Noob question - Quad cant handle a little extra weight

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deejayspinz
Posts: 23
Joined: Thu Feb 20, 2014 12:01 pm

Noob question - Quad cant handle a little extra weight

Post by deejayspinz »

I built my first quad and am learning the ins and outs, so be gentle :-) Ive got 1100kv motors, Qbrain 20A x 4 esc, 8 x45 rotors.. the quad flies fine with the 2200mah batt with a weight of 950 grams. The batt is 3s 11.1v. However, I have a 4400 2s 7.4v batt that weighs about 80 grams more and the quad does not get off the ground when I try to use it. It bounces. Is it because im using a heavier and lower voltage battery? Ive read elsewhere that maybe 10x45 rotors would help ? Or am I outvto lunch? Im using MWC 2.2.

scrat
Posts: 925
Joined: Mon Oct 15, 2012 9:47 am
Location: Slovenia

Re: Noob question - Quad cant handle a little extra weight

Post by scrat »

2s and 8x4.5 wont work. Try 10x4.5 maybe. I have 1000kv motor and have 10x4.5 props with 3S lipo. 4 motors and these props can lift 3200g. And quad with battery weigh 1260g.

deejayspinz
Posts: 23
Joined: Thu Feb 20, 2014 12:01 pm

Re: Noob question - Quad cant handle a little extra weight

Post by deejayspinz »

Will do thx. I have some 10x4.5 on order.

QuadBow
Posts: 532
Joined: Fri Jan 04, 2013 10:06 am

Re: Noob question - Quad cant handle a little extra weight

Post by QuadBow »

Try http://www.ecalc.ch/xcoptercalc.php?ecalc&lang=en in order to estimate the required accus and propellers.

waltr
Posts: 733
Joined: Wed Jan 22, 2014 3:21 pm
Location: Near Philadelphia, Pennsyvania, USA

Re: Noob question - Quad cant handle a little extra weight

Post by waltr »

Yes, the problem is the battery Voltage, the motors kV and the props.
Unloaded, the 1100kv motors on 3S will spin at about 1100kv * 11.1V = 12210rpm. However on 2S they spin at 1100kV * 7.4V = 8140rpm which does not generate enough thrust. Look up the thrust verse rpm charts for the props you are using to see why the 2s battery is not working.
Last edited by waltr on Mon Mar 03, 2014 5:51 pm, edited 1 time in total.

deejayspinz
Posts: 23
Joined: Thu Feb 20, 2014 12:01 pm

Re: Noob question - Quad cant handle a little extra weight

Post by deejayspinz »

@waltr - thx for the info. Never seen these sort of calcs before, but it puts it in perspective. I have some 10x45 props on order that I will test on the 2s battery. I also have some more 3s batteries on order, so I can decide where I want to land then. 2s @ 10x45 props or 3s 8x45 props.

NorcoT
Posts: 6
Joined: Wed Feb 19, 2014 9:37 am

Post by NorcoT »

To give you comparison I run 900kv motors with 3s battery and 10x4.5 props. I can get about 800g of thrust per motor, for my quad it can produce 3200g of thrust. Rule of thumb is that you want double the max thrust to weight ratio, so consequently my quad is designed to 1.6kg, this makes my quad hover at about 50% throttle on my transmitter which is perfect.

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