Wazowski upgrade

Wazowski upgrade

With 2205 motors, this weighs 232.8 grams

  Wazowski was my first attempt at building ultra light weight quadcopter for racing purposes. This was built on summer 2017 and since then, it has been going though constant upgrades to achieve better flight experience.

Goals for this upgrade was to:

• reduce weight even further
• strengthen the tower structure
• have onboard DVR
• have clover leaf antenna instead of dipole antenna (allows racing with multiple pilots at the same time)

Parts used for this upgrade:

On board DVR	HMDVR-S
Top plate	QAV-ULX carbon fiber top plate
Standoffs	Anti-vibration damper with fixed screws
VTX antenna	UXII Stubby LHCP UFL 5.8GHz 1.6dBi
Propeller	HQ 5*4.3*3

Personal rate settings from Betaflight (enlarge image size to see details)

  I have been using the default rates setting so far so I wanted to try other rates setting that is more optimized for FPV racing. Big thanks to Seth from Georgia Tech Unmanned Flying Club who shared his racing quad's rate setups, I found a new setting that is more precise at the center joystick control and more maneuverable at the end control.

Left: traditional rotation,  Right: reversed rotation

  Picture above depicts quadcopters in forward flight. Blue arrows mean the quadcopters are moving forward, white arrows show the rotation of the propellers, and red dots show the center of thrust of each propeller.
  I swapped all 4 motors and propellers to have propellers spinning in opposite direction compared to the traditional rotation. There are aerodynamic benefits to this setup for racing and this video explains the theory in detail. As the quadcoter moves forward, the spinning propeller's advancing blade produces more thrust than the retrieving blade. This shifts the center of thrust towards the advancing blade. Regardless of the prop rotation direction, rear propellers work less efficiently than the front propellers in forward flight because they have to deal with turbulent air created by the propellers spinning at front. Center of thrust at the outer position compensates this inefficiency due to principle of moment. It is also said that in reversed prop rotation setup, rear motors can work more efficiently under fast yaw movements.
  Other advantages are since the propellers are now spinning outward from the camera lens, I don't have to clean the lens as often since it is free from debris coming from propellers. Also, since the propellers are now pushing "away" whatever objects coming towards at the center of the quad when forward flying, it is less likely to get tangled up on things like tree branches.

  Also, new propellers (HQ 5*4.3*3) are installed. I found them durable and efficient, I can see why many fpv racing pilots say this is one of the best props in the market.

Bottom view

What have I done...

  This is a sketchy way of making traditional motor to be naked bottom. (No, I'm not being dirty. That is what people call motors with minimalistic mount design.) Just dremel off the unused aluminum excess material at the bottom and this saves approximately 2~3 grams per motor. There are 4 motors in a quad so total of about 10 grams were saved by doing this mod. It's always good to have motors as light as possible because with less weight at the outer edge of the quadcopter, motors have to work less to overcome the inertia in order to change drone's orientation.

Close up views of rear(left) and front (right) motors

  The stators were exposed since the motor is now naked bottom. So to protect the copper wires, I surrounded them with thermally conductive, but electrically insulating epoxy. Notice for the frontal motors, I left the aluminum material remaining at the outermost corners of the drone. This will protect the magnets from getting hit when crash happens.

HMDVR-S onboard DVR and LHCP antenna installed

  I've been using dipole antenna for the vtx before. It is light and works well when flying alone but it tends to cause interference when flying with many other pilots. Thanks to rapidly advancing drone technology, I found a left hand circular polarized (LHCP) antenna that is small and light (only 1.6 grams with UFL connector!). It's still 1 gram heavier than the dipole antenna I was using before but I can live with that number. The antenna is mounted tilted backwards to optimize signal radiation coverage when the drones is tilted forward during forward flight(which is majority of the case when drone racing).

  Onboard DVR is added on the back of the quad. This only weighs approx 4 grams total with the micro sd card and heat shrink cover. Advantage of having an onboard DVR is that it can record video footage without capturing all the signal glitches seen on the goggle.

