AML Sprint Cat 36 conversion

[mocephus]

Hello, all......I'm going to put this here, as it is a 'build/rebuild', but it is also a "HELP!!!!"

Many moons ago, I purchased this Aeromarine Laminates Sprint Cat, and nitro powered it(**gasp**). It ran decent, but nitro is a pain, and life got in the way, so on a shelf the boat went. FFWD 15 years or so, and my kids are bugging me about 'getting the boat running' again. I want to go electric, but I know next to ZERO about them. I was running a .46 nitro engine. So, guru's of OSE, help a somewhat newb out:

1) Is this crazy, converting a heavy, nitro hull?
2) If not, where do I start?
3) Will my flex shaft from the nitro engine work with electric power?
4) What kind of battery/motor/esc combo will I need for "reasonably fast", but safe enough speeds for the kids to operate?
5) Will my ancient Futaba Magnum Sport radio be sufficient, or do I need a new radio, too?

Some pics of the new paint going on.......from left to right, base coat, top 'kandy' coat, clear, clear.........
IMG_3425.jpgIMG_3429.jpgIMG_3452.jpgIMG_3454.jpg

Oh, and I could use a new hatch/cowl.....the old one was cut up to clear the nitro engine and exhaust......anyone have a spare? Didn't notice them available from Aeromarine anymore.

[mocephus]

Gee, everyone's mum.........Bueller? Bueller?.......

[CraigP]

You’ve got some work to do, getting that hull ready for an electric motor. Need to clear that frame in the center, probably get rid of the side mount bolts. You state you want fairly fast, but kids can run... Those two seldom walk hand in hand. If you’re just running for fun, then you’ll want some decent run time. So I’ll take a crack at a recommendation. I’d use 8s, made from two, 4s@5000mah batts wired in series. Those need to go into the sides of the boat, so you’ll need to get your cutting wheel out and remove some side frames. I’d put a SW 200A Pro+ ESC with a Leopard 4082 1000kv motor. I would NOT use the old flex shaft, but get a new 3/16” flex and running gear.

For the kids, I’d run a M445 prop on it. To go faster, a M547. These are reasonably priced props, there are better, such as the ABC props, but pricey and hard to get. I also recommended the more reasonably priced ESC and motor. If you’re not racing, then don’t fall into the low voltage, high amperage trap. That will just suck dollars out of your pocket. High voltage will keep your amps down, run longer and be easier on the gear. If you prop up too much, then you’re going to find trouble. Know where you want to run and have fun and stick there... BTW, where are you in OK? I’m in Tulsa...

[mocephus]

Thanks, Craig. No, no racing, just fun-running up at Grand Lake. I'm also in Tulsa, at least for 8 hours a day. The rest of the day is spent in Collinsville.

"Easier on the gear" sounds good......like I said, I know nothing about these electrics, and have no desire to 'release the magic smoke' from any components.

I should add, the kids are 17 and 12.....they're pretty well versed on RC, just not a boat. Maybe I should have said it as "we don't need to go 60+ mph.......yet".......

[CraigP]

Well that M547 will get it close to 60... A fellow FE boater in Tulsa! Now that's a rare find! I have a 32" Skater Cat hull. Maybe the fastest way for you to get to speed would be to drop by my place after work with your boat. I can show you how I outfitted my cat, and if you need, give you some advice on how to convert your hull over. I would need to see it to tell for sure. If your interested in meeting up, drop me a PM.

[mocephus]

Hmm, just by a prop-switch.......that may be just the ticket. I may have to take you up on that offer, but it would be next week at the earliest, will keep you posted. What is the ESC brand? Is that a Swordfish?

[CraigP]

Yes, Sword Fish... The Pro+ has a built in data logger, pretty handy thing when getting into FE for the first time. I am in town next week, that may work out for us both.

[TRUCKPULL]

In a Sprint Cat 36 you may need packs that are lower in height to get them under the side decks.

These packs are made for this, I have seen used in many Sprint Cat's

https://www.mojoracingproducts.com/collections/graphene-2-0-giant-power-70c-140c-lipos/products/4s-14-8v-5000-mah-70c-140c-graphene-2-0-super-kitty-stick-lipo-battery-pack

Larry

[NativePaul]

You can convert a nitro boat, it is not ideal, but it is not crazy either.

