Speed calculator accuracy?

[Wtaylor3]

I was playing with the speed calculator on this site just to see how fast I could possibly get my outlaw jr to go...I checked it with a leopard 5460kv and 4s lipos and 85% efficiency and 25% slippage and an x442 prop and it told me a top speed of like 113 mph....is it really possible to get a rtr v hull to run that fast? I'm torn between slightly modifying my outlaw jr and building a catamaran or buying either the traxxas spartan or miss geico and modifying them or the genesis from hobbyking and running twin leopard motors....I'm looking for 70-90mph but if I could touch 100 that would be even better....I'm the type of person that needs to have the biggest baddest thing on the lake but I don't have $700 to drop on a neu 2230

[BHChieftain]

The answer is no... you'll hit some physical limitations first.

A 5460KV motor on 4S is over 80,000 rpm, it would be challenging to build a drive system that could handle that... Also, RTR hulls are generally not strong enough to handle those speeds-- you'd be getting flexing all over the place and that would make it tough to keep on the water (or just flying apart at the seams). You'd also need a huge high capacity speed controller to handle the amp load.

If you really want to faster than 50mph, I'd recommend getting a high quality cat or hydro hull (fiberglass or carbon fiber hull). You could also get into riggers. Mono hulls need a lot of power to push them throught the water and you would need huge motor and speedo to deal with the amps, and they become unstable at high speeds-- most of the superfast SAW builds you'll see here are cats or hydros.

Me personally, I target around 30K RPM, and dial in my setups to keep the components cool and reliable-- my boats run in the mid 40's to low 50's (if my imagination is having a good day). Somebody here on OSE has the tagline I really like: "Cheap, fast, reliable... pick 2 out of 3". High speed/high power boats need expensive components and will chew them up quickly.

Chief

[Wtaylor3]

Thanks for the advice....I'm actually looking into cats the main reason I bought the outlaw was to outrun my dads supervee 27 but we ran 6s in the supervee and it was ridiculous fast and i couldn't run dual packs in my outlaw due to no y harness...so you're saying if my hull did handle it my driveline would be the weak link? 50-60mph would be double what it's doin now so I suppose that would be a great start

[keithbradley]

The calculator only works for reasonable setups. If it was just a matter of plugging numbers into the calculator you could power a 92" cat with a $9 motor and go 200mph.