Let's Make Robots!

PicoRoach - 3 Servo Walking Robot

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Now available from PicoKit!
 - A cheap and simple 3 servo robot walker that anyone can make for under $40. My students in Industrial Technology loved this project, as they could program it easily with PicoFlow Alpha. We used a PIC12F508 from Microchip Technology, and programmed it using the PicoFlow USB (in circuit) PIC Programmer. The plastic parts were cut from Polycarboante so they wouldn't break. Check out the development stages below.
 
Cost: under $40
Design Time: about 90 hours
Build Time: about 3 hours
Tools used:
  • soldering iron
  • screw driver
  • pop-rivet gun
  • sharp art knife or dremel
  • pliers
  • file
Early Development:
The first stage was to design the walking mechanism. I used autocad to record my developments. This first pic is of the inital mechanism idea, which changed substantially over time (although it always stayed a 3 legged robot).
Early Development in Autocad
The main decisions encountered at this stage were the linkages and how much movement should occur. Should all three legs tip (alternately) and move back and forth? You can see, on the main pcb shape, two little pivot points jotting out, one on each side. These were possibly going to control alternate up and down motion, so the center leg would control the pivoting of the front and back legs. This design failed because it would not allow for the motion of the robot to turn on the spot.
The next picture shows the progression of the design, finalising angles of rotation, and progressing on the pcb layout.
Early development 2
Here, I was toying with the idea of using a fixed linkage system between the legs to transfer movement from the back legs to the front. Although I ended up simply using some MIG wire which is very stiff and holds shape quite well. You can see from the pcb shape that I was still considering the center leg to move backward and forward, which wasn't going to work. I was also building into the design, the size constraints of the servo motors.
Prototype:
Stepping much further ahead, this picture shows the diptrace software I used to create the printed circuit board. I imported the outline of the pcb from a dxf file, because the measurements were quite important. Using the pcb as the main body of the hexapod was one of my best ideas, because it really cut down on the complexity of running the servo wires, and wires to the microswitches. Really, I can't actually remember not wanting to use the pcb as the body. It must have been one of my first thoughts.
Diptrace PCB prototype
This design is actually my most recent, because I have plans to add a 9V battery bracket in there, with some rubber insulation. You can see the cut-outs for the servos aren't actually 'cut out', but the board manufacturer had no problems with this. I use PCB cart in china, and they have been really helpful at times, picking up on my little mistakes, even before they made the pcb. All credit to them. I only ever had one issue (about 6 years ago) where they drilled some holes .2mm undersized. Other than that, they have always checked their products for quality, and made new pcbs when they have stuffed up.
The prototype below was not my first. I actually hand make my circuit boards first. But this one shows the initial rubberbands for feet - lol. And since this prototype, I have actually flipped the pcb over so the battery hangs underneath to provide a lower center of gravity. The video doesn't show it, but on a smooth surface, the PicoRoach started backflipping because the weight of the 9V was too high.
Early Prototype 
You'll also not, the long servo wires and how ugly the microswitches are on top of the pcb. I also originally used breadboard jumper wires to connect the front and back legs. With the plastics, I tried acrylic, which had a much nicer finish, but the 0.8mm holes in the 3mm acrylic kept snapping if the wire linkages were bent over while in the holes. Changing to polycarb worked nicely, but I'm about to trial acrylic again, as another teacher has pointed out a good way to make a thicker walled hole. We're looking forward again to nice colours, and smooth edges.
Programming:
Programming the PIC MCU (Micro-Control Unit) was easy using the PicoFlow Alpha software. The three servo motors work by loading the with values from the Lookup Tool. The four Lookup Tools record the stepping sequences for Forward, Backward, Turn Left, and Turn Right movements. The Forward Lookup Tool is the standard motion, but when an antennae is triggered, the motion changes to 6 backward steps, and then on to 6 turning steps. 
PicoRoach 3 Servo System Control flowchart
Future Development:
And with appearance, I've just milled out a mould that I designed in autodesk Inventor. It has a recess for the switch (which is now on top) and once vaccuum formed, the side recesses will be cut away to leave openings for the legs.
Vaccuum Formed Mould 
I can't wait to paint some eyes on the enclosure when it's made. Should look slick! I'll post another video when it's done.
Please ask any questions about the build, or contact me personally.
Cheers,
Phil
 

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Hi Birdmun,

I guess 2009 is old these days for microchips. I picked the 12F508 because it was cheap. Lol - Aussies are cheap too.

I've been programming now for about 6 years, and it's amazing what can be done on a really low cost microcontroller.

I've got a 16F505 with only 1k of memory running a led matirx with rotation and shift manipulation on four separately controlled channels. This way leds can rotate or shift on one layer of the led cube and interfere with leds that are rotating and shifting in a vertical column.

And Yes - I am a little crazy, but it sure is fun.

Which 12F6xx are you talking about in particular. I had a quick look at 609, 615, and 617.

Personally, I really like the 12F1501 which has four channels of PWM, an NCO, logic modules and a 5 bit dac all for a bit over 50 cents.

Cheers,

Phil

 

I was thinking of the '629, '675, and/or the '683. I know Microchip has a fantastic range of chips to choose from.

Hi birdmun,

I do like this 8 pin PICs also.

But for a cheaper price and much better features - you should try the newer and better PIC12F1822 or the PIC12F1840

They leave the 629, 675, and 683 for dead.

Cheers

I would have thought you would have stepped up to a 12f6xx series chip.

Hi Birdmun,

Thanks for the comment. Personally, I use a heap of different PICs, and usually just choose the cheapest with the right peripherals. 

I now like the 12F1501 and use it for a musical star project I made. It's a super cool chip. Highly recommended.

Cheers

Hi Merser,

fantastic. lol. I was born in VIC though, so we must have passed on the same train or something.

Seems I can't read too. Can't follow, lazy, and bad at reading - lol.

What's your last name Merser (and OddBot)? Maybe there's some sort of connection. Maybe Redcliffe is a robot breeding ground. Do any of your siblings have two robot heads? oh no, that's Tasmania.

OK, I'll put more build details on, and remove the business stuff.

Cheers

Rules? Aussies don't have rules.. or at least they never follow them.     : D
If you weren't a bit lazy in detailing your build I would say it would pass as a robot post. Congratulations on your kit. A lot of us here never finish a project let alone make it available as a kit.
I have a connection with redcliffe too. It goes back 47 years to where I entered this world - the redcliffe hospital. Got family still living in the area.

Just updated the page with design and protoype details. All comments are welcome. I hope you enjoy the developments.

As you are advertising a product you need to move this post from robot projects to the advertising forum. Please read the rules.

 

Clontarf? I was living in Redcliffe before I moved to China.

Hi OddBot,

Sorry about that. I truly didn't see that in the rules. I've tried to make it a robot development page instead of an advertisment. Could you possibly look over it again, and let me know if it still needs moving.

Redcliffe and China. That's a coincidence. I've lived here in Clontarf for 32 years, and next year I'm moving (with my family) to China. Are you still there?

Cheers,

Phil