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View Full Version : Brushless Motor "THRUST" HELP!!!


Marty7
12-16-2007, 06:02 PM
I am sooo confused, I have a RTF 330l Extra which came with a B2025. KV5400 in-runner brushless motor, gear ratio 8:1, this is run by 3Lipos 11.1v and has a 13X6.5 prop. The model wieght is 630g.

The plane just about prop hangs which suggests it's max thrust is around 650g with a 5400KV motor therefore my question is this:

If this set up produces 650g of thrust then how can this one below with only a 1135kv rating produc 1.2kg!!?

http://cgi.ebay.co.uk/3714-RC-F3A-3D-plane-Brushless-motor-max-thrust-2-25kg_W0QQitemZ370004089899QQihZ024QQcategoryZ34055 QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
<TABLE style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; BACKGROUND: #ccffcc; BORDER-LEFT: medium none; WIDTH: 738px; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; HEIGHT: 160px" cellSpacing=0 cellPadding=0 bgColor=#ffff99 border=1><TBODY><TR><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: windowtext; WIDTH: 214px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>KV ( RPM)</TD><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: #d4d0c8; WIDTH: 422px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>1135</TD></TR><TR><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: windowtext; WIDTH: 214px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>Type</TD><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: #d4d0c8; WIDTH: 422px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>Outrunner</TD></TR><TR><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: windowtext; WIDTH: 214px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>Recommended ESC</TD><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: #d4d0c8; WIDTH: 422px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>Emax 40A , Emax 60A</TD></TR><TR><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: windowtext; WIDTH: 214px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>Recommended propeller</TD><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: #d4d0c8; WIDTH: 422px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>9*4.5 / 10*5 / 12*6</TD></TR><TR><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: windowtext; WIDTH: 214px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>Max. Thrust</TD><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: #d4d0c8; WIDTH: 422px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>1.35kg / 48oz (10*5 props @ 11.1v, 33A max drain)</TD></TR><TR><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: windowtext; WIDTH: 214px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>Typical thrust</TD><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: #d4d0c8; WIDTH: 422px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>0.7kg / 24.7oz (10*5 props @ 7.4v / 17A)</TD></TR><TR><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: windowtext; WIDTH: 214px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=1> </TD><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: #d4d0c8; WIDTH: 422px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=1>1.2kg / 42.3oz (9*4.5 props @ 11.1v / 25.5A)</TD></TR><TR><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: windowtext; WIDTH: 214px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6> </TD><TD style="BORDER-RIGHT: windowtext; PADDING-RIGHT: 5.4pt; BORDER-TOP: #d4d0c8; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0in; BORDER-LEFT: #d4d0c8; WIDTH: 422px; PADDING-TOP: 0in; BORDER-BOTTOM: windowtext" vAlign=top height=6>0.9kg / 31.7oz (12*6 props @ 7.4v / 26A)</TD></TR></TBODY></TABLE>


Could someone help and suggest a more pwerful setup for my plane which can enable better 3D?

Thank you very much :red:

Larry3215
12-17-2007, 05:47 AM
There are exactly 2 things which effect thrust.

1)prop diameter is by far the most important. Thrust varies as the 4th power of the diameter. If you double the diameter of the prop (and the rpm stays the same) you will have 16 times the thrust.

2)RPM. Thrust varies as the 3rd power of RPM. If you double the RPM (and the diameter stays the same) you will have 8 times the thrust.

So diameter is far more important.

You can increase the thrust by increasing the diameter even if the rpm goes down some.

Here are some on-line calculators

http://www.lcrcc.net/thrust_calc.htm

http://members.jcom.home.ne.jp/4223215501/staticthrust.htm

There are others.

Also, you have to keep in mind that most all the specs published for the cheep chinese motors are just guesses or are completely made up. They usually have nothing to do with reality.

Larry

CHELLIE
12-17-2007, 06:05 AM
Clean up :)



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Marty7
12-17-2007, 08:47 AM
Ok, that has really helped. Thank you both. I didn't realise there was so much effect on thrust by the diameter and RPM of a prop - although it now makes complete sense.

