Crap-Crab ... The quadruped

Let's Make Robots Robots
1

Look maaa', no tools! :D

Well, that's not entirely true, but it isn't far off. I have constructed this robot with a minimum of tools (and materials) , for the simple reason that I don't really have any (nor the skills to use them).

So given that it's a somewhat crappy build, made mainly out of crap I found lying around, held together largely by double sided tape, plus that it looks sorta like a crab, I thought the name Crap-Crab would be appropriate. And besides it does have a bit of a ring to it, doesn't it? :D

To be fair I did use some screws here and there, but ONLY when they could be fitted without doing any drilling or anything "complicated" like that.

So far the tools I've used are:

- A screwdriver
- A pair of scissors
- A 50 cents dull hobby knife
- A lighter (for heating up a bended paperclip)
- A paperclip (for burning screw-holes in the CD)

The materials used are:

- 12 small servos (plus horns)
- A Sharp IR-sensor
- A Two CD
- 4 rubber bands
- 16 32 assorted screws
- Double sided tape (quite a bit)
- Normal tape
- Instant glue

Besides, I used 8 16 of these thingies (see foto below). I have no idea what they are. I was simply walking on the street, thinking about how to construct a robot leg, and I found a bunch of these lying on the ground (near a construction site I believe). They're kinda like meccano-pieces, only made of plastic and weigh nothing. If anyone knows what they are please let me know :)



And finally I used 12 28 of these (see foto below) in combination with the screws. I don't know what they are either.


 
Anyhoo, the legs are a bit wobbly as is, so I'm currently thinking about reinforcing the upper joints with an extra construction-site-thingy. Not sure how yet. I'm thinking the best way would be glueing a nut to the servos on the opposite side of the shaft. I made a demonstration hereof using tape (see foto below). Any ideas here are welcome.

The brains of the robot will be an Arduino (Duemilanove) and a breadboard mounted on top of the CD.

The (main) purpose of the robot is to experiment with adaptive/heuristic walking methods, using various forms of internal sensing (eg. servo feedback) and AI's (eg. neural networks). For instance I would like it to automatically improve it's walking gait by practicing and be able to adapt to walking on uneven surfaces, where a fixed gate would be inappropriate. But I'll get into that later. For now I just wanna finish it and experiment with different types of fixed gaits.

Here are some more pics of Crap-Crab:

 

 

UPDATE 26-8-2014:

Not much progress today. Went to several shops looking for screws/nuts suitable for reinforcing the upper leg joints (as mentioned earlier), but small screws aren't that easy to come by it seems. Still open to ideas on this issue.

On the up side... My father-in-law sawed my old breadboard in half, so now I have two small ones (nice!). I also bought som pin headers and prepared the board for the servos, plus I made some jumper cables for the bot. All of which can be seen on the pic below.

So now I guess I have to add my cheap old soldering iron and a nail-clipper (for seperating the pins) to my otherwise spartan tool list. And perhaps a saw too, allthough I wasn't the one wielding it :D

Oh and thanks for the nice comments. Appreciate it. It's good to be back on this website, after a long break from this community and robot-fiddling in general.

Cheers!

 

UPDATE 27-08-2014:

As mentioned earlier I need to reinforce the legs (with an extra "bracket"), as well as the body (with an extra CD), but for now I put that on hold until I figure out the best way to do it. Instead I connected all the wires (see foto below) and started playing around with the leg movements.



But I'm having a lot of troubles with the servos. Instead of posting them here I created a forum topic to ask for help on these issues. If you are able please feel free to give some input on the matter.

I'm also having some problems with the weight distribution, but I suppose that's simply because the Arduino board weighs more than the breadboard, so I should move both back somewhat to maintain the center of gravity in the robots center.

 

UPDATE 31-8-2014:

As mentioned I had some problems with the servos. Turns out powering 12 servos through a breadboard isn't a good idea (noob mistake). But that left me with a dilema, since I am reluctant to give up the breadboard at this stage, thus leaving little room for experimentation.

