The latest 2-Cell 2-channel plane
Proof that 2-cell scale planes work!
For the real thing see http://draganfly.com/products_4eh.html
Basically 4 motors pointing up, opposite motors are counter-rotating.
This project was started around October 2000 and abandoned at the early prototype stage. The design uses an AXDL202 2-axis level sensor to detect tilt of the flyer, combined with a gyro to detect yaw which these there is a fighting chance of controlling it. The control algorithm is in an 8-bit 18F64 PIC running at 10 MHz which handles all the mixing.
The following is a block diagram of the schematic
The original code is here.
The original prototype used 4 geared down scalextric motors. To get to the astounding height of 3 inches 17Volts was put up them, causing overheating after a couple of minutes- but it nearly flies. However this was enough to show that the algorithms worked although gain is a problem - too much and the system oscillated, too little and the sensors may as well not be there.
Geared Kenway N-20 motors available from Bob Selmans site are the choice for propulsion. An IR control version may well follow but since the original was based on the 4 channel GWS receiver then this will be used in the new design. I now have a new GWS that will be stripped down to minimum weight. The intention is to use surface mount electronics, the following is the parts list:
ADXL202E 2-axis level sensor, I've not found a source in the UK for this (analog devices sell direct in the US) - I'm using free samples try analog devices (even better!) the other parts are listed with farnell part numbers.
PIC16F84A-20SO 343-5106 p558 £4.66 IRF7456 353-8096 p375 £1.40 Need 4 20 Mhz resonator 648-190 p601 £1.72 Resistors 0805 size 100R 109-306 p170 £0.026 (min 50) 1K 109-312 p170 £0.026 (min 50) 680K 109-329 p170 £0.026 (min 50) Diode LL4148 739-182 p401 £0.054 (min 10) Capacitors 805 size 0.1µF 644-160 p8 £0.109 (min 10)
IRF7456 FETS have been chosen since they seem within spec. and are fairly cheap; the SO-8 layout gives the opportunity for swapping with other
devices.
The schematic is below, note that the gyro takes care of the yaw and is simply in-line with the receiver output. Provision is made for David Tait style
in-site programming. An RS232 output provides a means of diagnosing the code.
The new design uses 5ms sampling on the ADXL202E, and I've changed the filtering from 10Hz to 50Hz (To save on buying more capacitors!). The code above as not been modified for the 20 MHz PIC or to take into account the above changes.
The following board layout was originally a bit tight around the level sensor, I've increased the pad size accordingly. Print at 600 dpi and it should come out as 31.22mm by 28.16mm!!
Here is an overlay of where the components go as shown in the following picture (before the FETs go on).
In-circuit programming adapter
Here are some links for PIC programmer software and hardware and compiler that I am using.
11/12/2000 The latest code getting closer!
12/12/2000 The first test rotor is under way!
13/12/2000 Tests on the scope indicate the the FETS are being driven OK less than 10mV across the FET when switched on. The algorithm is a bit out, it only gives full thrust on full throttle, full left and full tilt to the right! The 300Ma batteries are giving well over 2A (shorted with a 1R resistor) on there first charge!
29/12/2000 Photo of the completed chassis with four of Dr. Chris's rotors::
Position of the GWS receive underneath the PCB:
The problems so far:
Not quite enough power to lift the batteries this may be solved by cycling them? For now I'm using an umbilical cord.
With the motors running, the level sensor does not appear to work, the flyer flips over.
Even with the level sensor disabled the PWM of the motors is not working correctly - is this supply ripple???
3/1/2002 Looks like it is supply problems, Ive just disabled the level sensor and temporarily powered the motors from a bench supply. Managed to just leave the ground to about a height of about 5mm for ½ a second!! - It is difficult to mix manually!! I'll rig up something more satisfactory and do some more tests.
