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

[kfxguy]

***disclaimer*** this better not turn into an argument

First off, I'm not sure what the big deal is about running 40k rpm on a regular basis. I see people on here just
Get bent of of shape about it. Make remarks about it.....but I've yet to see some damage or proof that doing this is no good. I can understand if you using some El cheapo motors, yea, the rotor is going to come apart. But what about higher quality motors? I've never had a castle motor come apart. I had a reedy (cheap line of their motors) come apart. I was spinning it about 50k rpm. It was rated to run on 3s and that's what I was doing. Took it so art and saw why it came apart. Cheaply built.

I want to hear/see some proof that running a motor at 40k rpm that's rated for a make of 60k rpm has blown up. I've seen people say that a boat is different that a land vehicle because it's direct drive. Well it is and it isnt. It's direct drive to a prop but a prop will always have some slip. Yes I understand a prop has more drag on it that a land vehicles drive line, but if you don't over prop it, what's the issue? Over propping it isn't going to cause the rotor to come apart from high rpm, is it? I would think no. I'd think it would be a different type of load on the motor. One that heats it up and over taxes it and the esc.

My whole point is I'm tired of the scoffing, comments and negative things being said about running this rpm range. Come on people, this isn't the 90's anymore. Things have improved alot. Come a long way. Let's shed some light on this. I'd like to see some proof why you can't do it.

[properchopper]

I have to give you a lot of credit for raising this issue and stating it in an honest, forthright and non-confrontational manner. It'll benefit all of us if a mature dialogue can be established to finally address this.

I'll be the first to admit that I fall into the old fuddy-duddy category who has always kept the revs down below 35K or close to it. Even my SAW record holders don't breach that number and for sure my fleet of oval race boats go lower. It seems that only those interested in peak top speed want to go higher which is understandable and given that a well set up rig can do 40K or more might quench that thirst, there may well be ways to accomplish these goals without hazard. I do have some compelling answers based on many years doing the FE dance, but I'll sit on them to see if I can pick up some re-education as this thread develops. My ears are open

[ManuelW]

Thats the sound of rpm, at idle that setup will spin over 77.000rpm, under load still over 60.000

[Grazacind]

Yummy

[jcald2000]

I wonder how efficient our props are at over 400 MPH tip speed in water?
Also find a dyno run on an electric motor and notice how the torque curve drops like a rock at high RPM.

[Mad Racer]

Very interesting topic.

I have been told and read on this site that 35 to 40k is max for racing. I understand why and respect all the extremely knowledgeable guys in my clubs & on here . In saying that my latest race "cheap" spec motors in my 4s twin cat is pushing very close to 40K if my calculations are correct. In all honesty I'm more worried about getting run time ( 5 race laps & 2 mill laps) so some more testing is needed. If or when it turns sour it's all my own undoing & will were egg on my face

Very interesting indeed.

[kfxguy]

I have to give you a lot of credit for raising this issue and stating it in an honest, forthright and non-confrontational manner. It'll benefit all of us if a mature dialogue can be established to finally address this.

I'll be the first to admit that I fall into the old fuddy-duddy category who has always kept the revs down below 35K or close to it. Even my SAW record holders don't breach that number and for sure my fleet of oval race boats go lower. It seems that only those interested in peak top speed want to go higher which is understandable and given that a well set up rig can do 40K or more might quench that thirst, there may well be ways to accomplish these goals without hazard. I do have some compelling answers based on many years doing the FE dance, but I'll sit on them to see if I can pick up some re-education as this thread develops. My ears are open

Thanks Tony. I was getting tired of people saying you can't do this you can't do that but when I ask why, I get no concrete answer or proof. I'll admit, I'm still a newb at this, but I'm no dummy when it come to mechanics, electrical, building and fabricating. ..and I'm sure I've established that with you guys. I just felt like I needed some proof in this matter that it's bad to turn 40k rpm. I don't think a burnt esc is indicative of this either....in my opinion it's excessive load that causes the smoke to escape (most of the time anyway....a bad combo and many other things can cause it too) not motor rpm. I am speaking from my experience which I'll admit is limited in the boating world, but all my setups have been running at or around 40k rpm and I've yet to have a motor failure. I had one esc fail ***but*** I think it was a combination of problems unrelated to motor rpm. I felt I over propped the boat and I feel like the esc was a bad apple. This particular esc is well known to have a high failure rate anyway. So let's get back to it. Anyone got some carnage to show as a result of running high rpm?

