shishtawoo

Well, coming from rc nitro planes the thought of using electric isn’t appealing. Although my dad said electric might be fine i did some math , converting horse power to wattage to compare power, and discovered that a g26 marine engine would give me 2000 watts of power compared to the 100 watts produced by two electric motors. All i need to know is if these figures are completely off.

Oh and the motors are going to be powering a 4 prop 7.5 ft, 85 pound scale model off the uss north Carolina which i want to go fast( for its size).

piper_chuck

My Feedback: (12)

If I were building such a scale boat, I would choose electric. The primary reasons are that it's much simpler, and is significantly cleaner. Electric is also much smoother, which means you'll have less problems with little details falling off. If you go electric, you can put one motor on each shaft. This gives you the ability to do interesting things, like reverse, without having to use a gearbox. Also, I assume you'll need ballast for this boat, right? Why not use batteries as your ballast so it's performing a useful function?

Oh, and good choice of boats. I've visited it a bunch of times, if you're talking about the BB 55. It's got a remarkable history.

Ron Olson

My Feedback: (1)

I'd go electric with that ship also. With them that size you can get motors from out of junk cars to power it. The weight of the big battery/ies) will help it get down to the waterline. You might as well put useful ballast in it.

shishtawoo

yea i completely agree with you guys on the aspects of useful ballast, which is why i considered using electric, but are the power calculations i made accurate they showed using a single g26 gas engine would be literally 20x more powerful than using two electric motors and approximately the same price, if not cheaper.

ryan_t888

I also would go electric.

The Zen makes about 3.5hp. That is about 2600 watts of output power. It would be around 3000watts of brushless input power or about 3600watts of brushed power.

I don't know what electric motors you are/were looking at but 100w in total for 2 means a very, very small motor. If you got 4 300-400watt scooter motors that should be plenty for your hull. Although I don't have experience at that level.

Ryan

shishtawoo

Well i was looking at the Graupner Motors Speed 900 which has uses 8 amps of draw at 12 volts wouldn’t that translate into 96 watts and if i had two i would have a vessels powered by 192 watts of power. I’m kind of confused about how the electric engines would generate 3000 watts of energy without having enormous coils and if they are available can someone give me a brand and model because if they put out those numbers at a reasonable price id buy them tonight, again i can’t stress how new I am to electric motors lol. Oh and I can’t stress how thankfully I am for all your help.

ryan_t888

I run a Graupner 700 8.4v and get 432watts from it.
An 800 motor I have used ran 550 watts. (both input wattage)
I believe a 900 would be similar.

The figures you are looking at are always for long life of the motor. We always feed them more voltage and draw more current then what is there.

Like I said, you may want to look at scooter motors not high RPM Graupners.

There are motors that will produce 3000+ watts but it will be about 1500US for the ESC + motor

Ryan

piper_chuck

My Feedback: (12)

Do you know how much power you actually need? You're not building a race boat after all. If I remember correctly, a displacement hull can only develop a certain amount of speed. Once you reach that speed, no amount of additional power will make it go any faster. Instead of assuming you need the power of a G26, see if you can determine what power you need, or alternately, how much you can afford.

Also, you will need to think about how you're going to control the motors.

As I mentioned before, since the boat has 4 shafts, you can also go with 4 motors if you want. This would allow you to use smaller and less expensive motors, although you would need more of them.

ryan_t888

If an engine was used it would need a gearbox as 14 000RPM is not very useful on a scale boat. I still say scooter motors would work best. They provide the RPM's necessary to spin a large prop at low speeds to produce maximum thrust. Listening to a Zen at 14 000RPM moving at 5-10mph is not going to be all that quiet.

Ryan

piper_chuck

My Feedback: (12)

True, but it'd certainly be quieter, and more appealing (or less unappealing?[sm=bananahead.gif]), than listening to 4 screaming nitro engines.

