HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Apr 25, 2012, 11:42 PM
Registered User
Joined Apr 2012
8 Posts
Help!
I NEED MORE SPEED!!! need some help!!!!

hey i have an electrifly cosmic wind. i am running a rimfire .10 (35-30-1250) with a silver series 35a esc. it hits about 85mph with a 8x8 prop. i am trying to hit 100mph. any ideas for an outrunner motor with a higher kv that will give me that extra 15mph or any other ideas to get that speed
cjmartinez103 is offline Find More Posts by cjmartinez103
Reply With Quote
Sign up now
to remove ads between posts
Old Apr 26, 2012, 12:39 AM
characters welcome!
Mark Wood's Avatar
United States, CA, Bear Valley Springs
Joined Feb 2000
25,931 Posts
Easy. Use an 8x10 prop. Just make sure that the amp draw doesn't exceed your ESC rating.

Got whattmeter?

mw
Mark Wood is offline Find More Posts by Mark Wood
Reply With Quote
Old Apr 26, 2012, 07:44 AM
Registered User
United States, OH, Youngstown
Joined Nov 2004
593 Posts
http://www.rcgroups.com/forums/showp...&postcount=171

http://www.rcgroups.com/forums/showp...&postcount=160
RedLine19k is offline Find More Posts by RedLine19k
Reply With Quote
Old Apr 26, 2012, 10:11 AM
Registered User
Joined Apr 2012
7 Posts
Towerpro 10x5E propeller
ecshop360.com is offline Find More Posts by ecshop360.com
Reply With Quote
Old Apr 26, 2012, 10:47 AM
Suspended Account
Joined Apr 2012
18 Posts
This will get you there but you will need a 60 Amp ESC and about 2100 3S 30C or better. This motor will take up to a 12x8 prop so you could run a 10X10. Also, it is heavier than the Rimfire so you may have to adjust for balance.

https://www.leaderhobby.com/product....=9394001220783


One thing about the Rimfire motors is the they are over rated. I have a couple of the .10 size and they claim 330 watts but I can only get about 250 to 275 watts out of them. These little EMP motor are very high quality, I have been using them for some time now and I really like them.

Now go fast..
SlickT is offline Find More Posts by SlickT
Reply With Quote  (Disabled)
Old Apr 26, 2012, 02:34 PM
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia / UK visits
Joined Jan 2010
7,356 Posts
Quote:
Originally Posted by cjmartinez103 View Post
hey i have an electrifly cosmic wind. i am running a rimfire .10 (35-30-1250) with a silver series 35a esc. it hits about 85mph with a 8x8 prop. i am trying to hit 100mph. any ideas for an outrunner motor with a higher kv that will give me that extra 15mph or any other ideas to get that speed
Remember these immortal words :

KV + LiPo S = rpm

Prop Diameter = Thrust

Prop Pitch = Speed

So taking the three - you have to balance all three to get maximum effect - in your case you want speed. So you have to UP the pitch and get the RPM sufficient to realise the speed potential. But Diameter is important in two ways ... a) you need size of prop disc to get sufficient thrust to back-up the pitch, but b) you need to be careful not to increase diameter such that you increase torque effects making model difficult to handle. You also have to make sure the LiPo can handle the demand .......... and in this I have to comment that no speed freak that I converse with uses Nanotech's ... we all use conventional C rated Lipo's ... Why ? Too many examples seen of Nano's after a few flights failing to deliver high amps ...

I have a small excel spreadsheet that takes KV ... LiPo S .... prop pitch and calculates the theoretical distance the prop will travel in 1 hour. So far my actual speed results measured by Eagle Tree Speed Sensor show that theoretical calculation is overstated as expected. The actual usually works out to be about 60-65% of theoretical. (Based on using a suitable diameter prop).

One of the biggest problems with getting the extra speed is not sorting the gear to do it - but achieving it without excessive AMPS demand ... blowing ESC's, puffing LiPo's, overheating motors etc.

