Just like with the Sequana I decided to go the brushless route.
One challenge is to find a BL motor that is both compact and slow(ish).
I got this one from HobbyKing: hexTronik 16gram Brushless Outrunner 1700kv.
First tests in the
hydrodynamic tests tank bathtub show that the motor is a little too fast but nothing really bad.
Another contender is this one - a little slower: Turnigy 1811 Brushless Indoor Motor 1500kv.
What worked on the Sequana was just scaled down: a car brushless ESC.
Despite mixed reviews it turns out this small ESC works great. I got the HobbyKing Programing Card for Car ESC as programing through the TX doesn't seem possible. Programing with the card was easy. Programing was done before the servo plug was changed to a smaller 1.25mm Molex Picoblade Plug.
Motor start is very smooth and motor can run at very low RPM. Throttle response is very linear.
Low-voltage cut-off kicks in at 3.3V (default) and just kills power leaving you stranded. Gradual slow down doesn't seem possible. I usually always have two boats with me but it would have been nice to have something a litte more forgiving.
I usually call it quits after 30 minutes so as not to end up stranded. Batteries are so cheap that you can afford a couple of them if you want to sail longer without worrying about the LVC kicking-in while in the middle of the pond.
I got a few of these: Turnigy nano-tech 1S 1200mah round cell.
They're compact. With a discharge current of 1.5A down to 3.3V I got 1200mah out of them.
I get over 30 minutes of run time from one one of those batteries. RX, servos work great even down to 3.3V. The problem lies more in the ESC.
I originally wanted something closer to 15mm (to make an even smaller springer) but there aren't many sub-20mm on the market.
I decided to go with a cheap Graupner 2307.20 plastic 3-blade propeller.
Aside from being cheap this prop has another benefit: it's low pitch of 10.5mm (0.50). This will help with motor being a little too fast.
The Prop Shop UK also has small props in their Standard Scale range: as small as 12.7mm (1/2") or 15mm (0.6"). But their pitch seems a little high to me.
I got a small Robbe M2 propulsion set which includes an M2 stainless steel shaft, a brass stuffing box, a shaft collar, a 30mm plastic propeller and a (strong) rubber coupling.
Well it wasn't necessarily the best buy: I won't be using the propeller. Stuffing tube won't work either as the length doesn't match. I'll only salvage the shaft itself, the rubber coupling and the shaft collar.
It still made sense to get the kit as I was ordering other stuff from the same shop but you could probably source just an M2 shaft. Rubber couplings (pack of ten) are available from Robbe, part number #1386, but any stiff 1mm silicone hose should do the trick.
I also ordered some
M2 threaded push-rods
from HobbyKing. It turns out they're closer to 1.7mm rather than true 2.00mm. Works as a push rod but as propeller shaft
or rudder pin there's too much wiggle/play.
Anyway I also ordered some brass tubes: 2.1mm ID, 3mm OD. Will use this both as stuffing box and as rudder post.
Rudder will be 3D-printed. Rudder post will be made of 2.1/3mm brass tube. And a leftover piece from the M2 propulsion shaft will be used as rudder shaft. To keep the rudder removable, a 3D-printed tiller arm will be glued onto a 2mm shaft collar.
I decided to get an OrangeRX R415X DSMX/DSM2 4 channel RX.
RX works well even down to 3.3V. No idea yet what range I can get but I don't intend to sail too far away with that little tug.
Servo plugs are Molex PicoBlade 1.25mm connectors.
There are three types of micro-servo/RX connectors making it a bit of a mess to find the propper servo.
I got a tiny HK-282A Single-Screw, Ultra-Micro Servo 2g.
Plugs right in the R415 RX and is designed for single cell operation.
That thing is tiny !
Micro RX components stray from the standard connectors.
The batteries came with no connectors at all (just two tabs on each end). The ESC came with no connectors either.
Connector on the servo matches the RX (Molex Picoblade 1.25mm).
I got a pack of JST 1.00mm to Molex 1.25mm adapters. I'll cut and solder the right connector to the ESC.You might want to keep a Molex 1.25mm to JR standard adapter at hand mostly if you want to reprogram the ESC (prog card has a standard servo plug).
ABS is a little picky when it comes to glues.
Acetone can be used to "weld" ABS parts together. Acetone "melts" ABS and when Acetone has evaporated you should get a very strong bond. You can dissolve some ABS scrapes to an almost putty-like state and use it as glue/filler. Work in a well-ventilated place!
When it comes to bonding ABS to other materials I used two types of glues: two-component acrylate and cyanoacrylate (CA).
In Europe there's Pattex Stabilit Express and UHU Plus Acrylit. Though I've only used Stabilit Express so far (on the Odin who has an ABS hull), UHU seems pretty close. Resin comes in a tube while hardener is a powder. Both compounds have to be mixed at the appropriate ratio. Pot life is pretty short (5-10 minutes).
HobbyKing has some cheap 2K-acrylate glue. I usually throw one pack in my order (or epoxy) if I still have some shipping weight available. I like it better than Stabilit Express as it comes as two viscous resins (like epoxy) much easier to mix than powder and resin. Pot life is just as short though.
I like epoxy much better but epoxy doesn't bond well - if at all - on ABS.
For small parts, CA works great. But parts cannot be moved/repositioned.
Stuffing tube was actually hammered in place as the printed "channel" was tight-fitting to say the least. Glue was barely needed anyway.
I went with 3mm "flat head" LEDs. LED bodies were painted to match the prescribed angles of visibiliy.
LEDs can be powered from the main propulsion battery but I decided instead to power them from a CR2032 battery.
CR2032 batteries are cheap and can be bought off eBay (and a CR2032 battery holder too !). LEDs are hooked to 120-ohm resistors to keep current down.
All four LEDs combined draw a little less than 9mA. A single CR2032 should be able to power the LEDs for a few hours. And I won't be sailing at night too often.