Part 2: Size and Weight
by ElectroMaster , 27th July 2009 at 12:12 PM (1234 Views)
A big part in this project is choosing the size to build the HK, and also the weight. To figure this out I have been trawling the internet looking for potential motors and batteries that will be suitable. By knowing the thrust of a motor it will allow us to determine the maximum weight that can be supported and then will give us an approximation on how big to built the HK. Also knowing the battery will give us some insight into how long it will be able to sustain flight.
So in my search, I actually came across some great info. It was quite a big learning curve as I never even knew about brushless motors. I was somewhat blown away by their power and efficiency! They are smaller, quieter and more efficient that a normal bushed motor. Excellent! I found one motor which weights 76 grams and can output 1000-1500 grams of thrust. Having two of these would support anything from 2000, to 3000 grams in weight (theoretically). Batteries have also come a long way since I last checked in. Last time I remember, there was just one common type of battery (that was affordable), and that was a typical Ni-Cad 7.2 volt. However, once again it seems like there have been improvements and I have my eyes on a Li-Po battery which is about half the weight of the old Ni-Cad battery type weighting only 180 grams and has the same, if not more power.
It seems we can reasonably get about 2000-3000 grams of thrust from two brushless motors powered by a li-po battery (or two?). However, it's important to note that 2000-3000 grams would be a measurement based on the maximum load of each motor. If the HK weighed this much it would more than likely only able to hover, and would have very little agility or acceleration, if any. In conclusion and after careful thought, I believe the best weight for the HK would be around a total of 1kg. This should allow enough power and thrust for it to quickly change course if needed or rebalance itself if hit or affected by its surroundings. At 1kg I would expect the HK to be around 50cm long.