Drones - APM

Package delivered autonomously by AirbotServices' X8 model

hugues — Tue, 28 Jul 2015 17:27:17 +0000

I - Intro

This blog shows an autonomous package delivery with the X8 drone model from AirbotServices.

It further synthesizes hardware, software configuration information to explain how to make a drone delivery, fully autonomous mission based on the opensource Pixhawk autopilot hardware and the APM copter and mission planner software.

Video of Drone package Delivery Mission - AirbotServices X8 - Pixhawk - APM:Copter V3.2.1

II - Delivery mission’s preparation:

II.1 - Safety message:

This video does not intend to promote an illegal nor reckless use of drones. So first thing is ensuring you are in legal order to execute such a delivery mission in accordance to your local regulatory authorities. The mission is here executed fully above privately owned properties with agreement of their owners, in a rural non populated area, keeping permanent line of sight, either from the departure or arrival location (two operators are prepositioned at departure and arrival sites for precaution and take manual control over in case of emergency.

II.2 - Analysis of the delivery mission’s path:

A careful analysis is required of the delivery path the drone will follow in order to: avoid obstacles as we do not have any technologies to detect them yet real time in flight (such as electrical lines for ex), fly around any populated areas to avoid them, take into account the terrain’s topology along the way to avoid hitting hills, mountains, trees,...

To take into account the topography, you have two options in current’s mission planner:

you can plan you waypoints at different altitudes, taking into account the relative altitude differences between waypoints (manual altitude offset management – that is the method that was chosen for this mission as described further);

you could plan your waypoints as usual in mission planner and check the “verify height” checkbox in mission planner’s flight plan window. In this case, the google map ground altitude for each waypoint is added to your waypoint desired altitude. This is theoretically a safer way to go than first method; however we noticed in our tests a few issues: mission planner’s ground altitudes are not the same as google earth altitudes (strange discrepancy) with differences of a few meters (enough to crash!) and google altitudes are incorrect (sometimes also by a few meters);

A future third method will be the best of all, once ready for use: in a next release(s) of APM:Copter, terrain following will be made possible (already available in APM:Plane 3.x). That consists in storing, on Pixhawk’s autopilot microSD card, a terrain database which gives the terrain height in meters above sea level for a grid of geographic locations. Terrain following is different than the current “very height” method as the autopilot will permanently check the topology’s height variations to correct the drone’s altitude (versus the verify height method that only checks the altitude at waypoints, but not between them).

For this current delivery mission, the following manual topology analysis has been done, preferring to calculate and plot the terrain’s height variations manually. The following picture and graph shows the altitude (in meters) of the delivery mission’s path, with departure location (“Home” point) on the left and the arrival location on the right (“delivery target”). The intended delivery mission paths, roundtrip, is a little bit more than 1,5km long (or about 1 mile long for non-MKSA countries):

The picture shows a visual Google Earth representation of the full delivery mission and the ground’s altitude topology along its way.

From such a graph, we now know that:

Home altitude is 265 meters
Target altitude is 298 meters

By difference, an offset of 33 meters must be added to the destination’s waypoints altitudes; further add a safety margin of a few extra meters in order to take into account of :

Pixhawk’s barometer drift issue (that we have discussed already a few times on diydrones) when flying more than a few minutes.
the Google Earth altitude precision errors
your own eventual calculation precision errors!
Total ground travel distance is 765 meters, one way. Be aware that, when flying, your drone will also spend some “travel distances” vertically between waypoints to reach desired altitudes (that has an impact on your batteries/autonomy calculations!)
In this example, there are no higher obstacles above 298 meters. There could be towers, electrical lines, etc…DO NOT FORGET to add a safety margin on your waypoints altitudes to mitigate these eventual obstacles! The only good way to do this is a ground survey at destination. Do NOT RELY solely on Google satellite images as they may date from few years (and in the meantime some pylons, towers and trees may have grown J).

Thus make a thorough terrain reconnaissance, not only at departure and arrival points. Check google map data and complete its imprecisions with a field survey.

