A Stable, Precision Engineered Quad For Sport Fun And Aerial Photography!
As with most modern technological developments, the seeds for todays accomplishments were sown by thinkers of antiquity and rotorcraft are no different. The Chinese experimented with toy helicopters almost 2000 years ago and Italian genius, Leonardo da Vinci, explored the concept of human flight using rotorcraft in the 15th century. Practical experimentation in rotorcraft flight didnt have its start until the 18th century and the first quadrotors didnt appear until the early 20th century. Since the concept hit the hobby RC market, development has been feverish and innovation constant. The main drivers that fuel todays evolution in this field are military and university research, along with the varying obsessions of hobbyists everywhere. A recent entry to the quadrotor market is the Gaui 330X, a low-cost model aimed squarely at the beginning hobbyist interested in aerial photography.
The Gaui 330X and the JR 9303 transmitter I fly it with.
So what is a quadrotor? Those of you with calluses on both thumbs may want to skip to the next paragraph while newcomers may benefit by continuing. Quadrotors, in simplest terms, are VTOL (vertical take-off and landing) aircraft with four motors and four fixed pitch propellers wherein all motion in three dimensions is controlled by motor speed. Thats it! Now just think about the consequences of that configuration a bit.
FLIGHT SYSTEM BASICS
The following discussion assumes the quad is being flown in the x configuration, that is, two motors facing front and two aft. If you had all four propellers rotating in the same direction, all the propeller torque effects would accumulate and the aircraft would spin around its central axis (yaw). Pretty cool but not entirely useful in an aircraft youd like to control. When you have two props rotating counter-clockwise and the other two clockwise, torque effects are cancelled out and the spinning has stopped. Because you now have props turning in different directions, two must be pusher props and two tractor props to get the thrust from all four motors oriented correctly. Pusher props have the reverse pitch of tractor props. Since you now have an aircraft that is, theoretically at least, stable in yaw, movement in the other two axes is pretty basic. To pitch forward just speed up the back motors and slow down the front. To roll right, speed up the left motors and slow down the right. Moving in yaw, or spinning around a central axis in either direction, can be done by speeding up one pair while slowing down the other. And by adjusting motor speeds proportionally, total thrust will stay the same. Wait, cry the trig experts, vertical thrust in pitch and roll is now diminished because of the new horizontal component and must be increased to maintain level flight. Good observation, reward yourself with a pat on the back if you echoed that cry. For the rest of us, lets not worry about it since the control algorithm or your left thumb should take care of that little detail.
This tool simplifies precise application of CA.
For now, the 3D crowd is out of luck; inverted flight or knife edge is just a wispy image from a quadrotor dreamscape. No doubt some of the pioneers out there are already experimenting with variable pitch props and we at the magazine would sure like to hear about any successes. Thats a pretty simplistic overview and most, if not all, quadrotors have ancillary systems that help stabilize the aircraft. Without this help only 13-year old arcade champions would even have a chance to hover one of these things. These aids include simple gyros and accelerometers to help stabilize attitude; Sonar, IR or barometers to help with altitude and range to full-blown controllers that house enough electronics and control software to maneuver autonomously.
I crash proofed the 330X using a cage made of pool noodle foam”worked great.
Quads can be set up in two orientations, a + configuration and an x configuration. The motors are numbered 1 through 4 in a clockwise direction. In the + configuration the centerline of the quad runs through the center of motors 1 and 3. In the x configuration the centerline runs half-way between motors 1 and 4 in the front and 2 and 3 in the back. Both configurations employ somewhat different control algorithms to move in the three axes but are otherwise essentially similar. Other flavors of rotorcraft come with six or eight motors and some with just three motors which use different control methods. Ill leave discussion of those to another time.
OK, the box with the 330X-S has arrived so lets get this baby built up and take it for a test fly. First impressions are positive. Packaging is well thought out and the contents well-protected from over-exuberant postal employees. Parts are well-crafted, the cutting exact and pieces fit together perfectly. Total build time runs less than the average RC ARF and should typically take about two to three hours for someone familiar with model building. The instructions, although an obvious translation, are quite clear and, if followed diligently, should result in an airworthy model. Pay attention to the radio input checks near the end of the manual to ensure proper setup of the electronics.
TIPS FOR SUCCESS
Dont slop on the CA glue. The tab and slot construction along with the connecting hardware provides a pretty solid chassis. Ive made a little CA application tool out of two pieces of thin music wire which allows total control over the positioning and amount of glue I apply. I added only a touch of CA where the tabs enter the slots and so far, despite a few less than feathery landings, the chassis remains intact and solid.
Dont put the propellers on before spooling up for the first time. Rather, put a oneinch tag of tape on each motor; I used colored tape similar to electricians tape. This allows you to check motor rotation direction by observing which side of your finger the tape is hitting, something not advised with propellers installed. This is a safer method of setting throttle limits on the ESCs since part of the process involves the transmitter throttle being full on.
I wondered how well the propeller retention nuts would work and I would have preferred to see some locknuts used. However the spinner type nuts included look really cool, so I put some blue Loctite on the threads. So far, despite some full throttle ascents and the previously alluded to nonstandard landings, the props have stayed put.
