|Dec 17, 2012, 12:04 AM|
An Introduction to the Multicopter World
An Introduction to the Multicopter World
So you have aspirations to learn to fly multicopters? You say you canít decide whether to build or buy an ARF- RTF version. You say you have no previous experience with helicopters or multicopters but hey youíve been flying RC airplanes for many years, how hard can it be? Well my response to these questions would be how hard and how costly do you wish to make it?
Building and flying multicopters is very different from other types of construction and RC flying. This type of flying is very rewarding but without a little modest research, self-training, experimentation and an enthusiasm to learn it can be a very costly endeavor. I will strive to explain the process by introducing you into the world of multicopters with this article. I will attempt to illustrate certain options available to you and the rationalizing for each.
I Want It All
I realized after the number of threads I have browsed on RC Groups and other net groups that many of you come to this segment of the hobby for the photographic and FPV possibilities. You like what this platform has to offer but you have little or no flight experience in multicopters.
When it comes to photography many desire a large multicopter capable of carrying a Canon DSLR or similar camera and hovering hundreds of feet in the air shooting live video and stills. Some individuals wish to fly across the countryside shooting FPV video and conveying the best parts of flying free as a bird to others. Some hope to use the multicopter as a business tool, from real-estate to archeological expeditions or even delivering tacos. The sky is truly the limit with a multicopter right? Well yes and no. We do have guidelines we must follow to fly these fabulous machines which I will be discussing later in this article. For now letís start at the beginning.
Learning to fly
As I mentioned before multicopters are a breed of their own. They have both characteristics of airplanes and helicopters but do not function like either. This necessitates a learning curve to master multicopter flying. Multicopters have no wings to create or maintain lift; hence all lift exclusively rest on the number and size of your blades and the amount of motor thrusts (torque) you can achieve. Multicopters have no ailerons, elevators, rudders, collective or cyclic to change the flight attitude or altitude. So how do you control the multicopter?
Todayís multicopters are controlled by sophisticated Flight Control systems that wouldíve made the Apollo Moon Lander engineers green with envy. The Flight Control system is the heart of the multicopter. It identifies your Transmitter inputs and regulates the outputs to the motor/blade combinations permitting your copter to hover, pitch, roll and yaw on command. By using complex mathematical algorithms (firmware), feedback PID loops and sensors the FC knows not only exactly where it is located in 3 dimension spaces but its exact attitude. With additional sensor (fusion data) information it can navigate through 4 dimensional spaces just as any RC aircraft or helicopter can with extreme accuracy. This information also allows it to precisely hover over a designated location at a selected altitude, complete waypoint navigation or RTH and auto-landing.
With all the sophisticated complexity and refinement of todayís FC systems they are still dependent on the pilot for the appropriate data and inputs to ensure a successful flight. For this to occur you need to learn to crawl before you can walk, as the saying goes. This means you need to start with a copter that you can handle in tight quarters (indoors or outdoors), crash - pick up and fly again, and has a low cost vs. experience gained relationship.
Your first multicopter should be a copter such as the MQX. This copter comes either in ARF or RTF form. If you have a spare radio lying around such as a Spektrum DX6i for instance you can program the copter into your Transmitter memory in acro mode.
Why a MQX? The MQX has been around now for a few years and was the first quadcopter of this type with capability to be bound to a regular Transmitter such as the Spektrum. MQX also has a large following and parts support. If you were able to break this copter (not impossible I know) then even the FC board can be bought off eBay for $15 or so and takes 5 minutes to replace. (Donít ask) MQX also has a RC Group thread devoted to the pilots of this quadcopter.
I highly recommend the copter for simplicity, precise flying capability indoor and outdoor up to 7mph winds, and for orientation/hover practice. I personally use this copter each day that I go flying to warm up and practice before flying the big quads and Hexacopters. I especially use it at a distance for orientation training and practice.
This makes great sense for a number of reasons. It saves you money and reduces the number of crashes you might encounter otherwise. I recommend a good 2 battery flying session first before flights of the big copters. I myself actual practice what I will be doing that day with the big copters so I have no surprises that I might not have foreseen.