[kfxguy]

I will admit when my rotor came apart in my buggy, I did get something out of it....a nice laugh. Lol. The buggy slammed on the brakes and slide to a stop. After figuring out the problem all I could do is laugh. Threw another motor in it and went back at it. Here's the carnage (understand this is an El cheapo motor)

[srislash]

Thanks Tony. I was getting tired of people saying you can't do this you can't do that but when I ask why, I get no concrete answer or proof. I'll admit, I'm still a newb at this, but I'm no dummy when it come to mechanics, electrical, building and fabricating. ..and I'm sure I've established that with you guys. I just felt like I needed some proof in this matter that it's bad to turn 40k rpm. I don't think a burnt esc is indicative of this either....in my opinion it's excessive load that causes the smoke to escape (most of the time anyway....a bad combo and many other things can cause it too) not motor rpm. I am speaking from my experience which I'll admit is limited in the boating world, but all my setups have been running at or around 40k rpm and I've yet to have a motor failure. I had one esc fail ***but*** I think it was a combination of problems unrelated to motor rpm. I felt I over propped the boat and I feel like the esc was a bad apple. This particular esc is well known to have a high failure rate anyway. So let's get back to it. Anyone got some carnage to show as a result of running high rpm?

Yes!! As long as you are not trying to spin a 450 prop on a Castle 1515 on 6s and run something reasonable, say a 442, 642. This all depending on the boat, setup, and how much prop in water of course. I have been running my 35" DF with 1717(1580kv) on 6s for going on three years on same everything. But I run 45-48mm props.

[don ferrette]

In terms of heat racing alot of the "preferred" rpm numbers come down to maximizing prop efficiency and battery consumption. As a generalization typical heat racing props are most efficient in the 25-35,000 range. As far as rpm numbers, even though motors may be "rated" for 60K it doesn't mean they will live at or near there continuosly. The only motors I'll twist the snot out of are my record trials motors but that is an entirely different scenario as those motors only spend a brief amount of time winding into the stratosphere rpm wise.

[Grazacind]

Well mate I run a twin rigger with 2 Neu 1527 .5y on 6s. This is a saw setup only for me but the main issues I have experienced are parts being out of balance. You can get away with pretty good balance at 30k at 47k it is so so critical. I think this out of balance helps motors let go with the excessive vibration. Running high rpm is fine if you pay a lot of attention to balance of the whole driveline. Most don't so 30k is a more reliable setup. Just my thoughts anyway.

[Fluid]

I think that the OP has interpreted many of his "naysayers" incorrectly. Most were not implying that the motor would fail because it it spinning so fast (although some cheaper motors will lose a magnet or a bearing - it's happened to me). Running a motor at extreme rpm can shorten its life, but that's another issue. The real problem is amp draw and the ESC. A setup which runs 40,000 rpm or more (I have many SAW records set near or above that rpm) is usually a low-turn motor which can draw massive amps at lower rpm. Running at 40,000 rpm the setup may only draw 200 amps, but slow the motor down just a few thousand rpm and it can spike amps to well over 300. Get on Neu's site and play with their Advanced Motor Calc to see what can happen to amp draw if a slightly too-large prop is chosen. Try a Neu 1527/1D motor on 6S and see the difference in amp draw just by reducing the rpm from 41,000 to 38,000 - it increases from 230 amps to 320 amps. Just changing to a slightly larger prop can cause an ESC meltdown - and I have the ESCs to prove it.

But a quality 200 amp ESC can stand a 300+ amp load for a brief time because it is the heat which destroys controllers, not the amp draw. So making a pass or two with an extreme setup and bringing the boat in can be successful. Making ten passes will likely result in damage. But most sport boaters will not be happy with just two passes, so it is far safer for the majority to use a less extreme setup - hence the recommendations. Believe me, in the past thirty years I have seen more burnt boats from guys running too high of a Kv motor for their setup than from about any other cause.

It is certainly possible to safely sport run at 40,000 rpm, but not that many do so successfully. Too many boaters (particularly newbies) seem to believe that the only way to go fast is to turn 40,000+ rpm because they read about it somewhere. Not true, I ran almost 90 mph last year in LA turning under 35,000. Going fast isn't all about high rpm, it's about putting together a system to reach your target speed. There are various ways to get there, some carry more risk than others.


.

