Simon's 18" Balsa cat

[Simon.O.]

I am now building two cats at once and the build logs will be similar for the first few posts and then naturally there will be variations in the build that needs a separate thread thus we have two new balsa cat threads.

This is a scaled down version of my bigger Cat and should work out well, There are no plans at all and both of these two new ones are being built by eye with a few rough scetches on a pad on the wall.

I will announce the power setup as soon as I have chosen one !!

As it is common practice to measure a Cat from the rear of the last step this counts as a 18" There is a good rear overhang and the the strut will be aft of that too.

Some pics for now.

[Simon.O.]

Power setup is now chosen.

Motor
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6262
ESC
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10015
Packs
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=10290
Prop
X432 Octura

This will be a 2P stup as the packs are small.

The foaming "Gorilla-Glue" That I am using is a bit messy but very strong.
I am confident that this and the 13" hull will clean up well even before I paint them.

A couple of pics from today. The Hardwood for the strut mount is there and I am now ready to foam fill the sponsons prior to decking.

[ED66677]

Another nice pair of built Simon!!!
have you ever thought to build a cat hull, and especially the sponsons in a simpler way... instead of building the entire structure out of wood and fill with foam, do it the other way round, shape foam (hot wire cutting and sanding) and then form wood all around? you would need less wood! this is just a thought from the time I was building giant RC plane, that's how I was making wings!

[crabstick]

cool boat Simon, is it going to be a 3 point like the baby freya or are you adding ridepads later?

[Simon.O.]

ED I had considered building a wood over foam (WOF) as it was suggested by Paul here (NativePaul).
It would cost me as much to drive somewhere to get the good blue foam as it would to do it this way.
Weight is not an issue now that I run BL+Lipo in the wooden hulls, in fact most of the hulls I run have lead ballast !!

This hull as with the smaller 13" have a few build ideas that are proven. The spray foam is a new thing for me and I'll see how that pans out.

I have not lost a hull yet, I have rooted a few and one is now a museum piece but I have always recovered a hull :rockon2:

A 26" twin is on the paper now !!

[blackcat26]

Looks good bro! I like the inner-workings, much simpler than some that I have seen and still looks good and sturdy.

[Simon.O.]

I was off to cut a doorway in a solid cast concrete wall yesterday so decided to foam fill the 2 cat hulls before I left. I came home and near wet myself laughing at the mess.

Well a bit of cutting and sanding today got me this.
I have most of the decking on and will start on the hardware soon.

This one looks a bit tall in the hull to be a real beauty but it is what I have.
I cut a piece of card to show a possible canopy shape too.

A few pics for you all.

[CornelP]

With this shape it will be a case of "Wait till the fat lady sings!!!"... beautiful as always.




cl # 2 = ONLY

[crabstick]

Rofl, looks like they got Elephantitis in the first pic

[blackcat26]

I see pic number 2 has some boating fluid sitting there on the right.....Right on brother!

[ED66677]

yeah that's where the foam comes from! :banana:

[Simon.O.]

I see pic number 2 has some boating fluid sitting there on the right.....Right on brother!

That is a very special fluid that I dip my pencil in when I draw up one of these hulls.
It needs to be emptied and then refilled after each dip
Luckily I also have a fairly extensive refill supply as I make it right here.

BTW That foam is some sticky stuff before it cures. :laugh:

[blackcat26]

I have used 2 part polyurethane foam with good results also. That stuff is so bad after it cures. Actually adds rigidity along with it's waterproof ability.

[Simon.O.]

The bottom getting close to ready
This will be a very similar shape bottom to the cat that died a few weeks ago due to excessive speed and lack of strength. (that one was built for brushed cans)

There are no steps at the moment and I hope that I can get away without them, I can always cut/sand them in later.

The decking is 90% there and now that I have the power system I can setup the inside and the rear.

The power system is:
450 size Heli motor 3850kv with a possible power output of 450+Watts
Esc is 70-80A with Bec
Packs are 1800mAh 40-50C which are good for 72-90A, in a 2P setup I will have a lot of headroom here.

This setup will allow me to feed in a bigger motor if I have to. We'll see !!

I think I will shorten a lot of wires yet before the connectors go on.
I will run 4mm gold bullets all round here as I have run 4mm in higher amp setups with happiness.

Pics from today

[Simon.O.]

A bit more progress, curing the balsa sealer in the cold weather takes time and I have other things to do as well.
Hatch is now made.
Motor is mounted.
Stuff tube and servo mount are now in.
The transom hardware for this hull is taken from the old 25" cat that died but is now on a shelf.


