Please help me understand BL motors

[ScarabChris]

Being new to this I know very little about brushless motors. I understand how they work. So what I am looking for are some tips in choosing the right motors.

I am seeing so many different motors that I'm afraid I will be in the dark choosing motors for my 50" twin deep vee build.

Reading the posts I see you guys flashing numbers and I'm like HUH?

[Flying Scotsman]

Chris, how much cash do you have budgeted for this project, what hull and proposed battery power setup?....Speed expectations?.....twin motors on a cat ...are cool....on a Mono... hmmm

Douggie

[ScarabChris]

I don't really have a budget in mind, it is whatever it turns out to be. Here is the thread with my project idea. http://forums.offshoreelectrics.com/...ad.php?t=19522

The hull is my 50" Aeromarine Apache that I will be taking the 26cc gas engine out of.

Battery power setup? See thats just it I have no idea what I should be choosing in the way of batteries and motors. I know I want to see at least 50 MPH and I want twin motors. I will be using twin MHZ (MTC) power trim drives.

Nothing wrong with twins on a mono.

See my first FE build here...
http://forums.offshoreelectrics.com/...ad.php?t=19457

My question was really about what all the numbers mean for these BL motors. Is there an equation that you use to decide what motors you need?

[Flying Scotsman]

10 or 12S 5000mah 45C per motor, unfortunately the motor model numbers can be very specific to each manufacturer, but you need motors with long and large can diameters with high torque and low rpm per volt. This is an expensive project and you may wish to use a different hull to achieve 50 mph, maybe someone who has converted this hull may chime in with some advice.

Douggie

[ScarabChris]

Hell this hull saw 50 MPH with the gas engine and what I have seeing from these BL boats 50 MPG should be a snap with twin BL motors.

I'm not going to use a different hull, I already have this one and I know its more than capable of this build.

I already ordered the drives, rudder and trim tabs from MHZ. I have the hull and radio gear so all thats left is motors, ESCs and batteries.

Expensive? Maybe but it will be cheaper than if I had to buy a new hull to start with. And you gotta pay to play.

[siberianhusky]

For the most part twins in an rc mono don't particularly work well, especially surface drive! How do you plan on keeping both props in the water when you turn?
There are reasons you don't see many monos running twins.
If they worked well you would see lots of them.
Cats and riggers don't heel over in a turn.
One big motor on 10 or 12 s would probably be a better setup.
I'll fully admit I'm new to electrics but been running nitro since the 80's, seen a lot and tried a lot.
The principles on how the boats run is the same no matter what is turning the prop.
Twins don't usually drive a boat much faster, acceleration is wild but overall speed doesn't change that much, you might get a few more mph or it may go slower because of the added weight of having to double everything up and the added drag. prop speed is prop speed and they are only going to move so much water at a given rpm, having two of them doesn't change how fast the prop is turning.
You may be able to prop up a little bit but you are still pushing a lot more weight.

[keithbradley]

There is a formula on here a guy posted to figure out what kind of speed difference you will see with 2 props vs. one. In my opinion, it is a significant one. Twins also have the potential to run cooler. I think this is a cool project and I cant wait to see it come together. I know you mentioned in your other thread doing trip outdrives on it...I would still like to see that on a mono. I think it would look kinda scale and different than most anything out there.

Neu makes a 1527-1.5y which is 850kv. That would be perfect for the voltage range that douggie mentioned...I just dont know about the weight of two of those and how it will affect handling. There is also the option of going the budget route and using castle 1717's. They on clearance and a great bargain right now. The downside is tehy are 1580kv, which means you would be running 6s, and you couldnt turn as big of prop without drawing a ton of current.

Hopefully someone with a bit more experience chimes in...I have no idea what kind of weight a 50" mono can take...I would think if you did run 1p as douggie suggested it wouldnt be much of an issue though.

Either way I think 50mph is a conservative goal and shouldnt be hard at all. I ran a 40" mono with a single motor over 70mph...I dont see why a 50" mono with twins should have any trouble surpassing 50.

[ScarabChris]

I don't know, I have been into large gas RC boating and have seen countless monos with twin surface drives. You put them close together so one doesn't blow out in a turn.

I'll just wing it and post the results.

[Rumdog]

Go for it! It does work. I'd use twin Neu/Castle 1520's or 1717's on 6s each. It will haul ass.

[keithbradley]

I don't know, I have been into large gas RC boating and have seen countless monos with twin surface drives. You put them close together so one doesn't blow out in a turn.

I'll just wing it and post the results.

Yup.

Looking forward to seeing what you come up with. I loved the little scarab you did.

[ScarabChris]

Just an update. My good buddy couldn't bare the thought of me tearing apart that 50" Apache so he offered to buy me any brand new hull if I gave him the boat intact.

Sooo...now what 50" hull?

[Flying Scotsman]

I would go with a cat built by the genuis in Switzerland....Hanspeter....HPR series

Douggie

[Rumdog]

Definitely a HPR or MHz mystic!!

[ScarabChris]

No cats, I want a killer mono, deep v.

I would just order a brand new Aeromarine Apache 50" but I think there might be something better.

Now that I have this offer I really need to think on this.

I want a killer deep v. I may just get the Outerlimits from Aeromarine. They have always treated me good. Hell they did a custom build for my Scarab build.

[keithbradley]

HPR is supposed to be offering a mono...