III - Hardware & Software configuration:

III.1 – UAV ship hardware selection

For such a delivery mission a reliable ship must be used. It must at least comply with the following requirements:

its lift capacity must exceed with a margin the all-up-weight including payload;
must have an autonomy that exceeds with a margin the total flight’s duration;
must have longest range as possible telemetry for command & control capabilities (+RC transmitter as a backup);
must have redundancy on all critical components for a safe auto mission: redundant motors, two GPS, external compass, etc…

These minimum requirements de facto exclude the use of drone toys or quadcopters. Do not use a drone that is designed for video/pictures applications (such as an IRIS, a Solo, a DJI phantom) to deliver packages: they will not have the required level of safety, nor the capacity to do it.

Being a custom drone builder, AirbotServices chose its X8 model as briefly described in pictures below:

III.2 - Package lock/drop mechanism:

The transported package must be securely fixed to the drone and a release mechanism must be triggered automatically by the autopilot. A good way to do this, limited to packages lighter than one kg, is using Nicadrone’s electro permanent magnet (EPM). A newer EPM version is said to carry heavier payloads but I can’t confirm it. The principle of EPM is a magnet that can be activated and deactivated dynamically by a commanding signal.

The EPM has four mounting screws to be fixed to the drone. A standard PWM servo cable is plugged on one side on the PWM EPM input, and on the other side on one of Pixhawk’s AUX1 (RC9) to AUX4 (RC12) outputs. Actually, for a reason explained further in the trigger mechanism, only RC9 to RC11 can be used with current stable APM:Copter 3.2.1 firmware.

A metal plate such as this,

is fixed to the package. This iron plate matches the magnetized square surface of the EPM device. Although EPM holding strength has been tested by others to maximum 1 Kg of payload, I recommend to mechanically block any “yaw” movement of the metal plate against the EPM magnetized surface; indeed the strength of such magnet is in the vertical Z direction, not in the X or Y directions, where the payload can slip very easily. In this particular case, four little aluminum blockers were glued parallel and against the four metal plate edges. In a way such that any yaw movement of the payload versus the EPM base is avoided.

Furthermore, as a lesson learned the hard way during testing sessions, be careful not to fix the metal plate directly on a metallic package: indeed the magnetization flux is dispersed outside the fixing plate and the overall resulting locking strength is weakened doing so!

Attachment point and vibrations considerations:

A package adds a large surface area to your drone that will as a consequence catch more wind than usual. Furthermore, vibrations of your transport ship will be affected by the added mass and the way it is fixed (how rigid it is) to it.

APM:Copter is sensitive to vibrations and to keep vibrations low is critical for a safe flight as it impacts the compasses, among other things. Without a working compass, a flyaway is guaranteed…In future 3.3 version, vibrations management has been improved but for now, keep them low. It is thus a good idea to dampen and isolate the transported package from the part of your ship’s frame carrying the Pixhawk autopilot. It is even better if you can fix the package to a vibration free zone of your ship you use usually for your cameras.

During testing sessions, it was found that a “hard screw” fixing was the least reliable solution to secure the package and mitigate vibrations; with package losses due to forces exceeding the 1kg holding force of EPM. Reliable results were found with rubber bobbins (secured enough in tensile strength but still offering some elasticity between the payload and the ship’s structure).

On the side of the package fixing point, where the metal plate is fixed, various methods were tried from simple scotch tape to hot glue, etc.. Best method was simply…Velcro. Velcro does not melt under the sun (as would hot glue during a summer delivery mission) and offers some elasticity and vibration isolation.

III.3 – EPM lock/drop control configuration:

The EPM gripper works by sending three different PWM values to its servo input:

a neutral value of 1500 us when the EPM gripper is at rest. This rest state does not consume any power so it is best to leave EPM’s state at neutral when it is not in the action of locking or dropping the payload;
a low value below 1100 us to drop the payload;
a high value above 1800 us to lock the payload.

So the functioning sequence becomes:

to lock the payload : set the PWM signal high for a duration of about one second (the EPM secures best when it is able to cycle a few times its magnet. This takes a bit of time. One second is typically good). Then set the PWM value to neutral.
to drop the payload : set the PWM signal to low for a duration of one second. Then set the PWM signal back to neutral.

According to APM:Copter online documentation EPM PWM signal may bet set via a consecutive pair of DO_SET_SERVO commands. However this did not work in practice as these commands do not allow to maintain the commanded PWM values for a predefined duration (ideally one second). Apparently the default duration of these commands is too short to reliably command the EPM gripper.

