Picture of Simple Bots: Inchworm
If you can count on only one thing, it would be a ruler. Now, don't get me wrong. I am not talking about supreme despots for life, or anything of that sort. The rulers that I am referring to are the measuring kind. After all, how can you not count on something with so many sequential numbers? That is why, when it came to deciding what the armature for Inchworm Bot should be, the only thing I could think of was my good, dependable friend, the ruler. After all, in the grand scheme of things, there is merely inches of similarity between the two.

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Step 1: Go get stuff

Picture of Go get stuff
You will need:

(x1) continuous rotation servo modified for direct drive**
(x1) 18" aluminum ruler (or longer)
(x2) small plastic container
(x2) 2" - 3" fixed casters
(x1) bic Classic pen
(x1) comb
(x10) small nuts and bolts
(x4) small washers
(x1) 2" - 3" metal standoff
(x4) zip ties
(x1) DPDT lever switch
(x1) 4 x AA battery holder
(x4) AA batteries
(x1) red and black wire
(x1) electrical tape

**Learn how to modify a servo motor for direct drive at this page.

Step 2: Cut the ruler

Picture of Cut the ruler
Use a hacksaw and cut the ruler into two 9" sections.

(The convenient thing about cutting a ruler is that it comes pre-measured.)

Step 3: Fold a notch

Picture of Fold a notch
On one of your 9" sections, make two cuts 3/4 of the way through the ruler at 1/2" from the edge and 2-1/8" from the edge.

Place the ruler in a bench vice so that the bottom of the cuts are level with the top of the vice.

Hammer the section between the two cuts flat such that it is made perpendicular.

This will be your motor mount.

Step 4: Drill holes

Picture of Drill holes
Place your servo motor into the slot you just cut and use a pencil to mark where its mounting holes are.

Remove the motor and drill through your marks with an 1/8" drill bit.

Step 5: Drill more holes

Picture of Drill more holes
Drill a 1/4" hole that is 1/2" from the edge of the the cut ruler section. Repeat on both.

(Obviously, on the piece that you have already worked on, the hole has to be drilled on the opposite side of the motor mount)

Step 6: Even more holes

Picture of Even more holes
Detach your servo horn from your motor (the gear-looking object).

Use your servo horn as a guide to both mark and drill 1/8" holes through the section of ruler that does not have the motor mount.

These holes should be drilled roughly 1/2" in from the edge of the ruler.

It is preferential if you simultaneously drill the servo horn, as to ensure identical sized holes.

Step 7: A few last holes.

Picture of A few last holes.
Drill an 1/8" hole, centered upon the section of the ruler with the motor mount, that is 5" from the edge with the mount.

Drill a 3/16" hole upon the section with the servo horn mount that is roughly 5" from the edge with the servo horn mount and close to the edge of the ruler. Drill a second larger 1/4" hole that is 4" from the servo horn mount and centered upon the ruler.

Congratulations! You are finally done modding the ruler.

Step 8: Mount the motor

Mount your motor to the ruler, using nuts and bolts. Make sure that the motor mounting holes are on the same side of the ruler that the mounting bracket protrudes towards. The only mounting hardware that should be on the other side of the ruler are the screw heads. This ensures a low profile when the two sections of ruler move back and forth.

Attach that servo motor's horn, if you have not done so already. Use nuts and bolts to attach the other section of the ruler to the servo horn. Again, the screw heads should be facing inward towards the other set to ensure a low profile.

Step 9: Modify your comb

Picture of Modify your comb
Use diagonal cutters to remove two inches worth of teeth from one side of your comb. However, I found it is beneficial to leave a few teeth on right at the edge. Later on, these few extra teeth will help act as a safe guard to keep the comb on track.

When you are done removing teeth, sand that section of the comb smooth.

Lastly, drill an 1/8" hole on the opposite edge.

Step 10: Attach your comb

Picture of Attach your comb
Pass a screw through the hole you drilled in the step prior.

Once it is passed through, place 2 - 4 washers on it. The point of these washers is to push the comb towards the other section of ruler (once mounted).

Next, pass the screw through the middle hole, in the section of ruler with the motor, from the inside out. Use your bolt to securely fasten it in place.

Step 11: Wire up the switch

Picture of Wire up the switch
Remove your switches' mount nut and insert it into the 1/4" hole on the servo horn section of ruler, Make certain to pass it through, such that the switch lever is facing inwards. Lock it in place with its mounting nut.

Solder a red wire from the bottom left corner pin to the top right. Solder a black wire from the bottom right, to the top left.

While you're at it solder the red wire from your motor to the pin on the bottom of the switch with the red wire and the black wire from the motor to the pin on the bottom with the black wire.

Lastly, solder a long red wire to the middle pin on the side with the red motor wire and a long black wire to the middle pin on the side with the black motor wire.

If you are confused, just look at the wiring diagram below.

Step 12: Standoff

Picture of Standoff
Mount the standoff to the servo horn section of the ruler such that it is facing inwards in the same direction as the lever switch.

The comb will rest atop the standoff.

