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

[keithbradley]

Higher RPM does increase the likelihood of certain types of failures, there's no denying that. That doesn't limit you to running super low RPMs all the time, but it should be considered when choosing a setup. Some motors don't deal with RPM well, that's just how it is. Centrifugal force is a constant that will not be changed by any means. Some low RPM setups are problematic for different reasons.

I think the main issue with high RPM setups, is what most of you are eluding to. Many RPM ranges can be successfully utilized if done correctly. The guy who just runs a 4s setup on 6s to go faster is the one who looses here. Most people would never believe the ACTUAL current peaks you see on some of these cowboy setups if you get a logger that is sensitive enough to properly log them. I've seen peaks over 1000A on overloaded motors. This happens not from spinning a motor fast, but from overloading it, which coincidentally is easy to do when you run higher RPMs. I can't say how many times I've seen this in FE. The happens with factory RTR parts, but the most notorious aftermarket is 6s/2200kv. I think this is because the combo is used in so many 1/8 scale cars and people are first impressed by this setup before they ever get into boating, not realizing that pushing a 1/8 scale car to 60mph is not a heavy load at all...nothing in comparison to what we see in FE boating. Some people never learn how to properly set up a boat and just default to increasing theoretical RPM to increase speed. Not only does this increase risk of failure, but it really limits how fast someone can go without learning how to set their boat up.

When I see these guys run I wince a little...not because they're running a particular RPM, but because they're running MUCH slower than they should be with a given motor/voltage/prop combo, which is a tell-tale sign of an overloaded system. If boat "A" can run 70mph on 5s/2200kv/x442, and boat "B" runs 70mph on 6s/2200kv/x645, it doesn't take a genious to see that the "B" guy is doing something wrong.

[keithbradley]

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.

I just noticed that you're running 6s/2200.lol
That wasn't an underhanded reference to you in my last post, just coincidence...I hope you got that. I was just mentioning that combo because of how many times it has been done incorrectly, not anything in regards to your setup.

Just curious in regards to your river cat...is that the only prop you've tried?

[Fella1340]

What wouldn't be considered a cowboy combination on say, the rivercat. What would be a good combination to bring it up to 70mph and not use the 6s/2200kv that so many seem to be using. I have seen many of these power combinations pointed out to be the wrong approach but nothing is ever offered as an alternative. Just curious what the correct approach is.

[keithbradley]

What wouldn't be considered a cowboy combination on say, the rivercat. What would be a good combination to bring it up to 70mph and not use the 6s/2200kv that so many seem to be using. I have seen many of these power combinations pointed out to be the wrong approach but nothing is ever offered as an alternative. Just curious what the correct approach is.

I think perhaps you misunderstood the point. I didn't say 6s/2200kv was a "wrong combination". The problem is when guys are running setups that are mathematically 90+mph setup and they're going 70. They always say that their setups run cool, but it doesn't really matter. Energy is not magic. The energy that should be adding another 20mph to that boat is going somewhere.

In my opinion if you want to go 70 in a rivercat, build it as a twin. You won't regret it, I promise.

[Fella1340]

Thanks Keith. I understand your meaning.

[kfxguy]

I just noticed that you're running 6s/2200.lol
That wasn't an underhanded reference to you in my last post, just coincidence...I hope you got that. I was just mentioning that combo because of how many times it has been done incorrectly, not anything in regards to your setup.

Just curious in regards to your river cat...is that the only prop you've tried?

Lol, I didn't take it like that. The rivercat is just expand to make a few fast passes and bring it in. I guess you can say saw setup. The reason I did it this way is higher rpm and a small prop. I haven't tried anything else either. I've run it only once. Kinda been messing with the mini and the cheetah. I got the cheetah running perfect and the mini run perfect but takes on water. I have to do a few things to make sure water isn't coming in anymore. It runs (well theoretically) around 45k rpm's. It has an 180 kv motor on 6S. We hammered on it a while and everything seemed well. Motor Temps were 95.5f and the esc was about the same. I just wanted to see how fast she would go (redneck 6s setup lol! ) and I plan on trying different props and running it on 5s normally. Enough about that lol. Guess I brought it up because the rpm I was spinning. I'm uploading a video right now and will post it in my mini thread.