The learning curve with the MQX is really no different than any rotor craft. You will learn first to hold a hover. Once you can hold a hover over a designated point then you can learn the plus formation of moves. You will move forward and stop, backwards and stop, left and right and stop.
Then try a box formation now using corners for your stops. Once you can do this in a precise manner try doing it with the copter pointed toward you during flight. Itís harder than you though huh? With time it becomes easier and this will help you tremendously with multicopter orientation.
After youíre accustomed to the above flying maneuvers you can start flying figure 8ís always turning away from you. Then you can try figure 8ís turning toward you.
Do you feel you have the maneuvers somewhat down and you are ready to fly the big copter? Great! Before you ďkick the tires and light the firesĒ letís look at a short list of items I recommend you complete before your first flight.
Basic Multicopter Maneuvers
Here are my recommended steps for learning quadcopter maneuvers with the MQX and later with your new multicopter. Please do not skip this step once you move to your new multicopter thinking the new copter will fly like the MQX. Any new multicopter that differs from your previous copter will always have different flight qualities. You must re-learn handling and weight alterations to understand complete copter flight regime.
Rear of quadcopter facing you in Hover.
Visualize a box for these maneuvers or mark on out on ground for practice.
Hover from 2 points side by side.
Hover from 2 points front to back
Hover in a box formation
Hover in a triangle formation
Rotate quadcopter nose left and nose right in one spot
Sideways hover from 2 points side by side
Sideways hover from 2 points front to back.
Sideways hover in a box formation
Sideways hover in a triangle formation (remember, do both directions)
Slow forward flight in circle around pilot (Pilot rotates to face quadcopter)
Slow forward flight as above but stopping & restarting every 1/4 rotation
Travel Side to side, pointing nose in direction of travel
Slow flat figure 8 maneuver only after very confident with above maneuvers.
Optional before advancing to full forward flight (but HIGHLY recommended)
These maneuvers are Front of quadcopter facing you.
Rotate to nose in and back, hold as long as you can then rotate to tail in or sideways.
Nose in Hover one spot
Nose in Hover 2 points side by side
Nose in Hover 2 points front to back
Nose in Hover in a box formation.
Nose in Hover in a triangle formation
Slow rotating hover, keep quadcopter in one spot using yaw only
This item should be at the top of your list when operating rotor craft or propeller driven aircraft of any sort. Imagine for a moment that your new quadcopter is a platform with 4 high speed table saw blades attached. Now imagine the first time you reach for or set down your transmitter accidently allowing the strap to fall or pull on the throttle control. What will you do?
Like 99% of us, veteran or new comer alike, you are going to reach for the copter central hub to stop it from taking off arenít you? AhhhÖ come on now, be honest. When you do reach you will find out what 6000 rpm blades can do to your skin. It isnít pretty.
I Ďve seen many reports with pictures , on the RCGroup and other nets, showing fingers, hands, faces, arms and legs with many stitches from just this type of situation. Believe me; your hands will react much quicker than your brain. Its like instinct, it moves you grab. If you are lucky you escape unharmed but the odds are against you. What about the spectators?
So what can you do in this type of scenario? Will you decide, continue the grab for the transmitter while holding down the copter and try to shut down the copter? You may decide to use your shoe and try to hold down the copter while grabbing for the transmitter. Will that work? I donít know how good are you at twister? How about just letting the copter go and grab for the transmitter and hope to fly it out of the situation? You may find yourself trying any one of these solutions butÖÖÖÖ..
Maybe we should take a step backward before this accident presents itself and think this out ahead of time. How can I prevent this scenario and others from occurring in the first place? Answer: Think before you act always around rotor copters.
If you have a nice padded strap for your transmitter then consider getting a transmitter tray. This is not only more comfortable but keeps the straps and other items away from the transmitter. Once youíre ready to take the Tx tray off use quick releases so you retain the strap while setting the tray on the ground. Many of these trays now come with special straps and back supports so you can use quick disconnects. You can even make your own, they are easy to build.
