Hexapod based on LEGO Technic 8482 Cybermaster

Principle

There is a total of six legs in three groups:

1. The left legs. These two legs always move synchronously and are driven with the left internal Cybermaster motor, geared down 1:16. They only move back and forth, not up/down.
2. The right legs. Same as the left legs, only right.
3. The centre legs. These only move up and down. When the centre leg on the left side moves down, lifting the left side of the hexapod, the centre leg on the right side is raised above the surface. And vice versa. The external motor drives these legs. The motor output is geared down 1:3 with the crown gear, and then 1:24 with the 24t cog driven by the worm gear in the yellow gear boxes.

This is the algorithm for walking straight ahead (the group of legs moved is shown in braces):

• (3) Raise the right side
• (2) Move right legs forward
• (1) Move left legs backward
• (3) Raise the left side
• (2) Move right legs backward
• (1) Move left legs forward
• Repeat

Be warned that this thing walks really slowly. I would say it spends several minutes to do one meter.

Software

Here is a program in Dave Baum's NQC used to run it: walker.nqc

The hexapod is physically capable of walking both forward and backward, in addition to turing either ways. The program above only supports walking straight ahead, though, as there was no more memory avaliable for anything else. I suppose I could have achieved more complex steering by controlling it directly with the PC, but I generally prefer to build over program.

Model

Here's a diagram of the walker unit, with lots of missing details. I will briefly describe the missing elements below.

The Cybermaster mobile unit is not drawn into the model above. If you have seen it, you're sure to understand where it goes, though. The two internal motors drive the axle #2's with bevel gears you can see "floating" in the picture. And the 2×2 plates with holes go under the battery compartment of the unit.

There are some beams which aren't drawn in the picture above. Some are holding the black steering gear brackets which can be seen "floating" in each end of the hexapod. This is a very simple structure consisting of a 17×5 rectangle made up of two layers of standard beams. It simply snaps into each end of the Cybermaster unit. Note that the worm gears are located inside this "box". The "box" itself rests on grey liftarms holding each leg, providing some rigidity.

An external motor goes into the grey mounting brackets on the top. This motor drives a 24t crown gear with an 8t gear. You may have to adjust the length of the centre legs or adjust the angle of them before using the model. I drew the angles perpendicular for simplicity.

You'll need to attach one sensor which is pressed when the centre legs are "square". This isn't drawn in the picture above. Attach this sensor to the "IN_1" port on the Cybermaster unit.

On the front of the model, there are two axle #8's sticking up from the 3×1 cross blocks holding the legs. I've put these axles into the axle hole number three in technic cams, with the pointy ends pointing inwards. Each cam points towards a touch sensor, which thus detects when the legs are "square". The touch sensors attach to the "IN_2" and "IN_3" ports, respectively. Of course, you don't really need these touch sensors. You can just monitor the speed of the motors, and run them until the legs hit the chassis. Much like in the startup procedure in the program. That way, you can use the sensors for bumpers, say.

Back to LEGO® ergo sum.