[olwarbirds]

Neu 1515 2200kv 6S X642 prop same setup I'm using in my genesis. Temps under 100 on everything except lipos, need more mah. What I see being said here is that my 80mph Genesis, could get those same speeds with a lower kv motor running a bigger prop. Does not running a bigger prop put the amp draw high too just like running a higher kv motor ? There is a point to both, its all in finding that fine balanced tuned setup. Have not most of the new SAW records been set using higher KV motors ?

[kfxguy]

Neu 1515 2200kv 6S X642 prop same setup I'm using in my genesis. Temps under 100 on everything except lipos, need more mah. What I see being said here is that my 80mph Genesis, could get those same speeds with a lower kv motor running a bigger prop. Does not running a bigger prop put the amp draw high too just like running a higher kv motor ? There is a point to both, its all in finding that fine balanced tuned setup. Have not most of the new SAW records been set using higher KV motors ?

I started off liking the bigger props. Easy way to go faster. But then I started running into other issues like prop walk and torque roll. Yea, I'm not the best ever at sharpening and working props, but I'm not a dummy either (someone posted earlier about almost every time he saw prop walk/tq roll was from an improperly prepared prop). So I've found in my testing that I can go a little smaller prop, higher rpm and arrive at the same thing. I feel like it's 6 one way, half a dozen the other. I'd rather run a little more rpm and my boat go straight you know what I mean? Maybe it is my prop, but i dont have 50 bucks a pop to try a bunch of different props prepared by someone else. I plan on getting one and comparing to mine however....just to see how my prop fares against a pro. It will be a back to back test gps, Temps etc will be taken. I did confirm my suspicions about something I posted in this thread today. I'll be posting a new thread named "you gotta see this" once video footage finishing uploading. I'd suggest checking it out. It'll be interesting.

[srislash]

A hull handles better with smaller props, especially a twin. My Shocker really wanted to just go straight with 50mm props on it, made the race course tuff.

[kfxguy]

A hull handles better with smaller props, especially a twin. My Shocker really wanted to just go straight with 50mm props on it, made the race course tuff.

Exactly my point :)

[T.S.Davis]

. All I have seen so far is 1 and alot of posting from " FE engineers" with some good points and info....

I don't know what that even means. I think it means no practical knowledge. Just theory.

The only rpm related motor failure I've seen was a Hacker 9L. Wasn't my boat. That was many moons ago. 2003 I believe. Pre-Lipo. None of us up here had run more than 18 sub C back then so it was like science fiction trying to figure it out. Too many volts on an Milwaukee drill motor splayed the plates on the armature. Glorious. Junks. Did that multiple times but those don't count.

I listed the reasons I don't do it. None of those was due to "motor failure". Yes I have had high rpm setups so not just theory.

I once bench tested a high rpm setup before I put it in the water. You know, pull the trigger, check for rotation. Wire drive with ball bearings. Clean straight setup. Well I thought it was. Apparently something was out of balance because the shaft bent at the stub and thew the prop. Hit me in the throat. Got really lucky. That was NOT a motor failure. That was an idiot failure. I do have some experience and still managed to nearly injure myself. I wasn't going to mention it because my mistake was clearly next level stupid but if someone else takes a little extra precaution then great.

Point being, you guys that encourage high rpm setups may well influence a virtual newbie that heck yeah it's zero problem to run high rpm. Someone is reading this thread right now and thinking "Hey, if 40k+ is good why not a 100k? I'll be extra super fast then" We'll have guys that don't even understand the mathematics of these things trying to build super high rpm beasts. The motors aren't the issue. Think newbie with 50k in a Geico on 6s. Might as well throw the parts in the lake. We see that one on here about every 6 months it seems. Sometimes it's the Motley.

I'd like to see some links to where people have implied there would be motor failures simply due to rpm. Did I miss that somewhere?

There are a myriad of other potential issues. All addressable of course but miss something.........

[kfxguy]

I don't know what that even means. I think it means no practical knowledge. Just theory.

The only rpm related motor failure I've seen was a Hacker 9L. Wasn't my boat. That was many moons ago. 2003 I believe. Pre-Lipo. None of us up here had run more than 18 sub C back then so it was like science fiction trying to figure it out. Too many volts on an Milwaukee drill motor splayed the plates on the armature. Glorious. Junks. Did that multiple times but those don't count.

