Super Cheap 3D printed 12 DOF legs - Mega 2560

Here's some 3D printed legs I am working on. Shame I can't embed the youtube vid, but here is the link:

Link update on 25-06-15 to show newest video!!

I'm trying to avoid using servos and all pre-made code/parts/systems etc as I am trying to build a much lower cost system for robotics. I believe that the current obsession with the most expensive servos and controllers is a problem. Robotics shouldn't just be for 40+ IT professional blokes.

These legs with the motors, drivers, rotary encoder sensors and Mega 2560 (clone) comes in at around £30.

As you can see, it's in the very early stages. I am basically trying to make a complex biped similar to NAO, Darwin, etc, for below £100. I reckon it's possible for £60.

I've written an arduino code that remember positions and recalls them when a number is entered into the serial, but now I need to write one that replays those positions over in sequences so I can form complex movements.

Will post some updates when I've got it walking!

Let me know what you think!

I should add, the 3D printed parts were designed in the 2008 free version of Google Sketchup, which is unfortunately no longer free. But luckily I still have it installed on my old macbook! With a little practice you can pretty much do everything you need interms of 3D printing.

I should also add, that whilst I'm using a clone Mega 2560 for this project I did buy the official Uno when learning bout arduino.

The parts were printed on the Velleman K8200 3d printer. The K8200, that's another story, it took me a whole weekend to build!!! But soooo worth it. I waited until maplins were offering it for £450 and snapped it up. I can see places on the internet offering for £400. Maplins now does it for £600. Feeling smug!!!

If I can get it walking and add a torso etc, I may event polish it up and do a proper instructables with info on the parts, techniques, code, STL files etc.

At present the knees, hips and ankles are struggling. They easily hold up the two 9 volt batteries that power it, but I wonder how well they would do with a torso and arms etc. The end goal is to have something that can walk and interact with object around it.

CRAZY LEGS!!!

Well, not quite walking yet. Spent some time working out how to code the legs to learn positions and then play them back over a sequence. Should be simple but took me ages to work out. Haven't been coding for very long.

Frustratingly, I am having real difficulty creating the slow, controlled motions required for walking. The problem is, I can't control voltage output to the motors because the ard outputs digital and the dc motors I'm using don't respond well to PWM because they require a charge to hold the gears in place, otherwise the legs become unstable and cause wobbling issues.

My plan was to create a variable for each motor that increments smoothly between two set movements and the motor would try to follow that variable, but alas there is something about the way I am coding which creates a horrible jerking motion when the motors follow the incremental variable. Probably not quick enough to measure that variable and keep up.

The crazy legs above is playing back a sequence of 20 taught positions in fast succession that I taught it by moving them into position and then pressing 'l' and a number to save those positions into the eeprom.

It's powered by two 200mAh, 9 volt batteries at the moment so you can hear towards the end the batteries start to get tired!! They don't last long!


EDIT!!! After much consideration I have decided that I am going to ditch this configuration of legs. The knees,hips and ankles need an extra cog each to make it so the legs can maintain a position without a charge being applied to the motors. This basically means an entire redesign and tons more 3d printing. What it also means, is that the result is going to be 1.5 times bigger. This takes the overall humanoid size to about two foot!! Which I'm sure you'll agree is pretty big for a beginner roboticist! Well I won't post any more updates until I have the new design, designed, printed, constructed and programmed.

What I do have from these legs however is an interesting talking point the next time I host a party, and absolutely tons of ready made design concepts and code, that I can bring to the bigger design.

Hi everyone, Since I first posted this a while back, I have made leaps and bounds and will post a new video below!! Redesigned the legs and got much better at programming. I have implemented PWM control on my cheap DC gearboxes and I've really got to grips with most of the more common c++ programming techniques now. Let me know if anyone is interested in hearing more. I have a page for this project on letsmakerobots.com here :

But what I'm most excited about is the video of it moving around :

So - I didn't delve into your LMR postings in great detail - but I was wonder what 3D printer you are using to create the parts? All in all, though, it looks like you coming along really well with the project. I can't wait to see future updates! :slight_smile:

Hi cr0sh, thanks for looking. I use a velleman k8200. I got it on offer from a uk shop called maplin. It’s really great but it is let down by a bad z-axis wobble which causes the prints to have horizontal ridges, which can really detract from the overall accuracy of the print when making mechanical parts. I am planning to fix the wobble by straightening the lead screw and also implementing a flexible coupler as many others have done.