What coupling end did you use on your nitro flexshaft? If it was a collet type or a grub screw type you will be able to get a similar coupler for a motor and use the same shaft, if it is a square drive you are unlikely to find a motor coupler and will need a new flexshaft.

Craig's power system recomendation is a good one apart form the props. I endurance raced my 36" sprintcat on run 8s 5000-6600mAh, through a Suppo 200 ESC, with a Neu 1521 1200kv, to a detongued X440, this netted speeds in the low 50s which the boat is pertty stable at so I would say it is a setup suitable for kids of your ages, with a runtime of 5 minutes + mill +inlap. If yours is much heavier you may not be able to get away with a prop that small with reasonable slip, so you may need to step up to a 442 and get a bit less runtime with similar speed. For 6 lap sprinting I found an X646 to be the hot ticket, but at 3x the average current draw. I wouldnt sugest you buy the Neu I have, not because there is anyting wrong with it, but I bought mine when there were no budget 40mm motors on the market, nowadays Turnigy, Gool RC, Leopard, TP, HET and others all make decent budget options, and even if you have the money, you would be better of spending the price difference on a fresh hull. I have had great luck with my Suppo 200 but they dont rate them for 8s now so I couldn't recommend it for this application but it was rated to 8s and was the only budget option at the time, these days I would look to Castle, Flier or Swordfish, you will want over 150A rating.

I cut my rails down to about 1cm and put 4s in each sponson, but you don't have to, Jay Turner has raced his sucessfully with 6s2p on top of the tunnel and it handles fine.

Consider whether either you or your kids may want to race in the future, while 8s uses less amps for the same power so is good for fun running and the class I raced in the UK, in the USofA it would not fit a class, so I would suggest dropping down to 6s if racing is even a slight posibility down the line. Also many 8s capable ESCs are in the makers HV range and are much more expensive than regular 6s versions of the same amp rating.

It may work but I would heartily suggest that you upgrade that AM radio set to a name brand 2.4ghz set. It sounds like you will have your kids at the lakeside, and the last thing you want is a runaway boat. A 10lb boat at 50mph has more kinetic energy than a .44magnum.

[NativePaul]

Larry are there any lumps and bumps in the middle? What I am getting at is I am wondering if they are actually unusually long and thin cells or whether it is just 2x 2s packs packaged end to end with REALLY long wires, making them into a 4s pack?

[CraigP]

Paul, I recommended the props based on a 1000kv motor. It seems your setup was 1200kv, a bit of a difference. If the OP can cut weight out of the boat, he should get decent run time without high current draws. This is where the OP has to decide what the boat will be used for.

To the OP: 6s will push you closer to needing a 220A ESC, and battery C Rate to match. If you want to race, you should state that clearly, otherwise you may get racing advice that will not benefit you as a sport boater.

[NativePaul]

Sorry Craig, I could have sworn you said 1200kv, but I must have misread it.

[mocephus]

Thanks, guys.

Old drive shaft is a flex-shaft, not square drive. I forget the diameter. It was a collet-type mount to the nitro engine. It's all hardware from Aeromarine, so I'd like to reuse what I can.

I am a purely sport-boater, no racing intended. If the boys decide to get into that, they can purchase/set up their own boats.

[CraigP]

Sorry Craig, I could have sworn you said 1200kv, but I must have misread it.

No worries, it’s easy to miss info! I did go back and ran some numbers using your kv and prop size, got about the same speed! I was surprised the prop size dropped so fast with rotation speed... that 1000kv motor Leopard’s got has a great KT too, so given the weight, it should be the right motor without going stupid fast. I got 45mph with the M445 and 59mph with the M547. Nice battery recommendation Larry...

[CraigP]

Thanks, guys.

Old drive shaft is a flex-shaft, not square drive. I forget the diameter. It was a collet-type mount to the nitro engine. It's all hardware from Aeromarine, so I'd like to reuse what I can.

I am a purely sport-boater, no racing intended. If the boys decide to get into that, they can purchase/set up their own boats.

If we can meet up, I can mic that shaft out for you, and try a fit to some couplers I have. I did see only 3 of those motors left on OSE site. You might want to snatch that up. Leopard is switching to the new X2, and these motors are going to get hard to find!