Stability and Drift of Quadcopter VS Co-axial copters - RC Groups
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May 03, 2010, 09:54 AM
Registered User

Stability and Drift of Quadcopter VS Co-axial copters

Hey guys,

I was just wondering afew things.

1) Which would be more capable of maintaining a static hover with the least intervention from the pilot, a quadcopter or a co-axial copter?

2) In relation to question 1, which has more drift effect? Or rather, which is more susceptible to it?

Would the answers still be the same if i say that each heli needs to carry a payload of 1kg(excluding its own weight)?

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May 03, 2010, 11:05 AM
Cranky old fart
Balr14's Avatar
The determining factor are cost and the environment you are operating in, especially when you add a 1kg weight. Both coax and quad are poor choices, unless you intend on spending upwards of $10k. A conventional single rotor CP heli with a proper electronic stabilization system would be a much better choice.
May 03, 2010, 11:18 AM
Registered User
Ill be flying indoors with very minimal external wind. I understand that totally removing drift is rather impossible, just looking for one which is the most "stable".

On a related note, how is a single rotor+ tail rotor heli more stable their either of the 2?
May 03, 2010, 11:35 AM
Cranky old fart
Balr14's Avatar
A fixed pitch coax or quad creates lots of it's own air currents, especially indoors. One capable of carrying 1kg is going to be very large and move a lot of air. It will be floating and drifting all over the place and have very poor response. A good portion of your control is constant throttle adjustments, which means changes to air current, which requires constant throttle adjustments. A conventional CP heli with stabilizing system is much more responsive, is less susceptible to air currents and pitch changes hold position better than throttle changes. It would also be a lot cheaper.

Again, if you are talking about $10k+ systems, there are some triples and quads that are hard to beat. Since you haven't specificed a price range, I'm guessing this is an under $500 wild idea. Anyway, to answer you original question, the quad wins by default. There's only one coax currently available that would handle a 1kg weight (HeliBaby) and it is neither stable or reliable.
Last edited by Balr14; May 03, 2010 at 11:51 AM.
May 03, 2010, 04:20 PM
Registered User
ah yes, the goal here is to be as cheap as possible. Im planning to adopt 1 of the multiple rotor setups(CP/FP single rotor+tail, co-ax, quad) and incorporate them into my own device. Which means im making my own "heli".

The only maneuver the "heli" needs to do it fly up 20 to 30cm, fly forward 10cm and land. The idea is to carry a payload and fly over a coke can.

Ive been speaking to some people in the hobby shop and although they have not seen a quad in action, they were saying that it would be really hard to balance all 4 rotors, the way each motor speed changes to maintain yaw/roll and pitch and how each of these changes will affect the lift and everything else hence making the entire thing very unstable unless some superb mixing is being done.

I dont plan to get any of the specialised boards or use the open source thats available.
May 04, 2010, 06:20 PM
Cranky old fart
Balr14's Avatar
Here you go! Only about $2000 - $2500, too!

HexaKopter - MikroKopter (9 min 57 sec)
May 07, 2010, 06:32 PM
Flight Instructor

Fly a tricopter!

Here's some food for thought... I have a tricopter which carries a 1.5 pound payload for 5 minutes. How much did it cost to make? $50 for the frame, $56 for the 4 gyros, $30 for the 3 speed controls, $27 for the 3 motors, $5 BEC, $10 for the props (including extras), $50 for a 3000 mah 3s battery. Add your own radio system and your ready to go. Total price? $228 dollars. Don't get me wrong because I do fly a t-rex 450 and 600 but when you crash it costs many times more money compared to crashing a tri or a quadcopter. If you protect all the electronics onboard (and don't ask me how I know this) you can drop a quad or a tri from a 100 feet and all you'll be replacing is the props, maybe an arm or two, and maybe a motor if it crashed upside down. Total repair cost? $50 dollars for my worst crash. Crash a heli....replace the main blades, the tailboom, main shaft, flybar a this is being conservative. Minimum cost of a 450 size heli crash? $60. And this is the minimum cost! Main blades are not cheap for a heli in comparison to a tri or a quad and it's definitely something you break in 90% of crashes. In order to make a heli stable it would take the same electronics that it takes to make a tri or quad stable. Go with a tricopter! Screw the Heli!
Last edited by mspencer; May 07, 2010 at 06:37 PM.

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