  Also, RFX185 frame's top plate is replaced with QAV-ULX's top plate which has more material around the M3 holes to hold onto the screws.

Flight controller is happy with rubber rings + 2 floors of vibration dampers 

  I am still using LUX 32bit flight controller which is known for having overly sensitive gyro. Soft mounting all four motors weren't enough to stop the quad from twitching at the mid throttle and throttle punches so I added rubber rings under the FC and 2 floors of vibration dampers below to filter out unwanted vibrations. This significantly improved the flight controller's performance as no more random twitches were detected during flight. Also, using vibration dampers as standoffs make tower designed frame structure stronger as it uses metal screws compared to using nylon standoffs (these shear easily in crash).

All up weight is 404.6 grams with 4cell 1500mah LiPo battery

Rear view

  I'm a broke college student so I try to upgrade as much as possible before moving on to building another completely new setup. Most of the upgrades are therefore hardware related modifications while I try not to replace all the expensive electronics. Some tinkering with the betaflight software are usually part of the upgrade as well. Wazowski has been going through upgrades for almost a year now and I think it is now reaching it's limit in terms of flight performance unless its flight controller and all 4 motors are replaced with better components. That would be a huge investment as those are usually some of the most expensive parts in a quadcopter. Anyways, I say Wazowski is still a solid race quad as all the upgrades and improvements done to it compensates for the old components it is using.

Upgrade summary:

• reversed propeller rotation
• replaced dipole antenna with clover leaf antenna
• remove excess weight from the motors
• replace top plate with beefier plate
• HQ 5*4.3*3 propellers
• replaced nylon standoffs with vibration damping standoffs
• added onboard DVR (HMDVR-S)
• newest Betaflight filmware at the moment (Betaflight 3.3.0)
• optimized transmitter joystick movement
• permanently turned on airmode, anti gravity, and dynamic filter features
• disabled arming angle
• adjusted rates for more race compatible setup
• added prearm feature for extra safety
• etc... (miscellaneous small improvements)

Improvements for future iterations:

• top mounted battery placement
• better flight controller
• better motors
• 6cell LiPo
• I might as well just build another drone

Heart gears

Heart Gears (Screwless)

"Got a whole lotta love!" - SC2 Marauder

  I've always wanted to build heart gears. I think it is just way too cool. Thanks to emmett from thingiverse (link to CAD source), I only needed to customize the print setup before printing to have the parts in my hands.

Goal of this build was to:

• kill time (might have been a better idea to study more system dynamics exams :p)
• prove that I have a heart

Parts I used for this build:

Filament	PLA plastic (black)
Paint	Enamel spray paint+primer (red)
Coat	Enamel clear coat spray

First few layers

  3D printing was done in Invention Studio at Georgia Tech using Ultimaker 2.

Finished print

  The parts are printed with 1.2 mm wall thickness (a bit of an overkill) but that was to compensate for the dreadful amount of sanding required to minimize unevenness of the surface due to print layers. 

Parts polished with dremel and sand papers

It was dark outside so it's not my fault that the parts look like freshly extracted organs

  Parts are spray painted with color in multiple repeated process of slightly spraying overall and then drying. This is to evenly distribute paints and prevent them from concentrating in one place. After the color is set, clear coat was sprayed in similar process to protect the painted surface.

This thing rotates pretty well

  The 3D printed pins that connects the gears to the center piece were widened at the middle with pliers so that the gears are less likely to get disassembled from parts rotating. After that, the gears were assembled and rotated for personal gratification.

Improvements for future iterations would be:

• apply on the surface with putty or anything that can fill up the uneven texture
• maybe use a red filament in the first place
• use SLA print for finer resolution instead of FDM print

Dynastinai

Dynastinai - 3lb Modular Combat Robot

full of potential, but hampered by faulty drive system

  Dynastinai is my first attempt of building a battlebot with modular weapon system. It was greatly inspired by leading 3lb battlebots Silent Spring (link to Jamison's blog) and Margin of Safety (link to Aaron's blog). The name Dynastinai comes from dynastinae, which is a scientific name for rhinoceros beetle. I changed the letter "e" to "i" to respect the naming tradition of Robojackets Battlebot (all battlebot names end with letter "i"). Also, I thank Robojackets and its members for providing me the tools I needed and doing a design review for this project.

