MicroQuad Rev 2.1 PCBs

I received the Rev 2.1 PCBs from Advanced Circuits.  Most beautiful PCBs i’ve ever seen!  Well, that I’ve designed myself…  Anyway, I had to order a new set of ultra low dropout regulators since I lost the first ones I ordered – literally tore apart my room trying to find them.  A fresh MPU-6050 Rev C silicon and fresh BMP085 also got soldered on.  Going to get ahold of some Amtek solder paste (per recommendation of Limor Fried, Ask An Engineer).  Speaking of which, I won a Chumby NeTV on the trivia question!   Arrived yesterday, will upload pics/post soon.  Erik Noren will be next to win (thanks for the karma).  Back to the PCBS, I hooked up the LDO, had a bit of debugging to do with some pesky capacitor shorts, but now that everything is talking it’s time to get started on the code.  In the payload I’ll have to interface to the MPU6050, BMP085, HMC5883 (all I2C), Adafruit Ultimate GPS versions 2 & 3, Copernicus II GPS, SFE OpenLog, and the ERA900TRS radio (all RS232).  The box interior can be incredibly small, only 5×5″ because i can stack all the electronics pretty tightly.  Batteries will be 3 Energizer Ultimate Lithium cells (3000mah = at least 24 hours of continuous operation).

From top left clockwise, Ultimate GPS v2, OpenLog, V2.1 PCB, Rick Winscot’s EasyRadio breakout, and Ultimate GPS v3.

 

Copernicus II GPS on the bottom

 

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Antenna Test Success

I finally got out to test the antennas, went about a mile line of sight with no issues!  I got the PC drivers for the development kits from LPRS sorted out after a few emails.  The connection is only one way after they antennas get about a half mile apart, but it’s a solid link!

Dev board hooked up to the receiving helical, feeding into the EasyRadio Companion software.  This was a test of a few hundred yards, my dad was on the transmitting end at the top of the hill.

 

1 Mile test, receiving at the top of the hill, my dad at the very end of the road at the top of the picture.

 

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LENSE v2

Another update on my HAB project.  I’ve been working on the radio system for the past month or so.  Mainly I built two antennas that were capable of reaching the required 50 mile or so range. When I first started researching the required antenna specifications, I was extremely confused by all the different measurements and types of antenna.  This is where talking to a real expert can be awesome.

David Patterson of Edge Research Lab kindly assisted me in figuring out all the fine details of making my antennas and design considerations I needed to take into account.  After an exchange of emails, the feasibility of this radio link hinged on a line of sight connection and a high gain antenna setup.  For starters the antennas have to be circular polarized so the spin of the payload does not cause any loss or noise from signal bounce.  Additionally, the recieving antenna must be high gain to capture the weak signal, while the transmitting as omnidirectional (low gain) as possible to broadcast the signal so it can be picked up from all sides of the payload.

Specs of the receiving helical:

  • 4.15 inches diameter drain pipe for the former
  • 8.5 feet in length
  • 30 turns of 1/4″ copper pipe
  • ~30dbi gain
  • HPBW of 20 degrees
  • Ground plane reflector is 10 inches in diameter 3mm  below the last turn of the helical
  • Soldered on to the first quarter turn is Alex Greve’s (IBCrazy on RCGroups forums) waveguide impedance matching strip; the bare helical measures about 140 ohms, this should match it to the radio’s 50 ohms.

The cloverleaf is based off this design by Alex Greve.  I had to enlarge it for 900mhz dimensions, which made the construction a bit more difficult than for the more common, higher frequencies used in RC aircraft.  I used 12 gauge solid core copper wire for the lobes, carefully soldered to RG58 coax.

One of the snags I hit was the RG58 I had on hand was part of a SMA cable with too-large connectors.  Thus i had to order a properly sized one from Digikey, but ended up destroying part of it in the process.  Turns out the center conductor is not mechanically fastened, so when i tried to strip the cable it pulled out and rendered it useless.  That night I scrapped a few of the stock dipoles that came with the EasyRadio modules, soldered the SMA connectors onto a fat length of the RG58, and built the cloverleaf on that.  I had to build a jig to hold the wire lobes in place while I soldered, then covered the joint in hot glue.  Both antennas are right-hand circular polarized.

Camera

For this launch, I’m going with my Canon SX210IS.  I loaded and tested the CHDK build for it, works like a charm.  I did some battery life tests and the intervalometer took 1400 images on a 10 second interval.  It’s pretty large but has good specs and I don’t want to buy another camera.  The only reason I’m not using the SX110IS from last year is the screen has broke and I want a few more megapixels and sharper images.  I took apart the zi8 that failed last year, might include it if I can get it to record 30 minute clips with the pic32, but at the moment it seems like a lot to work with.

Payload Container

I’m using the same 1.5″ thick pink insulation board, in an 8x8x6 inch cube.  The interior dimensions are a lot smaller and the payload a lot lighter.  On the bottom will be a hole drilled in the center for the cloverleaf antenna to poke and rest on the bottom.  Since the antenna is fragile, It will probably be covered in a plastic Tupperware for protection.

Flight String

I bought another 1200 gram balloon from Kaymont, and the smaller payload (under 1.5 pounds I hope) should allow me to reach 100,000 feet and higher quite easily, while maintaining a high decent rate.  The parachute is a 48″ from RocketChutes, same one I used last year with great results.  Some 1/8″ nylon cord will finish off the flight string.

Telemetry

The ERA900TRS modules should provide two-way communication the whole way, but I have the SPOT II onboard as well.  It tested well on the first launch.  It only sends a GPS locatin every 10 minutes without altitude, and cuts out above 60,000 feet, but keeps transmitting when it gets below 60,000 feet again.  Hopefully on my third launch I can omit this and lighten the payload further.  Sensors onboard will include a Copernicus II GPS i verified on my first launch, two versions of the Ultimate GPS, BMP085 barometer, and maybe some MEMS devices if I have time to hook them up.  Temperature is measured by the barometer and radio, as well as the MPU-6050 also onboard.

Testing and Launch Date

I plan to launch in eastern Washington on September 22nd.  This past weekend I attempted to distance test my antennas, but the easyRadio software wouldn’t cooperate with my laptop although we tested it successfully last weekend.  Troubleshooting isn’t fun :(

Sponsors

Low Power Radio Solutions has kindly donated lots of time and radios for my project.  The EasyRadio modules are very nice to use and I got them up and running quickly with my uController.

Adafruit Industries also donated several Ultimate GPS breakouts, and have been helpful to my questions when I go on the weekly Show and Tell.

Many thanks go to David Patterson at Edge Research Lab for helping me with the whole RF system and sending me a Airview9 spectrum analyzer and Rick Winscot who helped me get the EasyRadio modules online and donating a few breakouts to LENSE.

Hopefully my next post can include some test results and pictures of my PCBs when they come in!

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MicroQuad Update #7

I have mentioned before that the controller for my microquad project doubles as the controller for my high altitude balloon project.  Since I have set a launch date for early September, I have decided to put aside the quadcopter project for the next few weeks and focus on the launch.

That said, I have been revising my PCB and finally received some new ESCs and props from HobbyKing, some 2.5×1 props and 4 more ESCs to replace the hokey ones I’ve got.  Changes to the PCB include:

  • Removal of the TPS61200 boost converter.  It never played nice with my other components
  • Removal of the USB hosting port.  I decided to use a very small bluetooth module instead
  • Addition of the TPS73233 ultra low dropout linear regulator.  3.3v, 250ma, and 40mv of dropout
  • Addition of the OSHW logo!  I’m going to get these files on GitHub soon.
  • Fixing the MPU-6050 layout.  I had a capacitor on the charge pump that wasn’t working correctly and some mixed up pins.
  • Fixed/new GPS chip antenna layout.  Running antenna feed lines through vias isn’t a good idea.  I decided to mount the antenna on the bottom of the PCB, as if it was radiating into the ground.  But, I cut a slot underneath it and mount the radiation pattern showing through the slot and up towards the sky.  This should give a better signal.