Out of curiosity, am I the only one who finds it interesting that we're having a gas vs electric, scale boat discussion in the "Speed - RC Nitro Boats" forum? Even more interesting is that people are helping instead of just saying go elsewhere. Speaks volumes about the value of RCU and how helpful its members can be.

joseywales

Go electric!!! Nitro are a big pain!! Costly fuels and glow plugs!! Motor can be a big pain to tune in to when weather changes.

ryan_t888

Chuck,

By scooter motor's, I mean the 12/24v 150-400 watt electric low RPM motors. They turn only a few thousand RPM's and are deadly silent. Two of those could go along way with a 90" hull.

Ryan

piper_chuck

My Feedback: (12)

Yup, realize that. My noise comments were about the Zen vs Nitro engines. Some kind of electric motor, such as you described, is definitely the way to go.

ryan_t888

Here are 2 scooter motors starting at $70. They will be able to power 2 large 4 blade props each. You may also find other motors with less power on eBay as well which may be better suited.

http://cgi.ebay.com/Kollmorgen-400-W...QQcmdZViewItem

Forgot to say that the speed control is built in. No need to buy a MSC or ESC. A servo could be used to control throttle.

Ryan

piper_chuck

My Feedback: (12)

Interesting. It says they can be rewired to rotate in the opposite direction. Wonder if this can be done outside the motor so reverse can be controlled by the radio?

shishtawoo

I think im gonna buy the ones off ebay thanks for your help these motors seem great.

piper_chuck

My Feedback: (12)

If you're planning on having reverse, confirm how you'll do it with those motors before you buy them.

ryan_t888

Good point, I've never owned a boat with reverse. It's the last thing that would have crossed my mind.

Also confirm if 400watts is sufficient. If these motors work at full bore that is about 30A. Both motors together will draw 60A. With that said run time would be based on (battery capacity/current draw.)

If you were to prop the motors lightly, you will reduce the current draw and extend run time.
Good Luck

Ryan

piper_chuck

My Feedback: (12)

Scales are a bit different from what's normally discussed here. Instead of going WOT around the pond, I've seen scale boats put through courses where they need to make tight turns, back up, dock, and other things. Being able to individually control (forward and reverse) each motor is a basic requirement.

shishtawoo

Well im sure this sounds dumb but ill ask anway lol. im assuming you power the scooter motors with 2 or 4 12 volt abtteries in series

ryan_t888

For 24v, use 2-12v Pb packs in series. If you use 4 packs, wire 2 of them in series and the other 2 in series. Place the remaining leads in parallel. This will give you double the capacity and maximum current draw @24v. It is important wiring is correct, or you will let the magic smoke out.

I would recommend using Large Lead (Pb) Acid batteries. Similar to Car/Truck batteries except deep cycle.

If the motors happen to be too powerful for what ever reason, you may reduce power by only using 12v or one lead acid battery pack.

Ryan

shishtawoo

Now its almost a given that these motor are going to make a "boat" load of torque at a low rpm, so would it be a good idea to but a big gear on the output shaft and smaller gears on the prop shaft to increase rpm and lower torque.

ryan_t888

For a large Scale boat I would imagine you would want to turn a large prop at very low RPM's ~2000RPM. Large boats need thrust to move not speed.

Ryan

shishtawoo

Well i won the bid for the Kollmorgen 400w Motors, does anyone know where to purchase a gearbox to distribute the power to two props, without building a custome gearbox. Oh and how hard is it going to be to integrate the D shaped shaft witht he system. Oh and what are some of your suggestion for prop typse and size.


http://cgi.ebay.com/Kollmorgen-400-W...QQcmdZViewItem

shishtawoo

Well i won the bid for the Kollmorgen 400w Motors, does anyone know where to purchase a gearbox to distribute the power to two props, without building a custome gearbox. Oh and how hard is it going to be to integrate the D shaped shaft witht he system. Oh and what are some of your suggestion for prop typse and size.


http://cgi.ebay.com/Kollmorgen-400-W...QQcmdZViewItem