Introduction: Theo Jansen Inspired Walking Robot Insect

About: I'm a Movie Special Effects Design Engineer - which is probably the coolest job I can imagine! I mostly work on Mechanical structures but occasionally (increasingly it seems) get involved in Electronic &…

I built this Walking Insect, inspired by the creations of Theo Jansen who used a Genetic Algorithm to find a set of linkages to form a leg where the foot moves in a locus suitable for walking. What he came up with has a very organic look to it in the way it moves.

He has used this linkage to produce the most wonderful kinetic sculptures including the Srandbeest. My creation is nowhere near as amazing - but is, I guess more a humble Engineer's interpretation of his artwork.

The parts were all cut on my CNC Plasma Table, published here as an Instructable, but you could equally well have the parts laser cut - or even cut them out of thick card with a scalpel from the DXF files provided.

I built this originally to take to the 2015 Newcastle Maker Faire in the UK to demonstrate the kind of thing you could make with my Plasma CNC which was my main exhibit. If anything, the robot received more attention than the Plasma Table!

Step 1: Cutting the Legs

As I said in the introduction, the leg linkages can be CNC Plasma Cut, Laser Cut - or at a pinch, 3D Printed. I've attached the original Solidworks part files here as well as STL files to help.

Each leg segment (two legs) contains 13 parts (plus nuts & bolts).

1 x Body Plasma
2 x Shoulder Plasma
2 x Top Link Plasma
2 x Bottom Link Right Plasma
2 x Calf Plasma
2 x Shin Plasma
2 x Foot Plasma

To walk smoothly, you need 6 legs (3 Leg Segments) on each side. Although this adds up to a lot of individual parts (78) they are mostly repeats of one another.

When I cut the parts, the definition of the fixing holes was not that great. If I were cutting it again, I would have the plasma mark the centres of the holes (info on line on how to do this) and drill them manually. I had to drill out the holes to the correct size after cutting. If you get the parts laser cut or 3D printed, this will be unnecessary.

Step 2: Drive Motors

I have used electric window motors from a Range Rover P38 which are available very cheaply in the UK. The one pictured above only cost £10. In other countries, this may not be the case but if you have a look on eBay, you should be able to find something similar.

The motors themselves are 12v Worm Drive with a reduction ratio of about 50:1 - they produce bags of torque but still a respectable speed of about 180rpm.

Window winders are ideal as they are normally made in Left and Right hand versions - which are a mirror image of one another. This means two can be fixed back to back and the drive shafts will point outwards to the leg mechanisms (or wheels if you wanted to build a more traditional robot).

As you can see in the photograph, the motor has a drive gear. I found that you could just lever these off the shaft (with a bit of brute force!) without damaging the gearbox.

Each motor has several fixing holes which I drilled out to 6.5mm to accept M6 Studding to bolt the motors together.

Step 3: Crank Shafts

The crank shafts are all 3D printed. I went through many iterations to make these strong enough as, without bearings in the leg joints, there is quite a lot of resistance to the legs moving.

This is the version that worked the best!

The crank shafts are made from two pieces repeated (one pair per leg segment). The two pieces simply snap together with one Body plate inbetween.

You must assemble the two halves of the crank with 120 degrees rotation between them as shown. Make all six identical.

The STL files for the 3D printed parts are included in the next step.

Step 4: Spacers and Other 3D Printed Bits

There are a few other sundry parts including spacers to separate the leg segments and a spacer on to which Battery Holder Clips attach. I made these to suit a LiPo 3S Battery I have - but you'll likely have to adapt them to suit what you have.

Also in this file are the Drive Adaptor & Drive Pin. The Drive adaptor will press on to the splined output shaft of the motor and has a 5mm hole in the side into which you can wind an M6 Grub screw / bolt. It will cut it's own thread as it goes!

Step 5: Putting It All Together!

The images above are fairly self explanatory. In the last image, you can see a carrying handle. This is included amongst the DXF files and in the Solidworks models. I should have included it in the first and subsequent assembly steps - but I forgot!

I originally built mine with an Arduino, motor controller and a load of sensors intending that it crawls around autonomously. After a fair bit of work - it did. However, I decided that for a Maker Faire (think Children & over-curious Adults) it was too dangerous! The spikes on the legs are just a bit too sharp and I could see myself on the wrong end of a 'no win-no fee' Lawyer!

Instead I made it Radio Control with a cheap transmitter & receiver and a couple of electronic speed controllers intended for RC Cars. In retrospect, an RC metal insect is more fun anyway!

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