[flraptor07]

Well mate I run a twin rigger with 2 Neu 1527 .5y on 6s. This is a saw setup only for me but the main issues I have experienced are parts being out of balance. You can get away with pretty good balance at 30k at 47k it is so so critical. I think this out of balance helps motors let go with the excessive vibration. Running high rpm is fine if you pay a lot of attention to balance of the whole driveline. Most don't so 30k is a more reliable setup. Just my thoughts anyway.

Deffinetly! Vibration plays a huge part in motor reliability, espcially harmonic vibration. It causes things like shaft flex and that in turn causes rotor failure along with centrifical force. In the last 5 to 10 years epoxies, adhesives and manufacturing processes have come a long way and that's why we don't see the failures in quality motors that we used to. Ok there's my 2 cents on the subject

[kfxguy]

I think that the OP has interpreted many of his "naysayers" incorrectly. Most were not implying that the motor would fail because it it spinning so fast (although some cheaper motors will lose a magnet or a bearing - it's happened to me). Running a motor at extreme rpm can shorten its life, but that's another issue. The real problem is amp draw and the ESC. A setup which runs 40,000 rpm or more (I have many SAW records set near or above that rpm) is usually a low-turn motor which can draw massive amps at lower rpm. Running at 40,000 rpm the setup may only draw 200 amps, but slow the motor down just a few thousand rpm and it can spike amps to well over 300. Get on Neu's site and play with their Advanced Motor Calc to see what can happen to amp draw if a slightly too-large prop is chosen. Try a Neu 1527/1D motor on 6S and see the difference in amp draw just by reducing the rpm from 41,000 to 38,000 - it increases from 230 amps to 320 amps. Just changing to a slightly larger prop can cause an ESC meltdown - and I have the ESCs to prove it.

But a quality 200 amp ESC can stand a 300+ amp load for a brief time because it is the heat which destroys controllers, not the amp draw. So making a pass or two with an extreme setup and bringing the boat in can be successful. Making ten passes will likely result in damage. But most sport boaters will not be happy with just two passes, so it is far safer for the majority to use a less extreme setup - hence the recommendations. Believe me, in the past thirty years I have seen more burnt boats from guys running too high of a Kv motor for their setup than from about any other cause.

It is certainly possible to safely sport run at 40,000 rpm, but not that many do so successfully. Too many boaters (particularly newbies) seem to believe that the only way to go fast is to turn 40,000+ rpm because they read about it somewhere. Not true, I ran almost 90 mph last year in LA turning under 35,000. Going fast isn't all about high rpm, it's about putting together a system to reach your target speed. There are various ways to get there, some carry more risk than others.


.

Your right, may have interpreted incorrectly...but....I was automatically taking into consideration that the prop is matched for the setup...why would high rpm cause it to fail? Maybe we should say that past 35krpm you need to make sure everything you can balance, is balanced. I started balance my collets/couplers and I feel that goes a long way to help things last

[BHChieftain]

I take the practical view of running spinning things as low as RPM as possible to get the job done. I do it for my boats and my helicopters. I try to run the biggest prop I have in my box at the lowest RPM to get the output I want with correct handing characteristics. So far I have not needed more than 32K RPM (that's a 29" mono) to make the boat go faster given my power system and available props. Most of my boats are under 30K. Less RPM= less vibration issues (unless you *really* have a perfectly balanced driveline-- hard to achieve), less wear on strut and bearings.

If I were trying to build a boat for pure speed and ran out of prop, sure I'd think about cranking up the RPMs, but I would make that the last variable to change.

I guess I'd turn the question around and ask if there is any benefit on targeting a higher RPM than needed to achieve the speed target? If there were some benefit, then we could start looking at the vibration/wear factors more closely to realize that benefit. If there are no other options to hit the speed target than to increase RPM then we are back to my first point... now you are very likely trading reliability for speed which may be the tradeoff you want to make.

Chief

[ray schrauwen]

It is certainly possible to safely sport run at 40,000 rpm, but not that many do so successfully. Too many boaters (particularly newbies) seem to believe that the only way to go fast is to turn 40,000+ rpm because they read about it somewhere. Not true, I ran almost 90 mph last year in LA turning under 35,000. Going fast isn't all about high rpm, it's about putting together a system to reach your target speed. There are various ways to get there, some carry more risk than others.


.

