Saturday, October 31, 2009

Spiderwheels: smaller servos...

Wow, it feels like forever since I've blogged. I learned how to design circuit boards a few weeks ago. It is a lot easier than I thought it would be. While I was waiting for some new bits to come in the mail I started working on my Spiderwheels project again. I've been experiencing issues with my netbook since I got it and just recently found out what was wrong with it. It looks like the graphics card is overheating under normal use and cannot run for more than 20 minutes. I was really upset at first. I'm over it now. EBay is not always the best option.

Considering the netbook I got for this project is non-functional I have decided to look into building a smaller robot without the burden of the 2 lb netbook. This idea hit me when I stumbled across these servos. They weigh 9 grams and cost $3.50. Compared to what I was spending for the larger 55 gram HiTec servos, +/- $30, these are a steal. I went ahead and ordered a few to do some benchmarking. So far I am very impressed. I want to construct a leg and get a feel for accuracy before ordering more. With these prices this project may well produce a six legged walker from the start.

Here they are side by side:

Here is a close up of the 9 gram servo:

Sunday, October 11, 2009

Spiderwheels: I have so much to learn...

I realize this is my first robotics project and I should stick to wire nuts and breadboards but I want to learn as much as I can from this project. Frustratingly enough, this means I must take several steps back and pursue PCB fabrication. I built a mill and am getting close to being able to mill boards. The next step is learning how to design them. This is a very overwhelming subject for me and it is hard to know where to start. I have decided to go with Eagle as my layout editor mainly because the RepRap team uses it and this is all I have to go on when it comes to board fabrication. So, I guess the first step is to follow some tutorials. I have chosen this tutorial because it will also serve as an introduction to the FT232RL chip, which is used in the Arduino. Time to learn.

Monday, October 5, 2009

Mill: starting yet another project...

Every once in a while I get the chance to re-evaluate my vision and the direction my research is going. Every time I get the chance to do so I identify a gaping hole in my current tool set. For the last six months I have had a working 3d printer at my disposal. However, when I started working on my first robotics project I found that it wasn't enough. I am missing an easy and accurate way to fabricate PCBs. Of course I could purchase the chemicals required to etch, but I have a small apartment and I haven't seen much precision out of people who have gone down this route. Since I started building a RepRap I have been aware of CNCs capable of milling PCBs and have even given this a try on my Darwin. I quickly found out that milling on a Darwin isn't the best idea.

Thus, a new project is formed. I don't have a lot of time or motivation these days and so I wanted to be smart about getting a cheap solution up and running with minimal time / resources. I decided to go with a time tested design called the Rockcliff. It's not an open source design, but the plans only cost $20. They are well worth it! Here is an animation of the design I went with:

It is mostly made out of 3/4 inch MDF and 5/8 inch steel rod, which cost $60. You will also need some bearings, motor couplings, stepper motors, and driver boards costing upwards of $400. However, considering I have a 3d printer I was able to print the bearings and couplings. Here is video of what the printed bearings look like:

CNC parts printed on a RepStrap from gavilan on Vimeo.

I am also borrowing the driver boards from my printer while I mill another set.

In total, I think this CNC will cost me around $240. Not bad for 0.003mm precision.

Here is a picture of the mill as it stands.

More to come on my goes at milling PCBs on this Rockcliff.

Sunday, October 4, 2009

RepStrap: a Darwin x motor bracket...

I finally got around to printing my x motor bracket the other day.

There are a few structural weaknesses due to my Z axis, but I think it will hold together. I am getting close to replacing all my hand made parts.