Know How...

Jan 4th 2018

Know How... 363

MultiRotor 101 - Part 1

Sure you can BUY a quadcopter, but do you know how to design and build one? Can you fix your craft when it breaks? Can you upgrade it into the EXACT tool you need?
Although the show is no longer in production, you can enjoy episodes from the TWiT Archives.
Category: Help & How To
Fr. Robert and Jason Howell take you on a journey of Multi-rotor discovery with this first part in a series about the basics of building and flying these toys-become-tools!
How do Quadcopters work?
The Challenge of flying a Quad vs. plane or a helicopter is that it doesn't have those traditional lift and control surfaces.
** A plane has elevators, rudders, and ailerons
-- Those surfaces, combined with a propulsion unit (jet or prop) allow you to deflect enough air in the proper direction to get the desired motion.
-- A plan can also glide with the shape of its wing
** A helicopter has a single or dual large rotor and some sort of tail assembly to counter the torque
-- In a single-rotor helicopter, a tail rotor or thrust assembly counters the rotation of the rotor
-- Adjusting the power and pitch of the large rotor allows your to rise or fall, and move in all directions
-- Adjusting the power of the tail thrust assembly lets your control yaw
In a Quadcopter... there are no wings. No rail rotors, no variable pitch propellers.
** So how in the heck does it work?
The ONLY control we have over a Quad is in how we spin the motors and propellers
In a Quad, the motors that are diagonal from each other spin in the same direction.
-- The motors that are adjacent to each other, spin in opposite directions.
** This means that there can be a match in the amount of torque being generated by the rotors.
-- Increasing thrust on the remote increases Thrust on all motors... which means they're all developing the same amount of torque... which is getting cancelled out by the motors spinning in opposite directions... 
-- So the Quadcopter stays true -- we hover.
Moving directionally
-- When we want to move directionally (Forward, back, left, right) we can increase the thrust from the motors on the opposite side of the movement, and decrease thrust on the side that we want to move towards.
-- In other words, we dip the Quad in the direction we want to move. 
Rotation (Yaw)
-- When we want to rotate the Quad, we unbalance the torque being generated by the motors and props.
-- Let's say that the right-front and left rear motors are turning CCW
-- The left-front and right rear motors are turning CW
** If we increase the power going to RF&LR while decreasing power to LF&RR, then we've got more force going CCW... this makes the quad turn CW
** If we increase power going to LF&RR while decreasing power to RF&LR, then we've got more force going CW... this makes the quad turn CCW.
As a general rule, the faster that a motor spins, the more efficent it will be. However, the faster an electric motor turns, the less torque it generates.
* Inrunning motors turn VERY fast, and produce little torque. Instead, they go through a reduction gearbox that spins the prop at 1/x times as fast as the motor shaft
* This means you can choose from a variety of propellers by changing the gear ratio of the gearbox. (i.e. you can make the propeller spin at its most efficient speed while not changing the RPMs of the motor.
By the Numbers:
Kv = "Voltage Constant
-- This is the THEORETICAL number of times the motor turns for every volt it is supplied 
-- In reality, the number is slightly less because no motor is 100% efficient.
Turnigy 1704-1900Kv Outrunner
* When we give it 11.1 volts, it will turn 21,090 times per minute (1900 X 11.1)
Neewer A22112/13 KV1000 Brushless Motor
* When we give it 11.1 volts, it will turn 11,100 times per minute
Emax MT2213 935kv
* When we give it 11.1 volts, it will turn 10,378.5 times per minute
Choosing your Motors:
This is a problem --- because other than the Kv, motors from different manufacturers don't really report their specs in the same way:
** Some give you thrust (like the Emax with 850g of thrust)
** Others just give you the max power (like 1740, rated for 49 watts)
** Still others will give you NOTHING
-- OR --
Power Distribution:
Flight Controller:
Straight Pins $3
Connectors $3.0
Config 1 $236
Config 2 $214
Wire Cutters
Insulation Strippers
Soldering Iron + solder
Helping Hands
Screwdriver w/Phillips and Hex bits
Velcro Strapping
1. Decide which arms will be fore and aft, then mark your arms #1-4 (Clockwise from front left)
2. Mount motors on arms with 8mm M3-0.5 screws, lightly covered in Locktite Blue
3. Thread Motor leads to top deck of arms
4. Mark ESC motor leads - leaving room for Bullet Connectors
5. Cut/Tin motor leads and power leads on ESCs (unless pre-cut and tinned)
6. Solder Female 3.5mm bullet connectors to the ESC motor leads
7. Solder Male 3.5mm bullet connectors on the ESC power leads
8. Insulate ends with heat shrink
10.Connect bullet connectors of ESCs to motors
11. Zip Tie ESCs to arms
12. Cut/Strip/Tin 8 x 2" lengths of 14 AWG silicone wire (4 red, 4 black)
13. Cut/Strip/Tin 2 x 5" lengths of 14 AWG silicone wire (1 red, 1 black)
14. Solder a female 2mm bullet connector to the end of each 2" wire
15. Solder both 5" lengths of wire into a Male XT60 connector
16. Insulate ends with heat shrink
17. Solder the other ends of all wires into the Power Distribution Board
18. Using nylon spacers, mount the Power Distribution board, contact points upwards to the lower frame plate
19. Attach arms to the lower frame. 
20. Run power and control leads from ESCs to interior of craft
21. Connect ESC power leads to PDB power leads
22. Mount top frame plate on arms.
23. Connect ESC leads to Flight Controller
24. Connect Receiver leads to flight controller

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