What I am trying to stress here is to think of every possible situation that could occur and plan accordantly so that you know what to do instinctively. Donít forget to plan what to do if spectators show up. Remember to think and plan for the unexpected. If you fail to plan, then plan to fail.
Log Books from day one!
With the complexities of multicopter operation today it is very important to treat our copters like real rotorcraft. One of the best ways we can get a grip on our machines and increase the dependability, and longevity of them is to keep flight and maintenance logs. You should treat these copters like real unmanned aircraft (UAV), which the FAA, AMA and Government feel they truly are. Congress along with the FAA is writing legislation and passing new rules on their operation which whether we like it or not will control how and where we fly our multicopters in the future.
If we start today keeping logs should a mandate come down in the future and you wish to use your multicopter for Civilian, commercial, archalogical or any worthwhile endeavor you will need to be able to prove that you maintained your copter. From many years as a commercial pilot and aircraft owner, I donít think the FAA is just going to take your word that you have faithfully maintained your multicopter and have X amount of flight hourís experience. If we start getting use to logging our flights and rotorcraft maintenance then in the future we are going to be way ahead of the curve. We will be able to show a professional flight record, able to show our actual logged flight time in multicopters and our accompanying maintenance logs.
How will we save money? A well kept Pilot log illustrates a thorough explanation of cost and each test, change, adds or deletion you make to your copter. Your Flight Maintenance Log at a glance tells the time on props, motors, batteries, what modes I used during flight, total time on airframe, reaction in flight etc... This information is vital if you are to set up a good Maintenance Schedule for your copter. This information is also handy during troubleshooting of an issue down the road.
Without this type of information you would not know when itís time to change out your props. As an example, if you begin keeping a history of flight maintenance you will find over time when you would need to replace the propellers to avoid hub separations or failure. You would know when maintenance to the motor bearings would be needed to extend the motor life. There are many things you can add to your log heading to track applicable to your particular copter.
What other things should we consider placing in our Flight Maintenance Logs? How about things such as connector, wire or battery total times/ failures? You should keep a list of all replaced parts and at what airframe time that they were replaced. This reduces crashes due to failed parts. Log which props strike the ground on all tip overís or bad takeoff/landings. Once you strike a prop cut the prop life in half. Period! Donít forget to recheck the props balance also.
Anything dealing with Flight operations of the electronics is important. With todayís electronics you are able to keep complete telemetry flight logs on SD for review after the flight. Telemetry logs can be very important to determine if you may have an issue starting to develop that hasnít become obvious yet. You can also track trends and anything that deviates from the norm is an issue that may be developing. This allows you to investigate before you have an in-flight failure.
If you carry a GoPro camera onboard recording the flight save the video in an archive. This video and sound information is important to pick up on a change in sound from the norm or vibrations starting to occur. Example: I was able to determine from listening and viewing on-board video of each flight that over time I had a slight vibration and change in sound developing. From this and some investigation I was able to determine I had a motor bearing beginning to go. I was then able to replace the bearing before an in-flight failure.
Balance is Key
If you buy a RTF model multicopter then your copter frame should arrive factory balanced with all equipment installed. Additions you might add on afterward such as FPV or GoPro camera and mount will require the multicopter to be rebalanced for the weight.
If you have a quadcopter you will just lift the opposing arms on your fingers and check the balance. Then pick up the other arms and check. Use a string; suspend the copter from its vertical center. Adjust by rearranging your equipment or battery as necessary until balance is achieved.
This is very important for multi reasons. First, the IMU will not have to work as hard to hold a hover. Second, the more the copter is off of the center balance point the harder the FC will have to work to hold the copter in a hover which cost energy. The loss due to this imbalance could be minutes off your total flight time.
1.Blade Tracking - Most pilots overlook this one but it's, by far, the biggest contributor to vibration. Hold your copter up to an incandescent light source and look (not too closely) at the blade tips horizontally while it's spinning at low RPM. If you see a blur, rather than a fine point on them then your blade tracking is off. This is usually caused by mild crashes or blade strikes that you thought didn't do any damage but in fact slightly bent a blade. The solution to this is to toss them for FPV flight but they can still be used for an emergency prop.