Instead, the DO_DIGICAM_CONTROL command is used. This command offers the advantage that it works reliably, reduces the number of commands from two to one and allows to define precisely the PWM signal duration (by tenths of a second). This is how to configure it:

Connect a servo cable between EPM and one of the AUX1 (RC9) to AUX3 (RC11) ports of Pixhawk (AUX4 can’t be used as it is not displayed in mission planner camera trigger dop down list). Lets’ assume RC11 for this example.
Open and connect mission planner to Pixhawk. Go to the initial setup / optional hardware/Camera gimbal menu. Set the shutter option to RC11, set the shutter pushed value to 1900 when you want to lock the payload to EPM; or set it to 1100 when the payload is already fixed to EPM and you’re ready for the drop mission. As shown in pictures below:

Picture above : RC11 configured as the Pixhawk AUX EPM commanding port. Shutter pushed value set to 1900 to lock the payload.

Picture above : Shutter configured to 1100 value (unlock or drop value)

Open then the config/tuning “Extended tuning” window to set the Ch7 option to “Camera trigger”, as shown in image below:

To test the setup is functional,

To test payload lock: follow the steps above by setting the RC11 “pushed” value to 1900; then go in the main flight data screen; hold the payload against EPM; right click on the map to have thr drop down action list displayed and select “Trigger camera now”. You should hear a few clicks from the EPM indicating that the payload is secured.
To test payload drop: same steps as above except the “Pushed” value must be set to 1100. A right click on “Trigger camera now” should release your payload.

IV – Essential APM:Copter parameters to setup:

All parameters are describe in details in various APM:Copter documentation pages. We provide below a list of the critical ones for a delivery mission.

IV.1 – Failsafe parameters:

In a delivery mission it is most probable you’ll loose intermittently or permanently your manual RC control link and your GCS telemetry link. There are different setup choices of failsafe actions in these conditions but the obvious way to go is: “failsafe action and continue with Auto mission”.

In such a delivery mission you probably do not want the ship to land in the middle of the woods once batteries are exhausted. So the first obvious action is to double check your batteries are functioning properly and are fully charged. To verify your batteries are functioning properly and that all LiPo cells look good, we strongly advise to use a battery resistance meter (this check function is integrated in good battery chargers). The measured resistance of all battery cells should be around a few milliOhms and about the same value for all cells. If some cells have a significant higher resistance, do not use these batteries for such delivery missions! (use these batteries for bench tests or less hazardous uses). If a battery is puffed, do not use it!

About the battery failsafe action, you can choose ether for land or return to launch. It is a matter of opinion but I would advise in the context of such a delivery mission to use the return to launch action; it is indeed better to permanently damage your batteries than having your expensive ship landing in the middle of a forested area.

IV.2 – Geofencing:

Do setup the maximum allowed range (i.e. the radius of a circle whose center is the arming location) and altitude in accordance to the delivery mission’s profile. Doing so, check the RTL altitude to make sure it is higher than any obstacle on the mission’s path so that your ship will not return to home through trees…

During test sessions, try a geofence breach to verify it is working as expected. Geofence parameters and breach actions are setup in mission planner / config-tuning tab / Geofence menu.

V – Ground control resources and initial checks before launching the auto mission:

According to the topology of the terrain, the mission length, it might be required to organize more than one ground control team. At least a ground control station must be installed at departure’s location (“Home”). Its job will be to setup, verify and control parameters, ensure the ship is flying correctly in GPS mode before launching the auto mission. It will also ensure the returning ship lands properly.

A second team is organized at target’s destination. This second team will be given means to take over an eventual required manual control of the ship in case of emergency. This manual control can be direct or indirect via the home point’s team.

In this delivery mission, the remote team (at destination) keeps permanent GSM voice contact with the control team @home. Furthermore a video downlink is organized in such a way that both teams keep permanent video monitoring from onboard camera(s).

The ground control team is also responsible to check that the environmental conditions allow for a safe UAV flight. The following site : www.uavforecast.com is an excellent resource for doing so. It provides, per location, information about:

-wind speeds at the altitudes the drone will be flying. For AirbotServices X8 model, a maximum wind speed of 40km/h is fine.

-Kp satellite indicator, giving an indication of the GPS signals quality. It should be under 3.

-Visible sats : higher the better. 8 is a strict minimum. With a M8N, such as the one used on AirbotServices’s X8 model, a fix with more > 12 sats is the norm. It provides an HDOP around 1 ! (2 is the maximum for HDOP for flying an auto mission)

-Temps

-Cloud cover & eventual rain. You should not fly under rain and heavy cloud cover as this may produce important GPS glitches (and eventual material damages on your electronics if not at least IP67 compliant or above).

