Hardware Projects

This section contains information about a few of my hardware projects.

MultiWii

I recently built a [Quadrocopter] model based on the [MultiWii] design. The thing is flying reasonably well in Acro mode. Stable mode needs more tweaking though. You can find pictures of the complete build process in the [MultiWii Gallery] !

 

Parts used:

  • The brain of the MultiWii consists of an Arduino Nano, the guts of a Wii Motion Plus and a Wii Nunchuk. A SparkFun Level-shifter for 3.3V was used, but is not really necessary. The receiver is a Jeti DUPLEX R7. (A five channel version would have done the job as well.) I also upgraded my Futaba T7CP (35MHz) with a Jeti TU2 2.4GHz module for this project.
  • The frame consists of 10x10mm square aluminium "tubes" with two single sided copper plated PCBs for stabilization, which are also used as power distribution boards. The top one is connected to Battery Minus and the bottom one to Plus. Hence the four cuts in the bottom PCBs copper to avoid shorting the battery via the mounting screws!!! The motors are connected via 2mm epoxy mounting plates to isolate them from the frame. Painted ping-pong balls form the landing gear.
  • The drive consists of four Keda A20-28M motors using Turnigy Plush 10A ESCs and a 3S1P 2500mAh 20C LiPo Battery-Pack. One of the ESCs is also powering the receiver and electronic. I currently use APC Electric 7x5 and GWS 7x3.5 3-Blade propellers. The APC propellers have a lot of power and are very silent. The GWS are noisier, but also much tamer with the default settings.

Tips & Tricks:

  • On my Futaba T7CP i had to revert the direction for channel 2 and 3 (Pitch and Throttle).
  • A small adapter for calibrating all four ESCs at once is useful. Calibration was done with endpoints set to +-100% (1900/1100ms) on the remote and afterwards changing them to +-125% (2000/1000ms) for the MultiWi firmware.
  • I used the excellent [eCalc:_propCalc] to select the propellers. Recently an experimental [eCalc:_xcopterCalc] was also made available.
  • I must say i was not happy with the quality of the Keda/LaserCut motors, but for their price this is to be expected: If you are short on cash i still strongly recommend to order a few motors extra. (I had to replace one motor which was a bit wonky and drew about 2A more current than the others. Also the threads in the motors for the aluminium propeller back-mounts are too wide and not very precise so the screws don't bite.) If you can spare the cash do yourself a favor and go for Hacker or AXI motors immediately.
  • Flip the axles right after you take the motors out of the box and use propeller clamps that are fixed on them. You'll anyhow have to do this, if you want to use Prop-Savers. Note that for the APC propellers you need special Prop-Savers, the blue ones that are delivered with the motors don't fit.
  • The RC RATE in the MultiWii 1.7 firmware has no effect on throttle, so i changed MAXTHROTTLE to 1785 which results in a scaling factor of 0,65. That way it is much easier to hold the Quadrocopter at a certain level with the powerful APC propellers. Programming a throttle curve in your remote only works if you still keep the endpoints at 2000/1000ms for starting/stopping the motors and calibrating Stable mode.
  • VBATSCALE was set to 123 based on the resistors i used for the voltage divider for the LiPo Alarm. Just use a voltmeter and the MultiWiiConf voltage display to find the right scaling value.
  • If you change the Acro mode trimming on the remote, you have to redo the Stable mode calibration!
  • Also note that replacing any sensor with a different type requires completely retuning the Quadrocopter PID setup. Just recalibrating does not work, as the sensor values are not normalized!
  • If you build a new Quadrocopter from scratch, i suggest to go with a BMA020 instead of the Nunchuk: People say it's better quality and also cheaper!
  • If you want to layout your own PCB for the electronic, consider using [DesignSpark PCB]. In my opinion it is much more user friendly than Eagle.

Next steps:

  • I must admit that i lost a bit my motivation, after having found out that a complete retuning is required when you upgrade any sensor and also for upgrading to MultiWii 1.8 Patch 2 version.
  • I got an ARM Cortex-M3 development board with an LPC1769 in the meantime. Maybe i keep the MultiWii Electronic as-is and make it a winter project to design a replacement board with the LPC1769, an BMA180 and a ITG-3200 sensor. The problem is of course having to write your own Quadrocopter SW from scratch. Still, it would be nice to have a Quadrocopter with a state of the art processor flying.
Alix UMTS-WLAN Router

This is not really a big hardware project. I was fed-up with my old dodgy WLAN-UMTS Router which kept resetting every other day, due to proprietary unreliable drivers and low memory issues. So in the end i decided to sort this out once and forever and bought an [ALIX6E2] board together with a WLAN Mini PCI card, housing, antenna, adapters and a compact flash card. This is basically a full x86 compatible mini computer with very low power consumption. The PCI Express Card with the UMTS modem is connected via a PCI-Express-to-USB adapter. After a bit of fiddling, i managed to compile [OpenWRT] from scratch for it and haven't had any issues with my Internet connection since then. This was definitely my best investment in the last few years, though the box looks really boring i must admit. You can download a [Diff] based on Backfire_10-03.1-rc6 (SVN rev 28150) with the small changes i did to compile for AMD Geode target and to enable the watchdog. A preset that selects all necessary packets for my configuration (Ath9k WLAN card and Novatel Merlin XU870 on ALIX6E2) is also part of it, but you still need to manually set the buffer size for usbserial to 8192 for good performance. The [Configuration] i used for compiling is also provided here for your reference.

Elektor experimental RFID-Reader

I have built the [Elektor experimental RFID-Reader] which can read ISO14443A cards. Unfortunately Philips uses the proprietary and secret CRYPTO1 stream-cipher, so authentication with MIFARE cards is not possible. However it was a very interesting project to understand the basic principles of 13,56MHz RFID-Cards.

Headphone Amplifier

For work and home usage i built two headphone amplifiers based on the [MINT schematics] from Tangentsoft.

 

Miscellaneous

There have been other HW projects as well, e.g. i built two programmers for PIC Micro-controllers and a simple one for AVRs. Also the ALIX router got an UMTS directional antenna. Alas, I will just stick some pictures in the [HW Gallery] for now. If you are interested in more details, drop me a note.