Originally Posted by 89MIB
Hay guys very new to this type of boat i have brought this:
just wondering what type of motor and speed controller and how many cell lypo to get i would like to buy them off ebay as well
i would like it to be pretty quick and possibly water cooled? any help would be grate!
Kehrer Modellbau suggests a brushed 9,6v or 12v Speed 700-type, which, imho, is a bit of a joke in these days of affordable, high-powered brushless motors, and lipo batteries. It's not even cheap, so I completely fail to see any merit in using a brushed beer-can.. They run hot, they wear, they spit dirty brush-dust around, their efficiëncy is dysmal, etc. etc.
As such, my suggestions would be as follows:
-motor: Brushless 3660 to 3670 type, preferably 4-pole, a 2-pole with good quality neodymium magnets will work too (say, the big, Robitronic 3670 1/8 platinums). Watercooling is mandatory!
-Kv: about 2200 to 3000 max for 2s (3000kv needs a 80+ amp ESC!!) 1500 to 1800 for 3s, 1100 to 1500 on 4s. Rpm under load should be around 20000r/pm for this 28mm jet. Anything above that, will just make a lot of impressive noise, and cavitate.
-ESC : Any 80 to 120 amp watercooled brushless esc should do. I've run brushless boats with car ESC's with a watercooling block McGuyver'd to the cooling fins. Works like a charm, bit expensive, though. Specialized, high-amp, high voltage boat ESC's (mostly plane or heli-ESC's with watercooling strapped to it's FET's) are much more affordable -and lighter- than the programmable, but big&heavy, marvels that current-gen 1/8 car ESC's are.
-lipo: minimal 30c for 2s, and 25c for 3s and 4s. The Kehrer gobbles amps like nothing else, because a jet has a constant load, contrary to f.i. surface-piercing drives, who's load often goes to half of the original, when finally on plane. When using too low c-values on a jet, Your packs wíll puff, and they are ready for the bin.
Don't skimp on the wiring! At least 14gauge, but 12gauge is preferable, though a tad harder to solder with any iron below 80watts. Too thin wires will heat-up and soldered joints will come loose, believe me!
search for "seamonster brushless" for the cheaper motors with integrated watercooling. Size múst be 36mm diameter, otherwise the adapter won't fit.
I run my modded NQD wavechopper with a 28mm kehrer and a 2700kv watercooled 3660. The purple variation of the Seamonster, connected to a watercooled (!) 60 amp marine esc of undetermined make. As far as amps go, I'm really pushing it there.
on 2s 30c cells, it flies, on 3s it's completely mad, but starts cavitating at 100% throttle, plus the amps went through the roof.
(My sensible advise, though, would be to stick to 3s or 4s on something like a 1800kv 3660 motor. 2200kv if you want mad, instant acceleration, and don't mind the cavitation at full throttle. It'll keep the amp-draw reasonable)
Keep in mind that the Kehrer 28mm can only stand up to about 25000rpm, above that, the slightest imbalance of the prop, due to wear f.i., wil make it cavitate and vibrate, and it will hit the inside of the pump, wrecking the chamber.
don't expect record-breaking speeds, though. Jets are slower than surface-piercing props in boats. The suggested combi will get You about 30 to 40 mph in a small boat like the jetsprint, but instant accelleration! My modded Wavechopper tops-out @ 26mph on flat water. 3s makes it accelerate faster, but the topspeed remains in the low 30's due to the size&weight of the Wavechopper.
I also trimmed the Wavechopper fairly "wet" , which makes it track straighter and steer sharper in choppy water, but at a cost to top-speed.
For more speed, the jet pump should be bigger, 40mm at least.
hope it helps.