2. Motor bells - I found that prop balancers (even the precision magnetic ones) are often useless because they don't seat perfectly with the motor bell and you end up with worse (not better) balanced motor bells in the end. Solution is using a multi balancer because it has several different shafts from 2mm thru 5mm. You'll have to remove your motor bell and shaft to balance it. A common practice that I use to balance motor bells via trial & error is by using a tie lock tighten down to one side and run the motor up listening for vibration and tone of motor. Move the tie end around until you have the least tone variance then add weight to that side of bell. That is better than nothing but the balancer is much more accurate. It'll tell you exactly where the heavy spot is (even when there are multiple spots) and how much weight to add/remove to perfectly balance it.
There is also one more variance where the prop is left on the motor on the copter and one motor is electrically connected at a time. They use the throttle for spin up and access the tone balance adding tape to the prop to balance both the motor bell and the propeller at the same time. I like the other ways better due to I just can't hear the tone change with it on the copter but if you can it sure saves time.
3. Mount and Arms - Do not forget to verify your motors and arms are aligned in the horizontal plane to each other. This will alleviate a drift issue due to miss alignment of arms or motor mounts.
4. Props Ė Props are easier than Motor Bell balancing but can be just as time consuming. For this choir just use any decent floating magnetic prop balancer. I use the magnetic mount and balancer from WowHobbies. I balance my props and hubs using scotch tape for the blades and a small glue gun for the hubs. You balance them horizontally first then you balance them vertically.
NOTE: This comment I feel is very important. How do you correctly install the propellers on the shaft and tighten? First do NOT use Loctite OF ANY TYPE on your propeller shaft or crown. The reason, it is the number one cause of prop hub deterioration which leads to hub failure in flight! Instead find some thin nylon washers and use those under the prop. Insert a small screwdriver through the top hole of the crown caps and tighten it in a clockwise direction. When the crown cap lock touches the propeller, use no more than half pound of torque to lock the propeller in place. This is very important. Over tightening the propeller is the next major reason for prop failure and also damage to shaft and crown caps.
One last thing on props, NEVER EVER use a PETROLEUM BASED product on any part of the copter that will interact with plastic or Carbon Fiber. When you need a lubricant use Silicone instead such as on the prop shaft. Only use a tiny amount wiped off to create a film on shaft which will keep your props from becoming a permanent fixture to the shaft.
Rules and Regulations
As of this moment the rules and regulations for flying multicopters are the same as for any other RC aircraft with a few exceptions. Please make sure before you start flying your multicopter that you protect yourself and join the AMA. You will have protection and insurance to incase of an unforeseen accident or suit.
If you never have to use the insurance then fantastic, you will still not only enjoy the fellowship of belonging to an elite organization devoted to RC aircraft of all types but having a voice in Washington helping to protect your freedom to fly your RC multicopter. You will, of course, need to follow some simple rules and regulations. I have listed them below along with the additional rules for multicopter flight.
Reprinted from MODEL AIRCRAFT OPERATING STANDARDS http://www.modelaircraft.org/files/540-c.pdf
a. Select an operating site that is of sufficient distance from populated areas. The selected site should be away from noise sensitive areas such as parks, schools, hospitals, churches, etc.
b. Do not operate model aircraft in the presence of spectators until the aircraft is successfully flight tested and proven airworthy.
c. Do not fly model aircraft higher than 400 feet above the surface. When flying aircraft within 3 miles of an airport, notify the airport operator, or when an air traffic facility is located at the airport, notify the control tower, or flight service station.
d. Give right of way to, and avoid flying in the proximity of, full-scale aircraft. Use observers to help if possible.
e. Do not hesitate to ask for assistance from any airport traffic control tower or flight service station concerning compliance with these standards.
Additional standards apply when you are;
a. going to use youíre multicopter in FPV operations and those standards are found here; http://www.modelaircraft.org/files/550.pdf
b. Operating a RC multicopter utilizing a Failsafe, Stabilization and Autopilot Systems on-board; http://www.modelaircraft.org/files/560.pdf
Please take the time and read these guidelines and understand them for your own protection.
