Team Expat - Beetleweight Adventures

[razerdave]

Well I am using M4 bolts and 10mm HDPE, seems very secure to me. As for stripping threads, I would say drill a 3.5 (or slightly smaller) and drive bolt in with a drill/good electric screwdriver to help cut a deep thread and heat up the plastic around it to hold it in better.

[plargen]

what about something like these

http://www.ebay.co.uk/itm/M4-x-8mm-U...item3f16213303

or these
http://www.ebay.co.uk/itm/M3-x-8mm-S...item41696e7003

[leorcc]

The thread makes them better for fastening.

[Ellis]

Thanks for the responses guys. All taken in. I may do a combination of all these: just tap it to m4 for things like top panels, but melt in proper nuts for the major joins, or go the thread insert route.

Also, here's yet another design, partially based on team RCC's Valkiri 2.

[Max]

It may be possible to bend the plastic into shape by heating it up then bending it around a table edge- that way you avoid needing a fixing at all. You could also make up some little brackets from bent aluminium or little blocks of hdpe with holes drilled through them at 90 degrees to each other- then you can bolt the walls to these blocks with a nut on the other side rather than having to tap the hdpe.

[Ellis]

I'm going to have to do the latter to attach top panels etc ^

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Was chatting to Harry earlier, and we decided having a silly-fast beetle would be great fun. I had to go and put T2 as back together as possible anyway, so after that I fiddled for a bit. Got this far, angle grinding comes next and not sure how well that'd go down at 11pm, so I'll continue some other time!

[harry hills]

The question now is, do we make it go stupidly fast.. or gut wrenchingly stupidly fast?

[swanaldo]

the gut wrenching fast is good I will make one soon.

[webby]

That drive system looks awsome! Is the gear inside the wheel the main gear out of the drill gearbox? And for stupidly fast, what voltage and gearing will you have?

[Ellis]

Yep, that's the ring gear from a drill, with an HDPE hub pressed in (drill press poor-man's lathe style), and then an old Meccano wheel and tyre, pressed around the ring. If it needs it I'll solidify it with grubs but for testing it seems stiff enough.

The ratio is, calculated roughly, 5.3:1. With the 12v motor at 3s, that's 20,000rpm on the input, so after the reduction that's 3,750 odd rpm on the wheel. The tyre in the pic is 72mm, results in 30mph, the one I'm more likely to use is 55mm dia, giving roughly 20mph.

I think I'll go for the latter but the chassis I'll build around the drive will allow for the larger tyre, should it be desired!

[Max]

So you'll just use the first stage of the drill gearbox? How are you holding the 3 planet gears still? Or are you just using the second stage then holding the output shaft of the drill gearbox still and using that as you axel?

[RogueTwoRobots]

I don't think he's using either stage, looks like the motor will engage directly with the ring gear. I imagine the hole-shaped object (possibly a hole :P) in the HDPE hub will be where the axle/shaft goes.

[Ellis]

I'm not going to use any other drill parts, just the ring gear and the motor itself. The setup will run like this:



I'm off to Lisbon today to meet Alex, who's on holiday, and Guilherme. I cut a strip of 4cm tall 2mm steel this morning, which when I get back I'll bend around the wheel, to hold the axle, motor face, and be armour of sorts. I don't know how it's possible that I've gone from the weapon-ed beetle to focusing on this in about 36 hours, but I have!

[Ellis]

Did some more fiddling yesterday.



The steel was a pain in the behind to bend, just don't have the right tools and work surfaces to do it. It came out alright though. It's really heavy, as I expected, at over 200g for the steel alone. I'll be lightening it eventually.

The reason it's seemingly so oversized is because I'm building it to allow for the larger tyres shown above. 30mph is just too attractive a prospect to ignore! The gap between the two folds behind the motor is to take 10mm HDPE, which will fit into the mirror of this piece on the other side too. The robot will be built around the resulting H shape.

Next is to drill all the holes in the right places, wang a few nuts and bolts in, and stick a battery on it!

[razerdave]

Brilliant . No one will be able to catch it!