Minima - yet another quad copter build







Introduction

Minima is my minimalistic quad copter build. It was intended as a prototype platform for trying various software ideas and to get an idea of what it takes to make a quad fly. Since I usually don't have a whole lot of spare time (and a fairly limited attention span) I've been working on it on and off for over a year. (actually, looking at the PCB it appears the board is from Jun 2010  D: ). The hardware is functional so I am now mainly playing with the IMU. Currently the software is way too simple but working well enough to fly around carefully.


Obviously, there is a lot of room for improvement and maybe someone else get's to implement some better algorithms for the IMU before I get to it.
The video indicates that the flight stabilisation works in principle but could be better. I am actually quite surprised that it works as well as it does, given that it's only controlled by two perpendicular PD controllers running at a 100Hz update.
It's going to be quite interesting to fit a better algorithm into the little controller running at a low speed.

Also, check out MinimaBL which is sort of version 2.0



Minima specs

Here are some technical details:
  • Weight without Battery: 38.8g
  • Weight with Battery (250mAh): 46.6g
  • Dimensions: Motor-Motor 240mm (390mm prop tip-to-tip), Height 35mm
  • Props: 6030
  • running off a 1S LiPo (2S possible but not recommended)
  • firmware is upgradable over wireless or via ICSP pads

Mainboard features

  • PCB: 2-sided, 0.5mm thick
  • CPU: ATMega32L @ 7Mhz
  • Gyro: 3 axis, 2000deg/s  (ITG3200)
  • Accelerometer: 3 axis (LIS3Lv02)
  • Wireless: half duplex @ 19k2 Baud over XBee
  • BEC for 1S Lipo (2S is pushing some parts over their specs and will burn out the motors quicker. Not recommended, but damn it is responsive ;)
  • Battery monitor for LiPo protection
  • Power MOSFET brushed motor drivers

Parts list (reduced)

Hardware
  • 4x Motors $13 ($52)
  • 4x Props 2xCW 2xCCW , $1.50 ($6)
  • Carbon tube, 4mm, 5$
  • 0.5mm double sided pcb scrap $??
  • some 4mm acrylic sheet scraps for motor mounts $??
  • magnet wire, 0.25mm $??
  • some foam, super glue (foam safe), epoxy, $??
        ---------
        ~ $75        

Electronics:
  • Xbee + headers, $28
  • ATMega32L, $9
  • Gyro ITG-3200,, 25$
  • Accel (LIS3Lv02), $8.5
  • 4x Power Mosfets, <$1 (4$) 
  • LDO Voltage reg, $2
  • caps, resitors, diodes, led, bits and bobs ~$10
  • Lipo 1S 250-350 mAh 25C, ~$6
        ------------
        ~ $95

Misc:
  • 2nd Xbee for the Tx, $20-25 + XBee explorer USB type dongle  
Some creative sourcing and a more careful selection of parts can bring down the cost quite a bit more but I just used whatever I found in my electronics box. Not using expensive xbees would be a start (but they are nice for debugging since they manage the entire communication for you). There is now likely a cheaper 3 axis digital gyro around too, etc.


More of a build log can be found in the detailed parts list:

                        Read on >> detailed parts list



Videos

A bit of flying around in the basement. 
Apologies for the editing tricks, the camera was loosing focus for annoyingly long periods of time.
Btw. this is flying the gyro/accel control loop which tended to oscillate a bit and needs some work.
Using the gyro only completely eliminates this. The quad behaves more like a helicopter and needs 
you to fly it that way but it's a very smooth ride.




Here are some things to avoid. (The reason to always have superglue handy).


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