This is an example of what happens when you do not follow the guidelines. http://www.cnn.com/2013/03/04/us/new...ort/index.html
The FBI expanded on the FAA report, saying in a statement that the Alitalia flight from Rome was roughly three miles from runway 31R when the incident occurred at an altitude of approximately 1,750 feet. The unmanned aircraft, described by the FBI as black and no more than three feet wide with four propellers, came within 200 feet of the Boeing jetliner.
The FBI said it was looking to identify and locate the aircraft and its operator. A source with knowledge of the incident says investigators interviewed the pilot and others on the Alitalia plane.
You can bet the FBI and Local Law enforcement WILL find this person and they will pay big time in court, jail and fine. You must be responsible and know all you can about this segment of the hobby, ignorance is NO excuse! Enough said.
Ok so you feel you are up to speed and ready to comply with all the above rules and regulations, right? Great then itís time to go flying? Not quite yet.
Ah man what now? I want to fly!
Ok, I know you are itching to fly but first we must do a preflight before we lift off into the wild blue. Did you make sure the battery is charged and balanced? What about the Transmitter battery? Good. Did you make sure the battery was secured and checked that it will not shift or fall out of its battery strap?
This happens even to the best of us. After we are airborne things shift, things shake, things come lose. If this should happen to be the battery the Deanís connection will not hold it. You will have an instant power loss followed by a sudden death flip. Down you will go, ouch! So make sure the battery is secure.
Did you check the crown nuts to make sure they were tighten to 1/2lbs of torque? We sure donít want to lose a propeller in flight.
Did you make sure all nuts and bolts are tight and Loctite in place so they will not vibrate lose?
Are all your electronics cables secure and connections tight?
Always power up the Transmitter first before connecting the flight battery, and make sure you hear the beeps to confirm motors/escs binding and are calibrated correctly.
Remember when you power up that if you have a gps on board you do not lift off until the gps is LOCKED!!! If you do you may be in for a surprise.
When you connect the battery make sure your Transmitter strap is not hanging are laying where it can get caught on the throttle when you pick it up the transmitter or you will have more surprises.
When ready to lift off use a slight jounce of the throttle to pop the copter off the ground into a nice level hover a foot are two off the ground. If you slowly bring up the throttle as you would on a helicopter you may find the multicopter just flip on its back? As I mentioned earlier in the article, ďmulticopters have both characteristics of airplanes and helicopters but do not function like either. This is a learning curve but you will catch on quickly.
Another thing you will notice during the hover is that the throttle is very touchy. This is natural so donít think something is wrong with the flight setting. Again this is something you will get use too.
Unless you have compass on-board you will notice the copter yawing slowly left or right. This again is natural and will occur until you add a compass to the FC system.
Once comfortably hovering your copter increase the height to 3-5ft AGL. You will find once out of ground effect the copter will feel more stable and hold its point of hover better.
Once you have your first few hovers under your belt you can start expanding your flight envelop. Spend the time honing your skills before trying to set out across the countryside. After each flight do a post flight check of your copter. Always do a preflight before EACH flight. Never ever take anything for granted on a multicopter. If you do it will come back to bite you. Treat these copters just as if you were going to be sitting on board each flight. If you see something that may be an issue down the road correct it now. Donít be caught hundreds or thousands of dollars later wishing you had fixed it.
I wish you all the best in your multicopter flying and if you have questions donít be afraid to ask them on the multicopter threads. Thatís what they are there for.
Additional Reference Materials for honing your knowledge;
Batfire Blog with tutorial information for quad copters
Multicopter / Tricopter Index (Very large expanse of multicopter information)
Test Fixture Evaluates Motors/Props/ESCs for Quadcopter Performance
|Jan 30, 2013, 11:51 PM|
I've read this 4 times already, and each time it seems I learn something new.
I for one am grateful for your dedication, efforts and willingness to share.. otherwise NooB's like me would still be somewhere in the Twilight Zone when it comes to this subject..
With all due respect my friend.. Thank You.
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