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Microrobot HexAvoider

The HexAvoider from Microrobot is one of best kits I've seen in a while. The walking mechanism is a true six-legged walker, and has a much more elegant walking solution than that of the BugBrain. When the kit arrived, it was superbly packaged with the box opening up from the top and then sectioned into about 12 different compartments making component checking and the building process a whole lot easier.

Building

The robot was generally easy to build, being split into two main sections - the PCB and the chassis. Surprisingly, it was the PCB board that was the easiest to build - the instructions were all fairly straight forward, although occassionally I had to refer to photographs to get the polarity of a few components correct.

The PCB is quite densely populated, and uses a clever design that has the antennae section of the robot mounted on top of the main board (see below). This means the soldering definitely isn't for the beginner, but it doesn't offer any major challenges - anyone with a little prior soldering experience and a steady hand shouldn't have any trouble.

The PCB board [left], and the chassis [right]

The real difficulties started when it came to building the chassis and drive mechanism. Actually putting the chassis together was very simple and was nicely depicted in the manual using 3D renderings for clarity. The big problem came when creating the control rods that connected the servos to the legs. The manual has one simple picture showing the wires along with the lengths of the individual segments. There is no explanation beyond this - furthermore, the mounting diagrams were fairly hard to understand. The simple picture didn't represent the true 3D nature of the wires, and meant I kept having to rebend the wires to get the right shape. In Microrobot's favour, though, I did find a sort of "addendum" buried at the bottom of the kit, that tried to describe the shape of the wires a bit more thoroughly as well as some high-resolution reference images buried on the support CD.

Finally though, I managed to bash out out some proper control wires and everything went a lot smoother from there. The robot is fairly unique in that it uses it's own rechargeable battery. You will also have to solder a few pieces together to form a battery recharger. This definitely has advantages since you won't use up mountains of AA batteries, but there are a few problems too. The charger is separate, and doesn't have a place to be mounted on the main robot. The charger is tiny, perhaps 3x3 centrimetres, so will be lost easily unless it is carefully looked after. Also, the charger requires a 18V (or higher) DC power supply. I have four different multi-voltage DC adaptors, all of which stopped at 12V. Thankfully, Active Robots graciously donated a Switch Mode Power Supply which fitted the bill perfectly (as an aside, this power supply is excellent, with worldwide plug socket support as well a large variety of adaptor jacks). I finally had a fully-charged and mobile HexAvoider!

Performance

Once the robot is built, getting good performance out of it is very simple. The robot has two modes, fast and slow movement, as well as two calibration modes.

The calibration modes can be used to initialize the IR sensors, which are put through a potentiometer, so you can adjust their sensitivity under a variety of lighting conditions. The dual use of IR sensors and whisker wires make the operation of the HexAvoider near-perfect. In fact, if well calibrated, the IR sensors will pick up the majority of obstacles well before the whiskers are triggered. Eitherway, the robot will rarely get stuck on an obstacle, and the true six-legged walking gait means the robot can walk on a variety of surfaces without hindrance.

The HexAvoider also comes with an optional RF expansion module that allows you to remote control the robot. Hopefully Generation5 will have an opportunity to see this soon.

As with other kits in the Microrobot line, the support CD comes with complete source code if you want to reprogram the main CPU. This isn't a simple process, requiring a specialized compiler and a Flash writer, but the fact that Microrobot provide the necessary support is an excellent start.

Conclusion

This kit is fantastic, from the way it is packaged, to the way that it comes together as an assembled robot. The kit comes at a excellent price, since it doesn't have the overhead of an expensive microcontroller. Nevertheless, the CPU can be reprogrammed if you are so inclined. It was only a couple of glitches in the construction manual, especially regarding the control rods, that put the kit down at all. Despite this, the RF expansion module and excellent autonomous operation truly set the robot apart from other similar kits.

9.3

Price: £126.00

Liked: Well-designed and engineered, excellent operation, nice support CD

Disliked: Construction manual lacked, separate 18V battery charger

Website: http://www.active-robots.com/

Submitted: 21/02/2004

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