40,000 rpm........what's the problem

[larryrose11]

I have seem pics of LMT motors, and they are a completely different build.
Instead of manets bound on the surface of the rotor, held in place with some sort of wrap like CF, Kevlar and the like, the magnets are discs. The have a good track record at high RPM

http://www.kbbforums.com/viewtopic.php?f=31&t=1294&sid=329a294fbf070105006c878146ccec6e

[ls1fst98]

very interesting read. like the fact everyone is discussing for the most part and not going overboard. I would think at any rpm, balance is the primary issue, and at higher than what FE "normally" runs this is even more so (hence check and double check bolts to insure they are snug as any vibration will loosen a botl that is not tight to begin with regardless of rpm) . i would imagine it also depends on what motor you are running, as i would imagine (if already stated i apologize) a given motor has a point where more rpm just means more heat and not more power or speed. just like in my real life experiences with diesel engines, there is a sweet spot in the rpm/efficiency/power range. i certainly will not claim to know as much as anyone here, as i have no race experience. so this is just my opinion.

[kfxguy]

Not sure if I should chime in here or not but... The loaded RPM can be quite a bit lower than theoretical as Jay stated, I think we had an average of 7000 RPM lower on mild setups aiming for the 40,000 mark. I will be putting this to a test on my Fantasm with both Electrical RPM measuring as well as 'at the hub' with my Eagle Tree this year.

Boy, good thread here Travis, already on page 2

Thanks. I'm interested in seeing this.
I'm glad no one is arguing here and this thread has turned into something with a lot of meaningful and good information. Keep it going guys!

[T.S.Davis]

"5 minute race time needed on the 5000mAh"

That's 48 amps average if you draw to 20%. About 1300 watts out.....ish. Seems light for an 8s boat. What kind of speeds do you get with so few watts out on an 8s boat?

My 4s 4 minute boat averages about 110 amps or 1540 watts.....ish. I'm still working on my 8s offshore setup but I'm figuring for about 3000watts output to push that hog.

[jkr]

Also more appropriate would be ''where and when is better to use 40k rpms''.

A mono like the pursuit can run 4s 2560kv m445 62mph+ but if i want to go faster i can either prop up or run 5s.
My stepped 29 inch mono runs 4s 2200kv 40mm prop 52mph ~32k loaded but i can't prop up cause it is narrow and it is better to spin faster.

40k loaded rpms aren't necessary in most of the cases but i can't imagine a rigger to spin lower than 40k.

Ps.I like outrunners for <35k cause the sound is awesome.

[properchopper]

One important variable not to be overlooked is the means in which ones desired terminal rpm is not only achieved but maintained. Whatever the desired rpm is, the batteries need to sustain their voltage number to achieve this and Voltage DROP Under Load (VDUL) is worthy of consideration. For example (using round numbers to make the math easier to understand) if you have a 2000KV motor running 4S packs that start out at 16V nominal and under load they drop one volt (not unusual and mostly more) you lose 2K rpm right then. I've graphed the VDUL of lots of different brands of batteries over the years and found that the better packs sustain voltage way better than less expensive ones. Whatever your target rpm is, use the best batteries you can to get (and stay) there.

[iridebikes247]

I'm with properchopper on this, good batteries sustain voltage way better than cheap ones and this certainly benefits all of us when going for high speed high rpm. This is a sick thread but has anyone made the distinction between single and twin high rpm setups?

A lot of guys going fast with twin boats will run mega-rpm motors and they will last...for some time hopefully but I for one have NEVER built a super fast single motor boat. A twin cat or mono for example will accelerate much faster and have less prop slip than an equally fast single-setup but singles are a different animal completely when it comes to spikes, prop slip, etc.

Just thought I would throw this one out there as there is surely a difference between high rpm setups in singles vs twins when it comes to any and all electronic components. Also as Fluid said things change quite a bit depending on water temperature. In NY we run boats year round over the summer it can be 95 degrees and in the winter 25 degrees with the water a few clicks away from freezing. Motor and esc temperature change drastically so what works in March for 5 minutes of running may come in HOT in August.

