Balance Bot V2
My current balance bot sort of works, but it's surprising it does: it's centre of gravity is actually only about 60mm above the motor axis. The whole thing ways 320g. The 6 AAA batteries only weigh 70g, so despite being right at the top, the don't affect the centre of gravity much.
6 AA batteries would weigh about 180g. That would add a 34% to the overall weight, and move the centre of gravity much higher. Seems like a dramatic increase in weight: it would be nice to be a bit more incremental.
More AAA batteries isn't really worth considering: they only weight 12g, vs 30g for an AA. 4 AA would deliver much less power/torque, so that's no good. There's no middle ground, in other words.
I'm also going to make the whole thing a bit taller: I need more space to add more sensors in any case.
Last time I made the frame, I needed an elaborate jig to get it square and it actually didn't work that well. This time, I decided to use some short bits of angle as corner pieces to set the square, and didn't use a jig at all, just some little sprint clamps:
Now I look at the picture you can see the strut at the top is very slightly twisted which is a slight disappointment, but it's pretty tidy, and I don't think that's going to matter.
The corner pieces get glued in place, so there's much more glue surface holding the corner together, so it should be much stronger. Not that strength was an issue with the previous frame.
To get the opposite pieces exactly the same length, I have added a depth stop to the mitre guide on the band saw. The design is copied from a hand mitre saw I once had:
The two rods extend far off to the right, so I can make quite long cuts. I also added a toggle clamp to hold the work in place while I cut. The result is greatly increased precision, as well as quick repeatable cuts.
Last weekend I actually had a first go at milling. I look a couple of blocks of aluminium and made vice jaws with a shelf for my quick vice. The result showed I hadn't set of the vice parallel with the Y axis of the X-Y table. Also the jaws of my quick vice tilted when I used it. That reminded me of a much bigger milling vice I bought. I hadn't used it because I thought setting it up parallel would be hard, and also because the jaws were flat. It's been languishing in a drawer ever since. It was simply too heavy to be worth returning. I dealt with the first by using a centre finder. Not perfect, but better than a set square between the vice and the t-slot, it seems. The second I just bought some magnetic jaws with a shelf and v grove. Here it is mounted:
It's a bit monstrous on the little X-Y table (I didn't appreciate how bit it was when I bought it). I have to use the swivel base so the crank handle is reasonably conveniently placed. The pillar is still tall enough for most bits. I might have to get stub bits for >8mm. I also finally found a cheap lever dial gauge, so I should have more success next time I try milling.
Anyway, just today, this instructable arrived in my inbox, describing using grommets as a way of holding the edge of PCBs where no mounting hole is available. Actually it uses crossed struts so the size is adjustable. I wonder why it doesn't add springs for a quick release mechanism? I'm quite excited by this because all my other mounting techniques for the discovery boards are either inflexible or expensive or both. I can get 100 suitable grommets for £5, and then use whatever standoff, etc. I want.
I think this means I can mount the discovery board laterally, which gives better access to the USB port, and makes everything more compact.
6 AA batteries would weigh about 180g. That would add a 34% to the overall weight, and move the centre of gravity much higher. Seems like a dramatic increase in weight: it would be nice to be a bit more incremental.
More AAA batteries isn't really worth considering: they only weight 12g, vs 30g for an AA. 4 AA would deliver much less power/torque, so that's no good. There's no middle ground, in other words.
I'm also going to make the whole thing a bit taller: I need more space to add more sensors in any case.
Last time I made the frame, I needed an elaborate jig to get it square and it actually didn't work that well. This time, I decided to use some short bits of angle as corner pieces to set the square, and didn't use a jig at all, just some little sprint clamps:
The corner pieces get glued in place, so there's much more glue surface holding the corner together, so it should be much stronger. Not that strength was an issue with the previous frame.
To get the opposite pieces exactly the same length, I have added a depth stop to the mitre guide on the band saw. The design is copied from a hand mitre saw I once had:
Last weekend I actually had a first go at milling. I look a couple of blocks of aluminium and made vice jaws with a shelf for my quick vice. The result showed I hadn't set of the vice parallel with the Y axis of the X-Y table. Also the jaws of my quick vice tilted when I used it. That reminded me of a much bigger milling vice I bought. I hadn't used it because I thought setting it up parallel would be hard, and also because the jaws were flat. It's been languishing in a drawer ever since. It was simply too heavy to be worth returning. I dealt with the first by using a centre finder. Not perfect, but better than a set square between the vice and the t-slot, it seems. The second I just bought some magnetic jaws with a shelf and v grove. Here it is mounted:
Anyway, just today, this instructable arrived in my inbox, describing using grommets as a way of holding the edge of PCBs where no mounting hole is available. Actually it uses crossed struts so the size is adjustable. I wonder why it doesn't add springs for a quick release mechanism? I'm quite excited by this because all my other mounting techniques for the discovery boards are either inflexible or expensive or both. I can get 100 suitable grommets for £5, and then use whatever standoff, etc. I want.
I think this means I can mount the discovery board laterally, which gives better access to the USB port, and makes everything more compact.