There seems to be a good number of Newbies watching youtube vids of boats turning 40,000 rpm and thinking they can do it too because a motor has a max spec of 60,00rpm. Problems arise because of things like stock props (unbalanced and or unsharpened being used or too big of props.
It's not the experienced guys I try to warn, it's the new guys.There have been a number of boats in the swap shop with interiors that show obvious signs of esc detonations from users that aren't to regular on here or it was "not their cup of tea" after a meltdown and they sell it off and get out of boats.
It's all good if you have the experience to do these things or take the right steps to prevent meltdowns but, it's an area that has a definite higher failure rate than the lower rpm range.

[Chilli]

Motors get to a certain level of RPM and load and their efficiency goes way down resulting in rapid heat build up. As mentioned above, it's all about the application. If you are doing a couple of short runs or running a SAW's event where run times are short, by all means crank up the RPM. But if you are sport running for five minutes plus, you better keep a close eye on the temperature of your gear. In these applications you may end up having to prop down so low that your prop efficiency suffers taking away any advantage of running a high rpm set up.

Like Ray mentioned, most of us want FE newbies to have a good first experience with RC Boating. So preventing them from burning stuff up is why we err on the side of conservative recommendations. BTW- Same thing goes for prop recommendations for a given set up. If someone wants a prop recommendation, the first thing I ask is "what's your application".

[kfxguy]

I take the practical view of running spinning things as low as RPM as possible to get the job done. I do it for my boats and my helicopters. I try to run the biggest prop I have in my box at the lowest RPM to get the output I want with correct handing characteristics. So far I have not needed more than 32K RPM (that's a 29" mono) to make the boat go faster given my power system and available props. Most of my boats are under 30K. Less RPM= less vibration issues (unless you *really* have a perfectly balanced driveline-- hard to achieve), less wear on strut and bearings.

If I were trying to build a boat for pure speed and ran out of prop, sure I'd think about cranking up the RPMs, but I would make that the last variable to change.

I guess I'd turn the question around and ask if there is any benefit on targeting a higher RPM than needed to achieve the speed target? If there were some benefit, then we could start looking at the vibration/wear factors more closely to realize that benefit. If there are no other options to hit the speed target than to increase RPM then we are back to my first point... now you are very likely trading reliability for speed which may be the tradeoff you want to make.

Chief

My main reason for higher rpm with a small prop vs low rpm with big prop is prop walk. I found I can go just as fast with no prop walk doing it this way.

[iridebikes247]

Driveline is very important. I personally try to run bearings in all of my drives but there are plenty of SAW guys setting records using bushings in their struts with no issues. I think its just a general guideline to stay below a certain rpm. Not everyone can perfectly tune a prop, setup a boat, etc. Less rpm, smaller chance of toasting stuff. I too prefer more rpm and smaller props because of how prop walk can really hurt how a hull handles on the water, no fun.

You can spin a lot of rpm safely but I do agree with Jay that the electronics will take an exponentially greater beating if things are setup poorly in a high rpm setup. They're great if you don't screw anything up!

[ray schrauwen]

There is a slight problem with running oval races with higher KV and smaller props. If you come off plane a smaller prop will take longer to bite and get back on plane than a larger prop so for ovals it's a balancing act.

[flraptor07]

Everybody is making great points and I've learned many other way of looking at the RPM issue already, plus no arguments yet! But we're all forgetting one thing, 40,000 + RPM Just sounds so BADASS!!!

[T.S.Davis]

The rpm doesn't automatically dictate failure. It's the beating everything else takes. The motor is the least of the worries.

Begs the question "why?"

Why opt for high rpm? Potential resonance issues, potential for amp spikes, probable heat issues until you find the right prop, flex cable whip, pick up some weeds......baked, plugged water line.....baked, the risk of throwing a blade on a prop that can't take the pounding? You only find the blade thing after you throw it. That has happened to me.

Sure you could address all those issues with careful planning and exacting detail but why bother when smarter less risky choices are available that are plenty fast? I could probably make it work but I wont on purpose. I used to run Hacker 9L on 12 sub C. Tiny props for a P Sport. I saw a 9L run on 24 sub C through a gear drive. Sounded cool until the rotor exploded. We don't do it anymore because there are easier ways to get where we want to go.

Plus, some new guy reads......."50k rpm to go really fast" and figures he'll just throw that in his Spartan. Runs it for 6 minutes and ends up having himself a nice bake sale. This is why you typically read guys not endorsing the approach and even discouraging it.

Another thing about motors......those ratings of 60k rpm are rotational ratings. That doesn't account for any of the axial thrust we push on the bearings. So when you run those kind of rpm you need thrust bearings. Yet another thing to have perfectly balanced. Is the new guy going to know to put the thrust bearing in there?

