how do i get lots of rpms

[roy cherry]

hello guys i did a test last week i tried to run pipe rpm run with a 5s 2700 bat and a mvvs 950 with a 40 amp speed controler all i managed to get was 11200 with a 13 4 apc cut to 12 4 the aeroplane  took of like a helecopter but the lap speed was to slow 5.6 also i am on a renical timer  when i landed the motor was hot and the speed contrler was hot aso the battery was down to 9percent  what combo do i need to get 1200 max as the lower pitch made my plane fly realy nice it was not pluling my arm of and making the corners sweet so i feel the need to pursue this angle  i think this high rpm set up would be right for me  thanks guys roy cherry 

[Bob Hudak]

You don't mention how long your flying lines are, but you can expect your lap time to go down .1 second for every foot you shorten them. You'll also complete the pattern in less time which will reduce battery consumption. Running hot might indicate the need for more ventilation to the setup. Aim for three times as much exiting air as inlet air.
Bob

[Tim Wescott]

Nothing adds up here.  With that motor & battery you should be able to get 13k RPM unloaded (unloaded = no prop).  A 12-4 shouldn't load the motor that much, and besides, if you managed a 6 minute flight then the amount left on the batteries indicates you were only pulling 25A on average, which is well within the capabilities of the speed controller.

This probably means that there's one problem that we're not getting from your description, or you have more than one problem that are causing the symptoms separately.

You did not say what plane you're working with, or how much it weighs.  Nor did you tell us the model of the motor.  Knowing that should help.

If you can, take a picture of your plane and post it.  People will want to see your general wiring arrangement, and they'll want to get an idea of the airflow over your motor, ESC, and battery.

The KR timer regulates speed: it's possible that you don't have it set up correctly, or that it isn't set up to regulate at faster speeds than what you're getting.  Hopefully someone who's familiar with the timer will weigh in.

If you have any RC gear or a servo tester you can do a speed test.  Set the thing up with a receiver (or servo tester), put a small prop on the motor or a dummy prop made from balsa, turn it on, go to full throttle, and see what the motor tachs at.  If it can't get above 12000, it's not the timer.

If you have the equipment, checking the voltage and current on the ground, both running and not, is a good idea.

Check that you have cooling, like Bob suggested.

Also, unless your plane weighs over 65 ounces, check that the motor isn't rubbing anywhere and that it has good bearings -- friction at the motor would account for both the high power drain and the motor heating, although it wouldn't account for the ESC getting warm.

I can't think of anything else to suggest at the moment.

[Dennis Adamisin]

Motor not big enough for the prop load.  That can result in the RPM coming up short, causes high heat in the motor, high current (& heat) through the ESC, and high battery drain.  Bob H's suggestions for cooling are spot on, but you may have to dig a little deeper.

You might deal with it with smaller prop - at least for test purposes.  Try an APC 11x4.5EP which will need to turn about 12k.  If the smaller prop lets you achieve your target RPM and cools everything down then it would indicate the miss match with the orignal prop.  If it is still too hot then the things Tim W suggests are probably in play.

[Mike Anderson]

A couple of other points --

Is the MVVS a 10 pole motor?  If so, do you have the KR timer that is capable of dealing with a 10 pole motor?  If not, it will not have the overhead necessary to maintain RPM.

How long did the motor run?  When it shut off, did it shut off because the timer ran its programmed time, or because the ESC sensed that the batteries were run down?  In other words, did it give the warning motor blip, or did it shut off unexpectedly without the blip?
It may be that you were drawing MUCH more than 25 amps, if the run-time was not in the six minute range.  If the KR can't maintain the programmed RPM it shuts off.  If the ESC senses the batteries are getting low, IT shuts off.

[Jason Greer]

It's really nice to have one of these when experimenting with different propellers. You'll know right away if the power system combination will overtax any of the individual components that make up your power system.

https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=55323

[roy cherry]

hello every body the lines are 65 foot eye to the model is a saturn with a radial cowl and the cooling slot is six inches by two inches the motor is a mvvs sport 950  the flight i had one battery shut off comming out of the clover  the next trhee allowed a proper renical shut of but only barly the model is slxty ounces the speed controler hand hot not burning no eletrical smell  it seems i am losing some efficecy some where we are bit on our own here in the uk but keep the sugestion comming   als the speed controller ia a turnigy item   roy   

[Tim Wescott]

hello every body the lines are 65 foot eye to the model is a saturn with a radial cowl and the cooling slot is six inches by two inches the motor is a mvvs sport 950  the flight i had one battery shut off comming out of the clover  the next trhee allowed a proper renical shut of but only barly the model is slxty ounces the speed controler hand hot not burning no eletrical smell  it seems i am losing some efficecy some where we are bit on our own here in the uk but keep the sugestion comming   als the speed controller ia a turnigy item   roy   

Hey Roy -- I don't see a "Sport 950" mentioned on the MVVS web site, but I did find a "MVVS 8,0/950" -- is that the motor?

