Spring is Here

The springs have arrived from 'ondrives'. They also sent me a couple of nice thick catologues detailing all the stuff they sell.

Springs are approximately 30mm outer diameter and from 80-120 mm in length. Spring constants go (approximately) 40Nmm^-1, 25Nmm^-1, 4.7Nmm^-1 and 1.7Nmm^-1.

As I mentioned in a previous post, I will only end up using two of the four springs. I got four because I wanted to be able to experiment with what worked best. All the springs meet my requirement of being able to fit the M8 stud and nuts through the centre. They have been nicely grounded at the ends to give a flat surface.

I have brought some 38mm diameter M8 washers which will act as the stops on the end of the springs. Think I might use a couple of these for the stronger springs – the 40Nmm-1 one feels pretty solid when I try to squash it with my hands.

Finished the Load-cell Bracket

The load-cell bracket has been completed. When it is installed in the pedal there will be a spring on the bottom which gets squashed down onto the bracket by a shaft running up through the hole in the bracket and through the centre of the spring. To ease the motion of this shaft there are polymer plain bearings fitted at both ends of the hole. 
 

The metal 'L' piece is bolted to the rectangle section using five M4 bolts. These have been very carefully positioned to; (a) allow room to be tightened and untightened, whilst (b) not obstructing the base of the M8 eye nut which fits onto the shaft – this was quite tricky as the M8 eye nuts are quite large and there is only just room inside the pedal box for them to fit. In fact I had to tweak the design of the accelerator pedal to make sure of enough room between the pulley and main support.

The metal shaft on the load-cell bracket acting as the axle is 8mm diameter steel. This is resting on two polymer 'plain bearings'. The shaft is held in place with a 'shaft collar' on each end, I got both of these items from a place online called 'motionco'. Whilst the bracket won't actually rotate at all during use, it is important that the mechanism is smooth otherwise it could interfere with the force being transmitted to the load-cell.

The final link between the L bracket and the load-cell is the M6 bolts. The size of these bolts is determined by the load-cell itself as only M6s will fit into its holes. I use a couple of nuts either side to be sure of a firm contact. When I was drilling holes for these bolts in the L piece I had to be careful measuring as I found the holes tapped in the load-cell weren't quite exactly parrallel and so the bolts diverge out very slightly. Also, according to my plans these long M6 bolts should just about be clear of the pulley at the end of the pedal box, but it will be quite tight on space.

Next to the plans

 The other end of the load-cell is bolted to the non-moving 'main support' piece. This will be bolted between the two sides of the pedal box structure. To do this I will have to partially disassembly the load-cell bracket and reassembly once the piece is in place.

Electronically, for the brake to work the load-cell will need to be connected to an amplifier circuit. I have a real boner to make my own amplifier circuit as then I can say 'I did it all myself'. I have been researching amplifiers and trying to piece together enough information to make my own circuit.