Twin Cat Strut assembly on a budget -> help please ;)

[sailr]

yes, get the next size up brass tubing as the stuffing tube. Grease the flexshaft with good quality marine grease (waterproof grease).

Are you in Europe or the U.S.? If in the U.S., don't run metric shafts! You'll have a hard time finding the mating tubing and props.

[crabstick]

You can run inside just the brass tube and forget the teflon unless you need it for ease of strut adjustment. Most of the 'go fast' boys are running without teflon with great success. Less drag.

I concur. Teflon is not needed. It will only cause extra driveline drag IMO.

[norbique]

I'm in the EU, thus it's hard to decide whether to go with the US dimensions or the metric. I'm afraid in the end I will end up with Octuras, or other USA made props, which would be easier to mate with the imperial shafts and flex shafts. Tell me if my thinking is wrong.

[G Doggett]

You can run inside just the brass tube and forget the teflon unless you need it for ease of strut adjustment. Most of the 'go fast' boys are running without teflon with great success. Less drag.

The teflon tube is used so that the struts can be adjustable.
I haven't used a brass stuffing tube from the strut to the motor, just a short heavy walled teflon tube with the front end supported by a bracket.
Works for me.

Lets not highjack this thread with the teflon versus brass argument !

Graham.

[G Doggett]

Don't bother with SS bearing, brass or lead teflon works fine with plenty of lubrication, and if you use a 'hexflex' type coupling between your motor and shaft it will be supported just fine.
You can make it as complicated as you want of course, but I support the KISS principle of Keep It Simple, less things to go wrong.
Graham.

[astecme]

If in the U.S., don't run metric shafts! You'll have a hard time finding the mating tubing and props

K&S do the brass tube in Metric as well as imperial. It might be easier to obtain in their 3feet lengths in the US. This is what I use in the UK - imported from the US!!

[norbique]

The rule of thumb for strut length is 10% of hull length to front face of prop. So for you 110cm hull the strut should be about 100mm.
Graham.

Sorry to ask this but how do I measure the hull length? Do I measure on the bottom from tip to end of sponson, OR on the top from tip to the end of the hull?!

Norbert

[G Doggett]

Hi Norbert
From the front to rear of the sponson.
Not including any overhang or extension of the transom.
This rule of thumb applies to monos and DV hulls also, but keep in mind this is not an exact specification.
Hull or sponson shape and speed must have some effect on the ideal sweet spot for the prop behind the hull.
Graham.

[astecme]

Don;t get too hung up over that. You need the prop to be in free water in order for it to work properly is all.

[norbique]

OK Thanks!

This means my cat is only 105cm long. Can I get away with a 70mm long strut + Teflon trust bearing + drive dog ~ 80mm to the beginning of the prop?

Another thing:

I don't want to hijack my own, thread but I don't want to start a new one either just to discuss this. After long searching, learning, and studying I reached a point where I decided to go with the Feigao motors instead of the KBs. Although I've seen some vids made by Germans on Youtube running the KBs both L and XL with great success. I guess they all replaced the bearings as a first step. But it's working. For them at least. On the other hand I heard a lot of people who splutter the KB's calling them cheap rubbish.

So, I'll go with the more expensive Feigaos, (tell me if I'm stupid to do so!) only one question remains, I like two motors but which one to use?!

My Setup: (twin motor cat) / 6S 5000mAh 25-30C Lipo / ESC not really important here

I'm considering the following two motors: the 580L-08 and the 540XL-10.
Both have roughly the same KV yet one is a lot bigger than the other.

Here's what FEcalc showed me, picture attached: (Feigao 580L-08 on left / 540XL-10 on the right) with x632 prop

Please tell me what you think! Will the 2x 540XL-10 be enough for a cat of this size or should I go with the 580L-08 and don't worry about the extra weight?

My goal is to reach somewhere near 100km/h, while not killing the motors at the same time.

[astecme]

So I guess the XL10 will go faster - thats for two reasons...

1. small design change at Feigao gives more RPM in new motors
2. The 580 is REALLY Heavy - but all round probably has more torque to give.

[norbique]

Thanks Allan! I respect your opinion, and it makes sense, but let's wait a little more for others opinions.
Looking at the dimensions the 580L is roughly the same size as the KB45XL right?! That's quite huge.

[shockerman80]

i run twin speedmasters on my twin drive cat they work great/

[norbique]

i run twin speedmasters on my twin drive cat they work great/

Hi shockerman80! Can you be a little bit more specific?
It would be nice, since the cat in question is your balsa cat enlarged to 166%.

[shockerman80]

use the normal 3/16 speedmaster stingers. Then build a box on the bottom of the hull at the transom so that the upper adjustment location can fit into. I know its hard to explain and i dont have the pics here now to show you ill see if i can get them for you.