VI - Pre-flight/initial flight checks considerations:

The RC transmitter is used to launch the mission, by first taking-off in stabilize mode. This is indeed the only way to verify and “feel” that the ship behaves as it should. If during the short stabilize mode checkup, an unusual behavior and/or parameter(s) are noticed, mission should be aborted until problem is identified and fixed. If the stabilize phase passes successfully, the pilot switch for a short moment to “PosHold” mode. The objective is to verify that the GPS and compasses are working fine. If PosHold is not behaving perfectly, abort the mission. And again identify and solve the issues before launching the auto mission.

If Poshold phase has passed successfully, then the pilot may switch the ship to Auto mode, where the delivery mission really begins with the first waypoint, etc.

VII – Mission execution and results:

As shown in the attached youtube video above in this post, the mission was very successful, especially in a surprising target drop location’s precision, under a meter. This might be due to simple luck but certainly partly due to the use of a high precision GPS based on a M8N Drotek model which has an extra-large shield of 8cm x 8cm which is totally compliant to Ublox’s M8 GPS chip ideal antenna configuration.

Tags:

AirbotServices

Autonomous

Pixhawk

Arducopter

APM

How to power an APM drone : a practical build blog

bendev — Fri, 13 Jun 2014 08:59:50 +0000

Figure 1: general wiring diagram for an 8 motors
& APM drone

Practical build blog: powering your APM drone

1. Foreword & Introduction:

I would like to introduce a build blog on a critical aspect of a drone’s assembly: how to power your drone & APM. The objective of such a build blog is to be practical. Wherever possible in this blog links will be provided to get the described components. This blog is merely a synthesis of gathered advices I received from many helpful people within this drone community (particular thanks to Randy, Bill, Forrest and many others who taught me lots and are still teaching me lots of stuff)

As a topic I chose “Powering the APM” as it is in my opinion one of the most critical aspect you should care for in assembling your drone. I’d probably be not too far from the truth if I said a majority of drone incidents & crashes are related to power issues or bad wiring/testing (brownouts, wiring mistakes, ground loops, wrong voltage/amps dimensioning, etc.).

The blog does target people at early stages of drone build’s learning, like the state I was in a few months ago. It was very hard to find all bits and pieces of information to get a global detailed picture. Let’s hope this blog can help others in their build.

This blog will be written in successive posts as it is a fairly long subject and my time is quite limited. It will also allow others to interact and add complementary input between my posts; to be enriched progressively.

2. Powering an APM Drone: Objectives and Constraints?

Cf. figure 1 above illustrates a general wiring diagram for powering a typical drone. It illustrates 8 motors and ESCs but would remain applicable for fewer motors (battery voltage would probably go down to 3S or 4S for quad motors).

First, what are the objectives ?

-As illustrated in figure 1, a first objective is to power ESCs and associated motors with a high power source in terms of amps/volts, able to sustain the maximum throttle consumption and voltage required by the motors and propellers configuration (with a margin is even better). A good way to dimension this for your own setup is to either measure real values on a test bench (not so practical because it implies you would already know what to do and what pieces to buy), or more practically to use an online tool which is not so bad to give rough estimates here : http://www.ecalc.ch/xcoptercalc.htm?ecalc&lang=en

Another good information source about motor testing is an excel sheet with test bench measurements done by Forrest. Forrest, if your read this, could you post your excel sheet please ? Thx.

The eCalc tool asks you to enter your number of motors, the all up weight of your model, the battery type, the ESC capacity in amps, the motor’s brand and model, propeller’s type and model. You then click on calculate and the tool displays at the bottom 5 results columns. The most interesting columns for our exercise are “Motor@maximum” and “Motor@Hover”, because it will give you the consumed amps at maximum and at hover, the voltage and throttle % to hover (ideally should be at 50%). If you are under dimensioned or over dimensioned (under optimized), the tool will display some warning messages. The tool allows you thus to check that all the parts are dimensioned correctly to function together. For example, assume the tool tells you that your hover power consumption is X. However your motor’s maximum power specification is Y. Verify that X < Y. If not change the motors or use smaller props or lower pitch props (same verifications to do with max amps, max volts, max RPM, etc).

I have used this tool to produce a table for a particular motor brand, RC tiger motors here: http://www.diydrones.com/group/arducopterusergroup/forum/topics/tiger-motors-propellers-combinations-for-an-heavy-lift-octocopter?xg_source=activity

-A second objective is to power all other components that are not part of the high power gear, namely APM and all other bits and pieces around it: a receiver, a telemetry unit, a GPS/compass module, etc. Optional servos that are require to power for gimbals for example ARE NOT low powered items; they CANNOT be powered through APM but must be powered directly from the high power source (via UBECs). As far as electronics is concerned, the objective is to feed a very stable and reliable power source at 5 volts (there may be other specific FPV/OSD components that require other voltages such as 12v or 7v but I exclude these components from this blog for now). This second objective seems apparently easy to reach but it is actually a very sensitive and tricky one as we will see in more details later.

Second, what are the constraints ?

We want to reach above described objectives within constraints:

-The power chains must be reliable and as light as possible (typically if we can use the main battery for everything, it will be lighter than if you need a separate battery for every component).

-There is better one main battery as the power source for everything (which avoids different ground references, avoids potential ground loops, makes your build lighter). So we have a constraint to split the power chains to different voltages/amps (main voltage for ESCs and motors, and 5V for APM and associated electronics). These LIPOs are power monsters people should be aware of: they are capable of delivering very high amperage (e.g.: more than 100 amps in my X8 drone application) at a set voltage between 3S (11.1V) and 6S (22.2V) for most drones. If you make the math, we speak here of order of magnitudes of between 1 to a few kilowatts of power!

There is a link you may consult about batteries common brands discussion here: http://www.diydrones.com/group/arducopterusergroup/forum/topics/6s-battery-comparison-on-some-most-common-brands-turnigy-zippy?xg_source=activity

-The main power source must feed high amps and high voltage to the ESCs+motors. We have a constraint to measure both amps and voltage fed to the whole drone as it is a critical piece of information you want to check continuously on your GCS (or goggles) while flying. It would be insane to fly without such real time information, as you do not want to let your copter fall out of the sky once your battery becomes empty.

An assembly constraint is thus to wire every bits and pieces in such a manner that your current and voltage sensors measure the TOTAL (SUM) of all amps consumption. If you use two batteries , do obviously not connect your sensors after one of the two batteries. Another classical mistake is to connect items pumping current and voltage from the sensors wires!

Avoid connecting items in such a way you create ground loops. Connect everything in a STAR topology, with the center of the star connected right after the current/voltage sensor on the high power leads/wires. As it is difficult to visualize your wiring in the practice, make a wiring diagram of your connections and check it out (like I did on figure 1 for example)!

As you will notice on figure 1, I kept a ground loop with the ground wire of the Attopilot module, but it is impossible to connect otherwise. It is one of the weak point of Attopilot sensor usage, unfortunately. Some posts have been done about this here : http://www.diydrones.com/forum/topics/attopilot-volt-current-sensor-significant-parasitic-ground

-At the same time the main power source must be derived to feed a set of sensitive electronics at 5 volts. APM has a constraint to be fed at a voltage between 4.6V minimum and 5.25V maximum. If you are below the minimum voltage, your APM will brownout. If you are above you will fry APM. However it is not so easy to get a stable 5V source as the load varies. Take a look at the picture below that illustrates how unstable an APM 5V power source could be (and there is even worse):

Figure 2 : Bad Vcc illustration

Figure 2 shows a 5V power source from a switching BEC regulator. The measured voltage on this BEC was 5.14V unconnected. We observe from this log picture that once connected the voltage immediately drops down to 4.9V which is not good. Further a strong variability of the voltage between 4.6V and 4.9V is observed. This brings the voltage close to the power limit of APM’s power requirements with a risk of brownout. We will see later in this blog how this problem was solved.

3. Tested solutions to fulfill powering objectives and constraints:

3.1-Battery solution:

For the main battery, I chose a dual battery setup to reduce total cost of ownership (and increase max amp capacity). In an objective to increase flight duration to the maximum I looked initially at high capacity batteries such as maxamp 12.000 mah or equivalent from other brands. In a 6S voltage these batteries are awfully expensive (sometimes more expensive than a complete 3DR RTF kit!). Therefore, I found best for me to use two smaller 6000mah batteries. It weighs the same or even less than a 12.000 mah battery, it costs a third or a fourth of the price if you get a turnigy nanotech or zippy brand. There comes a physical challenge to install multiple batteries on a drone without ruining your possibilities to attach a camera gimbal underneath, and without ruining your possibility to use a protective dome for electronics on top. So for my octoquad, I’ve custom cut a dual battery holder CF plate that screws on the center plate, providing two side platforms left/right to fix the two batteries (thx VulcanUAV for their help!):

It looks like this once assembled on the drone’s frame:

After choosing the battery , we need to think about how to wirre in a STAR TOPOLOGY.
I found the easiest way to do this was to use a power distribution board, like this:

I personally chose to use a 250 amps capacity power distribution board from VulcanUAV here : http://www.vulcanuav.com/accessories.html

It is much better and safer than using cable solutions, for example like this:

3.2-Power distribution board

I will now start to detail this power distribution board, based on figure3:

Figure 3 : Power distribution board placement assembly

Part 2:

Figure 3 shows the different elements you should have on your power distribution board. I have numbered them on the picture for easier reference.

-Fig3 n°1: Attopilot circuit. The attopilot is a small pcb circuit to measure current and voltage,

You can find it at sparkfun in the US, or here in Europe: http://www.buildyourowndrone.co.uk/AttoPilot-90A-Voltage-Current-Se...

The illustrated version is the 90 amps attopilot. There exists also a 180 amps version. In practice, the attopilot is made so that the current sensor pin (I pin on the attopilot board) outputs a voltage between 0 and 3.3V (3.3V would mean 90 amps are measured on the I pin). This I pin is connected to an APM A2 sensor pin (see figure 1). APM measures on a scale between 0 and 5V. This in fact gives a possibility to measure a maximum current of more than 90 amps, that is (5x90/3.3)=136 amps maximum.

136 amps is largely enough for most drones. Otherwise you have to take a 180A Attopilot version. Do not try to oversize your attopilot circuit because you would loose in measurement’s resolution (precision).

As you see on Fig3 n°1, I tried to keep the integration of the attopilot module between the main battery leads and the PDB as compact as possible. This means it was impossible to use shrink tube to wrap the Attopilot and connections, because the wires being so short do not allow you to solder and place at the same time a piece of shrink tube between Attopilot and PDB. How to solve this? Use Plastidip:

http://www.plastidip.co.uk/eStore/index.cfm?Plastidip_Junior_Can_25...

It is a liquid plastic/rubber material that you apply with a brush on your parts. You can also dip your whole circuit in it. After drying (it does dry fast), the coating really shrink tight on the covered element. It makes a really nice alternative to heat shrink.

Note that you can choose where to position the different elements around the PDB. I specifically positioned the two main battery leads with the attopilot circuit on a position corresponding to the back of the drone. This will avoid battery wiring to come in front of the cameras I will use.

It is a good practice to mark with a permanent marker every useful information on the different components. For example, indicate with an arrow where the front is, number all of your motors/ESCs, etc.

-Fig3 n°2: the switching regulator to feed APM. You need a switching regulator that will be robust and reliable and that provides a stable 5V to APM, even under load. APM uses a few hundreds milliamps at most, so you do not need to feed APM with a 3A or 5A power source.

There are different types of switching regulators. Not all are good for APM.

Initially, I tried these Polulu switching regulators which I DO NOT recommend because they produce a very unstable 5V voltage on APM. I tried two models, one with fixed 5V output and another one with adjustable output: polulu 2107, polulu 2103.

It is a pity because they would be extremely compact and have nice theoretical features : takes an input voltage between 7 V and 42 V and efficiently reduces it to 5 V while allowing for a maximum output current of 600 mA.

However the 5V result on APM is dangerous, as it provides a highly fluctuating voltage down to 4.6V (although the circuit was tuned to produce 5.14V unconnected):

Bad Vcc instability

Instead I found an even cheaper circuit that works much better. It is this one: 12W Step-Up/Step-Down Converter 3-35V Input, 1.2-30V Output (adjustable) with 2amps max at 5v.

A 2A (5V output) can be achieved without additional cooling, the efficiency is up to 90%, the switching frequency at 150kHz. The module is protected against short-circuit (10 seconds), but not against reverse polarity.

And best of all, it costs only about 7$ (5€) !

You can find it on ebay or here: http://www.lipoly.de/index.php?main_page=product_info&cPath=880...

It uses the Texas Instrument LM2596 switching regulator circuit. The data sheet can be found here:

http://www.ti.com/lit/ds/symlink/lm2596.pdf

And it produces the following excellent 5V stable results on APM, even under load (with 3DR telemetry, GPS module, Receiver module, two LEDs, a buzzer connected and fed by APM):

Excellent Vcc stability

This switching module is ready to use out of the box (which is not the case of the Polulu because you still need to solder a capacitor on it). You just need to solder the wires that will connect to the PDB on one side, and on the other side you solder the two wires that will go on APM.

You will notice in Fig3 n°2 that I twisted the two wires that will connect on APM and used a ferrite ring. You will also notice that I did not twist the last two inches or so of these wires that will connect on APM in order to have minimum vibrations transmissions to APM through the wires (when you twist the wires they become more rigid and they transmit more vibrations).

Part3 :

-Fig3 n°3 :

Number of all your ESCs with a permanent marker. Place them around the power distribution board before assembly. The order of the ESCs must match the motor positioning as defined in the wiki. It depends on your setup: a quad, a X8, a hexa, etc.

Also mark the spot on the power distribution board where the ESC will be connected to.

-Fig3 n°3bis:

To limit electromagnetic disturbances to the maximum, use as short as possible power leads between ESCs and PDB. Some people prefer to use bullet connectors between the ESCs and PDB . I prefer to solder them directly on PDB as this is a much more secured way to avoid bad connections or even disconnections in flight (vibrations do wear connectors)!

Define very carefully what the length of your ESCs power wire should be BEFORE cutting them. For example if you have a folding frame and you need to flip arms, maybe you would need a bit of wire slack.

In my case I decided to use the aluminum arms as heat radiators for the ESCs. Therefore I need to glue the flat face of the ESC (the face corresponding to the integrated aluminum plate) on the arms. That meant that I had to twist the power wires on 4 out of the 8 ESCs (see figure 3).

-Fig3 n°4:

You should use only 4mm bullet connectors (or bigger diameter) to connect your motors to the ESCs. Nowadays, most ESCs and motors are delivered by default with smaller bullet connectors. They are very dangerous to use when too short and too small as they really could disconnect in flight due to vibrations or by accident if a cable is pulled a bit too much. With 4mm, they are perfectly fine.

Also BEFORE you assemble your ESCs and motors, number each of the three ESC wires according to the corresponding motor number. I reuse the same numbers as defined in the wiki, depending on the frame type. Also use three different c olors that will match the same colors on the motor’s leads. How do you do this ?

Take each motor individually and its corresponding ESC (they will be marked with the same number). Then plus the motor to the ESC, connect the three signal wires of the ESC to a receiver on its throttle channel, which is normally channel 3 in Arducopter (the receiver will be powered by the red & black wires), power the ESC with the intended battery. Turn on the radio and give a bit of throttle to check the rotation direction. If it does not match the direction as defined in the wiki for this motor number for this type of frame, then swap two of the three ESC-Motor wires. Check again. Once you’ve got the intended rotation direction, mark each of the three ESC-Motor wire with an identical color.

Repeat the procedure for each motor. After that you will have everything that is needed to assemble your drone without risking a bad connection or a wrong ESC-Motor wiring.

-Fig3 n°5:

Number five shows one of the ESC’s signal wire. I have cut the red and black wires as they are not used in the wiring diagram shown in figure1. You should do the same and not connect the red and black wires of the ESCs to the APM output rail (see figure1). Not only it would be dangerous to do so electrically speaking, but it brings the additional advantage of having a tidier wiring with less wires.

Mark with a permanent marker on each of the ESC’s signal wire (orange wires on figure3) with the same number as the motor number they correspond to. Indeed if you forget to do so, once you will have assembled the center frame, you shall not know anymore which wire is which to connect on the 8 APM signal outputs.

-Fig3 n°6:

Also mark precisely what is the front of your drone. This is important to optimize your cables placement. For example, I know that I should position the two XT90 battery connectors at the back of my center plate. The placement of your cables depend on your particular frame and how you’d like to pass your cables though the frame plates up to APM. This is why marking the frame and PDB orientation is important.

Indicating where the front is is also important to place your motor/ESC numbers at the right place (as defined in the wiki depending on your particular frame type).

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