Whilest pondering on the acceleration data obtained from the Nano 33 BLE Sense which I have incorporated into a hand thrown 'rocket' and wondering what mathematical manipulations to perform on it in order to obtain some understandable data, it occurred to me that I could perform a simpler experiment which might aid my understanding. I remembered from my A Level Physics classes using a paper tape ticker to measure velocity as a truck accelerated down a ramp, under the force of gravity. It seemed to me that I could use the Nano Sense to measure the acceleration of such a truck directly as it rolled down a ramp, which should be a much simpler task than understanding the acceleration of a hand thrown rocket.
The Truck
I just happened to have a longish piece of MDF (obtained from the off-cuts box at the local DIY store some months ago now - very low cost!) which would make a good track for the truck. Also, I realised that I could use the chassis from my 1DUltraBot (1DUltraBot #3 : Finished (and working!) ) by removing the top parts and fixing the existing Nano Rocket to it, as shown below:
Nothing else has changed so the circuit and the software can be seen in the previous Blog - see above. The batteries are just there to be extra mass so that the truck will accelerate more, they are not connected.
Then all that was necessary was to put the truck at the top of the track, push the reset, wait for the 'go' signal (LED flashed on for one second) and then tip it down the track, see the video below:
There was a teething problem in that when the truck hit the wall and stopped, the de-acceleration was so high that it rattled the battery in the battery holder and caused a hardware reset - which wiped out the collected data. So, A soft bumper, otherwise known as a jumper, was placed at the end of the track to reduce the de-acceleration. This did work, although not every time, as illustrated in the video. However, a satisfactory run was made and data collected. Using Google Sheets I plotted the acceleration data and produced the graph shown below:
Not quite what I was expecting. However, there is the initial 'quiet' period at the beginning and then some (slightly) increasing values as the truck accelerates down the ramp, followed by the abrupt de-acceleration period, clearly visible as the large spikes. What I was not expecting was the spikey nature of the acceleration data obtained between the start and the finish. It does seem as if the peaks are increasing towards the end, indicating increased acceleration. To try and obtain a clearer picture I just plotted the X coordinate of acceleration separately.
From this graph it looks as if there is no acceleration as such, but there is some sort of vibration.
After thinking about this I realised that I think I may have been confusing velocity with acceleration. The acceleration for this truck is going to be that due to gravity (reduced by the angle of the track) and should be constant. The vibration observed is probably due to the 'rattling' of the hard plastic wheels on the hard surface of the track. These peaks do seem to be increasing in size, as would be expected as velocity increases.
So, some nice results, I think! but not quite what I was expecting. But, it does start to help with my thinking of acceleration and velocity. I think I will need more experiments and some more pondering!
Dubbie
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