Michael Kohn - linksys copter

CONTENTS

Linksys Coptor

Introduction

So using my Atmel Pilot firmware and software around it, I wanted to build something that could fly from it, so I stole my friend Oliver Hillmann's idea of building a quadcopter :(. Sorry Oli :(. Anyway I did deviate from his idea in that I wanted to use a Linksys router instead of a radio kit of some kind or Fonera. Using the Linksys router all the commands to the micro can be done over TCP/IP with the Naken Web webserver. For more information on how this system works, take a look at the Atmel Pilot web page. There is an explanation of the system with a diagram and a video of it working.

Special thanks to Jay at http://www.hobby-lobby.com/. Ever since I started this project I've been emailing him every once in a while for info I didn't know about from prop sizes to batteries and now motors. I asked the same question about motors to 2 hobby shops in town who ended up being clueless and to a company that makes motors who were either clueless or didn't want to help me. Jay actually took the time and was able to answer my questions on current draw and thrust.

Here's a video of the latest attempt. Unfortunately one motor refused to turn on. Hopefully I'll have that fixed soon.

http://www.youtube.com/watch?v=EbjA9ZlrS80&feature=youtube_gdata

Explanation

So basically what this is is 4 DC motors with propellers controlled by the Atmel Pilot system. The throttle control of the joystick will control the speed of all the motors together. When the joystick is tilted the speed of the motors will become uneven causing the device to tilt.

Pictures

	A brand new Linksys WRT54GL router with a fresh install of OpenWRT Linuxsnapped apart. I think my warranty may be voided.
	A view of the wires I soldered to the UART on the motherboard of the router.
	All put back together with its new dual serial ports out the bottom.
	Here's the first propeller I got and motor mounted to a candle holder sitting on top of a scale. I was trying to use the scale to measure how much thrust this prop/motor combo would give using different power supplies, altho because of the way the motor was shaking, I think it may be a false test. Either way it only seemed to want to push about 25 to 50gm, which isn't enough for what I need.
	Here is the final product minus the 8 AA batteries that will go at the bottom. The frame is made out of all wood with lots of wood glue and epoxy to hold it together. Since the router was already mostly blue, it was pretty obvious I needed to paint the structure yellow so I could have my favorite color pattern: blå och gul.
	This shows the router sitting idle on a kitchen scale with the newest propellers I've been trying (bigger than the original). It's hard to tell from this picture, but the whole thing with these R/C airplane batteries (12 NiMH cells instead of the original 8 AA batteries I was using) weighs almost 1200g. I ran the router full blast and the scale dropped down to 700g showing I'm only pushing 500g.
	(June 28, 2009) -- So I goofed up while probing the original board with a 'scope and shorted something out which caused it to catch fire, so I redid the board a couple months ago and finally installed it yesterday trying to do a better job with the wiring and such. This circuit board has much better part placement and organization (as can be compared to the board above) so it's maybe not a bad thing this happened :).
	(August 20, 2010) - The old motors are impossible to get off so I started over with a new wooden structure :(. Here are all my cut pieces of wood sitting next to my professional paint brushes I bought.
	(August 20, 2010) - All glued together with some epoxy. Dimensions: Top/Bottom center: 187mm Left/Right center: 133mm Arms: 150mm (before the 45 degree cut) Motor Mount: 50mm Feet: 43mm
	Here it is painted with a Linksys on top.

Useful Sites

http://www.badcock.net/cgi-bin/powertrain/propconst.cgi
http://adamone.rchomepage.com/calc_thrust.htm

Latest News

August 16, 2010 - I ordered some new motors from a web site. I was looking for Mabuchi RS-380PH 3270 but the closest I could find were from a website selling .. well I guess an unknown RS-380PH model number with specs of 3-12v and RPM of 12500 which matched the Mabuchi RS-380PH 4045. The 4045 seemed to be okay so I got some. So we tested one with the 8x3.8 APC SF. Despite being in a bigger can than the RadioShack motors, the RPM was pathetic. Only 3200 RPM compared to the RadioShack's 5800. I guess what they say is true: it's not the size of the boat, it's the motion of the ocean.

Anyway, I'm now on a quest to find RS-380PH 3270's :(. Or any motor that can spin these props around 10,000 RPM.

August 9, 2010 - We tested 8x3.8 APC SF propellers and got up to 5820 RPM. still 1200 RPM too short of being able to lift off :(. There is a video here: http://www.youtube.com/watch?v=EikYLIS_9hc.

August 6, 2010 - I built a little IR circuit that while under an oscilloscope can determine the RPM of the propeller. Hopefully this weekend I'll hook that up to a micro so the microcontroller can count the RPM's, but for now it works with the scope. Anyway, with the current circuit, Radio Shack motors, and 10x3.8 APC SF propellers, one propeller appears to be spinning at around 3750 RPM.. which according to the thrust calculator from the web page above seems about right. The 8x3.8 propellers finally arrived today so hopefully we'll be testing these on Monday.

