Motor for a 12"-14" Cat (single)

[Simon.O.]

As you can see I am surfing for input for motors for 2 cats as I plan on building both at the same time.
This is for the smaller cat and I have ruled out an outrunner as a single and am now looking at these inrunners.

Which is the better choice and why.
http://www.hobbycity.com/hobbycity/s...idproduct=4200

http://www.hobbycity.com/hobbycity/s...ess_Motor_(FIN)

Both can provide me with the power (W) that I need, the esc and packs is the easy bit, I will provide the motor with plenty of energy.

I am looking to run M4 graupner K series small props on 3S.

[CornelP]

The 2835 will give you way more torque than the small 2040... plus the small one is KD, so maybe not so good quality as the Turnigy.

[Jesse J]

I need to learn lots more about small motors, I'm watching!!

[ozzie-crawl]

hey simon how about a little out runner

[Jesse J]

dunno, but you might need at least two of em ...

[Alexgar]

i run a 28-47 2700kv in a 16" vee on 3s and 4s with great results a little pricey but bought before i knew about hobbycity
link
http://www.e-fliterc.com/Products/De...rodID=EFLM2005

[Simon.O.]

Interesting replies so far. Notes taken.

Here is another option, the reviews below it indicate that a 300mm or less prop will be fine.
http://www.hobbycity.com/hobbycity/s...r_(WaterCooled)

I realise that it is 20mm dia and may lack a bit of torque.

[NativePaul]

I would go for the third one, I know somweone who ran the second one in a cat of about that size but there not the most efficient and it got hotter than I like to see even on short runs, it definatley needed water cooling, the first motor is just too big/heavy for a hull that size, more suited to your 18incher, over here we use speed400 size motors like that in our mini classes which are max 450mm (18") hull length and its the 5minute runtime we need, not the motor size that keeps the boats sensable, propped up for a few striaght line runs as I believe you run and there is plenty of power there to make a mockery of an 18" hull in all but the most glassy of conditions.









PS, Definately keep the prop under 300mm, I have a rule of thumb that says "when the prop diameter approaches the hull length, the chances of an adverse torque reaction increase considerably"

[Alexgar]

16" vee 3s 28-47 2700kv 40 amp esc, not to shabby

[BakedMopar]

What about these

http://www3.towerhobbies.com/cgi-bin...?&I=LXLWW5&P=7
http://www3.towerhobbies.com/cgi-bin...?&I=LXLWW4&P=7

You can get water Jackets here
http://cgi.ebay.com/aluminum-water-c...item439aa338fc

A 380 can IMO is too big and should be in hulls 16" or bigger.

[Simon.O.]

I would go for the third one,
I am now leaning towards it myself
I know somweone who ran the second one in a cat of about that size but there not the most efficient and it got hotter than I like to see even on short runs, it definatley needed water cooling,
Cornel mentioned that it is a dubious motor
the first motor is just too big/heavy for a hull that size, more suited to your 18incher, Could do
propped up for a few striaght line runs as I believe you run and there is plenty of power there to make a mockery of an 18" hull in all but the most glassy of conditions.
Propped up or celled up ? do I go 2S and go up a prop or go 3s and down on the prop.

PS, Definately keep the prop under 300mm, I have a rule of thumb that says "when the prop diameter approaches the hull length, the chances of an adverse torque reaction increase considerably"

Love a typo !! you know I meant 30mm

What about these

http://www3.towerhobbies.com/cgi-bin...?&I=LXLWW5&P=7
http://www3.towerhobbies.com/cgi-bin...?&I=LXLWW4&P=7

You can get water Jackets here
http://cgi.ebay.com/aluminum-water-c...item439aa338fc
Nice links an I'll keep them but for now the big issue is shipping, by the time i land them the post is more than the item.

A 380 can IMO is too big and should be in hulls 16" or bigger.

George, do you think the 20mm motor may be the go too?

[ozzie-crawl]

i still think the scorpion 22mm are better motors, yes they are more $$$ but rebuild able
and can take some very high temps. and this is a Aus $$$ not u.s
http://www.arkinnovations.com/shop/i...ex&cPath=16_46

[Simon.O.]

i still think the scorpion 22mm are better motors, yes they are more $$$ but rebuild able
and can take some very high temps. and this is a Aus $$$ not u.s
http://www.arkinnovations.com/shop/i...ex&cPath=16_46

Nice motors there Scott, but this will deffo be a Inrunner job. It will be small and narrow so an OR will flip it too easily.
I may yet go OR in the bigger 18"(wet)20"Loa cat.

Looking and looking for now.

[ozzie-crawl]

hopfully there in runners will be out very soon
up to 40mm are 4 pole over 40 mm are 8 pole .had a email from them about 6 weeks ago and they said 2-3 months

[Rumdog]

The ammo motors are excellnt! http://cgi.ebay.com/Great-Planes-Amm...item562e963947 Check out the other sizes and winds they have as well.

[BakedMopar]

IMO the 380 cans are too heavy (especialy the L versions which are 58mm long) and eat too much amps. While I can only speak for a 17.5" hydro thats my take. A buddy runs a couple of Minicat stuff with 20mm motors and they are fast and have decent run time. He gets around 4-5 minutes wide open in his hydro with a 2200 pack. I get 1-2 minutes out of a 2200 pack with a Feigao 8l.

If you really want a 380 size (28mm) go with a short can 45mm and under. With a 380 you can spin a bigger prop. But you need higher amp escs.

[Simon.O.]

I have done a bit more thinking on this one and have come up with an interesting idea.
My ~34"cat has about 1600W of calculated power and run well.
My ~25" cat ( now dead) had about 1000W of calculated power and was very fast.
I see a pattern here
About 70% hull size reduction runs on about 70% of the power, so far so good.

One new hull i plan on build will be 18"(wet) 20"loa and most of my reading points to about 750W power setups. This is where the light bulb came on.

The smallest cat on the paper at the moment will have aboat 13"wet and 14"+ loa. This should then get by with about 250W of power.

I did a few paper cutouts and have shown my "formula" to be based on plan view sizes. Given that my cats are close to the same design and proportional build construction I now see this as a power to size ratio.

Now all I need to do is suit up about 250W of power to feed to a 27mm Graupner prop.
I plan to use the Graupner 2318 series M4 threaded props until I find the right size and then if needed go to a metal one.

Possible power combo#1
20x40mm (130L) 4850kv Inrunner max load 25A?? (185W) Add more for short sprints with cooling !!
40A esc
1600 30-40C (48-64A) 2S1P pack

Possible power combo#2
24x35mm (370s) 4400kv Inrunner Max load 26A (192W)
Same pack, and esc.

Last resort is to go with a 380S.

I am leaning toward the smaller motors as that seems to be a fairly successful size to transplant into the Pro-Boat Mini-C and I have seen a few clips of them going nuts on small setups.
This is deffo a fun boat, not a saw or racer.

I am enjoying the research and thought that all of this takes.