Following on from our efforts yesterday, we mega-dosed some vitamin C, wrapped up warm and ventured out to the build space. We had high hopes of making it to wiring up the antweight. You'd think we'd learn by now ... Click Back after viewing an image.
To start out today we wanted to be able to mount the rollers. If you remember from the design there are rollers on the end of each wall for the outer shell to roll on. Due to the circular/arc/chord/impressive-eh? geometry, the walls have a funky length, which translates into a funky position for the rollers. The easy approach is to work from the design, and know that the pieces were waterjetted so are exactly as designed.
Through a combination of the hardened scribe points on the calipers, and some decent drilling we put the holes pretty darned close to where they need to be. We drilled the top and middle through with a 9/16" bit, and tapped the bottom for #6-32. We started wondering whether the spinning shell might cause the screws to unscrew ... should be interesting to find out!
Here we've countersunk the roller holes, and also touched the walls to the belt sander to round them a little. They look kinda ugly, but they'll work!
One other piece we need to fabricate is a mount for the weapon motor. Here we've chopped up some 1/8" polycabonate, and fitted tab A into slot B to make sure it fits okay. Talk about an Ikea-bot!
After come fairly careful marking, punching, and drilling, we wound up with a decent fit to the motor. You may notice that only 50% of the bolt holes have bolts in them - this isn't because we drilled the holes wrong - it's because they're a different thread than the ones that are done, and we accidentally threw away the instructions on mounting the motor, so we have no idea what bolts those were supposed to be, but they didn't come in the box with the motor ...
All right ... looking fairly good, but as you can see in this shot the frame isn't square with the motor installed. We knew this was going to happen, and were planning on Dremel-ing out the frame to accomodate the motor properly.
Interesting result following the Dremel-ing of the wall - the tiny screws that hold the gearbox on the Pololu motor unscrewed themselves! Took a few minutes to take the wheel off the gearbox and remount it, but no harm done.
Once all the Dremel-ing was done, we re-assembled the frame around the motor, and it fit great! Time to move on to something else ...
We never got around to ordering sprockets for Poor Punctuation 0.9 but a scrounge around the Build Space unearthed a couple of #25 sprockets, so we put them in place for fun.
Without the main sprocket you can see we inserted a bronze bushing into our milled UHMW block from yesterday for the main weapon axle. We're also going to have to make a spacer for the weapon motor.
Okay - today's major frustration - cutting a 2.25" piece of 1/8" polycarbonate tube for the weapon shell. We wasted major time today trying to figure out how to cut what we wanted Milly's lathe, before throwing our hands in the air and going old school: jigsaw and clamps!
Except the jigsaw wasn't very accurate, but finally we did get the job roughly done, and so as we were planning on firing up the belt sander to neaten up the part and bring it down to 2.25", we smacked ourselves in the head and realized here was something we could use Milly for. We loaded up and endmill and had at it!
Nice! 2.25" on the dot - thanks Milly! We could now think about assembly, with all the fabrication of parts completed finally. These little 'bots are darned fiddly!
Sanity check: these fifteen ounces are everything except a few bolts, and the teeth for the shell. Well ...
... Oops! Not quite ... we forgot the battery. Hmm ... 1lb and 0.1 ounces without the teeth or screws ... not good. We spent a little while looking over the parts to see where we could shave a bit of weight.
The weapon shaft, sprocket, and spacers we dug out earlier weigh a massive 1.7 ounces. We'll have to look around again and see what we can do to save some weight there!
So one thought is this plastic pulley - much larger tooth count, which will slow the shell, but half the weight of the metal one, leaving weight for teeth and bolts. Of course if we could lay our hands on a smaller plastic sprocket we'll be in even better stead ... time to go check out what SDP/SI has available ...
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