A Servo-based 4-legged Walker

Build your own (needlessly tech) servomotor-driven 4-leg walker robot!

First, a warning: This bot is basically a microcontroller-brain version of the classic BEAM 4-legged walker. The BEAM 4-legger may be easier for you to make if you aren't already set up for microcontroller programming and just want to build a walker.

On the other hand, if you're getting started with microprocessor programming and have a couple servos kicking around, this here's your ideal project! You get to play with walker mechanics without having to worry about the fussy analog BEAM microcore tweaking.

So although this isn't really a BEAM bot, the following two webpages are great resources for any 4-legged walker:

Bram van Zoelen's 4-legged walker tutorial has a good overview of the mechanics and theory.
I took my leg design off his website.

Chiu-Yuan Fang's walker site is also pretty good for BEAM stuff and some more-advanced walker designs.

Done reading? Ready to get building?

Step 1 Gather parts, measure, plan a bit

Making a 4-legged servowalker is pretty simple, parts-wise. Basically, you need two motors, legs, a battery, something to make the motors go back and forth, and a frame to hold them all.

Parts list:

2x Tower Hobbies TS-53 Servos
20in heavy copper wire: 12in for front legs, 8in for rear. I had 10-gauge. 12-gauge should work, but I'm guessing.
Battery is a 3.6v NiMH that was selling for cheap online.
The microcontroller brain is an AVR ATMega 8.
The frame is Sintra, which is hella cool. It's a plastic foamboard that bends when you heat it up in boiling water. You can cut it, drill it, matte-knife it, and then bend it to shape. I got mine at Solarbotics.

Other parts:

Drilled project board for the circuit
Snap-off headers (male and female) for the servo and battery connections
A 28-pin socket for the ATMega
Super-duper glue
Soldering iron and solder, wire
Some tiny bolts to hold the motors on
Drill
Matte knife

Here, you see me measuring out the parts, making a sketch for the frame, and then grabbing a ruler to make a paper template. I used the template as a guide to mark with a pen where I'd drill holes in the Sintra.

Comments

[krogie]

How much would it cost if I want to build oe of these?

[jimmy dean]

It depends on what you have laying around. If you already have soldering equipment and plan on going ghetto for the programmer, I would say around $20-$25.

[hellstudios]

ahh, i have two servos, an msp430 launchpad, I just can't figure out how to get them to talk to each other.


Might you, kind sir, help me with this problem of mine?

[The Real Elliot]

So the only trick with (traditional, analog) servos is that they need a 1.5-2.5ms pulse every 20ms. The length of the pulse determines where they turn. You just make the pulse train with the micro and you're done!

Good luck.

[hellstudios]

hmm, do you mean through the signal wire?


you probably mean the signal wire.

[jimmy dean]

Yes, you provide 5v to the red wire, ground to the black wire, and the signal to the signal wire.

On the signal wire you provide anywhere from a 1-2ms pulse of 5v every 20 ms. 1ms and 2ms make the servo move to its limits, 1.5ms centers the servo, and everything in between moves the servo everywhere in between. Good luck. :)

[creatorroboto]

Great project but is the Code in C or C++? I'm an Arduinophyte. Sorry, I'm not the most hardworking person...

Once again, Great Project

[geeklord]

I need to learn how to write in C. Can I use C to programall microcontrollers??

[creatorroboto]

Nope. I tried uploading C++.

C++ = busted Arduino (if you're using one.)

Try getting the Turbo C bible...worked for me.

[Veve Tech]

When I heard Servo, I was hoping for Tom Servo lol

[alterator]

glue some rubber stuff on the ends of legs, so it doesn´t slip..

