacers in. I did start off with them but soon switched to the 168d steel balls when some of the spacers began dragging rather than rotating.
The slightly bigger slewing gear and the new motor position required a cascade of changes in the slewing gearing, but there turned out to be plenty of room and it was largely a trouble-free change. One benefit of using the PDU was that I ended up with a sedate 4 rpm slewing speed rather than the 20 rpm speed that I've seen reported for the kit!
Taking the place of the kit's motor controller was an Arduino with a motor shield. An IR decoder and and old TV remote control provided the wireless control. I was able to recycle the code that I'd written for an earlier (less than successful) crane. The only changes I made were to run all the motors at full speed rather than use the PWM capability of the code to slow them down. As it turned out, the geared motors are slow enough by themselves. I did use the PWM on the slewing motor to slowly ramp the voltage down when stopping the motor. Even at 4 RPM, there was enough inertia/momentum to cause a noticeable bounce in the jib assembly when I just turned the motor off all at once. Ramping the voltage down over 1.5 seconds gave a nice smooth stop.
A pair of IR detectors at either end of the trolley rail allow the Arduino to detect when the trolley is about to be run into the end and stop the motor before that happens. I first tried using a simple IR reflection detector but as I suspected it had trouble even in room lighting. A modulated IR detector that only produces a signal when it detects the modulated IR light from its onboard LEDs worked much better.
I'm still toying with ideas on detecting both the slewing and hook positions. A single reflector on the big slewing gear would provide a position reference and counting how long a complete revolution takes might be enough for the slewing position. I haven't come up with anything resembling a good idea of how to figure out what the position of the hook is though.
I've programmed a rudimentary record/playback function into the Arduino. It records when a particular motor starts running, which direction it's turning and how long it runs for. Over 100 such "motor events" can be recorded for later playback.
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