Jan 252011

I’ve gotten into making my own PCBs so I had to get some drill bits. The folks over at drill bit city are really nice and I picked up a good assortment of new and used (cheap!) carbide bits. I even got some router bits just in case I want to get into CNC PCB manufacture.

I expect to break a lot of bits.

Maybe I should have made an unboxing video?

What you get in the PCB starter kit. 

 Posted by at 11:00 AM
Jan 242011

The Sparkfun AVC 2011 is coming up and this year I might enter a hovering robot. Quad rotors are all the rage now, but I’m not into high disc loadings. So I’m thinking about entering a robot that hovers on one rotor and uses control vanes to cancel the rotor torque and maneuver. This configuration is unstable, so I’ll have to close a few control loops. Once you get a stable platform, the navigation is simple: You just pick waypoints far enough away from the Sparkfun building and a do carrot and stick control law. Simple.

Anyhow, how much power does it take to hover? Momentum disc theory to the rescue. The result is (derive it yourself. It’s easy!)

T is thrust, rho is the density of air, and A is the rotor area.

Here are some curves for 1 kg and 0.5 kg vehicle.

I’ll double these numbers and pick a motor. It looks like a 300 W motor and prop bigger than 8 inches will do the job. Something like this motor fits the bill nicely. Notice that the motor is rated for 333 W and 3D aircraft up to 2 lbs. That’s consistent with my numbers.
 Posted by at 3:52 PM
Jan 222011

After a few minutes of searching around, I found a quick way to get LaTeX onto this blog. Although, it seems like WordPress is the way to go if I want to get serious.

Here’s a preview: $P_{hover} = \sqrt{\frac{T^3}{2 \rho A}}$

Crap! That script uses MathML and that doesn’t work with Safari. Back to the drawing board.

 Posted by at 7:00 PM
Jan 142011

I’ve finished my new Ardunio Color Organ shield and it works great. The PCB fab was pretty easy for my second try at toner transfer.

Here’s the finished product:

I had no 200k resistors handy.

No soldermask means it’s ugly and the prototyping area vias only show up on the bottom.
Quick and dirty, but it’s better than a breadboard.

It’s a lot sturdier than the breadboard version:

I’m probably going to get some nice PCBs made. Let me know if you’re interested in a kit!
 Posted by at 10:25 PM