RPM for H and M rigger

[RunningBeer]

Hi Skippers, I am building a Dr Super Evil and am impressed with footage of one running 6S on a 2200KV (4082). By my reckoning that's 48,840 RPM, Is this advisable? I've never built a rigger before and would love to hear from you gentlemen out there that run these type of boats and have setup recommendations. Thanks R.B.

[NativePaul]

I currently run mine on a Lenher 1940/10 1568kv (loaded), and have previously run it on a Leopard 3674 1700kv and Mega 22/30/2 1780kv all on <560g 6s 4500mAh, the Mega was the fastest but I couldn't get the 6 minutes run time needed to race with it. I can just about get 6 minutes with the Leopard and the Lehner with the Lehner being a little faster.

It is a big boat that can handle much more prop than the 38mm I have on it, and even if I wasn't constrained to run time I wouldn't want it that much faster due to the high amount of aero lift it has, I am sure I could push the hull to its limits with 1700 ish KV unloaded just by propping up a bit.

[Fluid]

That is a pretty large rigger, what does the OP want to do with it? That will determine the best setup, not what some goofball posted on YouTube. What you don't know is if the motor/ESC/packs grenade ten seconds after that video stopped. You don't know if the motor was demagnetized during the run. You don't know how many motors/ESCs/packs the guy burned up before he posted the video. Using YouTube alone as a boat tuning aid is a very poor idea.

If all he wants to do is run zipzip passes then the motor on 6S will work. Actual loaded rpm will be closer to 39,000-40,000 depending on how big the prop is. Frankly he doesn't need that much rpm for most running, and a lower Kv motor with a larger, more efficient prop will do just as well. I set a SAW record with my Q Sport Hydro running a 4092/1500 Kv motor on 6S with a large prop (~55 mm), average amp draw was under 275 amps and one pass was 99 mph. Prop down and he can run oval heat races without the excessive amp draw of a high Kv motor but with better acceleration out of the turns. What are his goals?


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[RunningBeer]

Thanks G Weasel and Fluid. I'm only a 'just for fun' runner (but serious rc boat junkie), and certainly don't want a hand grenade! I know 44000 RPM is crazy. I just don't quite know how the power etc. works in riggers. I like the sound of the better acceleration etc. Maybe 1500KV for 33000 RPM with 40-45ish prop size? what do you think? R.B.

[Fluid]

You will not see 33,000 rpm, that is the theoretical rpm without a load. 28,000 to 30,000 is more likely on the water. You could use a 45mm prop and it will work okay, but a 47mm or 50 mm would be more efficient. A lot depends on what your speed and runtime goals are for the boat.


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[RunningBeer]

Thanks Fluid, If I could get 3 mins run time that would be enough for me. I would imagine that runtime would set my speed limitation. What would you do in set up terms?
Thanks R.B.

[Fluid]

I have set my Q-Sport Hydros up for ~2-minutes of racing, usually with a 4092/1250 motor and a prop around 52-55mm. I use about 5000 mAh for a one-mile heat with mill. A rigger would pull a lot fewer amps so the 1500 Kv motor and a 47mm prop should work. Maybe more prop but you'd have to experiment to be safe.


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[RunningBeer]

Thanks Fluid, I have asked quite a lot of questions on this forum over time and I really appreciate the way you have helped me out. You've saved me a good deal of time, money and effort. One more question if I may, what strength servo would a boat like this need? Many thanks R.Beer.

[NativePaul]

I will answer you PM here as it may be of interest to others in the future.

My overall width is 595mm, with 170mm between each sponson and the tub, both sponsons parallel.

My strut is offset 3mm to the right, but remember I am averaging 1kw on a 38mm prop, with you wanting 3mins run will be averaging closer to 2kw and if you use a 47 ish prop you will want more than me, Jay would be able to advise how much better than me as I haven't run a prop that size in an oval boat since the brushed days.

I run a Hitec HS-5245mg servo which has 5.5kg/cm torque at the 6V I feed it. It is many years old and has served me well, being perfectly reliable and sufficient for all the Hydro2s I have had it in, but it is a mini servo and I am not sure how well it will stand up to the extra speed and weight that you want it to move.

Even with only 1kw to play with, a good proportion of the Super Evils that I have seen racing internationally have their sponsons modified to reduce aero lift with thin sheet spoilers following the line of the inside edges of the sponsons, over about half of the area where the bulk of the sponson drops away. As you are putting about double the power into it I would heartily recommend doing at least that to reduce the amount of blowovers you have. I would make sure that the range of AoA adjustment goes under the recommended 5deg as well as over it too.

[RunningBeer]

Thanks for your detailed and expert advise N.Paul. Cheers R.B.

[larryrose11]

Even with only 1kw to play with, a good proportion of the Super Evils that I have seen racing internationally have their sponsons modified to reduce aero lift with thin sheet spoilers following the line of the inside edges of the sponsons, over about half of the area where the bulk of the sponson drops away. As you are putting about double the power into it I would heartily recommend doing at least that to reduce the amount of blowovers you have. I would make sure that the range of AoA adjustment goes under the recommended 5deg as well as over it too.

Is there a picture of this, or perhaps a drawing?

[NativePaul]

I had a look and couldn't find any pictures, so I quickly knocked a couple up out of cardboard. They are not 100% accurately fitted but should serve to give you an idea of what I have seen.
IMG_0675 2.jpg
IMG_0677.jpg
IMG_0678.jpg

[NativePaul]

Oh, and I have seen various lengths of spoilers depending on how much lift the particular user wants to ditch, and the ones above are as long as I have seen, with the shortest being about half that length. I suspect that with you having double the power of mine and the ones I see racing you will want to ditch a lot of lift hence me making big ones. We typically weigh 2-2.5kg (4.5-5.5lb) for a 4-6s boat that uses circa 1KW average around the oval, and if you put a lot of weight into that extra power maybe you wont need as big.