Tags:
1. Feb 9, 2016

### harmyder

While watching lecture at Coursera, i tumbled over this fourmula

Moment
$$\mathbf{M}=\sum_{i=1}^{4}(\mathbf{F}_i\times \mathbf{r}_i+\mathbf{M}_i)$$
where F is uplift force from a propeller, and M is drag moment for a propeller.

But why they add drag moment(torque) like that? Maybe it will differ for central point.

2. Feb 9, 2016

### A.T.

Try it out by computing the moments of the blade drag forces around different reference points.

3. Feb 9, 2016

### harmyder

Thanks, it is true for two points on the picture, but can you name the rule? I want to read it whole to understand it better. Thank you.

4. Feb 21, 2016

### harmyder

Could somebody write what are these $M_i$? Because i still don't understand how it works, i think every moment must be calculated about some point.

I have found this formula
$$\dot{\mathbf{H}}_O = \sum(\mathbf{r}_i \times m_i\dot{\mathbf{v}}_i) = \sum(\mathbf{r}_i \times \mathbf{F}_i + \mathbf{M}_i)$$
but i don't understand from where $\mathbf{M}_i$ came, because i think that $m_i\dot{\mathbf{v}}_i = \mathbf{F}_i$

Last edited: Feb 21, 2016
5. Feb 21, 2016

### A.T.

Didn't you explain it yourself:
It's the total moment of all aerodynamic forces on the blades, which are in the plane of the propeller disc.

6. Feb 21, 2016

### harmyder

Well, yes, but here i want to know from where $M$ came in this general formula $(1).$ It is unrelated for quadrotor, just to understand underlying theory.

Last edited: Feb 21, 2016
7. Feb 21, 2016

### A.T.

In general it's just some external moment.