Systems Cat Rebuild

[mars]

Hi All,

I am new here but have had a Graupner Systems Cat since I was a kid. I used to run it on a double brushed motor setup with a single flex shaft and the Graupner outdrive. I imagine it ran about 20 after I put a couple of hot wound car motors in it.

I have decided to upgrade to modern electrics after being in planes and seeing the difference brushless power can make.

After doing a lot of research I have settled on a Fiagio 11xl with a turnigy 180 esc, an ose-80085 aluminum drive, and 5000Mah Hobby City 25C 6s lipos, and a x642 prop to start.

Does this sound like a reasonable setup? This is not a race boat, just a sport boat so I will be happy with 30-35 mph. Am I close?

Finally, Do I need to add some kevlar or carbon reinforcement to the hull? I have all the material as I custom build molded gliders pretty regularly.

Any and all advice appreciated.

Thanks,

Mars

[Fluid]

We ran a couple of those in the early 90s. I think 30-35 mph is a fine goal. I remember we got one up to 34 mph running NiCD 24 cells and an Astro motor. You'll get there with 4S and the same 11XL motor for a sport setup. 6S is heavy and really too powerful for the hull. An m440 to an m445 should put you in the speed range you are looking for.

The Graupner hulls of that era were very thin and light - code for weak and fragile at today's speeds. Years of age will add brittleness to the hull. I'd add reinforcement if I were you.



.

[mars]

Thanks Fluid,

I will definitely reinforce the hull. Is it better to do this with carbon or kevlar? I can lay a mat of one or the other or both onto the bottom of the hull.

Thanks,

Mars

[Namnuta]

I always wanted the systems cat when i was younger, but i got a keywest for xmas instead. Great boat.

I just recently did what you are doing. I put SV27 powerplant into my keywest, and wow. Im running low 40s on nimh. I did some minor reinforcements (Should have done more) and no cracks so far.

I love these old graupners, good luck with your build.

[mars]

Thanks Namnuta,

I am planning on doing some pretty serious hull reinforcement as I have all the materials on hand. I think I will do a kevlar mat on the floor of the hull and into the two hulls. Then I will epoxy reinforce all of the wood frame joints in the hull and lay some carbon onto the major wood components.
Will this be enough?

Thanks,

Mars

[Namnuta]

Thats a lot more than i did, but i am new to brushless tech as of this year. I think you will be fine though. Mine so far had had about 30 good runs this year, and one nasty crash, and my old hull is still strong.

I layed some fiber matting and epoxied it, making a PVC/fiberglass hull. I treated my wood with epoxy.

Yours will be much stronger than mine.

[mars]

Update

Hi All,

I have ordered an 11xl and (2) 3s 5000Mah batteries with a x642 prop. I was looking at this calculator:

http://www.offshoreelectrics.com/conversion.htm

and it looks like I can get 26mph if I run the motor on 3s. I may just start with the packs running in parallel to see if I am happy with 26 and then upsize the prop to a x646 for 29mph down the road. This 3s setup will only spin the prop at 14,000. Is this OK?

Then, when I am ready, I can get a stronger hull to run this setup on 6s. Or, when I am ready to trash the Systems cat I can try the 6s setup with an x442 for 46mph!

Thoughts?

Thanks,

Mars

[Jeff Wohlt]

Big cat ....get on out there with 6S! Forget 3S as you will only be stressing and dragging the system.

[mars]

Thanks!

So, if I run the system on 3s at 14,000RPM, is that hard on the ESC? The motor? I can't imagine it will be bad for the batteries as they will be delivering lower current but I could be wrong.

I am new to all of this and am curious to hear what part of the system will be working under the largest load on 3s and 6s.

Any help appreciated.

Also, if I start on 6s with a small prop like a x432 to keep the speed down will this put undue stress on any part of the system?

Thanks,

Mars

[Jeff Wohlt]

Would not hurt the cells as much as dragging around pulling loads of amps on your ESC and motor. Getting up and out on starts and getting the hull to run fast with little drag is key to any good running hull.

6S and a 432 on a big hull is way too small. Start with a m440 or X442. You shoul d be able to go up from there.

If you can't run 4S then go with 6S as you have a good motor for that. Good cooling to everything is standard business on these setups.

You will be much happier with that set up...why do it if you can't get a rush from having the power at your fingertips :)

[mars]

Another Question

Thanks Again Jeff,

So, my boat has a stuffing tube of brass with a teflon insert, but it is only about 1.5" long through the hull. In looking at most builds here the brass tube runs right from the front of the strut to the motor.

So I am wondering if it is OK to run an 11XL on 6s with so much of the shaft exposed or should I try to redo the tube to make it full-length.

Any and all help appreciated.

Thanks,

Mars

[mars]

Further Update

So, between work and kids I just ran this boat and setup for the first time.

I did a minute run and checked temps - a bit warm but nothing hot.

I did a two minute run of mixed throttle and actually got it to full throttle and checked temps after my hands stopped shaking (First time running a boat so darn fast!!!) - a bit warmer but nothing hot.

So, I ran the rest of the 5000 Mah packs out (5 minutes?) and the motor was HOT! boil water hot! I would estimate 250F?

When I opened the hull I smelled a bit of the bad smoke but did not really see too much of it. I let all cool off and tested the motor with no load and it seems OK.

So, I was running an x642 prop. I am assuming I can do three things to get the motor temps down:

- Run a smaller prop - if so what size should I try? I was thinking x438? x440?

- I am running a timing advance of 7.5 degrees. Should I turn this down to 0 degrees?

- change from 6 cells to 5 cells. I do not want to do this if I can get the boat to run well on a smaller prop.

I guess my real questions are these:

1) how much less heat will I generate with an x438 or an x440?
2) how much less heat will I generate with my timing set to 0 degrees?

I live in SF and will head out to Sprekels lake in GGPark on a Saturday morning and ask the experts but can not make it this Saturday and want to get a different prop if I need it.

Thanks and I can't wait for more fast running!!!

Mars

[mars]

Further Update

So I got a copy of FECalc and put my setup into the calculator AND - (drum roll please)

I am pulling close to 130 amps on my setup!!!

FECalc showed me that an x440 will pull around 90 amps at WOT and get me around 48mph - just 7mph slower than my setup with the x642 at 40 less amps.

I plan to order an x440 and an x438 to test.

Mars