3D Printed Quadcopter

About

The aim of this project was to build a UAV based on a self-designed 3D printed frame and the AeroQuad flight control board. Thereby, we aimed at simplifying the frame manufacturing process, making the flight platform easy to create in cases of crashes or the need for multiple copers. The project was embedded in ongoing quadcopter research at the Interactive Media Studies Group, University of Technology Vienna, Austria.

When we (David Griedl & Wolfgang Weltler) started with our work, we had a rough background in electronics, soldering, or remote controlled aerial vehicles. During the project we learned a lot and would like to share our insights with beginners in the field. Therefore we would like to provide a guide of what you need to consider when building a UAV and in which areas problems can be avoided.

In this instructable, we use the terms UAV (unmanned aerial vehicle), drone and quadcopter interchangeable, although UAVs a.k.a. aerial drones can have many forms and you should not limit yourself to a strictly four-propeller copter, a.k.a. quadcopter.

Also, always try the simplest approach if you are new to the whole concept of quadcopters. This can be a challenging hobby or project, and you should make it as easy as possible for yourself. You might even consider buying a DIY set instead of choosing parts on your own, but of course building it yourself might be why you want to do it in the first place

Our Quadcopter

The picture above shows our created UAV. In the following, we provide the details of all parts.

Frame

The layout is a standard x-layout, meaning two motors in the front, two in the back. They are numbered 1,2,3,4, clockwise, starting with the front left motor when viewed from above. Several layouts are possible, but this one is most frequently used.

The core are two square aluminum tubes with 2mm walls welded together. All other frame parts are made of Polymaker PolyMax, a very durable PLA material for 3D printing.

Propellers

Because of availability, we chose Graupner (a brand) 10x5 propellers, meaning 10 inch diameter, 5 inch pitch.

Motors

• Brand & Name: Planet-Hobby 3530-12
• Rotations/Minute/Volt: 1200
• Resistance: 75mOhm
• max Ampere (15secs): 26A
• ESC Ampere: 30A
• Propeller Size: 9x5 (meaning 9 inch diameter, pitch of 5 inch)
• Weight: 74 grams
• suggested model weight per motor: 600-1400g
• Link (german): lindinger.at

Battery

• Brand & Name: Wellpower SE ECO LiPo Battery
• Cells: 3
• Capacity: 5000 mAh
• Voltage: 11.1 Volt
• Weight: 402 grams
• Discharge Current: 50/25C

ESCs (Electronic Speed Controllers)

No-Name ESCs capable of handling 30 Ampere.

Electronics

Arduino Mega 2560 SDK with an AeroQuad Flight Board v2.1, running a fixed version of the AeroQuad flight firmware that can be found here.

Printing Template

You can download a MAX-File witn a 3D model of the quadcopter and a zip file containing all necessary printing templates in Step 4: 3D-Printing.

Step 1: Dimensions and Environment

General Considerations

The dimensions of your UAV are important on the influence of possible hazards and the overall stability in flight. Large drones tend to be more stable and less prone to winds, but also less agile. Small drones are agile and produce less air disturbances, but are limited in flight time and stability. The task of the drone must be carefully considered. If you don't have any specific task in mind, we suggest a small drone, as it is more agile and easier to maintain/repair.

The first two decisions for the dimensions is the diameter the propellers and the propeller layout. The diameter and pitch of the propellers influence the climb rate and the lifting power, together with the weight. A good climb rate translates into an agile drone with little endurance and lifting power and is achieved by small (6 inch) to medium-sized (8 to 10 inch) propellers with a high pitch (5 or higher). A good lifting power translates in a good payload and endurance, but also in declining agility and reaction. A large propeller diameter (above 10 inch, without limit) is best suited if lifting power is needed.

Indoor

For any and all indoor applications, the absolute minimum in dimensions and weight necessary should be the goal. Indoors a smaller quadcopter has several advantages. It is less prone to recirculation, which can become a big issue in closed rooms or navigating close to walls. Recirculation will disturb the flight of the UAV and can pull it towards walls, resulting in a collision. So, less power is better.

A smaller UAV has relatively more space for navigation and errors. And since a smaller size usually correlates with less weight, this has other positive effects. The lighter the drone is, the less fatal potential crashes are and less damage may be inflicted on the surroundings. For indoor applications, protective bumpers around the propellers should be considered and are highly suggested, as they further reduce potential damage to both the drone and the environment.

