Twin drive cats.....a discussion.

[lomdel]

For a 32" twin drive cat (yeah you know which one I'm talking about), what would you suggest to use as 3/16" stingers (http://cgi.ebay.co.uk/adjustable-sti...d=p4634.c0.m14 ?) and a cool looking push/pull rudder set-up?
And the inevitable question of motors, ESC and lipo's for 40+mph speeds??

[Simon.O.]

Lombard, I know which one you are talking about.
Me ? I would / will do my own wire drives 062"wires
L size motors on 4S.
Chinese 100A speedies.

This will be a long term project as I have another hull on the build board at the moment.

When I go to a twin cat I may have 4S2p and then out to the speedies.
I have a lot of stuff written down and will drag it all back up and post here for comment/ critique soon.
I am still working on a few formulas for this twin drive stuff. A data logger would make life so easy but I have always been one to do it the hard way.

JFK once said "We choose to go to the moon in this decade.....not because it is easy, but because it is hard"
I love that idea.

[lomdel]

How would two of these on 3S or 4S work? I think great! http://www.hobbycity.com/hobbycity/s...r_(WaterCooled)

[ozzie-crawl]

not sure but think they are the same as the turnagy ones if so they mite last on 3s but on 4s wont last more than acouple of minutes

[showstoppercat]

hello everyone - I wanting to put together 2 twin cat (32-40") range (maybe jollycay or something from H&M) an need some suggestions on what I'll need - I just want reliability - good balanced and Straight line speed 60+ range - No racing!! just fun - I already have counter rotating props (40's) .150 flex cables - that was the easy part - Can you'll suggest other items I need to achieve this gold BL Motors/ ESC's / Lipos - Note all suggestion welcomed - But I've got a felling this be a $$$ expensive build even though I don't want to burn holes in my pockets if don't need to ....

[Simon.O.]

I have done a lot of maths so far and need to know a few more things.
I know that 2 motors is 2x the power.
This does not equate to 2x speed, that I know from a few full size boats I have run.
I assume that the 2 motors will run higher rpm, compared to a single, as they are not as loaded.
This will reduce Amp draw and increase speed.
What I am looking for is a ball park % change.

Example, FE Calc gives me
12L 4S 69A 782W 26,600rpm 38 mph / 440 prop

What can I realistically see if I run TWO of these setups
I know there are a lots of what if's but I am lloking for a possible 5% increase in speed or 10% decrease in Amp draw. Just some percent figures to work with when doing twins.

All of this is applicable to the Agitator hull or its Chinese cousin, or in my case a home-brew wood based version.

This maths and research is a hoot.

[ED66677]

Simon, IMO it is not necessary to have counter rotating props but just easier to setup, also I've seen someone stating that when the right prop spins CW and the left prop spins CCW, the speed is higher, when the rigt prop spins CCW and the left spins CW is gives a better handling in turns.

[Simon.O.]

Simon, IMO it is not necessary to have counter rotating props but just easier to setup, also I've seen someone stating that when the right prop spins CW and the left prop spins CCW, the speed is higher, when the rigt prop spins CCW and the left spins CW is gives a better handling in turns.

ED I always appreciate the input from you.
As far a counter-rotating goes I am happy so far as I will initially use 40mm CF props and go up in diameter from there. The Graupner CF range is avalable in L+R so I can go either way. Running wire drives means I can swap props and go in a minute.

This is a research project for me as I will not be doing a twin cat for a while yet.
I have another boat on the build board at the moment.

[ozzie-crawl]

simon this is pobably not the answer you are looking for but i run a single motor 32' cat with a 7xl (2384kv) on 4s with a detounged x440 prop it pulls 79 amps max with a speed of 55 mph. so what iam looking at is the amp draw on a 7xl is only 10 amps more than a the 12l you are looking at with the fe calc yet gives another 17 mph. i run a ammo 2300 in my 25" mono on 4s with a x440 prop runs 45amps max at 45mph so in my 32" twin motor cat iam going to run 2 ammo 2300s on x442 props. hopeing to see 55-60 mph

[lomdel]

simon this is pobably not the answer you are looking for but i run a single motor 32' cat with a 7xl (2384kv) on 4s with a detounged x440 prop it pulls 79 amps max with a speed of 55 mph. so what iam looking at is the amp draw on a 7xl is only 10 amps more than a the 12l you are looking at with the fe calc yet gives another 17 mph. i run a ammo 2300 in my 25" mono on 4s with a x440 prop runs 45amps max at 45mph so in my 32" twin motor cat iam going to run 2 ammo 2300s on x442 props. hopeing to see 55-60 mph

Ozzie, I assume that twin set-up would be with 4S per motor as well? What is the Feigao equivalent to the Ammo 2300 and why not the Ammo 2600? Where did you get counter-rotating X442's?

[ED66677]

The Graupner CF range is avalable in L+R

be carefull not every size are available L&R, also you have to use drive dog and not M4 threaded props (those have L&R M4 thread!)

[Simon.O.]

ED props are here http://www.offshoreelectrics.com/categories.php?cat=44

Ozzie. That is excatly the kind of data that I need. This is where FECalc has some limitations.
You can not specify hull size or single/twin setups.
It show a 7XL 4S 440 giving 26643rpm 107A 43mph
Your data is clearly different and i do not doubt it at all.

This is where simple questions and answers build the picture for me.

I know that some of the Amp draws on FEcalc are a bit high and that is good as it allows me to design a system that has a safety factor built in before I put one in too.

Back to the Big question.
Will twins unload each other and therefore reduce Amps and increase rpms.???

[ED66677]

Will twins unload each other and therefore reduce Amps and increase rpms.???

IMO yes!

[ozzie-crawl]

yes the ammos will be run on 4s.its intresting the fe calc says 107 amps with a 440 i have pulled around that but with a 645. i will mention to all my props are detounged and i dont know how much this reduces amp draw

[Simon.O.]

Here is another one for the twin users.
If I am using two packs is it better to go for completely independant systems, being Battery-->Esc-->Motor.
Or to go for a Paralell on the power side, being Pack+pack(2P)-->Esc's--> motors.

Paralell power or independant setups??