head of the river cat hull thread

[ozzie-crawl]

short video of said hydro he was doing some testing in the small pond and it doesnt get to full speed in this video http://www.youtube.com/watch?v=n42TXtOCYZo

[785boats]

Hey Ozzie. How's trix.
I'm slowly catching up to you. the cat hit 50mph yesterday but i still can't get it to go around the corners at any decent speed though. The rudder seems to have very little effect unless I back off & then it just hooks & spins out, even with very little rudder throw.
If you, or anyone else, can offer any advice on why & how to fix it I would be very greatfull.
Cheers.
Paul.

[ozzie-crawl]

hi paul. as you know i dont race so with the cat it has been more straight line speed and fun. maybe someone like fluid or bonewar can give you an answer. one thing i did find was the rod for the servo bends very easily especially once you get up some decent speed and you loose steering. on mine i put in a high tourqe servo thicker stainless steel rod. once i had done this i regained my steering for about 4 laps and it broke the servo mount (origonal one made from ply) wich flipped the boat threw the air at about 60mph so i made a s/steel one
scott

[bonewar]

Rudder fix

785boats , As these cats are designed to turn at high speeds and will turn at high speeds, you have to set up your steering system very strong, as Ozzie mentioned a high torque metal gear servo around 10kg will do the job.Also make sure your servo mounting is strong . use a very stiff wire for the steering rod.There is another way to fix the problem using a lever effect , you can gear the servo 3:1 so you have 3 times the torque on the rudder as at the servo. set the links into the servo arm at say 6mm from the central pivot.At the rudder put them 18mm out,The 3:1 ratio gives you 30kg effective from a 10kg servo and you will have 30 degree movement at the rudder not that you need that much , 20degrees left,20 degrees right steering is plenty. hope this helps you Paul . Bonewar

[785boats]

Thanks guys.
I have upgraded the servo & installed a guide to stop any flexing of the control linkage. I've also maximised the linkage ratio (its got about 15 degrees of throw) but the problem is still there. The servo is only 7.5 Kg so I'll get a 10 kg one this week & see how that goes. The original was only 3.5 kg.
Thanks again.
Paul.

[ozzie-crawl]

just a thought paul but awhile back i found a articale on G forces of rc boats and one guy was saying that some boats would see 3-4 gs some people disagreed. one guy said he ran a g meter in his boat and was getting 3.5 gs. there is a formula to work out weight verses speed/radius of circle and work out how much force is actully on the rudder. think it would suprise some people how much force there is on turn fins and rudders.
cheers scott

[785boats]

I can see your point there Scott.
I've never had problems with rudders & turning with any of my other boats, but this is the first boat I've run with the rudder blade directly behind the prop so one would assume that the forces on the blade would be considerably higher from the propwash.
I'll try the higher torque servo & a few different props this weekend. & play around with the COG. If that doesn't fix it I'll make up a bracket & move the rudder to the side of the prop next week.
Thanks for the info.
Paul.

[SLAUGHTER_AUS]

paul, are you happy with the jacking plate you installed at the rear? i have shifted the strut right up and am going to try a 6xl in it on sunday to see how it goes? i am also trying tape airdams like the hydro guys are?

[lomdel]

Hello everyone, I just purchased the ARTR version of this Catamaran...

I can only find a link to the bare hull version. Anyone have a link to this 32" cat with hardware??

[lomdel]

Found the link...

http://cgi.ebay.com/32-catamaran-ARTR-set-with-motor-and-ESC-rc-boat_W0QQitemZ300283740890QQcmdZViewItemQQptZRadio_Control_Vehicles?hash=item300283740890&_trksid=p4634.c0.m14

[785boats]

Hi ben'
Sorry I didn't see your last post yesterday. But yes, the wedge seems to work fine.
I've convinced myself that it does create more pressure under the hull & lift it a bit.
At first I thought that it might be part of the handling problem, but then I realised that the boat had the same problem before I stuck the wedge on.
I didn't get to upgrade the servo before todays outing so the steering problem remained, even though I tried different props & moved the COG around a bit.
But it did reach 52mph with an X642 prop. Well you saw that. It was a fun day today. Good luck tomorrow. Wish I could be there. Let us know how you get on.

I guess we can all dream of doing this.http://au.youtube.com/watch?v=tIsqjAzkhXI
Cheers.
Paul.

[CircusCircus]

Nice Video!

OK I have purchased a Hydra 120, a Xpower 8XL 2085Kv motor and a 42mm prop
now I need to get some Lipos.

Can someone point me in the right direction on a good Lipo set-up? Im rather new to the brushless world and am confused on what to buy. My friend told me to buy a pair of 4s 14.8 volts lipos and run them in paralell? Im not sure he is giving me the right advice. Also whats the Cell Burst rating mean?

I am not out to break any records but want a Lipo set-up that will work, Id like to see 50mph.

A link to some Lipos and how to wire them would be much appreciated

[ozzie-crawl]

i run these rhino (zippy) batteries and have had a very good run with them http://www.hobbycity.com/hobbycity/s...2&v=&sortlist=

[CircusCircus]

Theres alot of batteries on the page, which one are you talking about? Model #

Thanks ozzie

[ozzie-crawl]

if you have the dollars the 4s 4000s would be very nice but may be a tight squeeze in the sponsons and yes run 2 in parallel. the 4s 2350s mite get you threw but dont know what your amp draw is going to be with that setup and with the 2350s you wouldnt want to pull anymore than 80-90 amps max. with the 4000s you could pull about 150amps.