[pokeroz]

Is this The right setup for the brains

[salahaddam]

 They had one like this at

 www.middlecreekmerchants.etsy.com

[amando96]

oh and ermmm, could i make this using 555's??? i think i might be able to make a simpler one... hmmm

[andy]

Using a Hex inverter is a good trick, 555's would be capable but not very elegant. I strongly advise you look into using a 74xx240 type chip (replace xx with ac, hc or htc (different tolerances - they should all do the job though)), there are plenty of tutorials and the components needed are minimal. The circuit type you need is typically referred to as a bicore(or bi-core) and there are tutorials showing how to solder these up without breadboards/circuit boards. Don't be scared off by different chips or schematics, best way to do. Hope this helps, Drew

[amando96]

ya defenantly helped, although i just bought an Arduino... lol

[andy]

Sorry for two comments, but I just noticed, if you want simplicity try the One Motor Walker on this site, here's a link to the free-form tutorial for its control system, it links to the one motor walker tutorial. http://www.instructables.com/id/How-to-freeform-the-bicore-BEAM-robotics-/
Hope this helps,
Drew

[amando96]

whats is the code for an arduino? is it the same as that one?

[kasman]

can u give me the schematic circuit please.. hanif,malaysia

[DieCastoms]

Based solely on this 'ible, I built a 4 legged walker. Instead of the plastic substrate, I used bent and formed coat hanger wire, and instead of the atmega, I used a Futaba 4 channel RC receiver and battery pack. During the construction (which only took a half hour) I worried about whether or not I could control it manually in a manner to make it walk. I worried about having enough timing and coordination to manually control both servos. As it turns out, however, by putting both servos on the same stick (mind you NOT the same channel), spinning the stick in a counterclockwise direction produced forward (RAPID) movement, and spinning the stick in a clockwise direction produced backward (extremely unstable) movement. I am impressed with how simple this project turned out to be and how easily I was able to get good results, and I thank you for posting the 'ible. Mike, from DC.

[amando96]

so you just used the RC sistem? no additional circuits? cool :)

[DieCastoms]

I used two servos, the RC battery pack, the RC receiver, and coat hanger wire. NOTHING else went into the construction of the robot. I have made several different .... contraptions in which to use my RC system and servos, including several different "Sumo" bots with varying size tires and construction materials, and the walker. Eventually I will post the videos on YouTube under DieCastoms. Take a look. Mike, from DC.

[iw28]

how do I make the ic the chip ore the brain to the walker

[amando96]

hey i just built this! But i put the whole thing inside a cardboard tube, and the PIC i used is 6' tall 140 pounds... :P

[amando96]

u can make it climb higher buy putting wider legs... :)
and ermmm where did you get the brain?

[iw28]

hey i just want to ask to how to make the brain to the 2 motor walker

[Mike060187]

hi, can you pleas send me a clear picture or diagram of the circuit of the bot? [e-mail] thanks

[619rey]

WHERE DO I GET Drilled project board for the circuit Snap-off headers (male and female) for the servo and battery connections???????

[Derin]

rat shack may have them,but try digikey

[619rey]

WHAT IS A GROUND BUS AND A +BUS???????

[Derin]

the ground bus is a bus that travels on the ground,just joking read real explanation below The + bus carries the power and is similar to the positive of a battery. The ground bus is the exact opposite

[robotkid249]

Can you please post the code to use with the atmega168?

[Ankush]

nice!!

[Nitin Sharma]

plz give a cleam picture of the brain of this instructible

[Nitin Sharma]

hey i am making my firsy bot can i use "futobo 3003" istead of "Ts-53" as i am having futobo with me i don't have to spend my cash on buying ts-53

[The Real Elliot]

I think those two models are almost exactly the same. And most servos run on standard timings. So you should be good.

[Nitin Sharma]

plz mail me a nice circuit diagram(with all connections) of ur instructable [e-mail]

[Nitin Sharma]

plz give a clean circuit diagram of the brain of the instructable [e-mail]

[Nitin Sharma]

can u plz show the back side of ur brain as it is difficult to understand the sketch u have given in ur instructable plz show the backside, i'll be thankful to u for this

[metldrumer984]

hey whats the schematic for ur lil parrallel programmer. like what pins were.