Pennybot chassis part 3

A chassis remade sans wheels

With the programming and breadboard design done, and the schematic finished it was time to start working on a board layout.  Not long into this process I worked out the chassis I had wasn't ideal.  It was only 8cm wide but 10cm long.  I didn't have room for a decent front scoop and the line sensors would be a very tight fit.  I was using a Tamiya base plate and I considered that I could simply rotate the board and easily make pennybot wider (out to 9.6cm) without having to change any of the holes I had drilled in the motor brackets which I really didn't want to have to make again.  Also the five AA batteries could now be mounted across the width of the chassis instead of along it so I would have more space at the front/rear and the centre of gravity would be all along the wheel axles.  I decided to cut down the motor brackets too so that they would only be the length of the motors themselves.  All this took a few hours on a Saturday.  The result was a wider pennybot with a better battery placement, but I had swapped one set of issues for another.  The Tamiya board is only 6cm wide, thus with the motors brackets and batteries there wasn't very much room (ie free 3mm holes in the board) on the front or rear to attach sensors, circuit boards, etc.  I could buy a bigger Tamiya board but had just done an order to Little Bird electronics and didn't want to pay postage again.  With a big sigh it was time to make a new chassis (number three) from scratch.

For my new chassis I wanted to make sure I remembered to do some key points.  I can get lost in problem fixing and forget the wider implications of design choices (and regret them later).  For all the mounting holes rather than drill straight through I would drill and tap 3mm threads.  This way I wouldn't need any bolts and wouldn't need space for the nuts.  That did mean I would have to cut down every bolt to size.  Bless the dremel.  I also wanted the base plate to be as big as I needed it.  Ie 10cm long and approx 8cm wide as the wheels and axles shafts would take the width to 10cm.  Looking through the scrap box I found an old plastic electronics project box which I never got round to using.  The box was curved on each side so cutting one half in the middle would give me a pre made scoop.  Also the dimensions fitted.  Some quick hacksaw and dremel work and I had a new base plate.  I put the axle shafts at the midway point and drilled and tapped the mounting holes.  I wasn't sure if the tapped screw holes into the plastic would be strong enough but they held.  Then the 5 AA batteries were placed underneath and things were looking good.

Batteries and sneak peak at the sensor board

Next up would be the front line sensor board.