Catamaran setup? doesn't go straight after a turn!

[SJFE]

the cat can start a nice straight run of 50 yards and suddenly turn right or left

ED somthing struck me when I read that coment. What radio gear are you useing?

[ED66677]

I'm using a 2ch Delta Star from Multiplex, probably 15 years old!
are you thinking of interferences?
Another important point, we have seen that the problem increase as we increase prop diameter but probably because we increased the thrust, we started with K39 (good speed), S36 (faster and less turning effect), K40,5 (more turning effect) and K42 (even faster and even more turning effect)

I'm going to sleep and give it a try without rudder tomorow morning!

thxs all for your help

[ReddyWatts]

same

You can also move the bottom of the rudder forward. Slightly tuck it under the boat. This will help it hold down the stern of the boat and raise the bow. It acts like you are adding a little weight to the back of the boat.

[ED66677]

guys,
I didn't try without rudder! but I put a bit more weight in it and it's getting much better, adding 700g (a battery pack) keep both prop sufficiently immerged so they both push the same

[ReddyWatts]

props

Polishing/sharpening your props can also help your problem.

[ED66677]

I use Graupner Carbon prop so there's not that much to do and they are already pretty ok but I will go for CW and CCW props, this will also help because prop walk seems to add a stronger effect on one direction.

[pompebled]

Bonjour Ed!

Lovely boats you've got there!

I like it when someone takes a plastic fantastic and makes it run as it was meant to run.

Which one in the pics is the cat you're referring to, the white, or the yellow one?

I have a couple of ideas, why the cat doesn't behave;

- The hull isn't the most stable, so it may actually twist under the load when turning.
- If I'm not mistaken, the trailing edges on the steps and transom are not sharpened, this causes drag and slows the boat down, also the sides should be sharp, so the water doesn't creep up.
- If the 700 motors run on 12-14 cells, you're using too small props, the inside prop will lose thrust and help produce the effect you mention, reinforced by the rounded edges of the hull, 43,5 or 45K should improve both speed and handling (provided the edges are sharp, or else it will get worse, up to flipping the boat...)
- it's a lot of work, but counterrotating props will improve the handling even more.
It is possible to re-time a sealed can 700 to run the opposite way, but the whole brush geometry would have to be altered aswell, or the brushes will jump up on the armature, doable, but a lot of work.

Regards, Jan.

[ED66677]

Hi Jan,
I'm refering to the white one, the yellow has not been modified.
You are right it is definitely not a performance hull so edges (every) are round and not sharp
we're running 12 cells but as soon as I got the Eagle Tree recorder we will probably go for 14 cells, in the mean time we will try larger prop as you said, motors are dead cold so there's room for power!!!
I didnt think about the re-work that counterrotating would mean, but again you are right, this requires to disassemble a motor so that brushes are working the way they have to!
Regards

[pompebled]

I would not take the trouble of re-timing a 700 if you're going for brushless in the future.
I do strongly advice to sharpen the trailing edges before running bigger props, as the effect on the handling will get worse, with rounded edges.

Do you have some pics of the details/interior on the Admiral cat, and maybe some running?

Regards, Jan.

[ED66677]

Jan,
check my web site I updated it with pics and video, you'll on pics that ther nothing to do on the hull it's ABS and I dont see how I could sharpen edges?... adding thin pieces of ABS to form perfect sharp corners?

[saleens7]

........................

[ED66677]

I'm uploading the wmv one! should be ok in few minutes

[pompebled]

Jan,
check my web site I updated it with pics and video, you'll on pics that ther nothing to do on the hull it's ABS and I dont see how I could sharpen edges?... adding thin pieces of ABS to form perfect sharp corners?

Adding thin sheets of ABS to create sharp corners is one way, but it's a lot of work on a cat.

I would use the same method I use to fill the imperfections in the plastic rudder and keelfin of my Voyager sailboat.
I make a goo from scrap pieces ABS, solved in either Acetone, or Ethyl Acetate, or the liquid glue for plastic kits.

I use a 35 mm film container which is airtight.

Once the ABS is dissolved, I apply the goo on the edges that need to be sharpened, with a small brush, you can add several layers to build up enough material.
Once the Acetone, (or... , or,.. ) has evaporated, the ABS has bonded with the hull and can be filed or sanded into a sharp edge.

Works like a charm.

Regards, Jan.

[ED66677]

GEE! That's the trick of the day!
I should have had this idea, I definitely should, this is going to impress my friends!!!
TRICK OF THE DAY!
ya da man Jan!

[pompebled]

Wow, I think I found the biggest source of your handling problems; there's a enormous piece of plumbing sticking out from under your boat!

These water intakes create a lot of drag and slow the boat down substantually.

Replace them with a spray pick-up behind each prop, and loose the periscopes on the bottom.
Make some extra goo to close the holes when you sharpen the edges.

BTW, nice neat plumbing inside the boat, using the airhose and couplers.

Regards, Jan.