Thanks for the comments guys. Has anyone else experimented with models in this size?
Here's a brief description. Power is 2 'pager' motors (mobile phone vibration motors) easily available in UK from the very helpful people at Precision Microdrives
. These motors are low voltage, 1.5v or maybe 3v. so power is supplied by a single AAA lithium cell. Props are crude brass disks bent to for 4 blades. There is a fixed rudder. Shaft is microbore brass tube with close fitting N/S wire and no seals are needed.
Radio is taken from a toy called X-Sub
which uses a knock-off Hong Kong chipset providing independent motor control with reverse and two forward speeds. As you can see the radio just happens to be the exact shape to fit in the Deans vac forming. The radio has a voltage doubler supplying 3.3v to the chipset. I greatly prefer the disposable cell to rechargeables because i know it won't die suddenly.
The radio is styled '40Mhz' but unfortunately the receiver has no selectivity meaning it is swamped by any other 40Mhz set in the vicinity. X-Sub is also available in 49Mhz so that you can use 2 together but UK importers don't understance this nuance and only stock one version! The radio also has very limited sensitivity meaning that the best range on the water is about 20'. There is a published mod to boost the Tx power which I have yet to try.
The photo shows the first ever simultaneous sailing of the picket boat with it's 'mother ship' in September. This only became possible when I moved the other models to 2.4Ghz. Even then it can't be demonstrated at club events because any other tx kills it. I've looked at many other R/C toys but virtually all of them use Limh or nicad cells in a 3 cell pack - far too much voltage for the motors. I've also looked at micro aircraft R/C setups but few of these provide 2 motor reversible operation. The best fit so far is a micro radio with proper superhet front end running a single motor and rudder operated by a coil servo and I intend to try this in the Admiral's barge. Of course all this stuff is 5v which is very awkward.
NHP651 is right about the surface tension effect and it's this that prevents the little boat being swamped by the first ripple. However, it's extremely vulnerable to fish and ducks nearby are like nuclear test explosions! Actually the boat does have positive boyancy but only just because the gubbins are far too heavy - Ive even got white metal ventilators! - and it would sink if the intended alkaline AAA cell was used, hence the Lithium.
The surface tension I was referring to in the title is the effect that occurs between the boat and the mother ship when coming alongside. Basically they 'stick' and it takes all the motor power of the little boat to break free again. I've thought about pouring paraffin on the surface but I'm not sure if Nick the farmer would be too impressed!
So why did I do this? Partly because that Deans vac forming was too much to resist. But mainly because I'd like a 'Turbinia' to sail amongst the Victorian fleet. Turbinia's hull is much more slender and displacement even less, so it's beyond the technology at present, unless you know better of course....