We suggest limiting any indoor drone to 6-inch propellers in an x-layout, preferably with even less diameter, like 4,5 inch. But we also had a drone with 8-inch propellers successfully navigating in a standard room (2,5m height), although the flight was autonomous (meaning the drone controlled itself).

Outdoor

Outdoor UAVs face completely different environmental issues. While recirculation will hardly ever occur, the main disturbance during an outdoor flight is wind. A larger quadcopter will be less, but still, affected by air currents. Since the size is less of an issue outdoors, a larger count of propellers and higher diameter propellers can be considered, which, depending on the exact specifications, can result in highly reliable and either enduring or agile UAVs.

But the greater operation height will most likely make crashes fatal for the drone. Consider that a lighter drone still has a higher survivability in this regard due to less force on impact. Propeller protection bumpers are always a good thing, albeit less effective against the forces of a crash from great height.

While originally made for indoors, our drone is much better suited for outdoor operation, so you could use our specifications for an agile outdoor drone.

Step 2: Performance Calculation

Basics

The four components that have to work together to lift the drone into the air are the propellers, motors, the battery and the ESCs (Electronic Speed Controllers). The ESCs connect battery, motors and the flight board. One will usually start by choosing propellers, then motors capable of handling the chosen propellers (and the estimated total weight). There are propellers intended to turn clockwise and propellers turning counter-clockwise (indicated by an ‘L’), and you need both depending on your UAV-layout. Once the motors are chosen, you need to match the motors’ requirements on LiPo cells and ESCs capable of handling the current usually indicated by the motors’ description. A LiPo battery can hold several cells, each providing 3.7 volt. In our example, we had motors requiring 30 Ampere ESCs and 2 to 3 cells. We decided on a 3-cell battery for more excess energy.

Don’t refrain from adapting any of the parts (propellers, motors, ESCs, battery) at a later point of planning, but always recalculate everything to ensure you are building a working UAV. The best help for the calculations is the xcopter calculator at http://www.ecalc.ch/ .It costs a little to access all features, but we found it to be very useful.

Motors will usually have following attributes:

• Brand & Name
• Rotations per Minute per Volt (R/Min/V)
  • High rotations per minute (e.g. 1400 R/Min/V) are better for agile drones, while a motor using the same energy but has lower rotations has more torque, which is better for drones with a lot of lifting power.
• Resistance (mOhm)
• max Ampere (15secs)
• suggested ESC Ampere
• suggested Propeller Size
• Weight
• suggested model weight per motor

These are values that might not tell you much, but are important for the calculator mentioned above. The suggested model weight per motor is good to find a good performance ratio. For an agile UAV you will want a ratio of at approximately 2:1 or even higher, meaning the motors combined could handle a model weight double its actual weight.

Batteries will usually have following numbers

• Brand & Name
• Cells
  • sometimes only written in the name as e.g. '3S', meaning 3 cells
• Capacity (mAh)
  • This is the decisive factor for the endurance of your drone. Higher capacity means more weight, but also more flight time.
• Voltage (V)
• Weight (grams)
• Discharge Current (for example "50/25C")

As with motors, you don't need to understand all of this, but the numbers all are important for the calculator.

We highly suggest doing a lot of calculations before buying anything, as this can save you from a lot of frustration.

We spend the first three weeks just researching and calculating, and we really got the performance we calculated.

2. Agility

To build a highly agile, fast turning and reacting UAV the propellers should have a high pitch but not a too high diameter. The usual hobbyist quadcopter will have 8 inch propellers with a pitch of 5 or higher. Also, the motors should be capable of high R/Min/V (1200 or more), which will result in a higher climb rate. This higher climb rate also results in fast turning, good reaction to changes and high maximum speed.

Be aware that this trades come at the cost of lifting power and endurance. There should be close to no excess payload calculated so no energy is wasted on lifting power. A lighter battery, therefore with less capacity, should be preferred with the option of quick changing if a sustained flight is not important. This kind of drones is most commonly used among hobbyist pilots and for flashy aerial maneuvers.

3. Endurance & Payload

To achieve long flight times the best results are achieved by minimizing climb rate and adapting the lifting power to mostly accommodate the weight of the copter, with little payload, although a high payload is less problematic when combined with endurance than with agility since they correlate on the need for lifting power.