To do:
Sand and seal more and then varnish.
Finish the steering linkage. This is made from parts taken from another shelf filler, the old hydro.

I think two more weeks and this will hit the pond !!

[Simon.O.]

It is very close now. I may get this one wet next week.
I have now gone for a 1P setup as the pack is capable of delivering 70A+ sustained and up to 90A burst. This is within the parameters of the esc and is more than the motor should be drawing.

A couple of things changed my mind on this and the first is the motor wires. They are quite thin and should not be subjected to more than 70A imo.
If I need more power then I will swap in a bigger motor and then revisit the whole 2P thing.

This power combo could go in the smaller cat anyway and make that all very exciting !

Here is a pic of the new layout.

[ED66677]

Many guys here should take a "scratch build" course with you Simon!
Look at this, hull, motor mount, drive line, rudder...

[Simon.O.]

Here is the rear hardware, it is ready to run when I get a small heatshrink sleeve onto the rudder pushrod tube.
It is functional and is a very similar setup to the Cat that it is replacing.
Some of the parts are recycled off old hulls or prototypes.
I keep all of my metal bits in case they can be used again.

A bit of time polishing all the metals bits may happen in the deep dark winter.

[Simon.O.]

While I was getting this thing ready to get wet today I hit a small stumbling block.
The poxy esc will not spin up the motor properly when there is a slight load like a prop in the water. It has the soft start and takes about 3 seconds of horrible cogging before it fires, when it does fire up it is with spectacular enthusiasm.

I tried all the beeping options to remove soft start and even to increase timing but no success. The reviews on HK website paint a similar picture.
It is fine as a Heli esc but not for an OR in a boat.

Not all is lost however as it has now been sent into the Canard to run the 540-8S in there. It works and as it is a bec out esc it removes the rx pack from that hull which is even better news.

For now I have a 100A mystery in the 18 with a 5xaaa rx pack. This will have to do for now for some basic testing while i wait for some new bits to come.

I got on the bay today and found a 60A mystery and a 3A ubec so they will be on the plane in the morning and hopefully in this hull late next week.

Out of interest is that the Heli 70/80A esc will spin up the 540 inrunner and the small 2828 OR in the 13 cat, just not the 2838 in the 18 cat. The smaller esc from the 13 cat will spin up the bigger motor just fine but as it is a 40A unit I will leave it in the 13 that it was bought for in the first place.

This is deffo the last time I will fark about with bec type heli esc's.
Mystery for me from now on. External ubecs or small rx packs are just as easy.

After all that this hull should still get wet tomorrow !

[CornelP]

Hi Simon, thought you'll read this also... New Zealand is now added to the list of countries. In doubt, contact webmaster@rc-raceboats.de.

[ED66677]

Simon,
you may not be aware but there are some ESC's (I'm thinking about the Scorpion's) that have a Boost Start feature to avoid this cogging, for their V2 motor generation, the one I'm using on my T-Rex 450 heli, the quality of the magnets is so high and of the motor design is so precise that the motor woud not spin at startup even unloaded.
also I have 3x 80A Mystery ESC's, 2 of them would do the same on my 8XL, just a very little bit on the bench and not when loaded! weird?... but cheap!

[Simon.O.]

It got wet and went fast !
First run today!

After rooting the motor in the small cat I decided to give this a whirl. I am thankful that I used the lower cost 430 that I got from the UK instead of my nice 432 as after about 2 minutes the motor coupler went to lunch and let the shaft go.

This one had the same torque roll issues that the 13" has but a bit milder.
It has a lot of potential and I got one pass that was near wot and it was moving well before the shaft departed and went to the deep.

For a first time on the water with a few calc/guess strut setting I am well happy and will continue to push this hull hard.

Keep in mind that the 13" is this ones baby twin so there is an avenue for hand me downs as far as power setups go !

The 18 may get a IR eventually.

I will learn more about OR motors and then be able to choose whether I run IR or OR for a given hull.

[Simon.O.]

It was raining, damp, windy and generally sh1tty weather here today so I was house bound or more workshop bound.
I decided that this should get a cowl after all and this is what we have so far.

[Simon.O.]

It is now looking more like "dad"

[Simon.O.]

I got a full pack through this one today as the pond was near perfect.
It went well and does not torque roll over as much as the smaller 13" cat does but is still a bit of a bear to get out and up on the plane.
I am running a x432 here and it looked nice but if it was at school the teacher would have written in the report card "could have done better"

Given that the baby cat it nuts with its new motor I may just do a swap and see how it all goes.
Failing that I can easily run this on a 2P setup with the 1800 packs and see how that goes too.

Given the weather here now this testing may take a couple of weeks.