My solution was soldering a tiny piece of perfboard which handles the main supply line for the servos, but then plugs into a breadboard feeding the individual servos. I put on a 1000uF cap for leveling things out a bit. This tiny buggar handles 6 servos, so I'm making one more.

I also bought some 0.1uF, 10uF and 100uF caps for trying out with the individual servos. Additionally I bought a 4017 decade counter to see if I can control the servos with that, as described here, thus freeing up a lot of pins. Started reading up on that.



Besides that, I'm STILL trying to figure out the best way to reinforce the uppper leg joints, which has turned into a bit of a conundrum, given that it's hard to find the things I need, eg. small screws WITH nuts. So again I'll just have to use whatever I have lying around.

For now I've come up with the following... I glued two of these tiny rubber thingies (see bottom left) to the side of the servo (using super glue), and then simply put a screw through the holes in them. At first it was too wriggly but then I put a bit of heatshrink on the head of the screw, and now it's a pretty tight fit. If I also put a tad of glue on the tip of the screw before screwing it in this might actually work, but I dunno...

 

UPDATE 6-9-2014:

Finally got around to finishing Crap-Crab version 2.0 :) Well it looks sorta the same, BUT this is a much more sturdy little critter. Here he is:

The body is now two CDs glued together, instead of one, and I added two tiny screws for attaching the servos horns, where before it was just fixed with the one screw through the servo axis plus double sided tape:

But most importantly I reinforced both the upper and lower parts of the legs with an extra "bracket" each:

Now the critter actually looks like something that could eventually walk without falling apart trying :D Guys I gotta admit... I think I'm a wee bit in love :P

Ah and also I finished and tested the two boards I soldered for providing the juice for the servos:

That's about it for now :)

This is a companion discussion topic for the original entry at https://community.robotshop.com/robots/show/crap-crab-the-quadruped
2

WOAH!

Wow that is super impressive, GREAT WORK! I cant wait to see the finished robot.

3

That is just NEAT!
I applaud your improvisational skills.

And I’d really like a bag of those plastic pieces you found so I hope somebody tells you what they are. :slight_smile:

I now think that rubber bands and paper clips should go on all BOM, if just to give people something to think about.

4

More like Lab-Crab than Crap-Crab!

Cool base! I’d never thought about using cds for plastic base! Glue or two screws should be enough to fix servo horns. Go on:)

 

5

That’s a nice - limited to

That’s a nice - limited to the minimum - build. I am looking forward to a video with your walking style. My Chopstick Junior did never receive an updated walking routine, hope yours will :slight_smile:

6

This is great. As for

This is great. As for reinforcement, I left the legs of my quadruped wobbly, because I noticed that it adds very nice amortization and makes it much harder to strip the servos – it can even fall from heights safely!

Then again, I have a larger quadruped for which the wobbliness is not so nice, so I plan to drill a hole in the back of the servo (it’s the part there the electronics board is, so there is some room) and put a screw through there. I guess you could use the hot paperclip too. That tape doesn’t look like it’s going to hold very well for a side force. You might also want to use a second CD on the bottom, to make the horizontal servos more stable too – especially when you add more weight to your robot.

By the way, if you are looking for rubber for the leg ends, I’ve successfully used rubber washers, headphone rubbers and most recently earplugs (noise stoppers).

7

Thanks :slight_smile: And me neither…

Thanks :slight_smile: And me neither…

8

Thanks for mentioning my

Thanks for mentioning my improvisational skills. Makes me think that all those hours of playing Jazz guitar haven’t been wasted after all :smiley:

And I too hope someone here will know what the thingies are. Whatever they are they must me cheap, since I found them on the street, and in this country (Argentina) NOTHING that has any value can be found anywhere. Even if you leave a cartboard box on the street someone will pick it up quickly and sell it as recycle paper for a few cents.

9

Yeah CDs are pretty cool.

Yeah CDs are pretty cool. But I believe I have seen them used in several robots around here.

