EJ. Assuming you are talking airboats and not ordinary floaters here,  Brushless is the thing to use for this, and usually coupled with, gulp, LiPo batteries. I should think there is not much corporate knowledge of such an animal on this site, I have a feeling that a model aircraft site may have more experience of things air propellery. Mind you, I suppose they wont then have ANY experience of airboats !  I am not certain but I think a twin engined, and by this i take it that you mean two props airboat is almost certainly going to need handed props, to stop torque reaction twisting the thing over, at least on startup and quick changes in motor accelleration. A model aircraft may dip slightly in the air but a boat stands a good chance of flipping over, or at the very least veering badly off course (and then tipping over). ….and depending on the projected size I am not sure there is a big choice of props in this regard. Is yours a traditional flat design (optional action man) or are we talking cutting edge, er, something else?? And what sort of size/weight.   Ashley

Hi EJ,

Check out Novembers Model Boat Mag in it is a Air Boat with Brushless motor and ESC,NOT cheap, the prices make me come over all funny!.

   Len

Hi EJ,

I’ve got the picture now.I have seen the  ready-to-run versions.

The wiring should be a piece of cake. I have two diagrams from my esc instructions which shows a single motor,esc,battery and receiver.It will make a big file so I will upload it to a file sharing site and send you the URL.

I suppose you want to save weight and also get as much power out the motor as you can.

You say you have experimented with gears and props so you may understand the prop torque,motor rpm and power chart of your motor. If not look at this link . If you don’t understand any part of it then ask.
It doesn’t go into the merits of props but shows you how to deliver the maximum power to a prop i.e. for a given voltage you want to aim for a prop which will slow the motor to half its no load speed.

Use your rpm or current measurement to hit point A for maximum power.You can then further increase power by increasing the voltage.The power loss at A is 50% of the Volts x Amps you feed into the motor.

Assuming you don’t run at revs that require ballraces,the motor power rating is in losses(not voltage) and is down to material temperature limits temperature of the cobalt magnets,enamel winding insulation and plastic commutator insulation you can see through the holes. You will see maximum power figures for 400(27 dia) and 540 and 600(35 dia) sized motors on the Johnsonmotor website.

The power ratings of ones with internal fans will be higher down to the fact they will tolerate higher losses before the hotspot reaches its design limit.Watch though,because these are designed to run at high rpm and they will have a low torque/current ratio.

Easy if you did it for a living.

ashley needham wrote (see)

60 Watt, How do you measure the rpm of an electric motor?? is there an easy way??  Ashley

The slide rule generation use a spindle type unit which you can locate by searching rpm meter and so on.That device engages a clutch and counts the revs on a dial for a given time.That was the thing I used when working in cramped confines.I only ever used that at 3000 rpm max and with big powerful motors so it may influence a385 or the like.I suppose the best way is to use search engines to find an instrument like that for sale.

These are remote sensing without that drawback………

I’ve had a few frequecy meters over the years and used a photo-transistor+resistor and painted a white line on my motor coupling.

If you have a spare £60 you could get a multimeter from Rapid Electronics or other electronic suppliers to do the same thing.

An oscilloscope does the same job but you need to eyeball it and have the same two components or ahall sensor and know where to stick it.

If you work in a school,college or business concern there is bound to be something else I’ve forgotten.Any instrument is as good as the person who uses it.

Electronic magazines and websites are full of crude and simple frequency instrument projects so you may find something suitable for veroboard and use mains frequency as a reference (not mains voltage!!!) I’ll have a look see.

Tom

ps For a rough idea you can use current ,as long as you are flat out or have a true rms meter.You can get a motor stall current at low voltage and back calculate but it’s tricky to measure and make sure your voltage is constant without a regulated high current supply capable of running a motor.

If you are agile you can manage that with one meter,batteries and your motor.

Ashley,.

You had authorship of the five latest posts until I put this up!