Ethan Ferrell's Posts (4)

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I'm starting to see tri-copters becoming more and more popular, so I'm asking the DIYDrones community if there is any interest in making a tri-copter frame that has interchangeable parts with the quad-copter frame.



I've put together a rough draft of a 2D laser cut sketch of a possible main board and carrier board. I think the only thing that would require some change other than the two boards would be the dome ring. The rest of the parts should be the same, and we can even use the standard quadcopter power distribution board too. I'm not very good at 3D modeling, but I'm hoping this could be a community effort.



And here are the 2D Illustrator files:

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It’s been awhile since my last build log post, but I’ve covered a large milestone. See my previous posts:


UAV with Chumby Hacker Board – Configuring a CHB

UAV with Chumby Hacker Board – Frame & Material Selection


Following up on my last post, my plastic pieces were ordered from Ponoko: two main plates made out of 3.2mm white Delrin plastic, and the carrier boards, motor mounds, and battery mount from 2.3mm white Delrin. I enlarged all but the motor mounts in order to scale up the size of the carrier boards to cleanly fit a Chumby Hacker Board (CHB). One addition I made to the main plates was adding a set of extra holes (inner holes) to line up with the standard power distribution board. I also used the standard 28cm by 14mm square tubes for arms.



The battery holder was enlarged in order to use the outer set of holes so that it wouldn’t get in the way of the power distribution board using the set of inner holes. I went through Hobby King’s stock of 3S 25C LiPo batteries to find approximately 5000 mAh while keeping it as light as possible. I picked out two Rhino 2350mAh 3S1P to tie in parallel for a total of 396 g. I can use only one battery if weight ends up being a problem.



The power distribution board from fits right in between the two main plates. As you can see from the image below, in order to make it fit I replaced the right-angled pins with a connector. I’ve read that some people have issues with the power distribution board causing interference with the compass, so this should alleviate it a bit by putting more distance and plastic between the two.




I still used a 10mm standoff from the main plate to the first carrier board to leave some clearance for Velcro. On the first carrier board lays the APM+IMU+Magnetometer and the radio Rx. I went ahead and ordered a sample of the Tempur-Pedic mattress foam and sliced it roughly 7.5 mm thick. If you haven’t found the thread on here, you cut it by freezing it and then cutting it with a bread knife. It may take a few rounds because it ‘thaws’ quickly.




The next carrier board up has the CHB, GPS, and XBee. I just completed building it so I haven’t fully tested to see if there is too much interference with it being close to the GPS unit. The CHB requires 5 volts so I use the DE-SW050 regulator tied to the distribution board. I also got the GPS connected via FTDI to the CHB for my WiFi stumbling project. 



Here is an approximate weight breakdown…

CHB+5vReg+WiFi: 57g

APM+IMU+Magnetometer: 42g

GPS: 8g

XBee+Adapter: 10g

Radio: 18g

ESC+Motor+Prop (x4): 332g

Frame: 418g

Total Weight without Batteries: 885g

Battery (x2): 396g

Total Weight with 2x Batteries: 1282g


Here is a zip with my EPS files I sent to Ponoko:


Things I’ve learned:

One mistake I made throughout this project so far was not ordering enough parts the first go around. I eventually found that Amazon sells bags of 100 M3-.5 nylon screws and nuts that work perfectly for about $6 per bag, which is the cheapest route for hardware I’ve seen in you live in the US.


I also learned that the Deans Ultra plug connectors and I don’t get along well. I ended up going to Radio Shack in a fit of rage and bought a bunch of 2 pin Molex connectors that work really well.

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3689392714?profile=originalFollowing up on my first post here, I have moved on to designing the airframe that will carry my Chumby Hacker Board.

I am by no means a mechanical engineer, and I have no experience with aircraft design. I decided to stick with the DIYdrone’s model quadcopter since it is open sourc. No offence to bunnie, but the Chumby Hacker Board is rather large in comparison to the APM and Oilpan. It would fit on the standard size carrier board, but it would cover up 2 of the 4 holes for the screws. I imagine it would make the plate pretty unstable so I enlarged the main plate and carrier board to fit.

Doing some rough comparisons between images of other quadcopters and my enlarged pieces, I don’t believe there will be any conflict in attaching the standard dome and landing gear to the arms. If anyone is willing to confirm via 3D modeling, I’d appreciate it.

I decided to use the Ponoko to laser cut a single main plate to see how the service and materials were. I chose 3.2mm Delrin plastic for the main plate and I am very pleased with it. It is very rigid and durable. I am thinking I could probably go with the 2.3mm sheet for the other pieces. It does not feel like it would crack or shatter like acrylic would in a major crash. The main plate weighs 53 grams. As for price, it was about $20.00 USD for the materials and labor, and Ponoko charged another $9 for shipping. A little pricey compared to other options, but I think it is a pretty good balance between durability and price. I will be submitting my order for the rest of the carrier boards and plates soon—all made from Delrin.


Here are some photos of the main plate:




Here are the EPS files for the enlarged plates:



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Others have asked about my project so I've decided to post as it progresses. What I am attempting to do is send a Chumby Hacker Board up on a UAV to map wireless networks. This method is much more convenient than driving along in a car. I've broken this project into few milestones.

* Get the CHB setup to scan and dump wireless networks.
* Build a drone, since I have never done so.
* Mount the CHB along with APM and all the needed electronics on the drone.
* Split the GPS connection to the CHB.

First, why I chose the Chumby Hacker Board? Well, to be honest it is the cheapest Linux computer I have seen small enough to fit on a small drone. I've looked into Gumstix, but they are far too expensive in comparison. CHB is also extremely ecofriendly--more like battery friendly. Gumstix are much more powerful and thus use more energy. Pico-sized motherboards would have the same problems as Gumstix, and to a much higher degree. I will post again on each of these sections as I work on them.

Setup for the CHB
The CHB comes with 3 USB ports, which is the perfect amount if there are plans for 1 wireless module, 1 USB GPS connection, and 1 USB APM connection. For the wireless module I chose something that uses the RT73 driver. I found the D-Link DWG-122 to be very cheap and nicely made because there is a small U.FL connector for an antenna built right on the board. I found some refurbished DWG-122 on eBay for about $8 each with free shipping.

I set up my CHB using the serial connection (FTDI). I compiled all of the tools from source on the CHB itself using a USB drive to transfer the tarballs. The tools you will need are: falconwing compiler for CHB, perl, python, openssl, aircrack-ng, libnl, pkg-config, iw, and for fun, elinks. The falconwing, perl, python, and libnl can be found on the CHB source list ( and everything else can be found on their respected websites.

In my opinion, the CHB partition structure is a bit whacky, and there are tutorials on how to “fix” it. I didn’t bother with it because I think that if you need to “fix” it, why is it shipped like that? So I just worked with the structure installing everything to /mnt/storage, which is the microSD card.

Here is a complete log of how I compiled them all:

#set filesystems from read-only to read/writemount -o remount,rw /

#set the date and time
date -s "2011-01-31 20:58"

#extract Perl binaries
cd /mnt/usb
tar xfz usr_arm_ext3.tgz -C /mnt/storage
#create a symbolic link to the storage directory for binaries
ln -s /mnt/storage/usr /psp/usr

#add the symbolic link to the global PATH variable
export PATH=/psp/usr/sbin:/psp/usr/bin:$PATH

#extract Python binarries (appears to actually be 2.6.3 --whatever)
tar xfj python_chumby_2.7.1.tar.bz2 -C /mnt/storage

#copy and extract toolchain from silvermoon
#might work for falconwing, not sure yet (it should)
#cp /mnt/usb/ /mnt/storage
cp /mnt/usb/ /mnt/storage
cd /mnt/storage

#move back to usb and extract openssl
#NOTE: aircrack-ng uses functions that were deprecated in openssl v 1.0.0c
#Use version 0.9.8q
cd /mnt/usb/
tar xfz openssl-0.9.8q.tar.gz -C /mnt/storage

#move to openssl-0.9.8q and config
cd /mnt/storage/openssl-0.9.8q/
#use the prefix to store the binaries on /mnt/storage in order to not modify /usr
#plus, there probably isn't enough room on /usr unless the partitions have been
#successfully modified
./config --prefix=/mnt/storage && make && make install

#move back to usb and extract aircrack-ng
cd /mnt/usb/
tar xfz aircrack-ng-1.1.tar.gz -C /mnt/storage
cd /mnt/storage/aircrack-ng-1.1
#first, the common.mak file needs to be edited
vi common.mak
#now change the following line
-I/mnt/storage/openssl-0.9.8q/include/ -L/mnt/storage/openssl-0.9.8q/
#this points to the openssl headers for compilation
make && make install DESTDIR=/mnt/storage
#add the new bin dirs to the PATH variable
export PATH=/mnt/storage/usr/local/bin:/mnt/storage/usr/local/sbin:$PATH

#libnl (netlink library) from Chumby sources, a dependantcy of iw
cd /mnt/usb
tar xfz libnl-2.0.tar.gz -C /mnt/storage/
cd /mnt/storage/
./configure --prefix=/mnt/storage && make && make install
#set the PKG_CONFIG_PATH variable for iw
export PKG_CONFIG_PATH=/mnt/storage/libnl-2.0

#pkg-config is also required for compiling iw (detects the version of libnl)
cd /mnt/usb
tar xfz pkg-config-0.25.tar.gz -C /mnt/storage/
cd /mnt/storage/pkg-config-0.25
./configure && make && make install

#now compile and install new iw-0.9.22.tar.bz2
cd /mnt/usb/
tar xfj iw-0.9.22.tar.bz2 -C /mnt/storage
cd /mnt/storage/iw-0.9.22/
make && make install DESTDIR=/mnt/storage
export PATH=/mnt/storage/usr/sbin:$PATH

#elinks web browser (optional)
cd /mnt/usb/
tar xfz elinks-0.11.7.tar.gz -C /mnt/storage/
cd /mnt/storage/elinks-0.11.7/
./configure --prefix=/mnt/storage && make && make install

Now you’ll want to create a boot up script to start up airodump-ng when the CHB starts up. The CHB uses the path /psp/rfs1 for boot up scripts. It will automatically start the script if you name it userhook1.

Using this blog post ( you can convert the dumps from airodump-ng to a format that Google Earth will recognize. This conversion can and should be done on the ground using your UAV to harvest the data.
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