  The modular weapon combat robot can be very effective in the competition because the driver can strategically choose which weapon to use against specific type of opponents. Depending of the types, battlebots are usually like rock, paper, scissors; one type of weapon is strong against certain weapon type, but is weak against another weapon type. For example, horizontal weapon is useful against many drum spinners with exposed vertical walls but is quite ineffective against wedges or vertical spinners with wedges at front since those deflect the horizontal hits. However, vertical spinner with two sharp prongs like the one designed above in the picture are effective against wedges or vertical spinners with wedges at front as those prongs put large pressure on to smaller area on the floor and this tend to dig under the wider wedges. This type of vertical spinner is at the same time, weak against horizontal spinners like the one designed above since those prongs are exposed to shear hits.

The goal of this project is to:

• build interchangeable weapon (one horizontal, one vertical)
• all basic structures made out of 3D printed materials
• compete in Motorama 2018

Parts I used for this build:

Aluminum parts on chassis	6061 aluminum
Aluminum parts on weapon modules	7075 aluminum
Wheel guard	HDPE
Chassis & vertical module	carbon fiber + nylon
Horizontal module	Kevlar + nylon
Horizontal weapon	AR500
Vertical weapon	S7 tool steel
Drive Motors	maxon gearbox + 1806 brushless outrunner
Drive Motor Controllers	ZTW Spider Lite 18A opto
Wheels	Fingertech robotics 2.5in*0.75in neoprene foam wheels
Weapon Motor (Horizontal)	Quanum MT 4108 700KV
Weapon Motor (Vertical)	NTM 450 series 1700KV
Weapon Motor Controllers	ZTW Spider 30A opto
Receiver	Frsky V8R4-II
Remote Control	Taranis QX7
Battery	3S 500mah 35C * 2 in series
Connectors	XT30U, MR30
5V BEC	Pololu 5V 600mA step-down regulator
12V BEC	TUZ 5V 12V 3A step-down regulator
Standoffs	M3*35 aluminum column spacer

CAD - horizontal

CAD - vertical

CAD - internal view

  This is the bottom view. The top plate does not have to be removed at all unless it gets damaged. Only one bottom plate can be removed to access batteries and the other bottom plate can be also removed to access drive motors. The dove tail design of the module interface and the aluminum posts makes difficult to rip apart the module from the chassis in all directions.

CAD - 3D printed chassis, electronics removed

  Aluminum standoffs are inserted into the 3D printed pieces. Top and bottom plates are then secured onto those standoffs with screws. This allows the top and bottom plates to clamp on the 3D printed parts and gives them compressive preload and prevents delamination. Screws and nuts hovering in the photo above are used to secure wheel guards on to the 3D printed chassis.

Half section view of horizontal module

  No screws go through the 3D printed horizontal module. The aluminum pieces are clamped from top and bottom to give 3D printed part compressive preload: prevent delamination.

Half section view of vertical module

  There are two bearings on each end of the vertical weapon. The motor is fully enclosed and is well protected inside.

Prototypes first before using expensive carbon fiber & kevlar

3D printing in action (horizontal module)

completed part

that's a lot of support structure to remove

 Vertical module is printed with its one side facing towards the bottom. This way, I could clamp the print layers sideways to prevent delamination.

CNC milling horizontal hub mount

Horizontal hub motor mount straight out of CNC mill

  Sadly, I didn't account for the tool deflection and the inner diameter where the bearing would sit was 0.002 inch smaller. The bearing would have still went in if I made a press fit but I didn't want that for the sake of easy maintenance. I used a dremel to carefully sand off the inner diameter little by little until the bearing could slide in with minimal interference. 

chassis assembly almost complete

On the vertical module, you can notice there are some nylon material extruded out and surrounding the vertical wedges. Without these, vertical wedges would be vulnerable to hits as it is just held by few M3 screws and it doesn't take a lot of force to shear those.

Where else would you find S7 tool steel laying around up for grabs?? :)

 I was fortunate enough to find the S7 tool steel in the scrap pile in Robojackets shop. They weren't gonna be used by anyone and apparently, they have been laying around there for a while. So I cut a small piece off from one of them, made a request to the machining mall to have it lathed, wire EDMed, and then heat treated to make a vertical weapon.

Assembly almost complete. Stator on the vertical module is also machined and epoxy glued.

Fabricated, with horizontal attachment

  Horizontal weapon was made out of 3/16 inch thick AR500 steel - waterjetted.

Bottom side

  Bottom cover is composed of two plates to easily access the internal components that are just needed. Also, too many screws on the horizontal weapon. I think I can reduce number of screws here for the next iteration.

With vertical attachment

Internal view

  Inside is full of spaghetti. I couldn't optimize the wire length because I had to borrow drive motors and drive ESCs from other robojacket team members since I didn't have those.

I can take off this cover and access the drive motors

  The drive motors are composed of gearbox and brushless outrunner. Because of this, rooms for the outrunners to safely spin had to be designed. Here I clamped the gearbox (not spinning part of the drive motor) in an elevated position so that the outrunners have enough vertical space to spin. Also, a thin wall was made to prevent any wires from making contact with the outrunners.

Stator inside the motor mount (top), assembled motor hub (bottom)

  The stator is is machined to fit into the hub motor. Also, it is covered with thermally conductive but electrically insulating epoxy glue to be more resistant to heat and take impacts better when it makes contact with the magnets around it. The aluminum hub is first waterjetted for the holes and general dimension and then tuned on lathe for precise cuts. Magnet ring from the original motor is cut and press fitted into the hub and is covered with same epoxy glue to keep magnets in their place.

horizontal module disassembled

vertical module disassembled

damage taken on the horizontal module during the rumble

  Even though the 3D printed part was clamped, delamination occured on the 3D printed part, and aluminum chunk was taken off from the hub motor mount. I will be strengthening this part in the future iteration.

damage on the right wheel guard

damage on the left wheel guard

 HDPE wheel guards held pretty well. It covered majority portion of the 3D printed parts and the wheels and took almost all the hits. The damages to the wheel guards don't concern me since they are designed to be consumable and are cheap and easy to make (it takes 20 seconds to waterjet one).

Dynastinai testing its horizontal weapon

  I see a lot of potential to this robot. There were many good aspect like the interchangeable weapons, efficient hub motor weapon, 3D printed chassis, 6 cell lipo battery. However, it was ultimately hampered by faulty drive system. Whenever I made sudden left to right movement or vise versa, the ESCs went into a reset mode and the robot was immobile until I put the control joystick at the center and wait for a second. In a fast paced, agility requiring combat arena, Dynastinai was immobile for significant period of time due to this mishap.

  Not having my own drive system was a problem too. I had to borrow other Robojacket member's drive ESCs and motors so I had to spend significant amount of time taking the drive in and out instead of test driving or checking out if there are any other problems.

  Also, I didn't put soft pads around the electronics inside so after hard hit from a vertical spinner, the weapon ESC got damaged and wouldn't spin up the motor anymore.

  Dynastinai never won and its win loss ratio is 0:2 from Motorama 2018. However, now I know what to fix so hopefully I can build a more formidable combat robot (Dynastinai V2) in the future.

For future iteration of this robot, improvements would likely be:

• have my own, reliable drive system (brushless -> brushed motors?)
• less free space for soft mounting drive motor, use double sided foam tape or polyurethane rubber
• more space for the wheels to rotate
• 6 cell -> 4 cell lipo ? (this way I don't have to use separate voltage regulator to power drive system)
• smaller horizontal module's hub motor design (for increasing weapon reach distance)
• horizontal, vertical weapon design change to allow bi-directional rotation
• weapon ESC firmare upgrade to allow bi-directional motor rotation
• aluminum hub or 3D printed hub with high tolerance for vertical module's motor (reduce vibration)
• pad all electronics with foam for protection

Vespa

Vespa - Stretched X racing quadcopter (November 2017)

Trade offs are unavoidable

  Vespa is a second racing quadcopter I built following Wazowski. The name Vespa comes from the scientific name of Hornet, one of the largest type of Wasps. The drone visually is sleek, relatively large for having 5 inch propellers. Hence the name Vespa. Vespa was originally designed to be my primary racing drone, taking Wazowski's place. 

The goal of this project is to build a racing drone focused on:

• aerodynamics (streamlined canopy)
• structural integrity
• high thrust to weight ratio

Parts I used for the build are:

Frame	QAV-XS Stretch-X with PC shell
Motors	Racerstar BR2306 2700KV
Flight Controller/ESC	Racerstar StarF3S 30A
Receiver	Frsky XM+
Beeper	Super Loud 5V active alarm beeper 9*5.5mm
Camera	RunCam Micro Swift 600TVL
Video Transmitter	EWRF-e7082TM
Battery	Infinity 4cell 1500mah 70C
Propeller	DAL T5045 V2
Connector	XT60U
Capacitor	Panasonic 1000uF 25V electrolytic capacitor radial

Mid assembly

  I am using an all-in-one flight controller that includes 4 ESCs, OSD, 5V BEC, etc. It is amazing how drone technology advanced within the last few years. This allows very clean and low profile build and all the components should fit into the canopy's limited space.

Soldering complete

  Vespa is based on stretched-X frame, which is a variation of the traditional X shaped frame. The frame is stretched in length wise so that there is more space between the front propellers and the rear propellers. The idea is that as the quadcopter advances forward, the front propellers create turbulence and the rear propellers end up taking those disturbed air. Giving more distance between the front and back props will reduce this effect thus making cleaner flight characteristics.

Camera mount was designed using solidworks and then 3D printed with PLA plastic

Close view of the internal electronics

   Capacitor is added next to the battery connector. It is common way to reduce electrical noise. More effective way of doing so would be adding capacitors as close as possible to the motor (source of electrical noise) but that would add more weight and since there is limited space inside the canopy, I used only one.

  Also, the video transmitter I am using has smart audio feature. That is, I can adjust the video transmitter's power output and frequency through OSD and radio transmitter without doing so manually. This is a very nice feature to have especially when you are flying with multiple drone racers and have to switch VTX setup frequently.

Build complete, Side view

   Motor wires are covered with electrical tape to protect the wires from external objects such as tree branches.

Front view

Rear view

Georgia Tech Unmanned Flying Club

  Vespa improved on every aspect I found flaws from the previous racing quad I built. The frame is a lot stronger (never broke an arm), canopy is aerodynamic, motor is more powerful. However, those improvements brought problems that weren't present in the previous quad.
  Vespa weighs 305 grams and that is 74 grams heavier than Wazowski. 74 grams may not seem a lot but it affects the flight characteristics significantly. Because of that, Vespa is less agile in flight, which is not a problem when going fast in a straight line, but it is bad when flying in race course that has frequent turns.

  Also, the PC shell canopy wasn't as tough as it should be. The front part of the shell broke off easily from mild crash and long crack lines were starting to form (that's what I get for buying the cheap chinese frame off from ebay for 1/4 of the original price).

Canopy damaged, cracks forming...

  The video transmitter I used for this build had good features (smart audio, light weight), but the video it was transmitting wasn't clean enough for flying comfortablely. Edit: turns out I had the antenna too close to the main power wires. EMI was distorting the video quality and after re-positioning the vtx, the video quality was much cleaner.

  I didn't like the problems above (especially the 74 grams heavier aspect) so Wazowski still remains to be my primary racing drone. Vespa is still a great, reliable quad so I'll be using this primarily for free style flying or as a backup to Wazowski for racing.

  From this build, I learned the importance of minimizing weight and how it can affect the flight characteristics. Every gram counts in the world of quadcopters!

For improvements on future build:

• sub 200 gram racing drone (not including battery)