From Facebook:https://www.facebook.com/photo.php?fbid=1737639643056030&set=pcb.1247612252243758&type=3&theaterCan a £5 brushless motor power a fast electric boat? - Neil McGrath I was keen to find out so purchased one of these:
https://www.banggood.com/Racerstar-BR2212-1800KV-2-4S-Brushless-Motor-For-RC-Models-p-1085434.html?rmmds=search&cur_warehouse=CNI also picked up a 40A brushless controller for less than £10 from the same supplier.
https://www.banggood.com/Double-Sides-Brushless-ESC-20-or-30-or-40-or-50-or-60-or-80A-Underwater-Thruster-RC-Car-Boat-Parts-p-1649988.html?rmmds=search&ID=516805&cur_warehouse=CNMy local boating lake is fairly small so I was not after mind blowing speed but would be happy to trot around at 15-20mph in my submerged drive deep vee.
The motor spec states that it should be capable of delivering over 200 watts at 11.1 v. This would be much more power than I had available in my fast electric racing days back in the 90s, so I had high hopes.
My battery of choice is a 2200mAH 3 cell pack which my local model shop is selling for just £11.99 and I predicted would provide about 5 minutes of run time.
The motor was mounted on an L shaped aluminium bracket with a U shaped aluminium tube attached to provide water cooling.
During the first trip to the lake the motor coupling could not take the strain and worked loose almost immediately.
On the second trip with a new coupling I managed about one fast lap before the same thing happened again (at least the motor has plenty of torque!).
I then invested in a collet style coupling, ground a flat onto the motor shaft and used plenty of thread locking compound to secure the grub screw - success!
On the third trip to the lake I did a couple of slow laps then opened it up. The boat was immediately up on the plane and was certainly giving the local IC boats a good run for their money. After a few laps I brought the boat in to check everything was OK. It did smell a bit warm and if I licked my fingers before touching the motor there would be that distinctive sizzle as the spit instantly boiled on the surface. The rest of the time at the lake was spent driving a couple of laps then allowing time for the motor to cool between runs. The ESC was getting quite warm but nowhere near as hot as the motor. The batteries stayed cool throughout the exercise.
With the final battery pack installed the boat was back shooting across the water but this time it was starting to stutter. It was then dead in the water and had to be recovered. Back on dry land the ESC shrink wrap had split open and my time at the lake was over.
After returning home, I ordered the 80amp version of the ESC then went out to the garage to dry off the boat. Once everything was dry I decided to see if there was any life left in the batteries. To my surprise, the motor burst back into life and everything was working perfectly. I was sure that the ESC was toast, but at least I can now carry out some further testing while I wait for the new one to arrive from China.
After this test it was clear to me that the boat was over propped. I was using a 35mm plastic propeller that is really meant for surface drive. The motor cooling was also clearly inadequate. I have now fitted a water cooled motor mount from Prestwich models, which should do a better job than the old L bracket with a bit of aluminium pipe attached. The next test will be with a 29mm prop which I hope will allow the motor to spin more freely, draw less amps and help keep the temperature down.
Watch this space. I will let you know how I get on. I picked up the test hull at a boot sale so I am not sure what it is. I think it was probably an RTR boat originally. I would be grateful if anyone can identify it. The brushless gear will easily fit in the smaller GT400 boat, so it should really be a pocket rocket! John Gaze can you suggest any KV/prop combinations that work well for you?