1. Feb 19, 2014

### Monsterboy

Hi ,

I am building a Quadcopter ,i am not sure how to decide(or calculate) the length of the 4 arms .I know that it depends on the propeller size ,i am not sure if any other parameters are involved ,is there any formula to find the length using the parameter(s)?

2. Feb 19, 2014

### Baluncore

There is no magic formula.
Longer arms will be heavier, but they do make it easier for a human to control the tilt.

3. Feb 19, 2014

### Staff: Mentor

I don't know much about quadcopters, but I would think they would need on-board stability control, in addition to the outside human input. Some sort of gyro-to-motor feedback stabilization...

4. Feb 19, 2014

### Baluncore

5. Feb 20, 2014

### Monsterboy

Is there any way to calculate the maximum speed of a Quadcopter theoretically? I know i can get the speed using the GPS system but is it possible to calculate it? can i get any links to some papers or something?

6. Feb 27, 2014

### noagname

7. Feb 27, 2014

### Staff: Mentor

How big of a copter are we talking?

Ya know, aerospace engineering really is rocket science; it really is that hard!

8. Mar 2, 2014

### Monsterboy

Yea i bought a kit and built one but now i want build one on my own ,i trying to get a bit less of a hobbyist and a bit more technical(upto my capacity)

Multicopters are not really as aerodynamic as other UAVs ,i don't know how measure the drag forces and stuff.
i am talking about a quadcopter that is 1.5 feet in motor to motor distance(along the diagonal).
Other than simpler mechanical design and cost savings are there any other advantages of quadcopters over other UAVs? i read that helicopters are more stable as they don't need electronic stabilization which is required by quadcopter.

Last edited: Mar 2, 2014
9. Mar 2, 2014

### rcgldr

MOdel helicopters can use a fly-bar to stabilize pitch and roll, but there's a transition to electronic stabilization via 3d gyros called "fly-barless".

10. Mar 20, 2014

### Monsterboy

http://brage.bibsys.no/xmlui/handle/11250/136686

I have doubt in the rotation matrices part ,i don't know much about.
I don't what they mean by 'overcoming gravity vector by rotating the orientation ,not in a physical way!!'can someone please explain?

11. Mar 21, 2014

### Baluncore

Think of the quadcopter as a disk that can rotate in the plane, about it's axis. That disk can also be tilted by varying the balance of power between opposing motors. The orientation of the disk is important because it decides which motor combination needs power adjustment to navigate in a particular geographical direction. The quadcopter does not have to physically rotate to fly off in a different direction, it only needs to multiply it's orientation by the needed heading direction to decide which motors to adjust in power.

Any tilt from the horizontal will require an increase in thrust to maintain the magnitude of the vertical component that counters gravity. That can be computed by rotation of the orientation vector without physical rotation of the quadcopter.

Last edited: Mar 21, 2014
12. Mar 21, 2014

### AlephZero

Judging from the abstract, I think they could explain it better in Norweedish than in Broken English. (I didn't read the full paper).

13. Mar 28, 2014

### satchurated

The only limit to the length of the arms is your money, nothing more...on youtube you can find multirotors carrying people, so...