Let's Make Robots!

Jansen Walker Toy (sized) Bot

Hello everyone,

This is my first post here, don't be rough.

I stumbled on the this site about a month ago while doing research on a bot i'm building that's similar to Rik's current Jansen Leg project, that's actually what I was searching for when I found the site.

Anyway, I wanted all of you input on my project, my version uses a similar leg design and I'm curently planning on powering it with two servos and an Arduino-clone.

 Leg-Pair-1-Animation_2.gif

I'm trying to decide on the size, either a medium sized bot that would be about 8 inches in height and width, or a tiny 3in version. There would be lots of space for sensors on the big one, very little space on the small one.

The obvious drawback to the big one is the cost of materials, it actually uses about 10x as much since the parts are bigger and thicker. The little one would be cheep to have cut, but would only have space for one or two small sensors.

I plan on making the plans publicly avalible to anyone that wants to build their own, which one would you like to see?

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So I've been kind of treating this thread as a dump for status updates on this project, if that's the wrong use of the forum please let me know.

Anyway, I spent most of last night designing the gears that will link the servo to the drive train, I'm hoping that a 1:1 ratio will be okay, the servos are surprisingly strong for how small they are.

By far the hardest part was getting the teeth on the inside of the servo gear just right, I wanted to just slip the gear onto the servo horn and have the teeth grip the ridges that are on the horn for gear traction. I was not sure if my laser could cut 15 teeth around a 4mm hole, that means the inside teeth are only about 0.5mm across! I was pleasantly surprised to find out that it could with exactly the right focus and power make a gear that grips the servo horn pretty well.

The teeth on the servo are so small that I had trouble counting them, I swore there were 16 the first 3 times I counted, but it ended up being 15.

Both gears will be 2 layers of plexi, one layer grips for rotation, the other stops movement along it's axis. The two layers are glued together to make somthing usable.

Here is a shot of my test material, a standard playing card, you can see the servo horn teeth well:

j13.jpg

 

Here is the first working acrlic gear, on the servo:

j14.jpg

Here is both gears together, note the screw that holds both in place:

j15.jpg

I just realized I did not  not take a picture of the other gear set, it was designed to fit around the nut of a 3mm bolt, and in comparison was pretty easy to design.

For my next prototype I think I'll try 2mm bolts on most of the parts of the leg, I think they are about half the weight as 3mm. I looked for alternatives like plastic ones at the hardware store, but they don't carry those kinds of things around here evidently.

I've offically posted this project as a bot, there's pictures of the 2nd prototype over at: http://letsmakerobots.com/node/6633

rik's picture

I beieve you're looking for the word "splines": grooves in a shaft.

About the forum dumping: you only run a risk that we will demand a proper writeup later on. Maybe better start now. This project has enough material and momentum to start a robot page now. Any good name for your vehicle/creature yet? Subscribed to Youtube, did you?

mintvelt's picture
I second (or third) the envy on the laser cutting. Those parts look just great.
rik's picture

CNC envy

Not so much envious about the 200x200mm restriction though. I would love to cut 12 parts from one sheet in one go.

OddBot's picture

I don't know about Rik but I'm suffering some serious envy over your ability to laser cut the parts. As for the weight of your nuts and bolts might I suggest nylon nuts and bolts. Some electronics shops sell plastic nuts and bolts for when electrical conductivity is an issue.

productLarge_1246.jpg

They will be lighter, look better and less likely to come loose. I find they tend to have more friction.

I've cut and mostly assembled the 2nd prototype, the design is getting very close to being finished.

This go around I added a battery storage area, and offset the driving servo so that gears can be used for turning the main drive shaft. I'm not sure what ratio I'll use yet.

There are still a few flaws that I'll need to fix, but ingeneral the design is very close to being finished.

Here are more pictures:

 

More Cut Parts, enough to build one walker:

j51.jpg

 

 The new battery compartment seen from the top:

j6.jpg

 

Battery Compartment and servos seen from the bottom:

j7.jpg

 

Base with Arduino mounted, I used hex stand-off nuts to keep the bottom of the board away from the other base mounting screws:

j8.jpg

 

The main body seen from the side, so you can see the layers of construction:

j9.jpg

 

A working leg pair, there will be one of these on each side, the legs are heavier then I expected with all the bolts and nuts required to tie them together. I may need to find smaller bolts for the extraneous joints. I'll also probably need to find some kind of rubber cap to put on the feet, they have very little traction.

j10.jpg

 

 One pair of legs on the body. Unfortunately the driving gear did not fit on the servo horn, so I will need to cut a new one:

j11.jpg

rik's picture

and blog worthy

Please post a photo from dead above, looking down on the legs. I would like to see how the layers of plex relate. Especially around the crank nut (which I call V).

Here is a picture from the top, it kind of hard to tell whats going on since all the layers look about the same from that angle, but i've put some notes on this one:

j12.jpg

rik's picture

That is hard to see. The transparancy does not make it any easier.

I did notice the spacers and extra nuts. My legs are designed as "floors of a building". Not a single floor is diagonal. Do I notice a few "diagonals" in your legs? That is, members that run from one layer (counting from the support layer) to another?