Hello David,

I was slightly surprised to read that you had wired the motors in series – usual practice is to wire in parallel to the ESC if operating from a single ESC. Was there a special reason for the series connection for the motors ?

Ian

If you have a digital multimeter with an adequate amp rating you could do a test in the bath (assuming that your model will fit in the bath). Graupner states that the 280 operates most efficiently when the current is about 1.6 amps with a 6 volt supply. Note that the current can rise to about 7 amps when the motor is stalled. Given that the motor will operate in excess of 10,000 revs even when loaded, you will need a very small prop to avoid overloading the motor. From your photos is looks like you have 3 bladed plastic props – I assume that they are small diameter (eg 20mm) ?

If you find that the motors are consuming too much current (ie they get too hot) you can insert a wirewound power resistor in series with each motor though this is obviously at the expense of efficiency. Let's assume that at full throttle each motor has an armature current of 2 amps. Then a 0.5 ohm resistor will reduce the voltage by 1 volt and will dissipate 2 watts (so you need a resistor with a power rating well in excess of 2 watts in order to keep the resistor temperature low).

Ian

David. thank you. I had to glue the "tank" draw shut, cuttoff and fill the wheel wells and modify the innards to provide some room for the bits. The only work above water was spraying the whole thing grey and painting the deck (using a very small brush) brown and blacking up the bollards here and there. The detailing on this, as a kids toy is very good. It needs no ballasting and is very stable. HOWEVER, it is much heavier that yours will be, and a bit wider compared to its width.

Try Marks model Bits for parts, propshafts.. he will make to order all at the same price. I happen to have some 3mm shafts and 25mm props left over from something else. I would have used a 4mm shaft if not, due to the difficulty (or expense) of finding props at this size. Graupner I thing may do soem at 2mm. An alternative would be to cut down a larger prop. I am aware that this will do nothing for the effiiency of the prop, but I think it will not make much difference considering the power available etc.

Ashley

Hi David,

for really small scale threads, ropes etc try the copper windings from a very small electric motor. Ok they'll be copper coloured, but they will be very small diameter and can be very lightly sprayed black with airbrush or black u/c. The thing is, being wire you do not need to tension, but you need to strectch on a former prior to use to get nice and straight.

I've used on small scale card models.

Kimosubby