To achieve 222kph (138mph) on my Parkjet was a real fight to keep LiPo / ESC from burning out. With re-assemble of Parkjet after various mishaps ... the 3700KV "450 Heli" motor (74gr) .. 3S 25C LiPo ... 50A ESC .... I hit 206kph (128mph).
Next .... when I put a 4S in to beat my own record ......... the motor shot it's magnets, 50A ESC went up in smoke, LiPo was HOT !

Power level on the 3S was already 550W ..... so imagine what the 4S was producing !! The Parkjet with 4S of the bungee launcher recorded a speed of 113kph in just the few metres before she cartwheeled in ! Who knows what she would have hit if she'd survived the launch !!
solentlife is online now Find More Posts by solentlife
Reply With Quote
Old Apr 26, 2012, 02:45 PM
Registered User
peterangus's Avatar
Blackpool, Great Britain (UK)
Joined Dec 2003
1,342 Posts
Scale speed for your model is 29mph.
peterangus is offline Find More Posts by peterangus
RCG Plus Member
Latest blog entry: Scaling Laws
Reply With Quote
Old Apr 26, 2012, 04:09 PM
Registered User
yomgui's Avatar
France, RA, Cormaranche-en-Bugey
Joined Feb 2011
515 Posts
Hi !

what a small motor for a 16.4 dmē aircraft reaching 85 mph ! must be hot...

obviously, more speed will come with more weight,
4S 1400Kv and 120g+ motor spinning a 7x7 ??
3S 1900Kv 130g motor with the 7x7 ??

what's the original setup ? 3S ?
yomgui is online now Find More Posts by yomgui
Reply With Quote
Old Apr 26, 2012, 08:24 PM
Registered User
Joined Apr 2012
8 Posts
Solentlife....
so what do you think would be a good combo to get the most out of what I have if I am trying to stay with the motor and 3s batteries. What size prop should I use
And what would be a good start to achieve more speed if I changes all aspects such as a motor, esc, prop, and used 4s batteries.

Yomgui...
the original setup is as I stated before. This is what the manual reccomends. The rimfire. 10 1250kv motor (35mm by 30mm)with the silverseries 25a esc. (I used a 35a esc instead)
cjmartinez103 is offline Find More Posts by cjmartinez103
Reply With Quote
Old Apr 26, 2012, 11:20 PM
characters welcome!
Mark Wood's Avatar
United States, CA, Bear Valley Springs
Joined Feb 2000
25,931 Posts
Did you not read my answer in post #2?

mw
Mark Wood is offline Find More Posts by Mark Wood
Reply With Quote
Old Apr 27, 2012, 12:09 AM
hul
Registered User
hul's Avatar
Switzerland
Joined Mar 2003
2,094 Posts
100mph takes almost twice the power than 80mph (1.95 times exactly). You need to make sure your drivetrain (motor, ESC and pack) can handle that. Then you need enough pitch speed, 8x10 may give you that, else reduce diameter and keep pitch. But you need power to go fast.

Hans
hul is offline Find More Posts by hul
Reply With Quote
Old Apr 27, 2012, 07:19 AM
Registered User
Dr Kiwi's Avatar
Chattanooga, Tennessee, United States
Joined May 2003
27,195 Posts
Mark, Hans and SlickT have all made good points... for speed you need LOTS of power... you might need well over 600W into a 9x9 or 10x10 (and on 3s that would be >55A).....the motor SlickT linked to might get you there if you thrash it.

peterangus's point might be the most telling!
Dr Kiwi is offline Find More Posts by Dr Kiwi
Reply With Quote
Old Apr 27, 2012, 10:11 AM
222 km/hr Parkjet flyer
solentlife's Avatar
Latvia / UK visits
Joined Jan 2010
7,356 Posts
Quote:
Originally Posted by cjmartinez103 View Post
Solentlife....
so what do you think would be a good combo to get the most out of what I have if I am trying to stay with the motor and 3s batteries. What size prop should I use
And what would be a good start to achieve more speed if I changes all aspects such as a motor, esc, prop, and used 4s batteries......
You need a far stronger bigger motor that can provide the probable power levels of well above 700W ..... but watts are not the answer as they can be absorbed into slow speed as well as fast. So we need a big powerful motor that can swing your prop or higher pitch at a much faster rpm. That will also mean a serious level ESC and a high C rated LiPo .......

