Should I build a big CNC router?

I know I would like to build a Computer Numeric Control  (CNC) router big enough to drop a sheet of ply in, but is it a good idea? It will take up a lot of my workshop space, and chew up a lot of time and money. It’ll allow me to makes some awesome large objects. Anyone want a kayak? It would be big enough to make small boat ribs etc. Storage boxes, and display panels, doll houses and 1/2 of the things in ikea. All doable. But am I going to do them? A lot of the CNC routers on the internet seem to get used to make more CNC routers. Thats fine by me, although a boat sounds more fun.

I’ve read about people who have purchased shopbot routers with the belief that they’ll form some kind of business around them, and some have successfully done so. It seems a bold choice to me, but as James Graham said.

He either fears his fate too much,
Or his deserts are small,
That dares not put it to the touch
To gain or lose it all.

Maybe now is the time to build a big CNC router.

PS. I’ve found a few places around that I can get stuff cut at. I’m going to test the waters out by doing a few projects on someone else’s CNC router first.

iPhone controlled paper planes!

I’ve long been a fan of paper planes. Some of my fondest childhood memories are of are of constructing and launching paper planes around the school yard.
For a while now I’ve been eyeing off the powerup paper plane power pod on thinkgeek. Debating if I should get one or if I should just stick with the paper in its
true form. Then I saw this on kickstarter. Remote control paper planes! Convert any paper plane into a remote control plane and steer it with your iphone. Its a two channel control system. If you want to climb, then throttle up. It turns through rudder (Yaw) control, so there is no roll control.

This is the minimum you need to control a plane. With the control unit and battery up the front and a propeller and motor at the rear, the body looks like a
thin black stick. You lay the system down the body of your plan, throttle up, and fly away.

For $45 deliverd to Australia, I’ll give it a go.

I also found an interactive bokken training sword on kickstarter. Its possible I’m addicted to kickstarter, but I’m resisting the sword. For now.

The Mini Mill is live

I picked up a 7×7 mill from Zen toolworks a while ago. I did the basic assembly and powered it up with an old 24v power supply. It moved, but locked up on the far X axis, and the far Y axis, and stalled with any high speed movement. At that point it all got boxed up for a house move, and stayed that way for a year. I’ve recently dragged it back out and thrown some more time at getting it setup.

I lined up the bottom frame using a machinist square. It was close enough that I could just shim out one corner with a piece of paper. The stepper motors  pull more power the faster they run. The old 2.5 amp 24V psu wasn’t providing  enough power as the acceleration kicked in. I’ve swapped it out for new 14.6 amp 24v psu. I still found some issues with the alignment of the anti-backlash nut on the Y axis. The problem with this is that you can’t easily access the anti-backlash nut. After a good look around the machine, and I decided to remove the 16 screws securing the back plate from the gantry. I could then access the mounting screws for the anti-backlash nut by loosening the  mounting screws and moving it to the far side of the Y axis. I could then tighten the mounting screws with the anti-backlash nut in the correct alignment.

Also, I got a video cam for my birthday, so here’s a time lapse of the job progress.

Quadcopter Update

Well, I’ve learnt the difference between ‘Acro’ mode and ‘Self Level’, and it only cost me one propeller.

This afternoon after work, the kids and I took the quadcopter to the local oval. It started out as a lot of fun, but I hadn’t realised that you can change the mode by stick input on the controller. Somehow I managed to knock it from Self Level mode (I need all the help I can get at the moment – I’m up to almost 6 minutes of flight time), into ‘Acro’ mode. I’m assuming ‘Acro’ is an abbreviation for Acrobatic, because it got very exciting after that. If you are expecting the quad to self level when you center the sticks, it takes a moment to realise that it isn’t happening. You don’t have a lot of moments available.

Here is how the construction has progressed. I’ve completed a bunch, and learnt that I have more to go. It’s flyable now (or it was before this afternoon’s adventure), but there is lots of room for improvement.



  • Install video cam
  • Install video TX

i’m not 100% sure what has gone wrong here. I wired the camera and the TX together using the supplied wiring harness and powered it up. The video TX blew and managed to ignite the heatshrink. I suspect its taken out the camera too. My best guesses are faulty wiring or faulty board. Without better diagnostic equipment, there isn’t much I can do about it. I’ll have to order replacements when funds allow.

To do:

  • Replace the rear props with some red ones. Its hard to maintain orientation with the yellow front and white rear. There isnt enough contrast. Also, I broke the white one. 🙂
  • Re-mount the KK2 and re-level it. It tore off two of four pieces of mounting tape in the impact.
  • ESC Calibration (electronic speed controllers)
  • Instal SimonK firmware on ESCs, I’m leaving this until I have a rainy day
  • build (anti)vibration isolation platform

Password storage in .net

Password storage is a pet peeve of mine. I’ve worked with systems that use:

  • bidirectional encryption for the passwords (you can convert the password into gibberish, and then back to readable text),
  • MD5 hashing (you can convert the string to gibberish, but not back. You test the password by hashing the password that the user is trying to log in with and comparing it to the hash in the database.), and
  • clear text storage. (This is the worst plan ever).

They each have their own security flaws. Bidirectional encryption can be converted to clear text, which means that if someone steals the user list, they can discover all the passwords. Likewise, you can build a dictionary of known passwords and MD5 hashes and use that to look up the password that made a hash. And storing a password in clear text is pretty much the same as just giving out your user’s passwords.

I’m currently working on a software application that uses the BCrypt hashing algorithm to store passwords. BCrypt is available for .net and other languages, and is very easy to use and implement. The BCrypt library produces a salted hash, and stores the salt and the hash together. This systems means that even if you had a dictionary of hashes, you would need to rehash your entire dictionary for each salt. As each salt is unique, this is going to take a long time. The algorithm is intentionally slow, but configurable. By default it runs about ten iterations, but can be adjusted higher. The trade off is between security and hardware. In theory, as the hardware gets better you can increase the number of iterations, and keep it difficult to compute. The estimated execution time for the default configuration is 0.3 seconds per hash.

So, to summarise, BCrypt is:

  • a one way hash (you cant reverse the password out);
  • uniquely salted, making pre computed dictionary attacks much less useful;
  • adaptive, so it can handle future changes in available compute power; and
  • easy to implement.

So people, hash your passwords!

More information at

Quadcopter update


I had a lovely sunday watching the Bathurst 1000 and building the quadcopter, with the assistance of my daughter.

As it stands so far we have:

Still to go:


Hobby King should come with a drug warning. It starts out safely enough, a couple of servos for an arduino project, a drive motor for something else. Next thing you know you’ve found out that you can fly aeroplanes and strange copters with video goggles on, seeing what’s in front of the plane. It’s like crack for geeks.

After watching one of Flite test’s youtube clips, I really wanted to have a go. But I have glasses, due to astigmatism, so buying the headset would also require custom lens inserts. It starts to look pretty expensive about then. That’s when I found this video, which shows how to setup a usable (not pretty) home made system. It looks cheap enough to try without breaking the bank, and it can be made to fit over my glasses. If I decide to go further with the hobby then its possible to hook up multiple goggles. So, this could become the guest headset.

I’ve managed to get hold of the lens and the screen, but you can’t buy the nice hotwire cut EPO foam mount anymore [edit: its back in stock!].