Hardware Acquisition
I have spent some time over the last week proving beyond a reasonable doubt that the parts are the correct ones for the job.
Using the specs for ducted fans shown on the Amazon listing, I have created a spreadsheet to calculate the costs and capabilities for each of several ducted fans available in the range of a supplier.
The above table shows the specs of the various EDFs in the range, and calculated remaining thrust capability (thrust remaining after the entire carriage weight is taken into account) and the unit thrust per £GBP.
The total carriage weight is calculated as:
2*(EDF weight+Recommended ESC Weight) + Recommended Battery Pack Weight + 500
With the final added 500g to account for the microcontroller, sensors, 3d printed chassis etc.
The table determines that the 3S 50mm and 3S 64mm EDFs are not adequate as the thrust produced by these models is less than the total carriage weight would be if these fans were used, meaning the carriage would be unable to move, even theoretically. The 4S 50mm does rise above this threshold, but only very slightly (by 40g) and these calculations do not account for air resistance, track friction or inefficiencies in the motor. It is therefore unlikely that this EDF will be fit for purpose.
The sensible options seem to be to either stick with the 4S 70mm for a 90% higher remaining capability and a 63% higher remaining thrust capability per £GBP, or downgrade to the 4S 64mm to save £15 total and potentially increase battery life by up to 44% (assuming constant peak power draw).
You will see I have also added the next highest model, the 6S 70mm to the table for completeness, but this model's power consumption is far greater than that of any of the “lower tier” models. Because of this it requires a much heaver and more expensive battery pack and does not provide a clear warranted use case.
I have decided that the higher remaining capability of the 4S 70mm will provide a greater thrust window with which to experiment and is therefore worth the price. I have ordered one with which to begin testing.
Unfortunately, the delivery time from this supplier is 8-14 days and I could not find any other suppliers selling EDFs with similar specifications in a more suitable timeframe. I may have to order a smaller and less capable EDF and ESC if I can find one with a quick delivery window in order to get some experience writing code to interface with the ESCs and control the EDFs.