RC boat electronics

by Gilbert
(Tasmania. Australia)

I have built a model boat which is 1.2 meters in length and I am up to the fitting of the electronics. Problem is, I have no idea about electronics. I have tried to get information but people are reluctant to give any. I need an electric motor, radio transmitter and receiver, ESC speed control. Could you tell me what I want for the job. Thank you.

From your question I'll assume you know the hardware end of things, so I'll leave that out of the discussion. From what it sounds like, here is what you need:

  • Motor:

    • You need to figure out your power needs. I wrote a page about sizing the power of a model boat motor. I'm guessing 60 to 120 Watts would be sufficient. I'm guessing a Graupner 600 with integrated gearhead could be a good place to start if you can find a place that sells them. Unfortunately, surplus motors in this range are rare, but it can't hurt to look around.

    • As I mentioned, you'll need a geared motor. Depending on your propeller, most electric model boats do best with 1,000 to 4,000 RPM at the shaft at full gusto. The bigger the model, the lower the RPMs typically. This also differ by boat type and scale so use the numbers as a guide only. To accomplish this you need a gearbox between the motor and propeller shaft. You can build your own, but it is much more convenient and probably less expensive to get a geared motor. Aim for 2:1 to 4:1 gear ratio.

  • RC Battery Packs:

  • You've got plenty of options here but the best choice, in my opinion is to use a NiMH pack. They are reasonably priced and the market is full of good options. The buoyancy of your model could easily handle a lead acid cell, I'm sure. Problem is, lead acid puts out a lot of voltage with little or no load. Most ESCs can't handle more than 12V, so you'll be chancing the life of your ESC.

  • ESC:

    • You want to make sure it comes with Reverse.

    • It must be able to handle the max voltage of the RC battery pack plus a margin.

    • It needs to be able to handle the maximum current your motor will draw under normal use.

    • There is usually a mention of "numbers of turns" on the motor. If you're using stock motors, you have nothing to worry about.

    • Consider the connector type on your battery pack: Tamiya, Kyosho or Traxxas. There are adapters, but it's so much better to plug-and-play.

    • Watertight is a plus.

    • ESCs these days come with a BEC (Battery Elimination Circuit). Essentially a power drop to your radio. The era of always having separate batteries for your receiver is now gone. Having said that, some feel having separate power is a good thing, so your choice.

    • I'd highly recommend a potted ESC, such as the Pro Boat PRB2314. It is rated at 40 amp continuous. At 120W and 8.4V that comes out to 14.3A - plenty of head room.

  • Radio:

    • I believe the 2.4GHz radios are here to stay.

    • Get a FHSS (Frequency Hopping Spread Spectrum) radio.

    • Stick or wheel depending on your preference and number of channels you feel you need.

    • Most radios no longer come with servos. Your boat would probably do well with a standard servo for steering. Click here for more on RC servos.

    • I recently purchased a Tactic TTX404 and I'm very happy so far. It feels a little "plasticky", but at this price I think it's the best in its class.

  • Other

  • You can add other specialized electronic modules. The most common are running lights, motor sound, pumps etc. Running lights can be connected through a manual switch somewhere on the model. The others are generally more involved and ought to be on it's own channel or piggy-backed off another channel using a Y-cable. I feel that going any deeper is beyond the initial question.

Comments for RC boat electronics

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by: Anonymous

Thanks Petter, for clearing my radio confusions up, I have a much better idea of what I am looking for now. I am learning slowly, But your expertise is very much appreciated.

Radio channels
by: Petter

Sounds like you're making good progress. Good work!

First, "surface radio" is referring to the regular bands that the AM, FM and PCM technologies were tied to. Essentially, certain bands were dedicated to airplanes so if someone were out flying and you decided to test your radio to your boat nearby, the plane wouldn't crash.

Unfortunately for us, most of the radio market is in RC aircraft. I believe for two reasons: 1) More people are flying than running boats and 2) They are harder on their equipment so buy to replace at a higher frequency.

Based on radio configurations, it's easy to see what application comes next: RC cars and buggies. I'd say 99% of surface radios are synonymous with RC cars with two or possibly three channels and mostly pistol grip.

The closest application to multichannel RC boats, in terms of radios, is probably what the Robot War community has dreamed up. It's a good place to glean ideas from. More about this later.

With the technology that the 2.4GHz band brought with it, there is no division between "air" and "surface". So you can use it for whatever you want. Problem is, on multichannel radios the sticks are laid out for the purpose of flying. For a boat with throttle on the left vertical stick and steering on the right horizontal, you're left with two proportional channels one on each stick.

So to the question, yes you have two proportional channels left to control pumps, running lights, winches, smoke etc. But the sticks to control them may seem awkward, especially with the spring detent to center.

You can make them less so by doing some surgery to the radio itself by removing the return-spring for the channel/stick.

This used to be a very easy thing to do. I have not peeked inside a radio less than 10 years old, so the springs may be more buried than they used to.