I listed the reasons I don't do it. None of those was due to "motor failure". Yes I have had high rpm setups so not just theory.

I once bench tested a high rpm setup before I put it in the water. You know, pull the trigger, check for rotation. Wire drive with ball bearings. Clean straight setup. Well I thought it was. Apparently something was out of balance because the shaft bent at the stub and thew the prop. Hit me in the throat. Got really lucky. That was NOT a motor failure. That was an idiot failure. I do have some experience and still managed to nearly injure myself. I wasn't going to mention it because my mistake was clearly next level stupid but if someone else takes a little extra precaution then great.

Point being, you guys that encourage high rpm setups may well influence a virtual newbie that heck yeah it's zero problem to run high rpm. Someone is reading this thread right now and thinking "Hey, if 40k+ is good why not a 100k? I'll be extra super fast then" We'll have guys that don't even understand the mathematics of these things trying to build super high rpm beasts. The motors aren't the issue. Think newbie with 50k in a Geico on 6s. Might as well throw the parts in the lake. We see that one on here about every 6 months it seems. Sometimes it's the Motley.

I'd like to see some links to where people have implied there would be motor failures simply due to rpm. Did I miss that somewhere?

There are a myriad of other potential issues. All addressable of course but miss something.........

I implied motor failure because I was making guesses as to what would happen as a failure. Until now it hadn't really been discussed too much ad to what would or might happen. I just kept reading people saying don't do that. I wanted some concrete evidence as to why not. There's been some goo info in this thread. Not really any concrete proof on failures really, but good info that makes sense. Seems that if you do it correctly and take precaution, plan out your combo and don't be an idiot, then yes you can run a high rpm setup with success. I seem to be doing it with success and so are a bunch of others.

[gr8evo]

I read allot here and thank every one for there knowledge and opinions.

High rpm setups have a number of downs sides witch have all bin covered. I don't know the sample rate of the data loggers out there, however I would think they sample at least a few times a second. In the automotive world we data log 30+ parameters at 250 samples a second for reference and that's the cheap stuff. I don't think most people have the patients or care to retrieve and use the data. With the ability to have amp draw data it would be very easy to push the limits without going to far. I love data. In my race car I log everything I can including 3 axis g-force. If the wind blows and moves my car I know it. If I blow stuff up I can review the data to put the pieces of the puzzle together.


People here are very nice and forth coming with knowledge. They try to save the new guys the r&d and most importantly the time and money. Its simple if you don't have the budget don't push the limits. Nothing wrong with learning from our own mistakes and pushing the limits, just remember that the kind people here have shared the knowledge and warned those who do not want to blow stuff up.

For me I love hp over torque. My race car motor turns 11k rpm and my fe boats all turn 40k plus. I blow everything up in the quest to build a better mouse trap.

Happy boating

[olwarbirds]

"FE Engineers" was a compliment not meant to be taken to a negative remark....I have a Miss geico 45,000 + ...BJ Twin 45,000 + ....this does not mean I'm suggesting newbs try this, these hulls have been seriously upgraded and "WE" tell the newcomers these are not something for them to start with, so "misleading" I dont think so. I dealt with this same type of comments when I was involved in the prototype design testing of the first EDF (electric ducted fan) RC Jets and the first brushless motors.

[T.S.Davis]

, these hulls have been seriously upgraded and "WE" tell the newcomers these are not something for them to start with, so "misleading" I dont think so. .

Yes, perfect. You used your experience to make it possible for that to work. You knew if it blew off going fast it wouldn't survive impact with a stock hull. Then you try (best ya can) to let people know it's not as easy as just throwing more kv at it. That's all we can really do.

I think I understand where the confusion crops up. Somebody asks about turning a gOjillion rpm to go fast and people (some) discourage it. Primarily because they know what "can" happen if you get it wrong. Not because rpm are the devil or the motor will absolutely fail because of the rpm. It's the whole package that turns some of us into negative nancy. I know I'm guilty. We never know who is on the other end of a question.

haha Have we thoroughly beaten this to death yet?