21
votes
Why do most drones have upward facing motors?
One practical advantage is increased ground clearance, reducing the likelihood of a prop strike on landing or take-off.
Aerodynamically, a pusher1 design can be less efficient because the propeller ...
- 6,056
20
votes
Why are larger propellers generally more efficient than smaller ones?
Thrust is proportional to the change in momentum of the air passing through the prop - i.e. how much the prop speeds it up.
The power required to do this is proportional to the kinetic energy of the ...
- 7,428
17
votes
Why do most drones have upward facing motors?
Expanding on @Kralc's answer:
Here's a study (unfortunately behind a paywall) that I'm going to copy key parts of below:
The hexacopter was mounted on a load cell test stand, and data were collected ...
- 752
17
votes
Accepted
How does a quadcopter yaw?
Any vehicle yaws (i.e. turns) by having a net torque applied. What's interesting about a quadcopter is not just how it yaws, but how it yaws and doesn't roll, pitch, or climb at the same time.
To ...
- 1,892
17
votes
Why are larger propellers generally more efficient than smaller ones?
An explanation for why this is can be found in this Aviation.SE answer: Why aren't large, low-speed propellers widely used?, which I'll paraphrase here.
The thrust a propeller generates is a function ...
- 6,018
13
votes
Accepted
How does one hold the motor bell still when tightening prop nuts?
You know those rubber wristbands that are given out at lots of events?
You can wrap one of those around the motor bell to get better purchase on it, and then torque down the prop nut.
There are also ...
- 4,422
12
votes
How does a quadcopter yaw?
The yaw effect created by the same effect that would cause a helicopter to spin if it didn't have a tail rotor.
On a multirotor, half the propellers spin clockwise (CW) and half counter-clockwise (...
- 6,056
12
votes
Accepted
Why do drone propellers have blades with thin chords?
Overview
The most efficient propeller is single bladed, has infinitely narrow chord, has infinitely thin airfoil, has an infinitely long blade, spins infinitely slowly, and requires infinite torque. ...
- 1,892
11
votes
Accepted
Do propellers layered on top of each other have twice the thrust of one propeller?
At least at the small/model scale, the answer is no. There is significant efficiency loss due to the stacked propellers not receiving the same clean air as they would if they were horizontally ...
- 6,018
10
votes
Accepted
How do laterally folding propellers affect multirotor flight?
In theory, you can't accelerate and decelerate the props as quickly. If the motor accelerates, the props lower angular velocity keeps it from accelerating too quickly. Same for deceleration: if the ...
- 577
8
votes
How do laterally folding propellers affect multirotor flight?
Surprisingly, that flexible coupling is actually a good thing. If you look at helicopters, this is called a lead-lag hinge, and it allows the propeller to match flight loads when flying around. What ...
- 1,892
7
votes
Accepted
How to measure the pitch of a propeller?
Theoretically the pitch of a prop is supposed to be the distance it would move in a full rotation (in an ideal world).
As most modern props vary pitch along their length, a single number is almost ...
- 468
7
votes
Accepted
Do I need CW or CCW props for my plane?
The decision between CW (clockwise) and CCW (counterclockwise) propellers has to do with the direction your motor/engine will spin, not really in regard to where you're putting the engine on the plane....
- 6,018
6
votes
Accepted
Does the sharpness of a propeller blade affect efficiency?
Rounded leading edges are better for subsonic aerofoils.
Props and wings have to work at a range of angles of attack. The airflow has to split to pass either side of the aerofoil, and a rounded ...
- 7,428
6
votes
Why are larger propellers generally more efficient than smaller ones?
Comment number 7 at this link is an excellent source (and fairly trustworthy as it was written by Joshua Bardwell).
The main reason specified for the efficiency is that for a given amount of thrust, ...
- 4,422
6
votes
Do propellers layered on top of each other have twice the thrust of one propeller?
TLDR: The thrust would not double. You can get close but it won't be easy.
There are a lot of factors affecting this but in my experience the distance between props dominates.
I once built a push-...
- 161
6
votes
Accepted
How to keep my prop from flying off my motor?
It looks like you are missing a piece of the prop adapter.
There should be three pieces, the nut, the central shaft with a thread for the nut on one end and a taper on the other, and a collar that ...
- 7,428
6
votes
Accepted
How do I attach a propeller to this motor?
You use one of the provided rubber rings to attach the propeller to the motor. The 2 protruding screws with their heads are the anchor points for the rubber before it is wrapped over the prop to the ...
- 106
6
votes
Accepted
Help with finding a motor to rotate the plane of a propeller
I think what you are looking for is a servo. At least, that's what it's called in the hobby, officially it's a servomotor. Each unit consists of a motor, gears, a sensor to measure the position of the ...
- 7,428
5
votes
Accepted
What propellers should I get for my drone?
The first step to getting the right propellers is to figure out what size propellers will fit your drone. What you can do is measure the distance from the center of the motor to the closest thing (...
- 5,792
5
votes
How does one hold the motor bell still when tightening prop nuts?
You don't need to hold it with a tool, it's enough to pinch it with your fingers. Using a tool to hold it increases the risk of damaging the threads if you are not careful.
But I can understand if ...
- 2,664
5
votes
How does one hold the motor bell still when tightening prop nuts?
There are commercially-available tools that are designed to grab around the bell using a rubber band, like this one:
However I felt that it's a fair bit too expensive for what it is.
So I made my ...
- 2,997
5
votes
Why do drone propellers have blades with thin chords?
As is explained briefly here on Aviation.SE and here on Physics.SE, the differences in chord length (and other properties of the propellers like diameter and pitch) are mostly derived from the fact ...
- 6,018
5
votes
Accepted
Do flexible propellers affect multirotor efficiency?
It's really a challenging question to answer because flexible and stiff propellers both have their advantages and disadvantages in terms of efficiency.
Flexible propellers are typically lighter ...
- 1,226
5
votes
How can I increase the lifting power?
Faster motors will definitely give you more thrust. However the relationship isn't linear but increases with the square of the speed. So doubling the kV will give you 4 times the power, and going from ...
- 7,428
5
votes
Accepted
Influence of propeller blade shape and tip shape on its behaviour?
The main thing the designers are trying to achieve is reducing tip losses by making the chord of the tip of the prop small relative to the rest of the blade. Tip losses are due to air moving around ...
- 7,428
4
votes
Accepted
How does a propeller with more blades create more "grip"
Aside from fancy material science which can result in propellers that interact with air more cleanly and is highly proprietary, the primary way a propeller could gain more "grip" on the air is by ...
- 6,018
4
votes
What factors affect the noise level of propellers?
Since only you can be the judge of what you feel is too loud, and noise level from a drone is the result of many parts working together, this is a tough question to answer and I'm not sure you will ...
- 1,226
4
votes
How to decide drone motors?
This is an age old problem, there is no solution, only methodology.
First, your budget is a HUGE constraint. To build a drivetrain, without years of experience, is very difficult, I doubt you will ...
- 1,068
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