I've heard of people rewire the radio to have a couple of switches mounted to the of the radio enclosure in place of the extra stick motions.

This is something I have not done, but should be physically feasible. A word of caution, it may be illegal to rewire RC radios where you live, so check your local regulations first.

On the receiver end you can now buy (thanks to the Robot Wars Guys) relays that you plug into your transmitter. Some are fairly sophisticated with several functions and relays for each channel. You can find more at Robot Marketplace.

I tend not to use more than two channels on my RC boats...at least so far. I have installed running lights and smoke in one instance, but resorted to manual switches that were turned on at the dock and left on.

by: Gilbert

Hi Petter. I have been looking around at radio transmitters like the Tactic TTX404, But I would like to be able to operate more than two channels. Every site I look at tells me I need a two channel surface radio.

Can I use the TTX404 so I can work other things Like pump, smoker, winch etc. The problem is I am not sure if it will operate a boat. I have fitted a auto fan motor to my boat as you suggested & have water cooling coil around the motor as well as air cooling & have a HiForce 320amp ESC air cooled to fit. It is coming along well now.

Glad I could help!
by: Petter

The more I think about it, the more I think this solution could be a really good compromise between money spent and pure function.

One more thing to keep in mind - the motor run best the closer to 12V you can get. At the same time you will most definitely fry the ESC if too much voltage is applied to it, so be careful. Check the ESC spec once you find a winner and stay within recommended max voltage.

Best of luck!

P.S. Hey, I never said I know what I'm talking about, but I'm glad I sound like I do! For the record, I've never built a boat as big as what you've got, so you are a bit of a guinea pig here. In all seriousness though, again, I think you're on a good path.

P.P.S. I'd love to see more pictures once you've got this all worked out. I'd encourage you to upload them into the model ship gallery.

Boat Motor & ESC
by: Gilbert

Thanks Petter for the information on the Motor and ESC. I will take your advice; find an Auto fan motor and look around for a ESC as you suggested.

That will not be a problem for me as I am a retired mechanic and spent many years marine Diesel fitting and hull repairs on fishing boats - some quite large wooden boats. That is why I have taken up model boats.

I will let you know how I get on. Thanks again for the help. It is great to be able to talk to someone who knows what they are talking about.

by: Petter

Because of the large size of your model, you are pushing up against the upper fringe of mass produced hobby gear, and starting to venture into low volume Robot-War components. It's rugged stuff, but pretty costly.

The Robbe 1000 motor is nothing special. I had to look it up, but it is clearly an automotive fan motor (made by Bosch or Siemens probably). For a direct drive, it looks about right, but I think you could find a very similar motor a lot cheaper. Just make sure, before you spend any money, that it will physically fit in the hull.

Your cheapest option would be to pick one up at a local junk yard. Most automotive fan motors have an 8mm shaft, so make sure you have an appropriate coupling. Also, some have open armature, which may not be ideal.

The ESC they proposed will most likely work but, as you noted, it's pricey. On the other hand, I wouldn't bet on the Proboat ESC holding up with these high-torque motors. The current when running under normal conditions is probably OK. However, here will be bursts though and the motor could stall (seaweed in the prop anyone?).

You could chance it by connecting a fuse in the motor circuit of say 25-30 Amps or research high-amp buggy ESCs. They may not be watertight, but should be able to hold up under normal use, and be a lot less expensive than the Viper ESC. I think some are sold without reverse, so make sure they do mention it in the spec.

Boat Motor & ESC
by: Gilbert

Hi Petter. I received an email from a place in Melbourne Australia, that I contacted some weeks ago. They suggesting that I use A Robbe 1000 Motor, and a Viper 75 amp ESC.

I would like to know your thoughts on them, They don't come cheap though. Motor $95.00 AUD and the ESC $120.00. I have told you in the last post that my boat was 1.2 meters which was not correct ,it is 1.5 meters in length.

I have a Raboesch 80mm four blade propeller fitted I could not fit a bigger one because I ran out of room.

Dual Motor Option
by: Petter

I started typing a response, but it was getting way too long. I decided I'll write up a page and post a link here. I also went ahead and bought some parts to test to make sure I'm telling you the right thing.

In short, you need:

  • One ESC per motor.

  • One v-tail mixer.

  • One Y-harness.

  • More in a bit.

ESC for twin screw
by: Manning Harvey

Petter, Good afternoon.

After some consideration with my Pilot Boat model I have decided to make her twin screw. I have purchased all the hardware and one ESC as you suggested. Do I need two speed controls? One for each motor? Or can I wire up one ESC for each motor? I'm thinking I need two. To get the full twin screw effect.
Thank You so much.

by: Petter

I appreciate the kudos. It's fun helping and spreading the inns and outs (as best I can) of this under-rated hobby.

This is Great
by: Manning Harvey

It's great to know I am not alone in this search. Petter has been I God send in the help he has shown me in this subject. I'm printing this out and posting in my workshop.

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