During the initial calibration phase, it was evident two motors were not responding properly to throttle inputs and after a lot of trouble-shooting and testing it was confirmed that two ESCs were faulty. Id like to insert a special thanks for the help from the members of the Gaui 330X thread on RCGroups who offered suggestions of potential solutions. An explanatory email to Vic at Empire RC had two new ESCs in the mail the same day and the rest, as they say, is history. After replacing the two suspect ESCs, the remaining setup went off without a hitch. I balanced and installed the props, confirmed the transmitter controls, triggered the proper response on the quad and set it down on the hardwood floor of my vestibule.
The controller on the 330X, called the GU-344, adds some intelligence based on a blend of the incoming RC signals and the outputs of an onboard 3-axis gyro. The GU-344 has variable settings for flight mode (hover or cruise), quad flying configuration (x or +) and gain. Gain, which adjusts the degree of influence of the gyro outputs, can be set onboard the controller with a pot adjustment or by altering end travel on the Gear channel within the transmitter. If the gain function is implemented on the Gear channel, the Gear switch can be used to toggle between Hover and Cruise mode. My advice: forget Hover mode. Im not really sure how the algorithm in this mode works, but it likely increases gyro response and adds some expo.
Two pool noodle sections on page 121. worked very well as landing skids for grass fields.
When properly set up, the 330X is easily hovered in Cruise mode and controlled flight is much more painless. The included orange ball sets the quad up for x configuration so that is what I used. I didnt test the + configuration. When using the onboard pot to vary gyro gain I got the best results by moving the slot approximately 90 degrees CW from the 0 position. When controlling gain via the Gear channel on the transmitter, I set the travel on the Cruise side to 50 percent to achieve similar results. Oddly, I had to add about 30 percent expo to get the quad flying like it did using the onboard gain. I suspect the onboard gain algorithm introduces some expo.
I had planned to make a crash cage for the quad out of a number of carbon fiber flat lengths but the ones I had were either too flimsy or too stiff. Plan B became an aluminum frame with pool noodle ends that can be attached with Velcro ties. This unit will get tested in forward flight practice once I have all the review pictures out of the way. Near the end of my review tests I tied on a pair of 10-inch pool noodle sections horizontally to the bottom frame of the Gaui. This was done to replace the wheeled landing gear which worked poorly in grass. I used Velcro hook & loop strapping to hold the foam. Other ideas would be to use plastic ties or even strong tape. The results were spectacular. With these Pool Noodle Pontoons I felt comfortable flying off my lawn in 20 mph winds.
I broke some propellers earlier in my testing and couldnt find any Gaui props locally so I switched over to APC 8 x 3.8 props. I had an odd problem with the Gaui props, a number failed in the hub area without having been impacted. This might have been my fault as I tightened them somewhat aggressively but Im not certain. The APC props have performed well.
Two batteries are recommended for the Gaui 330X: a 2S 2100mAh to power the basic 330X and a 3S 2100mAh when carrying any kind of load. In reality, this quad is capable of flying with almost any size 2S or 3S pack that doesnt bring all up weight much higher than 1100 grams. I found the 2S pack perfectly matched the basic, unloaded quad while the 3S pack was a bit too high powered for relaxed flying. Just as a matter of interest, a 2S pack only draws about 7.0 amps with the quad hovering in ground effect. The 3S pack was a perfect match for my Pool Noodle Protection gizmo.
Im planning to follow up this article with further developments in this new and exciting field. Further explorations with quadrotors will focus on stabilization, navigation, FPV and AP and as I write this, rumors circulate about a Gaui GPS add-on. Furthermore, let me state emphatically, if da Vinci had gotten his hands on one of these, I have serious doubts that Mona Lisas enigmatic smile would grace the Louvre today. And Leonardo hadnt even heard of aerial photography.
I planned to slowly spool up the throttle to see how the quad would react and before I knew it, I was hovering three feet off the ground. Not rock steady but I was staying in an area of about two or three square feet. Wow, that was FUN! I should explain Im not one of these 3D heli pilots with Â¾ of their brain dedicated solely to coordinated thumb movements, rather someone just comfortable with tail-in hovering who is exploring next steps. The next step for this happy guy was to move the car from the garage into the blustery winds of the front yard and start playing. In no time, I had trimmed the quad to hover almost handsoff and I didnt touch my initial gain setting of about 90 degrees. Reliable hands off operation would require more sensors to measure yaw, altitude and horizontal motion but the 3-axis gyro in this quad does a pretty good job in assisting basic stability.
During the build, I was skeptical about the wheels provided but was pleasantly surprised by how well they worked on the smooth concrete floor of the garage. However, the next day my skepticism was validated when one of the wheels flew off in response to a moderately hard landing on my gravel driveway. The wheels will be retained for winter indoor flying but a mod will be worked out for outdoor landings.
This machine is significantly easier to fly than my single rotor helicopters.
The next day the winds diminished and it was time to let the Gaui 330X really try its wings, within the limitations of this pilot. I was able to do some fairly aggressive flying while keeping the tail-in orientation and I reached a height of about 50 feet. My few nose-in attempts are unworthy of discussion and of course, are no reflection on the quads performance. Given my experience to date, I give the Gaui 330X-S quadrotor an enthusiastic two thumbs up!
Empire Hobby, www.empirerc.com]www.empirerc.com, (480) 227-6057