PS: I prefer the name Crap-Crab :wink:

10

Thanks. That was the

Thanks. That was the intention. And I should perhaps mention that while tools, mecanics and (to a certain extent) electronics is somewhat mumbo-jumbo to me, I do have a background in programming and computer science. So my interest in robotics is mainly due to the AI aspect. In other words I plan to spend a lot of time experimenting with different approaches to making it walk. That is… IF I get the damned critter working mecanically speaking :slight_smile:

11

Update!

Thanks for the comments guys. I added a small update to the description. Still open to ideas regarding the reinforcing of the upper leg joints…

Cheers!

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Again thanks! As for the

Again thanks! As for the wobbliness I think in my case the issue is getting rid of it as much as possible. In particular reinforcing the upper joints is a must I think, because it’s causing the legs to bend, even now with no weight.

I’m also considering how to add an extra CD to reinforce the body. Not sure how yet. What do you mean by “on the bottom”? I was thinking about either adding an extra CD on top of the existing one (the easy solution), or one just below so that the servo horns are sandwiched between the two CDs. Is that what you meant?

Also I’m not sure what you mean by “That tape doesn’t look like it’s going to hold”? If you mean the tape attaching the servo horns to the CD, I think it might hold quite well, since there is a screew there too. Even so I was thinking about adding two more screews per horn (and I just found 8 appropriate screews… though without nuts), but mainly to get rid of the wobbliness. But I guess it’s an allround good idea.

If however you mean the tape holding the two upper servos together, that’s possibly the most stable part of the whole construction. This double sided tape is pretty strong. I didn’t like my first attempt at joining two servos and it was actually extremely hard getting them separated again.

Ah and you noticed my attempt to make a “foot”. I tried using some insulating tape over double sided tape, and lastly some normal tape above to fix it better to the leg. It might actually work. But in that regard I’m still completely open, so thanks for the tips.

And in general thanks a lot for your input. I really appreciate it. Cheers!

13

Sorry I wasn’t clear. My

Sorry I wasn’t clear. My comments are all about the joint at the back of the servo – I noticed you used a double-sided tape to attach a bolt nut to the back of the servo, and that’s not going to hold. As for “cd on the bottom”, I meant doing the hole-and-screw thing at the backs of the horizontal servos, and putting another cd with holes on the bottom of the robot’s body, to hold the bottoms of the horizontal servos together, so that the whole construction is more stable – pretty much what you are doing with the femurs already.

It’s really hard to talk about this without having proper words for naming the parts. The leg segments are called coxa, femur and tibia, but there are no names for the joints, I propose hip (the horizontal one), knee (middle vertical) and ankle (last vertical).

So what I mean is to put a screw through the backs of the hip servos, and through the holes in another cd, so that the hip servos are sandwitched between two cds. Then you can put the battery in there (it’s heavy, so you want to have it low). Oh, and remember about washers for those!

14

Nice work on your very

Nice work on your very ingenuitive design. Forget a walk, this robot will stomp across the park! Look forward to seeing it in action.

15

Thanks!

And sure it will… or fall apart trying :smiley:

16

Ah THAT tape… Well that

Ah THAT tape… Well that was just made for illustrating my idea. It was never my intention to use tape for that. I was thinking super glue actually.

And now I understand what you mean by “bottom”. That is an option too, allthough by far the most complicated one. But I am considering it too.

And thanks for the lessen in nomeclature and your tips in general :wink:

17

New update and servo problems!

Added an update with the latest progress (or lack hereof). As mentioned I’m having a hell of a time with the servos. I created a forum topic asking for advice. Any help would be very welcome…

18

Batteries are by far the

Batteries are by far the heaviest thing on a robot, even if LiPo are light compared to other materials.

 

19

Ah yes that I am aware of,

Ah yes that I am aware of, but for now it’s running of external power. Besides I plan to place the batteries exactly in the middle under the CD…

20

Added an update. Progressing

Added an update. Progressing slower than I had wished. But nonetheless progressing :smiley: