A speed controler for SPEED400 motor

Mike Norton has designed a superb speed controler for speed 400 based upon a 12C509 PIC microcontroler.

The original paper can be found on Mike's Web page (in better English than mine ;-) at the following address: http://home.hiwaay.net/~mjn / .

With his agreement, I propose to you here an adaptation of his circuit to minimize the number of components (only 11 components; let's build light!)... I recommend you however to go and visit Mike's page where the design of the circuit and the software are very clearly explained.

In its initial version, the variator includes the following functionalities:

- BEC function

- exponential gaz adjustment

- propeller 's brake

- LED indicators for control

The electric scheme is as follows (except modifications in red for the light version ):

The BEC function is provided by the units R1, R2, R3 and Q1

the propeler brake function is performed by components R5 R6, C4, Q2 and Q3

the indicators function is provided by R8 and D1

The version I propose removes the brake and indicators functions, (see modifications in red in the scheme). It is necessary however to take into account the following comments:

- R4 resistance was present only to consume some current on the regulator so that the regulation is effective. I removed it assuming that there will be always a receiver and servo fed.

- the R7 resistor is used to force at 0 the GP2 exit (engine control) as long as the bootstrap of the software is not carried out. Since the brake of propeller is removed, there is no more risk of short circuit if the engine receives a short impulse at powerup. One can thus remove this resistor keeping in mind you should not leave your fingers close to the propeller at start up!

- a quick switching diode D1(schottky) must be reverse wired on the engine'sterminals when R5, R6, C4, Q2 and Q3 are.removed

The resulting PCB is small enough and normal components (not CMS) can be accomodated flat to minimize occupied space.


The servo cord will be welded directly flat under the printed circuit. The colors (brown, red, yellow or orange) as well as the order of wire correspond to the standardized plugs (Graupner, Hitec, Futaba...)

Green wire are straps to be welded first. One will use isolated wire, the radiators of U1 and Q4 must not be in contact with the strap which passes below.

One will take care to galvanize the power tracks copiously, one will advantageously fold up the legs of Q4 towards connected engine.

The software to be programmed in the microcontrolor is available on the site Mike Norton' S hobbies ,

To obtain a ready programmed PIC, directly go at Mike Norton .