This article covers the most common questions we get asked here at RC Boat Bitz.
Water issues/Protecting Your RC Boat
The number one issue with an electric boat is always going to be water entering the boat and your speed controller is the weak link here. Over the past 20+ years of building brushless boats I’ve seen vast improvements in factory ESC waterproofing. In the early brushless days marine ESC’s of all brands were not even splash proof. You could expect to throw your $300-$400 Swordfish 240a speed controller in the bin if it came in contact with even a small amount of water. Making watertight enclosures to house ESC’s from kid’s lunchboxes etc (which caused other issues in itself) was all part of the build process for a brushless radio controlled boat.
These days most marine speed controllers are enclosed in an aluminum case as pioneered by the most popular marine esc on the market being the hobbywing 180a. https://rcboatbitz.com/product/hobbywing-rtr-180a-v3-esc-151b91/
Being waterproof does not mean your esc wires can’t conduct electricity while submerged and cause a short, plus terminals will still corrode and cause bad contacts without proper maintenance.
Generally a brushless motor can get wet (even submerged) and carry on working fine. Its good practice to spray water disbursement (WD40 or similar) inside a motor if it gets wet then spin it up. Obviously motor bearings will be of varying qualities depending on the brand, and ideally its better to keep water out, but having said that motor failures are extremely rare due to fresh water damage.
Salt water on the other hand will cause all sorts of issues and its essential to disconnect and clean all terminals after each use (don’t forget about your lipo balance plugs!) and flush the cooling system thoroughly with a syringe and fresh water.
All boats leak for one reason or another like lack of grease on the drive shaft to hardware installation without silicone. In any case some dry paper towel inside the hull should be all you need. If it’s to the point of sloshing around after a 5 minute run you need to remedy that.
Drive shaft lubrication
A thin smear of grease on the flex shaft is all you really need. You will find most of it won’t go past the bearing as you slide the cable back in anyhow. If the boat is to be used 3 or 4 times over a couple of days just once is enough, it’s fine to be a bit lazy and spray wd40 or similar into the stuffing tube at the motor end between runs. That can get a bit messy but it will lubricate the shaft well enough between runs. If the last outing was more than a few days prior take the time to remove the cable and regrease. It usually requires just 2x 10mm spanners to loosen the collet and the cable slides out. If your boat is TFL branded a little more work is involved to remove the cable but I won’t go into that here.
There are specific rc boat greases on the market made by Traxxas, Proboat and others. The difference between specific rc boat grease and ordinary wheel bearing ‘marine’ grease is the thickness. Try the correct stuff and you will not go back.
Speed controller wiring/setup
All brushless motors have 3 wires that need to go to a speed controller. Connect them in any order you like and the motor will work. If it is not spinning in the correct direction, being anticlockwise for a single motor boat, swap any of the 2 wires around.
The terminals on the 3 wires must be insulated, they must never come into contact with each other or speed controller damage will occur.
These days most speed controllers will sense motor type, timing requirements, voltage etc and are plug and play. The most you usually need to do (if at all) is calibrate the radio to the esc. That is simply to tell the esc where full throttle and off is. It’s a 10 second job in most cases and only required for initial setup.
ESC Failures – How Do I Protect My Boats ESC?
When I started building brushless boats in the late nineties brushless systems in rc boats were pretty much experimental at best, and finding a seller who could answer basic questions were nonexistent. Therefore my learning process was steep and expensive. I would buy batteries in batches of 10 or more expecting to use each one once or twice before it was a puffy smoking paperweight. Same went for speed controllers, and waiting for stopped boats to float to the shore was part of my weekly boating experience. I could have saved a ton of money and stress and gone back to my gas and nitro boats, but I am a determined (ok stubborn) guy.
The weakest link in any brushless boat is usually going to be your ESC. The rule of thumb when choosing an esc is make sure it’s rated at least 25% higher than your expected maximum amp draw. Most brushless motors will give you a ‘maximum current draw’ rating, but this in no way is the actual maximum number. Factors like the voltage used, prop size/ pitch, hull design, weight, how the boat is trimmed and even driving habits will alter how many amps will be drawn.
If you are not experienced with brushless systems in rc boats you really need to ask a reputable supplier before purchasing. Don’t rely on you tube for answers!
5. Batteries – What Sized Battery Should I Use In My Boat?
Battery selection is just as important as choosing the right esc. The 3 specifications are-
I will only cover this topic briefly here and go more in depth in a later article.
Cell count is your voltage. Total lipo voltage is calculated from each cell being rated at 3.7volts per cell, so a 3 cell lipo battery will be 11.1v (3x 3.7v = 11.1v)
Confusion happens when people don’t realize that is only the storage voltage.
When charged each cell will be 4.2v so a 3 cell pack is actually 12.6v
Capacity is simple; it’s like the fuel in your car’s tank. The more Mah the longer the battery will last and also the easier it will deliver its power
C rating is the most asked question we get about batteries. It’s simply the amount of amps the battery can deliver at once. For example a 5A (5000mah) battery rated at 50C can deliver 250amps (5a X 50C = 250A. Basically the better the quality of the battery the higher the C rating will be. When looking at C rating if there is 2 numbers ie 45/90 you only look at the lower number. The higher number is for burst, the lower is constant output which is all that matters at the end of the day.
Unfortunately due to the nature of competition between Chinese battery manufacturers, combined with the difficulty in proving actual battery specs, C ratings are often exaggerated. You get what you pay for as they say.
Heat is your number one enemy in electrical systems. When you make a change whether it be a prop or motor you need to check temps after short runs initially.
Batteries getting hot are a sure sign something is wrong. If you have a decent C rating (50C minimum for fast boats as a rule) is the capacity large enough?
Motors and ESC’s are water cooled so testing the cooler doesn’t help much, test the ends of the motor/capacitors on the esc. Is the kv too high for the voltage chosen, perhaps the prop is too large?
Wires – test both battery and ESC to motor. Wires getting hot and desoldering solder joints can mean the terminals are too small.
This is your number one problem solving technique. If you can’t hold a wire or motor for longer than a few seconds you’ve got problems. Most of the time the prop is going to be is too big. Maybe the guy whose setup you copied on you tube doing 100mph on 3s with 10 minutes run time wasn’t entirely honest with his specs.