So far I am happy with it and can see a bit of potential. :thumbup1:

[Simon.O.]

I got a few runs with this one this morning, I have two packs and ran them both through it.
It is still not as much fun as the little 13" cat.
The first issue I had was with the esc but that was sorted later on the bench at home as it was a solder joint on a motor wire.
I threw in the 40A esc from the 13"and it ran well with no thermal, that tells me something at least.

I still think this motor is not the best, it may be a dud in a batch or the motor size is just not up to the job.
I know that many folk run this size (450-heli) OR motor and commonly use a 430 prop.
I was running a 432 which is a bit bigger, I know that a dia change make a lot of difference especially with my big esc eating rigger.

This hull did once perform quite well with a 432(p) but as it is a plastic and is quite bendy who knows what was happening once the power came on.

My options now are.
1. Get a 430
2. Get another 432 to cut down to 31mm or less
3. Grab a bigger motor off HK or the bay
4. Get a higher kv motor and run the 427 from the smaller cat

Bottom line is about the same. A new prop will cost me about the same as a new motor. I am sure that I will end up buying both eventually and am now deciding which is first.

I can get a new prop in 2 days and a new motor in 5-7 days, I will not be on the water for 5-6 at least so now my brain hurts. :confused1:

I'll get this little bugger up on its tail just like its baby brother one day.
If I have to big-block it with a 540 then so be it !!

[crabstick]

High Performance have small 1/8 shaft octura props

Last small one I bought was about $25 y535

[Simon.O.]

High Performance have small 1/8 shaft octura props

Last small one I bought was about $25 y535
You're right there Matt, I'll give Kim a call and see if she has a 430 in stock. I was up there last week to grab my 427, should have got the 430 then too.

To me props are an asset that don't wear out, ok we can bend and lose them but the don't burn up or fry etc. No harm in having a good selection of water throwers.

[crabstick]

To me props are an asset that don't wear out, ok we can bend and lose them but the don't burn up or fry etc. No harm in having a good selection of water throwers.

Yeah the smaller props are reasonably cheap.

For sure, thats why I will never sell a prop and am gutted if I ever loose one. Our club pond gets drained a couple of times a year I always go down and see what I can find, Last time I found an x632 and stub shaft I lost a couple of week prior.. The great thing about wattle is its only about 6 feet deep.

Make sure you try make it to wattle sometime soon, lots of boats for you to sketch!!! Chris ran his FE 1/8 hydro conversion for the first time and it showed great potential.

[Simon.O.]

I have been running this hull with a 427 for the last few weeks and it is insane. All the initial bugs are now gone and this hull is nuts fast. Too fast I think.

I have had the strut here there and everywhere and have gone from mental porpoising to just plain mental skipping.

I smoothed out the porpoise motion by removing the pos angle (prop up) from the strut and went to a straight out unstable prop rider that would blow over.
I then raised the strut to settle the rear and prevent the prop riding and it has got a little better but still skips down the pond.

The shaft centre line is now 6.125mm (near1/4") above the sponson bottom and with a 32mm dia prop this translates to 54% of the blade below the sponson bottom.

I may try the strut a little higher and see how that goes or another option is to add a bit of weight to the hull.

At the moment it is right on the edge of driveable at wot and is a real hoot to drive. At wot (a rare occurance) the hull literally flies on its strut and skips down the pond near 65kmh or 40mph.

Loads of fun :banana:......but I need to tame it a bit. :thumbup1:

[Simon.O.]

At last I have got this hull sorted.
It is now a very happy kitty and I am very happy to drive it.
The setup is almost the same as from the start but I have played with the strut to get it to perform.
3S 1800mAh 40C to a 3850kv 28/37mm Outrunner with a 60A Mystery ESC. Prop is a Octura 427.

It now flies on the sponson rears and with a bit of headwind will blow off. Down wind over a slight chop will slightly dance from side to side as it runs as a 2 point cat !

It is deffo on the edge and that is how I will keep it. It is now a template as to all of my cats should run. :banana:

For a power setup of under $35 usd I am happy.

Now to get the other small hulls singing

[crabstick]

Nice one Simon, sounds like a bit of fun, ive been looking at a block of bluefoam lately in my boat/server room thinking of making something small enough to run in the ponds at the golf course next to my place..

[Simon.O.]

Nice one Simon, sounds like a bit of fun, ive been looking at a block of bluefoam lately in my boat/server room thinking of making something small enough to run in the ponds at the golf course next to my place..
If you are after a golf course runner then have a crack at a 13"cat with a 450 heli motor, mine would be a blast on some of the water traps I have seen. :thumbup1: