Quad-copter using STM8s Discovery Dev Board

Ken M., Fri Apr 09 2010, 06:08PM

While discussing Brush less dc motors used in RC vehicles with some co-coworkers at work one day, when the guy I always work with went on a tangent and started talking about BLDC motors being used In EDF's (Electric Ducted Fans) for foam jets and and the thought of using some EDF's for a flying platform. We discussed the idea of a flying platform a little while but I shortly shrugged it off, but was still curios about EDF's when online did some research on them and the more and more Info I got the more the idea of a flying platform or Quad-copter came to mind. Later that night after work I decided to start researching quad copters (since most of the google search results lead me to hobby sites and the fun filter at work is pretty tough) I came across some design ideas over a RCgroups.com that demonstrated a basic quad-copter design is extremely simple, just by using a receiver 3 gyros, 3 V-tail mixers and 4 motors as well as a chassis, I knew then I wanted to build one. The next day went to work and started discussing the idea with the same coworker and he suggested the use of a micro-controller to do all the mixing and stabilization using an accelerometer I looked into the whole accelerometer idea and decided it was the better path since then I could get more control from the mcu and accelerometer then I could with just gyros.

Thus the quad-copter project began, started by figuring the minimum thrust to weight ratio I thought would be need to get the copter off the group and to move a MPH's as well as possible carry a small payload maybe a camera or a 1 liter soda bottle and settled at 2+:1 and since I still wanted to use EDF's I then set out to find the most powerful EDF's I could while still trying to keep cost and weight low while still getting lots of thrust. Came across a few 64mm EDFs with no motors at but some some of the better "claimed" thrust EDF's the weight of 4 of them plus 4 motors that would have enough torque, rpms, and be usable for them, the total weight for copter would be almost 4Kg and the complete EDF systems (motor and edf no speed controller) would have cost almost $400us I wasn't too keen on the idea not to mention after I did some more research on EDFs I found out they aren't that great for static thrust which is necessary for vertical lift.

So I decided to see how most of the other quad-copter people provided thrust and found out most just used 2 blade props, in order to find the proper prop to lift my calculated weight of ~2.5K (still sounds heavy but this weight is figured using the LIPO batteries I have around the house for my other RC vehicles mainly cars and trucks) so basing calculations off which allows you to select a propeller and either choose a target thrust or a target rpm, I went threw all of the props just to see which ones could produce ~1000g of thrust each to give me a calculated thrust of 4000g to stay around my 2:1 minimum thrust:weight ratio, most of the propellers that could used low RPM High torque motors which still cost a fair amount of money (less then the EDF systems but more then what I wanted to invest in) but their weights would put me closer to 1:1 or lower on my ratio. then I found these motors


not too heavy and a claimed prop size of up to 11x4.7 so I started going back threw the thrust calculator and looking at all the props below 11x4.7 that could handle that motors max rpm and still be able to provide ~ 1000g of thrust and thus I came a cross 10x4.7 or 10x5 inch props since I was gonna get those motors from hobbyking.com I looked into what propellers they had and found these



a little smaller then what the motors max is but that should mean a little faster rpm response from the motor and should require less power, resulting in longer flights and cooler components.

Now to actually control the motors using servo signals I needed an ESC still trying to save weight and money but allowing head room for current spikes temps and expandability later down the road just in case the props I got don't provide enough thrust I went with some 40A continuous and 50A peak for 10sec escs




Well with all this talk of servo signals Radio control and the fact that the ESc is ment to be used with a RC transmitter and receiver plus the fact that this is an aircraft and I'm gonna need at least a 4 channel transmitter for throttle, forward backwards and rotate (rudder control) my first choice was a Futaba but since they are a name brand in RC their stuff has a steep price tag, somewhere along the lines of $400 for a 6ch no receiver or transmitter module (2.4GHz) which are another $200 even the used ones on ebay are still about $200 for the older FM and AM ones, So yet again I'm looking threw hobby king and find this nice little gem, more channels then I need but still it allows me expandability to add more functions on later.




and this transmitter module

The transmitter outputs a serial pulse train with Channel 1 being the 1st pulse then Channel 2 and so on. The pulses shift as each channel is adjusted, and if each control stick is at center or neutral the pulse width is 1.5milliseconds with a minimum of 1millisec and a max of 2millisec heres a video of teh pulse train as I move the control sticks forward backward left and right, although you can only see Channels 1, 2, and 3 on the scope



More to come tomorrow.