Fixing wheels to shafts - suggestions please

[Gary]

I am trying to put together a simple BEAM-type minisumo robot as a project for my son's Scout group. The most difficult bit seems to be finding suitable whhels and motors and fitting them together simply!

I found these motors at MUTR:
http://www.mutr.co.uk/prodDetail.aspx?prodID=208
http://www.mutr.co.uk/pdf_files/inlinemotor.pdf
which look great for £1.62 each (we're on a miniscule budget here!)

MUTR offer these wheels which are also very cheap:
http://www.mutr.co.uk/prodDetail.aspx?prodID=140

However, the motor gearbox has a 5mm double-flatted shaft and the wheels have a 3mm hole.

Can anyone suggest a cheap and simple way of fitting these two together, or any alternative motor-gearboxes and/or wheels? I need to get a pair of motors, gearboxes and wheels for under a fiver. The method must be simple enough for 10-year-olds with hand tools. I will need to make 5 or 10 of these robots so it needs to be reliable and repeatable!

All suggestions greatly appreciated!

[slurp]

Funny you should ask that.... very similar to what I'm using in the cardboard 'bot best lowcost solution I've found

I've used the other wheel with the 2mm hole:-

http://www.mutr.co.uk/prodDetail.aspx?prodID=141

then part drilled thru' using a 5mm drill bit. Even if you work the 5mm drill by hand a press drill will help you keep the hole square - if there's a drill stop even better 'cos it can help you get the depth right.

Push fit means that the wheel grips the shaft but a small counter sunk screw will secure it there. Think I used an M2 or M2.5 will check later, and sketch out the solution so that it's clear.

I've used the 'o'ring tyres but have some self amalgomating tape to try a "sticky" tyre.

best regards,
colin

[Gary]

Thanks Colin, counterboring the wheels to 5mm I can deal with. Half an hour in the garage should see 10 pairs of suitably modified wheels that can simply be screwed on. I think we'll go for eleastic band technology to provide some traction...

Would really appreciate some details on the screws and a sketch. Thanks.

Gary

[slurp]

I hope this makes it a little clearer:-



I've a small number of M2x8 Counter Sunk Screws from the local fastener shop. Could pop there for more, and post them, if you've a problem getting some. I think they where in the order of 5-10p but the memory is dim.

I've misplaced my notes on the wheel mod but I'm certain that I stopped with about 1-2mm of the tip breaking thru'. The shaft doesn't go full depth due to the taper at the bottom of the drill bit.

Go carefully as the drill cuts into the polythene very quickly, pulling the drill bit in.

This is the cardboard bot wheel, drilled the opposite side to what I sketched!



Note these low cost wheels will snap together to make a wider wheel, push fits the boss on one wheel into the counter bore on another!

best regard,
colin

[Gary]

Thanks Colin, I should be able to find some M2 screws locally. Now I need to work on some nice cheap, reliable edge and opponent detection...

[slurp]

Now I need to work on some nice cheap, reliable edge and opponent detection...

You want the "card board 'bot"? Daft question what's the budget?

Physical Edge detection (if a MDF ring) micro switches... ebay sent this link by a mate who's previously bought. seems they guy has a big bag and the item keeps re-appearing.

I've not checked all the optical methods recently but the KTIR0811S at Rapid are only 28p at the moment and for opponent detection the TSOP1738 is 85p but I'm not sure how the latter might fit in beam.... PICaxes are lowcost and easy to program tho'

Best regards,
colin