Just looking at the specifications for the motor, it looks like it should do well in that plane.  I've never seen nor even heard rumor of MVVS motors, so I can't comment on how well they live up to spec, however.  Ditto the ESC -- if it's really honestly a 40A ESC, it should be OK.

Does the motor turn freely?  If you've flown electric before you'll know what that means.  If not, then figure that if you give it a flip (like you're trying to hand-start a piston engine) it should make two or three revolutions before it stops.  Cogging (where it kind of goes "bump bump bump" when you turn it slowly by hand) is OK, but grinding or catching isn't.

Does the plane make any weird noises in flight?  Any screeching or whining or other noise that's distinctly louder than the usual electric airplane run?  There are some motor/ESC combinations that don't work out well, and since I'm kind of arrogant about high-dollar equipment I would expect that a Turnigy ESC would be more likely to have problems in that regard.

It would help if we knew whether you've flown brushless electric motors of any kind -- RC, FF or CL -- because a motor that's working right is a motor that's working right, whatever it happens to be pulling through the air.

That watt meter that Jason recommends is exactly the sort of instrument that you need to do the test that I recommend -- seeing how fast it goes and at what current on the ground, with and without a prop, should tell you a whole lot about the health of your overall system.

[Keith Renecle]

Hi Roy,
I see that you're having fun with the "electrickery"? You should e-mail Loren Nell about what you're doing with the 8,0/950 motor, as he's had  some experience in trying to get the rpm up to use with Igor's system. It can work but will use too much current on 5 cells, so you're pushing the wattage limit. The MVVS website says that this motor is a 3 - 4 cell motor and that sort of KV is typically used in stunt with 4 cells. The higher the KV rating, the lower the amount of turns on the windings, so by pushing up the voltage you need to lower the load. This lower pitch prop story is a personal choice thing, like "feeling" that it performs better. Now....."feeling" is a difficult thing to define, and the other factor is that for the same flying speed, a lower pitch prop will use more power than a higher one. Using fine pitch props on IC engines was also done to keep the engine in it's "happy" band with tuned pipes. Sure I do understand the "less windup in the wind" story, but with electric motors and governor systems, keeping the motor in its happy band is a completely different story.

Just by the way, did you try using the prop at 13" and at a lower rpm? The suggestion of getting yourself a wattmeter is also a good one if you want to play with motors and props. That will give you an instant reading of how much power you are using.

Someone asked about how many poles this motor has......it has 16, so it is a nice motor and gives a nice resolution with my timer system. It is certainly one of the best quality motors around.

Keith R

[roy cherry]

hi keith loren e mailed me and i sent him the deatails just now it seems to me that i am pusing the limits with the set up    so iwas fishing around to see if any else had tried to do what i was trying to get the model it was on flies like a tiger 60 with a runaway on a 12 6 at 5 50 secs a lap the 12.4 cut down apc was very good at 5.2 secs a lap but every thing got hot i think i need a higher kv motor and sutible speed controler  but wich one higer kv motors are they up to 5 s 2700 bats i cant find any thing i have to go to my local dealer who has the ear of mr hacker to see if the can recomend any thing i will pursue this in the coming months as for me this sort of set up is what i want it suits my delicate style  we have lost the weather here in the uk now front afrter front is breaking in from the atlantic so himelf only knows when i can get out now  cheers for now roy

[Keith Renecle]

Hi Roy,
I have just sent Loren the details on a more suitable Cobra 3520/12 motor with a Kv of 820. That should be a good motor to try for the finer pitch props on 5-cells. It can handle 1040 watts on 5 cells and that Kv should give you enough revs. It is a similar weight to the MVVS 8,0 series and costs about half the price. I was a bit dubious because they are made by the same Chinese company that makes Pulso motors and I had some bad experience with them. Then I received some good info from the RC groups forum on the extra quality required by the Cobra guys, so they look like a good deal. There are plenty of Cobra motors being used now for stunt in the USA with very good results.

Try to get an APC 13 x 4.5 F2B pusher prop to play with and leave it full length to start with, then chop it down as you go until it is good for your "delicate" style! 

Keith R