MAV-blog

Stuff related to MAV's (and UAV's) from a hobbyist's point of view. Info

Micropilot MP2028 Review - Part 1

I’m lucky enough to have the opportunity to “play” a bit with the Micropilot autopilot module and software that comes with it. While going through all the steps before we have our MAV in the air, I’ll do my best to post some of my experiences on my weblog. Part one! A first glimpse at the autopilot.

The module itself looks very professional: All paths are in an inner layer, so none is visible. On top of that, a special coating layer is covering the PCB.

Some chips on the module caught my attention:

  • Sipex UART to RS232 on-board : Isn’t it odd that they use RS232 on the module and not just TTL to communicate with the modem (which also contains a RS232 to TTL chip) and PC?
  • MAX660 Switched Capacitor Voltage Converter I have no idea what they use that for
  • Cirrus Logic AD convertor This is just a normal AD-convertor
  • LCX14 Standard hex invertor
  • A 49.1uH inductor . I suppose that is for filtering? I’m not familiar with other uses of an inductor…
  • 3 gyroscopes and 2 accelerometers. The Analog Devices ones you find in most IMU’s.
  • One static and one dynamic pressure sensor. Also looks very standard.
  • XC9536XL High Performance CPLD This is a Xilinx FPGA. High performance, low power.
  • M410000025: This is RAM. I have on idea how much…
  • The main processor is a FreeScale one. I didn’t rip off the sticker on it to see which one :-)
  • Commonly used TIM GPS module from u-blox.
  • The servo board contains the 17HCT237 to demultiplex a 3-bit data input to 8 data output (to the servos)

Most of these components are pretty standard, but it is clear that this module has quiet some processing power!

The weight of the module is only 28 grams. Unfortunately, the standard GPS antenna that comes with it is 38 grams! The interconnecting cables that come with it aren’t made for weight-saving either. So if we want a really low weight, we’ll have to come up with some ideas ourselves. The manual refers us to the website for solutions for these kind of issues, but I haven’t gotten my Support ID yet to log in.

Speaking of the manual: it looks very complete (160+ pages) and there is even an instruction video explaining the basic setup procedures. Compared to some other autopilot modules i’ve seen, it all looks very complete and professional.
Every parameter of the numerous PID loops it contains is configurable, including min and max settings, which PID loop to use at what speed and some others I never even thought of myself (and still need to find the use of it ;-) ). For automatic take-off, there are also a lot of options.

The back of the module, with the servo board next to it:

The front of the module, with a small part of the cables mess to interconnect everything:

More to come! If you’d like me to cover a certain topic of the micropilot, let me know!

17 August 2007, 05:40 | Link | Comments [14]

Texas decadence?

Last friday I ordered 5 samples of a tiny smd op-amp from Texas Instruments. Very easy, no big fuss like the guys at Microchip are doing lately. I was very happy to see that they were shipping them with fed-ex and it would arrive on monday! They didn’t need to as samples are free, but well that was the only option :-)
They even put it in a huge box before they shipped it with fed-ex:

CO2 tax anybody?

(Oh yes, what did I order? A replacement for the AD8552 dual op-amp used in my thermophile sensor module. Analog didn’t give samples in the SOIC8 package. Texas Instruments did: the OPA2335
Note to self: + is Vss and – is Gnd ;-) )

6 August 2007, 00:28 | Link | Comments

How to desolder a chip

This weekend, I made a bad PCB. The only option that was left, was creating a new one. But my PIC was already soldered on! After a search on the net, I didn’t find any approach with simple tools to desolder an SMD chip (in a way that it will still work afterwards!).
This and this are brilliant examples of how not to do it :-)

So I came up with my own solution:

  • Put a lot of solder on the 4 sides of the chip.
  • Turn an iron (to iron your clothes) upside down on maximum temperature.
  • Put your PCB on it (no solder on the bottom).
  • Now quickly heat up the 4 soldered sides with your soldering iron.
  • The heat of the iron will make sure the solder remains liquid for a few seconds.
  • You can use your soldering iron to push the chip off the PCB when you’re desoldering the last side.
  • Do it quick so your chip won’t be burnt!

Good luck :-)

30 July 2007, 16:46 | Link | Comments

Autopilot phase 1 (stabilization & servo controller)

I’ve been slowly working on my own autopilot system for more than half a year. I spent most of my time gathering knowledge and components. The last few weeks I worked a bit more intense on the project and it paid off: the stabilisation and servo controller are finished. They have been tested successfully and proved to be reliable!

Schematic:

Now, what can my module do:

  • Calibration on startup (defining min and max values for the sensors, and the neutral point)
  • Manual mode: Pass transmitter signals to the servo’s
  • Stabilized mode: Read the desired roll- and pitch angle from the transmitter sticks and stabilize the plane in those desired angles. This stabilization works with thermophiles. They sense the temperature difference between the ground and the sky.
  • (mode is determined by a slider on the RC-transmitter)

Other features:

  • Delta mixing is done in the microcontroller so it’s not required on the transmitter (makes it easier to read pitch and roll input signals seperately)
  • DSP filtering. The PPM signal is taken from the receiver before any DSP-filtering is done, so we need to do it ourselves to eliminiate glitches. Features:
    • Checks if every PPM frame has the same number of channels.
    • Checks if every pulse in the PPM frame is within a valid range (1ms and 2ms).
    • When a bad frame is received: keep the last valid positions. Go to failsafe positions after 2 seconds.

Planned features:

  • Read input from UART instead of RC-transmitter (interfacing to other microcontroller or PC)

I tested the stabilization unit on a small delta wing (40cm span) because I see no use in testing it in an easystar :-)

Module on the bottom of the wing:

Sensors on top of the nose, slightly pointing up:

Now some showing off :-)
The stabilization works so well I can launch the plane with the transmitter on the ground! When I give full left, the plane understands this as “go as much left al long as you can still see the horizon”. Considering the IR-sensor lens of 100 degrees, this will probably be about 40-50 degrees.

15 July 2007, 13:34 | Link | Comments [10]

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