The latest 2-Cell 2-channel plane
Proof that 2-cell scale planes work!
Basically 2 motors one on the left wing, one on the right, alter the relative speed of each and we turn!
A couple of design issues:
Do we add to one motor and subtract from the other? Or only add or only subtract?
The arguments currently faovours adding and subtracting, this should leave the total power the same unless the motors are already on full power!
The code is based on the 4-motor flyer the code
Left' and right' will eventually outputs with an exponential feature the other two are linear.
For now left' and right' have a gain of 4 compared to the over two outputs.
farnell parts list:
PIC16F84A-20SO 343-5106 p558 £4.66 IRF7456 353-8096 p375 £1.40 Need 2! 20 Mhz resonator 648-190 p601 £1.72 Resistor is 0805 size 1K 109-312 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. Provision is made for David Tait style in-site programming. An RS232 output provides a means of diagnosing the code.
The following board layout is that for the 4-motor thing and could be easyly modified (exercise for the reader?) Print at 600 dpi and it should come out as 31.22mm by 28.16mm!!.
Across the top the connections are right', left', right, left.
Down the left hand side we have 0v, ch4, ch3, ch2 (throttle), ch1(roll) and +V. These should line up with the GWS r/x (see picture on 4-motor page).
The programming interface along the bottom has the following connections: prog, 5v, data, clk, 0v
In-circuit programming adapter
Couple of caveats:
The throttle is reversed to match the GWS speed control!
Isolate the circuit from the motor supply as best you can - a voltage converter is probably the best (The NiMh cells suffer a large voltage drop as they deliver current (4 cells drop down to 2.5V) but they are capable of providing the current).
Make sure the PIC gets a bit more that 3V (say 3.6V which is probable better for the GWS r/x) I suspect that below this the FETS may not switch fully on!!
There is no start up protection (like the GWS speed control) - I'm assuming this will only be used for small planes!