The direct drive motor looks great - I think I will go for that one.
I have 3 packs of 3cells lipo which is a pain, but they are all about the same age so I should be able to balance them and repack - would that be ok? Also my ESC is just the one packaged in the RTF and rated at 25 amps with no other writing on it - will that handle 4 cells?

Someone also posted this link which is handy:

http://www.commonsenserc.com/page.php?page=motor-wizard.php (http://www.commonsenserc.com/page.php?page=motor-wizard.php)

:ws:

ron_van_sommeren
12-17-2007, 03:59 PM
Helmut Schenk's calculator (in English & German)
www.drivecalc.de (http://www.drivecalc.de/PropCalc/)
-> Propeller Calculator

Rod Badcock's calculators:
www.badcock.net (http://www.badcock.net)

Vriendelijke groeten ;) Ron van Sommeren
brushless motor building tips & tricks (http://www.rcgroups.com/forums/showthread.php?t=240993)
diy brushless motor (http://www.yahoogroups.com/group/lrk-torquemax) discussion group
Drive Calculator (http://www.yahoogroups.com/group/D-calc/) download & discussion group

CHELLIE
12-18-2007, 03:22 AM
clean up :)

Marty7
12-18-2007, 02:48 PM
Great stuff, I am getting a good picture of how to put together a good system! My plane (see attached) has seen better days and could do with updating as well I think but I shall wait until I write it off! LOL

I added bigger ailerons and seperate servos via a Y lead which helps loads for 3D.


:ws:

ron_van_sommeren
12-19-2007, 11:40 AM
And by the way, motors do not produce thrust, propellors produce thrust :D

Marty7
06-01-2008, 10:42 AM
Hi,

I brought a motor which is now producing 1.6kg of thrust with a 10X5 APC prop running on 3 lipos.

My question is when I run the motor on the bench I get a surge of power creating 2.0kg of thrust and then after 5 seconds the motors reduces thrust to 1.6kg. If I then throttle down and throttle up again I again get 2.0kg of thrust for 5 seconds until dipping to 1.6kg. The battery is still fully charged.

Is this a normal characteristic of Motors/Lipos/ESC?

Many thanks ????

Murocflyer
06-01-2008, 12:14 PM
What motor, LiPo, and ESC do you have? I haven't seen that much of a drop when I have tested my setups. Anyone else?

Frank

Marty7
06-01-2008, 11:14 PM
Scorpion 3014-16 (10x5 APC prop)
http://www.micronradiocontrol.co.uk/scorpion_data/3014-16.html

Lipo (3 cell 2200mah)
http://www.heliguy.com/Extras/LiPo-Batteries/Lipo-battery-2200mah-20c-11.1v/

ESC (Cheap but appears to work OK)
http://cgi.ebay.co.uk/100A-Brushless-Motor-Speed-Controller-RC-ESC-Parts-T_W0QQitemZ270241213115QQihZ017QQcategoryZ123849QQ ssPageNameZWDVWQQrdZ1QQcmdZViewItem

Thanks for looking at this :)

Larry3215
06-02-2008, 01:30 AM
Most likely what you're seeing is the initial voltage drop as the lipo settles down to its under load voltage.

The resting voltage of the pack is typically a good bit more than its voltage under load. The higher the load is the greater the difference is.

When you first start up the motor, it will try to spin based on that higher initial voltage. It will therefore spin at a higher rpm. That higher rpm generates more thrust and draws more power.

The lipo voltage drops down pretty quickly to its normal operating voltage.

I dont think its anything to worry about as long as the amps your drawing - after things settle down - are within the range of what the pack, ESC and motor can handle.

Marty7
06-02-2008, 10:02 AM
Ok thanks. That makes sense actually.

You look like you know your Planes - What plane would you recommend for 3D and prop hanging using my engine and batteries (or would I need more voltage?)

Larry3215
06-02-2008, 05:44 PM
If your getting 1.6kg of thrust then Id say any plane that weighs less than 1kg - with your power system installed - would work fine. Something in the 500-800 gram range would be even better.

For good 3D lighter is always better :)

Larry