25 Nov 2011

Chassis v2

I got the second version of the chassis back from skpang yesterday and managed to quickly assemble it late last night to see how it is looking. Here’s a photo of it next to the v1 chassis: Chassis comparison

It’s virtually the same design but has a few refinements. This time you can see the “mudguards” which aren’t really mudguards but more like plates that hold the outer end of the axle in place. They seem to work quite well as the wheels are much less wobbly than on the v1 chassis. You can also see the drive wheel that fits on the gear of the stepper motor. Although this is looser than expected it gets held in place quite nicely by the mudguards. There are three of these in different sizes which should give a resolution of 0.5mm, 1mm and 2mm depending on whether you want speed or accuracy. Here’s a close-up:

Drive wheel close-up

The other major refinements in this version were the attachments for the rubber band to keep the pen arm in place. I’m really pleased with how this is working; there’s very little play and the tension holds the hinge in place really nicely. Here’s a close-up of this part:

Pen arm

The main area for improvement, however, is the mount that holds the servo in place that raises and lowers this arm. I’d hoped to rely on friction to keep this held tight, but I think with the tolerances of the laser cutter it’s going to be quite difficult to make this a reliable fit, especially with the elastic levering the arm against it in the opposite direction. Plus, if it gets taken apart and putt ogether again a few times this will likely become loose. Since the elastic bands are working so well elsewhere I’m considering designs based on one keeping it tightly in place, but it also needs to be quite accurately aligned with the arm otherwise it will slip off.

In any case, I should at least be able to get this version moving properly before spinning another revision of the chassis so I’ll hopefully be able to put up some video before too long. Expect the ususal quips about number 5 (or 2) being alive.