TLA: Truck Prototype
This past weekend I found plenty of time to work on the truck stage of the time-lapse robot.
I managed to get the basic track prototyped, using angle-iron, flat steel bar, a 3’x1/2″ threaded rod, and some other goodies. The design is fairly simple:
The track for the cart (on which the pan/tilt servos and camera/lens will rest) is made of two pieces of angle iron (later models will use aluminum, the mild steel variety was easier to source on a whim), held together by custom ‘u-brackets’ made out of the flat steel plate. Each bracket has two holes for bolting to the angle iron, and one for the bearing to go into (the bearing allows the 1/4″ shaft attached to the 1/2″ threaded rod to roll smoothly). The cart (not completed yet) is attached to the threaded rod by way of a couple of flange nuts.
The first step was to cut the flat steel to length (using a chop saw although a hacksaw would’ve sufficed – I like the sparks =), then drill the holes in the proper location. Once the holes had been drilled, it’s over to the bench clamp and anvil for shaping. Only after shaping, to deal with any imperfections, are the holes for the angle iron marked and drilled.
To attach the 1/4″ drive shaft (whose smaller size and smoother surface would do better through the bearings than the threaded rod, not to mention, I need to be able to attach a gear to one end.) to the threaded rod, I enlisted some threaded rod couplers, measured the length I wanted the overall system to be, and then taped them threaded to the proper position on the bar. At this point, the unthreaded portion of the coupler is filled with a metal bonding putty, and the shaft pieces inserted. To make it possible to remove the couple from the rod, a small amount of tin foil is placed inside the coupler to keep the putty from binding with the threaded rod.
Unfortunately, this is not an exact science, and my rods aren’t perfectly centered, resulting in some wobble in the rotation of the rod, and therefore lost power and gear wear. I will fix this later.
The following picture shows the drive end being filed down to take any burrs and roughness off from being cut with a hacksaw:
The remaining photos give a better view of the assembled work, note that the red PCB in the second picture is an L298 motor controller from Solarbotics. This is necessary as the motor draw a LOT more current than the pins on the arduino can handle.
Conclusion: it isn’t perfect, but it works – the nut pictured on the rod moves at approximately the calculated speed and in the correct direction as configured in the interface.