Based on speed readings every wheel rotation we can now calculate HP based on change in speed (acceleration) and the weight of the scooter with rider. The Scooter Computer keeps a track of max and min HP, where min is a negative number for calculating drag forces (i.e. deceleration).
The test on the lathe showed that it picked up small changes in the lathes RPM and registered small max and min readings. Turning the lathe off registered a massive negative HP (since the head has less mass than the Scooter Computer thinks it has) and ramping up speed has a massive positive number.
The test works but we now need to do a road test and see if we see typical Vespa rear wheel horse power.
Note: I have also programmed a reset button so we can do repeated tests while riding
Note 2: For calculating drag through a coast down test, I need to factor in rotating inertia which increases the mass of a moving vehicle. The solution is to do coast down test at different speeds to factor out the change in mass.
1st Road Test
I have attached the sensor and tested the performance of the Scooter Computer on the way to Uni.
There was the odd insane reading (e.g. 9000 Hp) but this is due to not yet accounting for clock overrun. If the scooter is stationary for a period of time the system does not reset the speed to zero and then wait for the first pulse to start over, instead it keeps counting forever with only a limited size of number (it's just a matter of implementation to fix).
The test was only rough:

I guessed the mass of scooter and rider at 220 Kg but I had a bag and a glovebox full of tools + the battery for the computer.

The traffic was heavy and there were only a few flat bits of road where I could ring it out.

I also noticed that the Scooter Computer speed reading was only about 6 km/hr less than the Vespa speedo (which normaly reads 10 km/hr high) so I'll need to test the speed against a GPS. The current speed is calculated by tyre circumference but does not take into account load affecting this value.
The first test went well. The max horse power recorded was 8.2 Hp, which is in the ball park of what is expected for a mildly tuned Vespa (this is true rear wheel horse power). This is a Pinasco kitted scooter with only a Sito plus, so it should get around 10 Hp, however once the variables of scooter/rider mass and wheel circumference are measured correctly we can start doing more accurate readings.
2nd Road Test
The 2nd test on the way home revealed an issue with low speed accuracy. In 1st gear I redline around 42 km/hr and that means we only manage to get about 9 samples in the whole rev range. On the way home I again got 8.2 Hp in first, however in higher gears I got 10.6 Hp and I put this down to more accurate sampling at higher speeds. A problem though is that at higher speeds drag forces start to impact, so I would get an artificially low reading.
The system works but I'd like to log the data more carefully so I can see what is going on...