[NativePaul]

The amp draw of that cat would be a little higher than 48 as I would have been leaving less than 20% left in the cells (I know it is not good for them) I cant remember exactly how much as it was years ago that I ran 5000mAh, the 6600mAh I use now have about 7% left after a run for what its worth. The boat is very much an oval boat not a SAW boat and as such I have never run the 110 to find out how fast it is, if I had to guess I would say it was about 50mph on 5000s and about 55 now on 6600.

[ray schrauwen]

Time for me to get a Data logger esc...

[tlandauer]

Time for me to get an electrical engineering tutor.

[flraptor07]

Time for me to get an electrical engineering tutor.

I feel your pain.......

[T.S.Davis]

I wonder if on a twin cat setup where the props are behind nice sharp transoms you get more predictable water. Think nice smooth sheet of water leaving the bottom of the boat. So your prop always has a blade in the water. Less slap slap slappy effect on squirrely water in the tunnel. So fewer spikes? Just a thought.

I SO wish I was an electrical engineer. My old man tried to teach me. It was hopeless. At one point he was a thermographer for Amway Corp. Worked in a ginORmous plant here in MI. They used thermal imaging to predict motor failures. They had many thousands to document. So cool. Way retired now.

[jkr]

Measuring tools always helps to understand how a setup works

[olwarbirds]

Travis, tks for starting this...just what you and I had been discussing.... I understand needing to keep rpm and amp draw at a limit that allows the completion of a heat race and having mah left in lipos at a safe level, but thats heat racing. All my SAW boats are running 45,000 and up. I've been told that this is "disturbing, wrong, misleading" ETC...I like the OP had got tired enough of it , that I had stopped posting and abandoned my threads.

I dont think that a first boat should be a screamer and safety is always a factor. With the amount of knowledge available on this forum, I have seen it used by newbs to build some very nicely done fast boats. Instead of discouraging this trend of higher rpm setups, why not help in getting it done the right way ! This trend is not going away, the rpm's are going to go higher.

We need to explain the differences sport, heat and saw. My sport setups, I like to run on the edge of equipment and hull limitations. This helps me in setting up my heat boats, is this wrong ? works for me ! Yes I have burnt up a few inferior esc's and most of those were my fault. No burnt motors , we use Neu/Leo/TP . We been running these 2000kv and up motors on 6S some for over 2 years now. So we got our monies worth if they blowup now !

So please like OP pointed show us these failures caused by running 40k and up. All I have seen so far is 1 and alot of posting from " FE engineers" with some good points and info....old dog who is not staying on the porch

[kfxguy]

Travis, tks for starting this...just what you and I had been discussing.... I understand needing to keep rpm and amp draw at a limit that allows the completion of a heat race and having mah left in lipos at a safe level, but thats heat racing. All my SAW boats are running 45,000 and up. I've been told that this is "disturbing, wrong, misleading" ETC...I like the OP had got tired enough of it , that I had stopped posting and abandoned my threads.

I dont think that a first boat should be a screamer and safety is always a factor. With the amount of knowledge available on this forum, I have seen it used by newbs to build some very nicely done fast boats. Instead of discouraging this trend of higher rpm setups, why not help in getting it done the right way ! This trend is not going away, the rpm's are going to go higher.

We need to explain the differences sport, heat and saw. My sport setups, I like to run on the edge of equipment and hull limitations. This helps me in setting up my heat boats, is this wrong ? works for me ! Yes I have burnt up a few inferior esc's and most of those were my fault. No burnt motors , we use Neu/Leo/TP . We been running these 2000kv and up motors on 6S some for over 2 years now. So we got our monies worth if they blowup now !

So please like OP pointed show us these failures caused by running 40k and up. All I have seen so far is 1 and alot of posting from " FE engineers" with some good points and info....old dog who is not staying on the porch

Right on friend! No matter what rpm your running if it ain't setup right, it can/will fail. I myself feel like a rpm isn't a one and only cause of failure. I have been pushing my setups hard and everything seems to be Ok. In my video of my mini rivercat I was running a 2650kv 1512 castle motor and a water cooled mamba mister 2 esc on 4s. That 44,520 rpm (unloaded with full pack and not counting voltage drop...so more like 40k rpm) and noting even got warm. My son was run inning it back and forth repeatedly. I know that was only one running session, but hey...it was successful! I have been running 6s in my rivercat on a 2200kv 1515 castle. That's 55,440 rpm. (Same stipulations as above). It has a x642 prop. I think my failure will come from too many amps if I use too much prop.