I put up a page for the propeller tachometer (schematics and firmeware) here.

Btw, here is a picture of what we got from the digital 'scope: 10x3.8 APC SF under oscilloscope. The speed was originally 8ms between peaks, but after running a little while it slowed down a little bit.

July 31, 2010 I have the ATtiny2313 firmware working now. And a new circuit built. I have 8x3.8 propellers in the mail too. Next week this will either work, or it's time to change the motors :(.

July 17, 2010 This week I finally got a chance to the test the battery. I think the circuit actually got destroyed tho (not because of the battery). Anyway it still wasn't enough to lift the thing. So I swapped out a couple of resistors and some traces fell off the board. I tried to fix that, but when I turned it on the last time, motors 1 and 4 were stuck on. After 2 min of running those motors and stopping them, they were smoking :(. So I have a few ideas what to do after building a new motor control board. First of all on the new motor control board I will an Atmel ATtiny2313 instead of the ATmega168 to save space on the board and simplify it a little. This will probably take a firmware change. Next, my current propellers are 9x6 in the back and 9x4.5 in the front. I've been discussing this with friends at work and we decided to try newer propellers with less pitch so there is less resistance against the motor. One of them found 10x3.8 props on Amazon.com so I plan on getting these. I also started looking for new motors, although I'm having trouble finding any that fit in my electrical specs. If anyone has any suggestions on propellers and motors, feel free to email me.. :).

January 3, 2010 Yesterday I finally ordered a LiPo battery (and got a neato charger) from HobbyTown USA in St. Louis. This battery run at 14.8v and can put out 66A. If this battery doesn't lift the router, then the motors/propellers need to be changed.

August 26, 2009 Just wanted anyone interested to know I haven't given up. So earlier this year, I hooked up my oscilloscope to test some things (I've had a horrible voltage drop across the motors with the batteries I had.. actually with any supply I put on the circuit) and I guess I hooked something wrong and ended up smoking a transistor. There was literally smoke rising from this thing :(. So I remade the circuit, which is probably a good thing cause I did it so much nicer this time (pictures below). So anyway around May I read that NiMH batteries need to be charged and discharged a couple times before they hold their full charge so I decided to try it. I charged the two battery packs up (my 20A @ 14.4v power source) and ran the battery down (playing with the throttle a bit to test a firmware fix) until the motors just quit (the router stayed on). I did it a second time but this time just leaving it run without touching it. This time when the motors shut off, the router shut off too. I thought this was kind of weird, but what was even weirder was the hissing sound and then the horrible smell. I carried the thing to the kitchen to see that one of the battery cells had popped and wouldn't stop smoking. Being afraid the other cells would explode I took the whole thing outside and let it smoke out. Took a while. So after this incident, I cancelled the project. For about 2 hours. So I was thinking about it and wondered if my voltage drop was due to the small wires I used to connect the motors to the PC board. So I first unhooked one motor, placed a 600gram guitar pedal on top of the router to help hold it down, hooked the motor to the 15A @ 13v power supply I have in series with an ammeter and measured 4.5A starting and 4A while running. I then connected the same circuit except direct to the motor (not through the small wires) and measured the same thing. By the way, according to Radio Shack, these motors draw like 2A max :(. So I hooked up the motor with the small wires back to the power supply and measured voltage across the motor and got 13v. No more voltage drop! And btw, with just this 1 motor running at 13v, that edge of the router was picking up off the carpet. If it wasn't for the shape of the base and the 600g guitar pedal, it probably would have flipped over. Looks like I just have to figure out the reason for the voltage drop (which I'm 99% sure I know what it is now) and buy a new battery, which I found already a LiPo battery capable of 40A which I plan to buy in a couple weeks. This project may finally be flying soon :).

Materials

4 SuperSpeed 9-18VDC Hobby motors Model 273-256 from Radio Shack (Seems to pull 0.25A unloaded and 4-4.5A with a 9x6 or 9x4.5 propeller)

MJ4701 Collet Prop Adaptor for 2.3mm Shaft From Hobby-Lobby
PE06055E 6x5.5E Thin Electric Prop From Hobby-Lobby
Linksys WRT54GL with OpenWRT Firmware
Atmel ATMega168
Electronic parts (read the schematic after it's posted)
Wood, paint, wood glue, epoxy. Lots of epoxy :(.

Weights

Router 350g
1 Motor 50g * 4
Wood 25g
Microcontroller circuit 75g
Battery:
- 8 AA Rechargable or Throw away 200g
- 12 cell NiMH R/C airplane batteries (I think 400g)
- LiPo (Electric Flight 2200mAh, 30C, 66A continuous)

Weighing the entire system together, it appears to currently be around 1150g.
January 3, 2010: Some of the above changed. I have a new motor control circuit with big big big resistors and I ordered the LiPo battery.
July 17, 2010: Weight is currently at 1100g.

I have a YouTube video of the thing almost working here: http://www.youtube.com/watch?v=eYOMHge0_yk

Schematic

Download

Coming Soon

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