Servo - June 2009

reverse knee style aesthetic that I felt was important for capturing the feel of the Mech. I quickly assembled a set of legs based on the MicroRaptor and started plugging away at getting them to walk. Figure 4 shows a photo of the leg design.

Many painstaking hours later and after watching Jon’s videos dozens upon dozens of times, my own prototype started taking its first steps forward. One thing I was very mindful of while doing this testing was the payload capability. I closely monitored the temperatures of all the servos (another great function readily available with the AX-12s) and had the distinct feeling that while they would be sufficient to carry the components required to compete, I would end up wanting to do more with this project than just the bare minimum. With that in mind, I moved towards building my proof of concept.

Hagetaka v1.0

Armed with a solid vision of the project in mind, I started on the first revision of Hagetaka. Why build the robot on a smaller scale when we’ve already verified that the design is functional and can walk? Well, one can plan all they want on paper, but having a real world scale model of your final version is invaluable for trial and error. My other reason for building the robot on a smaller scale was budget. I knew my ultimate goal would be to move this over to a custom aluminum chassis with much higher torque servos, but the cost for that would be considerable. For the time being, I could at least build a smaller version to experiment with, and use what I learned from that to move forward with the larger, final version.

With the legs more or less taken care of, I started to plan

out what else would need to

be added: an upper torso to carry the electronics, wireless camera, battery, and a method of mounting the weapons as well as aiming them, all the while keeping payload considerations in mind. I decided on a pan/tilt arrangement for the waist which would be the simplest solution for aiming and looking around. The airsoft weapons

and camera would then be

mounted in a stationary fashion to the upper torso, allowing me — in theory — to shoot whatever my camera was aimed at. I do most of my CAD work in Autodesk Inventor 2008, so I started drawing up a simple ‘roll cage’ style

Figure 5

upper torso design that would protect the electronics and provide a means of mounting the weapons. Pololu Robotics ( www.pololu.com) offers a fantastic, low cost laser cutting service that I have used on more than one occasion. I recommend them because of their customer service, pricing, and quality of work.

I’ve always been a big fan of building a chassis using flat frame pieces connected with standoffs: it’s inexpensive, easy to design, and quite effective. I also added Lynxmotion SES compatible mounting holes to the sides of the torso chassis to provide a mounting point for my weapons. Check out Figure 5 for a shot of Hagetaka v1.0.

I learned quite a bit from building the first version. For armament, I ended up using airsoft weapons intended for an R/C tank due to their light weight and small form factor. Mounting the weapons was fairly straightforward using some Lynxmotion tubing and hubs. While I did encounter a few challenges getting my original onboard micro, battery, wireless camera, and other supporting electronics mounted within the chassis, I would classify my prototype as a great starting point.

Figure 4

Hagetaka v2.0

Upgrading the servos in version 2.0 would not only increase the payload capacity to allow for a higher end video system and better weaponry, but it would also increase the overall size of the robot by a substantial