You will trade 2 things for speed :

1. Duration of flight will be markedly reduced as you compromise on higher cell count and higher C rating but keeping weight down.
2. Torque effects will be much greater and you'll find that launching / speeding up will have some strange effects until model is flying fast enough to stabilise via it's wing .....
I would suggest looking in the EDF motor ranges - but make sure that the shaft is locked BOTH sides of brushless can. Many EDF motors do not have a circlip as they are designed for one way mounting only unlike ordinary motors.

To give an example of the extreme power levels we go to for speed :

My Parkjet designed for about 2400kv, 2S - 3S lipo, 10A ESC and up to 5x5 prop .... is running a 3700kv 450 Heli motor with 50A ESC, 3S - 4S Lipo and 5x5 prop. That is producing over 550W ..... against the stock set-up of about 150W. I should actually runa higher rated ESC - but I'm running out of space to fit !

My replacement Parkjet ordered will have a 4400kv Heli Motor, 4S, 50A ESC, 5x5 or 5 x 6 prop. The intention to approach 300kph.
solentlife is online now Find More Posts by solentlife
Reply With Quote
Old Apr 28, 2012, 02:17 AM
Registered User
GryphonRCU's Avatar
United States, CA, SF
Joined Mar 2008
3,733 Posts
cjmartinez103,

Hans is correct about how much more power you need.
Here is how to do a bit of your own calculation in future:

Relationship between how much power you need to gain speed is pretty much a cubic rule.

100 MPH / 80 MPH = 1.25 times the speed is desired

1.25 X 1.25 X 1.25 = 1.95

Your desired(new) speed will need 1.95 times the power (95% more than before) while at max speed compared to your old power level at its max speed.
Static Wattmeter readings will help you a bit, but data loggers and ICE ESCs will help more.
Prop diameter to pitch ratios and also drag all play a role.

***The 1.95 times power level only applies if your new prop is not too small for your application at the new desired speed.....and the motor runs efficient enough!!!

________________________

Working that calculation backwards:

If you have 4 times the power level, what is the best you can hope for speed wise?
Cubic root of 4 = 1.587

best you can get is 58.7% more speed compared to before.

_____________

What about if you have just half the power?

Cubic root of 0.5 = 0.794

If your power level becomes half, you can still retain 79% of original speed.



Have fun,

Gryphon
GryphonRCU is offline Find More Posts by GryphonRCU
Reply With Quote
Old Apr 28, 2012, 10:39 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
near Nijmegen, Netherlands
Joined Feb 2001
10,162 Posts
Off_topic
Dr Kiwi, the other (not so good) doctor, Allan Levi, is trying to abuse your account/reputation through sock account drkiwi, see
http://www.rcgroups.com/forums/showt...0#post21459796

Ditto for user cryhavoc38, also abused by Allan Levi through sock account cryhavoc37.

About Allan Levi and his current spate of sock accounts
http://www.rcgroups.com/forums/showthread.php?t=1634901

Vriendelijke groeten Ron
diy motor tipsDrive Calculator
diy motor groupCumulus MFC
• Get a life ... get a Watt-meter!!! •
Ron van Sommeren is offline Find More Posts by Ron van Sommeren
Last edited by Ron van Sommeren; Apr 29, 2012 at 07:52 AM. Reason: + off_topic
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion need some speed please? mc clain 48inch rcta15 Flying Wings 2 Oct 17, 2011 06:56 AM
Discussion Need more speed um p51 bdboy007 Scratchbuilt Indoor and Micro Models 3 Oct 09, 2011 06:27 PM
Need some help identifing retracts and more Shroomer Fuel Plane Talk 12 Nov 26, 2004 10:58 PM
OK, Need some more help setting up a Network! mrebman Life, The Universe, and Politics 19 Mar 31, 2002 02:36 PM