A few changes

 

When i order Rev 2.1 I also want to get it from Advanced Circuits instead of SeeedStudio.  Hopefully it will take less time to get the boards back.  Also, I’m waiting on some 50 ohm coax cable I should get on Monday, there will be a big post about that!

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Film Rolls 1-2

Finished my first two film rolls.  Shot on a Nikon FE with 50mm f1.8 series E lens and Fuji Velvia 50 film.  I shot these at the glass sculpture museum in Seattle, a hike on the San Juan islands, and a small town in Kansas during my cousin’s wedding.  They were developed by Panda Photographic Lab in Queen Anne, then scanned by my not-so-good Wolverine scanner that managed to redshift most of the images and add some fuzziness.  I’m trying to get a  Canoscan 9000f or similar and get some real results.

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Radios Galore

Always a nice day when a package arrives!  Yesterday I received two EasyRadio modules from Rick Winscott.  I was on the Adafruit Show and Tell with him two weeks ago, he was showing off his Arduino breakout and said he’d send me a few to test with my upcoming balloon launch!  They are Easy Radio 434Mhz transceivers, came on a nicely laid out and socketed board complete with LEDs, a short dipole and a robust SMA antenna connector.  The 434Mhz version touts a 10mw of transmit power, which doesn’t sound like a lot.  But with the right antennas and line of sight transmission, a 10mw signal can easily to 20 miles or more.  Rick recommends something like a full-wave dipole antenna for the best reception.  Thanks Rick!

Nicely made board!

EasyRadio 434Mhz modules from Rick Winscott

I also picked up two Bluetooth demo kits.  One is the SmartRF05 EVB from Texas Instruments (the new Bluetooth LE modules) that came with two large dev boards with tons of capabilities.

Both dev. boards, antennas, and the USB module

Bluetooth LE dev Board from TI

The BT LE radio daughter board

Also is a small USB dongle that I may use for my MicroQuad if I don’t use the other Bluetooth kit i got, a very small RF256xT demo kit also from TI.  It features some extremely small breakout boards with Panasonic accelerometers, a USB interface dongle, a battery adapter board, and a demo program that lets you play Tux Racer wirelessly using the accelerometer!  Tons of fun, alleviated some boredom at school.  The second, smaller kit is only normal Bluetooth, but it is in an easier to use package with the USB interface dongle.

RF256xT modules from TI

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Future Project: Prosthesis

Prosthetic arms have been done before, I’ve been thinking about them for years.   I decided there was plenty of research in that field, and with Dean Kamen’s “Luke” prosthesis I thought there would be much faster advancements.  As it turns out, there is still need for a cheap, dexterous robot arm that can more easily act like the human hand.  Recently on Adafruit’s blog they posted this article, concerning a student who made his own robot arm from the shoulder down that could pretty accurately complete human gestures.  I saw some robot arms that use a big row of servos for each finger, and each finger in the joint is not controllable; either every digit in the finger flexes or none of them do.

My thinking is that instead of using a row of clunky servos, what if there was a small linear screw-drive motor for each joint?  Say three joints per finger, that’s 15 motors, plus a rotate motor for the thumb and pan-tilt head for the wrist, that’s 18 joints.  And if I could find a sufficiently small motor, I could house all the joint mechanics within a shape much closer to the human forearm.  The Screw-drive mechanism would allow much greater gripping strength, since threaded rods aren’t easily back driven.  Also, little if any power would be required to keep a grip.  This is unlike servos that face a rotational force, causing them to always exert force and maintain position.  With the direction of travel at an angle this problem is much less of an issue.

As for controlling it, one project i have always wanted to try is to rig up a set of pontentiometers or bend sensors to actively measure the joint angles of my arm, then duplicate them on the prosthetic.  Also, with a glove, I could possibly shake someone’s hand with a robot!

Still mulling this over, but it’s something I definitely want to try.

 

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