[kfxguy]

So basically what im gathering is a basic overloading of the motor is the result? What's the difference if I overload the motor at 30k rpm and burn up the esc or motor vs overloading it at 40k rpm and burning up the esc or motor? Is it going to explode into a nuclear like explosion? Lol j/j

[kfxguy]

There is a slight problem with running oval races with higher KV and smaller props. If you come off plane a smaller prop will take longer to bite and get back on plane than a larger prop so for ovals it's a balancing act.

Very good point! I like water wheelies!

[kfxguy]

Everybody is making great points and I've learned many other way of looking at the RPM issue already, plus no arguments yet! But we're all forgetting one thing, 40,000 + RPM Just sounds so BADASS!!!

Hell yea that rpm screaming sounds bad ass!

[ray schrauwen]

So do outrunners at 30,000rpm

Everybody is making great points and I've learned many other way of looking at the RPM issue already, plus no arguments yet! But we're all forgetting one thing, 40,000 + RPM Just sounds so BADASS!!!

[kfxguy]

The rpm doesn't automatically dictate failure. It's the beating everything else takes. The motor is the least of the worries.

Begs the question "why?"

Why opt for high rpm? Potential resonance issues, potential for amp spikes, probable heat issues until you find the right prop, flex cable whip, pick up some weeds......baked, plugged water line.....baked, the risk of throwing a blade on a prop that can't take the pounding? You only find the blade thing after you throw it. That has happened to me.

Sure you could address all those issues with careful planning and exacting detail but why bother when smarter less risky choices are available that are plenty fast? I could probably make it work but I wont on purpose. I used to run Hacker 9L on 12 sub C. Tiny props for a P Sport. I saw a 9L run on 24 sub C through a gear drive. Sounded cool until the rotor exploded. We don't do it anymore because there are easier ways to get where we want to go.

Plus, some new guy reads......."50k rpm to go really fast" and figures he'll just throw that in his Spartan. Runs it for 6 minutes and ends up having himself a nice bake sale. This is why you typically read guys not endorsing the approach and even discouraging it.

Another thing about motors......those ratings of 60k rpm are rotational ratings. That doesn't account for any of the axial thrust we push on the bearings. So when you run those kind of rpm you need thrust bearings. Yet another thing to have perfectly balanced. Is the new guy going to know to put the thrust bearing in there?

You make some good points friend. Your right, you can setup to do the same at lower rpm But I've gotten some mean prop walk with bigger props. I like my boats to go straight.....lol

[T.S.Davis]

I like the sound of high pole motors when you pull away from the shore.

When a speedo fails.....results vary. I've had them blow the deck off boats. I've had slow burns with a little puff of smoke and it's over. I've had them burn their way through the deck. The worse case scenario is the battery leads come off the boards and dead short the LiPo. That is truly nasty. That one I've been lucky enough to avoid thus far. Seen it though. yyyuck.

You can certainly overload a setup at 30k. The potential isn't as high though. There's also less risk of all those other annoying things I mentioned. Back in the brushed days it was always the armature that gave up the ghost for me. The endbells would melt right off the motors. I knew I had pushed too hard when I found plates from the armature smoldering in the bottom of the boat. "Toss another motor on the bar'bee."

One I didn't mention on high rpm setups, everything comes loose. You have to constantly check nuts and bolts. Motor screws to trim tabs. Better to Loctite everything. Still have to check them though. Manageable of course. Just an annoying PIA. Maybe for SAW where you run down and back and then check it all over anyway.

[T.S.Davis]

You have to find that fine line for which prop a boat likes. Each is a little different.

I have a P mono that I race that has a bit too high of RPM for my liking. All those RPM will make it swap ends on me coming out of a turn. Fix was a bigger turn fin on that side. Raised the strut a bit to keep more boat in the water too. Sometimes it's not just the big prop that makes the boat get all weird. Sometimes it's us.

[don ferrette]

You make some good points friend. Your right, you can setup to do the same at lower rpm But I've gotten some mean prop walk with bigger props. I like my boats to go straight.....lol

I can't even begin to think of how many "prop walk" issues I've seen over the years that were from poorly prepped props and nothing else. Just because it is "balanced" when you spin it and has sharp edges doesn't mean it's right. And that pales in comparison to poorly set up boats where the owner was blaming the prop for it's inability to track straight.