Let's Make Robots!

The rookie robot builder wannabe has drawings and a parts list!

Second blog on my first build, with some final things.
Well, final, is a drawing ever final until you've actually cut the parts and fixed them together?

Guess not, but we'll see about that later.

The drawing took me some days, since I had to figure out what CAD was again.
I did some CAD drawing in school, but that's about 10 years ago and I wasn't good at it then.
Searching for a freeware CAD program... Is there anything that Google does not have? Google Sketch-Up. The first 10 attempts at a leg assembly where horrible. It took me an hour to figure out how to draw a square in 3D, let alone draw something that looks like a leg.

A little explanation about the bot I am going to build is in place I think.
For one, it's not going to be the best looking bot ever. I am not trying to make an eyecatcher, I am trying to make a learning platform myself.
The parts of the bot will all be just square and practical. I already know how to use a saw, a drill, screwdriver and glue/bonding agent, so why go all the way?
I want to have a chassis that I can put together quickly and take apart just as fast, to experiment with what is possible.

So, what did I make?

First, the upper leg.
There is no servo in the picture, just some space for the servo.
I will make a custom bracket for it, but since I don't have the actual servo's yet, I can't draw that. Don't have the specific dimensions, just length, width and height.
Linky: http://i192.photobucket.com/albums/z50/benjipics83/Hexapod/upperleg.png 

As you can see, there is a little support piece for where the servo will go.
Also, I made a hole sunk into the material so I can put the servo horn in there, making it level with the surface. If this will work out as I like it to work out, I don't know. I'll see when I've cut out the first parts.

After that I created the lower leg.
This one is a bit different and took me a bit longer. Especially when I put all the parts together and found out that it wasn't long enough.
I had to adapt it, and I might have to change it more, or turn the servo's up side down, and thus change half of the drawings...
Here it is: http://i192.photobucket.com/albums/z50/benjipics83/Hexapod/lowerleg.png

Next was the chassis. I had to do the legs first, so I would know how much room I would need between my upper and lower deck.
The controllers will be placed between on the lower deck, so I have space on the top for other cool stuff that I have not figured out yet.
It's pretty much straight forward, 2 squares of 500*250mm, with some support posts in between.
Linky: http://i192.photobucket.com/albums/z50/benjipics83/Hexapod/chassis.png

Last piece I had to draw was the head piece. This will feature the only sensor I have planned so far, which will be an ultra-sonic sensor (the SFR04 for those familiar with it).
I made it more complicate than required, but I want it to be a sturdy piece that won't start wobbling around, giving me weird readings.
Click! http://i192.photobucket.com/albums/z50/benjipics83/Hexapod/headassembly.png

It took me a couple of days to draw it all, and I will most likely have to change everything a few times to get it all right, but you get the general concept.
I combined all the pieces to give myself an impression on how it's going to look.
Like I said, I just started using Sketch-Up, so some things are a little off. It's only an impression, so it'll look better when it's done (is what he said before he started cutting the pieces...).

Hexapod assembled

So, that's basically what it's gonna be. No beauty, just some square pieces smashed together.
When it is all done, walking and doing what I want it to do, I will spend more time on a good design and build a piece of eyecandy, and then just transplant all it's internal organs, but for now that is not my mission.

A you might be able to see, if I build it like this the ground clearance will be about 2 centimeters. That is not going to be enough for me, so I'm thinking of how to fix that. One option is going 3DOF right away, but that is going to be even harder to program as a first robot.
Another way is bending a part on the upper leg down, so it will have more clearance that way, and making it a bit more narrow at the same time.
The easiest way is extending the lower leg assembly some more. On the inner side it is already 8cm, so that will be a really long leg.
Option 2 seems the best one for now, I will head back to the drawing table for that this week.


So that is the drawings.
What is more important, the thing is gonna need a brain and something to drive those legs with.

Also, it needs to be built from something.
Some of you might have seen my topic on the forums, regarding the thickness of the material to use.
In that topic 2 materials came up.
Acrylic and Lexan.
I am still in doubt which I will pick. Acrylic is a bit more easy to process. Especially since I am going to have to use some bonding agent to put some parts together. The bonding agent for Lexan is an awful piece of chemical, which is highly carcinogenic.
Acrylic has a bit more friendly bonding agent, so that is certainly something that pushes me to acrylic.
Also, the price... Acrylic is much much cheaper. I know, Lexan is tougher, so I'm not completely sure what I will use.

in any case, I am going to buy 5 sheets of 500*500*3mm.
3mm Should be thick enough, and the 500*500 plates are the easiest to get shipped to my house.
5 might seem to be a lot, but I want to make sure I have enough, if I screw a sheet up and I don't have enough, I'm gonna be pissed. So, I'm just ordering a bit more, and if I don't screw up I have some in stock for future projects

Even more important are the electronics.
In my previous blog I already told about what I want to use, but I made it all final and put it on my shopping list.

Some notes on that:

  • The Servo's are not my final choice yet. They are not record breaking speed monsters or the strongest servo's on the market, but they are cheap and reliable. I might go with something stronger later on when I am more experienced and want to make a fast runner
  • I did not put all the basic stuff on there, like batteries and general electronics. I will purchase that as I go. I can have most electronic parts shipped to my house over night so that will not be an issue


The actual list:

  • 1x Lynxmotion SSC32 servo controller board
  • 6x Power HD 1160 A mini servo
  • 7x Power HD 2400 A standard servo
  • 5x 500*500*3mm acrylic/lexan sheet
  • SRF04 ultrasonic sensor
  • random electronics/batteries
  • random tools (saw blades, drill bits, etc.)

ofcourse there will be screws, nuts, bolts, washers, etc, but I have a shed full of those so I can pick up whatever I need.

That is basically it for now.

As soon as I get the hardware in I will start building some stuff and continue my journey in a project.

Any tips, comments or smacks in the back of my head are always welcome!

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GeneralGeek's picture

This is going to be cool! I can't wait to see the finished robot. This seems pretty ambitious for a first robot, but you have a clear idea of what you want to do and how you are going to do it.

Thanks for the reply.

Yeah it's ambitious. But why do something that has no challenge in it?
When I do something, it is going to be hard, take time and make me develop skills that I don't have yet.
If I know how to do something, I will only do it if I have some use for it.
This robot is not usefull, but the skills that I will have to develop for making it will give me the possibility to build stuff that I do have use for.

It's a hobby project  and it will take me a long time creating it, but I have the time and am in no rush at all :)

birdmun's picture

First, I would rotate the should/hip servos to be inline with the body instead of sticking out from it. Second, be sure to only add material for stuctures sake rather than to cover this or make that look pretty. You are after all going to be working with servos and the weight savings will go a long way to helping the robot move.

Thanks for the tips.
Yeah I was pondering on twisting the servo's a quarter so they would be inside the body completely.

As far as I can see there is nothing to make it all look pretty, it's all there to make the thing sturdy. I didn't go for looks at all, like I said in the blog, since it is a learning project.