Lifting power is achieved by large diameter propellers (12 inch or more) operating on slow R/Min/V (1000 or below might fit). Motors made for slower rotation speed at similar voltages usually have more torque. Be aware that large propellers are more inert, making reaction slower and therefore a less agile UAV. The battery can have a lot of capacity since the UAV will most likely be capable of handling the weight, but be aware that this uses some of the calculated payload.

For this kind of UAV one could also consider a different layout, but this is not mandatory. A higher number of propellers (and therefore motors) not only results in a better lifting power, but also in more reliability. A usual quadcopter can barely handle one motor outage. An octacopter is capable of losing any 3 motors without going out of control (if some form of auto-stabilizing is used).

Our quadcopter was designed for a high payload with small diameter, with some endurance in mind. This resulted in a 15 minute flight-time or 9 minutes with 1kg payload.

Step 3: Frame

Material

Oddly as it seems, there is not much choice considering material. If building an UAV with available parts, one will mostly face the choice between plastic and aluminum, with a few more expensive versions made of carbon fiber. The larger the drone, the less plastic is used since it cannot withstand the stress without bending or breaking.

3D-Printing: When building the frame from scratch, we can suggest 3D-printing only for the smallest drones, smaller than 6-inch propellers. The first image shows a very early frame part that broke under stress. The reasons for this are the materials available for the usual 3D printers, which are PLA and ABS. PLA usually is stiff and brittle, while ABS is tough, but slightly less stiff.

Because of issues with vibrations (which affect the sensor readings, which is BAD) and bending arms ABS is less usable than PLA, because the stiffness is needed both against vibrations and against frame instabilities which can result in unpredictable behavior. But even the better PLA brands or special materials will bend or break under the stress of any UAV except the lightest.

There are a lot of useful frame components that can be 3D-printed on any scale of drone. This could include an electronics suspension like in our drone, but also shells and bearings for additional sensors or antennas. But for the center frame we have a different suggestion.

The go-to material for self-built frames should be aluminum, for ease of use, stability and stiffness. This means little vibrations, no wobbling and therefore no unintended behavior. Also, many professional UAVs are made from aluminum. In our version, square aluminum tubes with 2mm wall worked great. The second image shows the aluminum frame with the attached 3D-printed parts. If possible, weld parts together, but wherever using bolts, always use stopping nuts or the vibrations of the motors will loosen the nuts, possibly resulting in catastrophic failure. While zip ties can be used excessively for fixating loose parts, they will break when under intense stress, for example when used to attach landing rods.

To summarize: Use aluminum for all parts under mechanical stress, use bolts with stopping nuts, 3D-print or carve special parts if necessary and use zip-ties for fixating loose stuff. With this, the frame will handle.

Planning the drone

There are many ways one could build a drone and should not be limited to the ways others have built them before. However, some points should be considered in the overall construction.

Make it symmetrical

The drone will perform best if you make the drone symmetrical. In our layout the top view shows the motors to form a square, and all extra components accumulate in the center.

Get the battery away from the electronics

The battery emits an electro-magnetic field which is capable of disturbing sensor data over short distances. So keep it as far away as possible from the electronics to avoid sensor disturbance.

Make the main switch or battery connection accessible

A situation might arise where you have to manually shut down the drone because remote signals don't work and the drone runs on full speed. OK, this really would be a terminator-style freak accident, but as we say around here: 'The devil never sleeps'. You should be able to separate the battery even when the motors are running.

Additions to Consider

If you find that you have vibration issues, consider using a dampening of the electronics. This can be bothersome, but helpful in the end. We used a special 3D-printed bearing (available in the attachment), but many semi-professional drones use simple vertical dampening. Any add-ons not under (strong) mechanical stress could be easily made using 3D printing technologies if available.

Depending on the intended use, lighter UAVs could benefit from adding protective bumpers around the propellers, although they mean more weight. They should be made from a stiff material, most likely the same material as the frame itself and possibly weighting the same.

Step 4: 3D-Printing

Even if you are not into that hype, you should consider the usage of 3D-printed parts. 3D-Print shops are increasing in numbers, and the costs for parts is not very high. And you might not even need to make the 3D-print plans yourself, you can use parts shared by others. While we sometimes overestimated the durability of PLA, the most common 3D-Print material, it made many matters easier by providing us with parts that were hardly possible with other building methods, or it used only a fraction of the time necessary to build the same part from e.g. wood.

The most elaborate 3D-printed part was the electronics bearing and dampening part above. It not only holds the electronics in place. The dampeners are angled at 45 degrees around x and z axis so that the dampeners can counteract vibrations and impacts from any direction. Commercial drones often just have the dampeners vertically in place, with little success dampening horizontal disturbances. And all this while providing attachment points above the electronics.

Also, with 3D-Print, we were able to experiment with different landing rods and propeller protection bumpers.

The only downside we found is that the material used in commercial 3D-printing can't handle the mechanical stress of a 1,5kg drone crashing. We had to replace a lot of parts until we decided to go for aluminum for the center frame. Nonetheless, there are many situations where a 3D-printed part might save a lot of trouble.

Step 5: Electronics

Flight Board

If the processing unit is the brain of the drone. The flight board is the nerve system. It connects sensors and motors to the processing unit. One could start with any flight or motor control board, but our experiences only include the AeroQuad Flight Board v2.1 (see picture above). AeroQuad produces several different flight boards and since a couple of months a new version with the number 3.2. Due to the autonomous flying capabilities of the projects quadcopter we additionally used a barometer and an ultrasound sensor. Without the autonomous flight the components you need to get the quadcopter off the ground are the AeroQuad flight board v2.1, a logic level converter and a 6DOF sensor from Sparkfun®.

This configuration requires an Arduino Mega 2560 SDK as processing unit. Note that another flight board in most cases needs another type of Arduino or even a different kind of processing unit altogether.

There is a very in-detail tutorial HERE for assembling the AeroQuad flight board, which might help even when using a different kind of flight board.

A word of warning: If the battery is close to the electronics board, it WILL disturb the sensor readings! We didn't do this and had a lot of issues only resolved by placing the battery as far as possible away from the sensors and electronics. We suggest placing the battery as far from the control board as possible.

Remote Control

The research group at our university provided the Spektrum-DX6i radio control to us. We never used another remote control so we can’t give advices or list pros and cons, but to any remote a fitting receiver must be used.

Pairing the both is an easy enough process described in the manual. We want to mention that several amazon comments and other forum entries describe the Spektrum-DX6i as very reliable and easy to handle despite the diverse possibilities to program the device.

Step 6: Summary

Plan ahead

• Have a goal what your drone should do, and calculate accordingly. We suggest this calculator.
• Keep the drone symmetrical and the battery away from electronics.
• Recalculate until the calculated performance fits your needs before buying anything.
• Use bolts with stopping nuts and excessively use zip-ties.
• Replacement parts are a good idea, especially propellers.
• Use a flight board and processing unit that has been tested already.
• When available, consider 3D-printing special parts like sensor bearings.

Suggestions for different goals

For an indoor drone:

• 4,5-6 inch propellers, potentially smaller
• light-weight motors over performance
• light-weight frame, maybe 3D-printed
• light-weight battery at the cost of flight duration
• no payload
• propeller protection bumpers
• quadcopter layout is the easiest

For an fast, agile drone:

• 6-8 inch propellers with a pitch of 5 or higher, maybe 10 inch diameter
• motors with high rotations per minute per volt (1400 R/Min/V or more)
• commercial plastic or self-made aluminum frame
• battery fitting your needs (5000mAh or more for long flight time, as low as 1000mAh for short flight time but better performance)
• little payload
• consider propeller protection bumpers
• quadcopter layout is most commonly used

For a durable, strong, enduring drone:

• 12 inch or bigger propellers
• motors with low R/Min/V, 1000 or lower
• aluminium frame
• high capacity battery (5000mAh or a LOT more, as fits)
• lots of payload
• consider layouts with more propellers, e.g. octacopters

Step 7: Final Words

Constructing your own quadcopter is a tedious task and highly rewarding. Always consider going the easy path and don't refrain from asking for help, but also be bold enough to try things out. Many hobbyists are, through experience, close to an aeronautics expert and will eagerly help if you find the right forum.

X-Copters in the forms of Quadcopters or similar are probably the easiest vehicle to control via software instead of traditional flight controls, so if you plan to build an UAV that should operate autonomously or that you want to control from your computer, X-Copters are the way to go.