Step 13: Spacers

Take your ballpoint pen and remove the ink cartridge such that you are left with a hollow tube.

With a razor blade, cut down on the tube creating two 1" sections.

Take the two sections and cut them in half, creating four 1/2" sections.

Step 14: Remove the wheels

Picture of Remove the wheels
Take your two casters and remove the wheels.

Set the wheels aside for some later project.

Step 15: Pivots

Center the caster frame atop your plastic container.

Use the holes in the caster as guides for drilling 1/8" holes in the lid of the container.

Zip tie the caster frame in place to create pivots.

Step 16: Power box

Picture of Power box
On one of the plastic container lids, drill an 1/8" hole in the corner.

Place the battery holder inside and pass the power wires through the hole.

(I know that it shows batteries in the holder, but I recommend not inserting batteries before you solder.)

Step 17: Put it all together

Using the caster mounting hardware and the pen spacers, attach the rulers to the plastic containers.

Basically, the ruler should have a pen spacer on each side to hold it in place. If it seems loose or tipsy, insert metal washers between the spacer and the ruler until it is not.

Step 18: Power connections

Picture of Power connections
Before you start, make sure at least one battery is not in the battery holder or the motor will turn on, making your job here very difficult.

Solder the red wire from the switch to the red wire from the battery holder and cover it with electrical tape.

Solder the black wire from the switch to the black wire from the battery holder and cover it with tape as well.

Step 19: How it works

Picture of How it works
Basically, it works by reversing the direction of the motor each time the comb hits the switch, which, in turn, forces its "feet" to slide back and forth. Since one side is weighted down with the batteries, it has more forward momentum in one particular direction.

So, as the motor turns, the comb slides to one end and hits the switch. This then causes the comb to slide back to the other end, to hit the switch once more. Rinse. Repeat.

If you find that the motor does not reverse when the switch is pressed and the bot folds itself up into an ugly mess, first REMOVE THE BATTERY! Once you have done that, rotate the switch 180 degrees. Now put the battery back in. When the switch is pressed, it should reverse direction.
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LEducated2 years ago
Thanks to you Man.I official made my first ever robots.This will be the start of my adventure to more robot applications.More power to you again.
My own version thanks.still open for revision.
randofo (author)  LEducated2 years ago
This awesome! Glad to see this worked out for you.
randofo (author)  LEducated2 years ago
Do you have a picture?!
boston094 years ago
this was a fun project, thank you.

i might add some wheels soon
I was so inspired by your work that I put an inchworm bot together out of industrial scrap at work.
The only thing that's new is the gear motor.

I look forward to building more simple bots like yours out of industrial scrap!

Thanks for getting the wheels turning in my head!
randofo (author)  strider_mt2k2 years ago
Hi. Your flickr link appears to be broken. I was wondering if there is anywhere else we can see pictures of the bot you made? I recall it being pretty cool.
where are the spacers used??
randofo (author)  vinayakniraj00022 years ago
They are used in connecting the rulers in the center of the caster. See step 17.
isadcari2 years ago
is this a 2 pole 2 trow switch?? ...
randofo (author)  isadcari2 years ago
this is the most complicated model to make...
really tough
my switch isnt being flipped
could someone help me?
randofo (author)  sviswanathan3 years ago
What happens when you turn it on? Does the comb keep trying to push down on the switch? If it keeps applying force and does not reverse, then the switch is backwards. Simply, spin it around 180 degrees.

If the comb misses the switch altogether perhaps try elongating the switch by hot gluing a pen cap onto the lever.

If it is doing something else entirely, explain what is happening and I'll see if I can help.
jmacco3 years ago
great projet, i like it and is my project for the science fair
khobis4 years ago
it's really an awesome project.. i'm gonna build it as soon as i collect those stuff's
zap80044 years ago
could you use a 12' ruler
randofo (author)  zap80044 years ago
Sure, but you would need two of them. I used a single longer one simply because it was cheaper.
zap8004 randofo4 years ago
do I need to change other mesurements
bears04 years ago
i want to use a servo driver for RC cars, it has two servos and i want to substitute a servo for a motor, i'm planning on making an electric boat and i cant use a servo to make it go, if someone could tell me how it would be greatly appreciated.
axeman9114 years ago
what is an arduino?!!!
randofo (author)  axeman9114 years ago
An Arduino is a small programmable micro controller (circuit board) that plugs into your computer and you can use it to read sensors or control motors, electronic switches and other things that move.
Carnavislol4 years ago
can the Tupperware be about 3" tall?
randofo (author)  Carnavislol4 years ago
I don't see why not. May as well give it a try
Carnavislol4 years ago
wait should i get the continuous rotation servo motor or t he standard one...
randofo (author)  Carnavislol4 years ago
It doesn't matter. The controller is removed and it never rotates far enough where it will hit the stop.
Carnavislol4 years ago
That so awesome! I'm gonna build it soon with my friends! Very explanatory guide!
hyw_scott4 years ago
Nice, try to make one.
Kiteman4 years ago
A few broom bristles, taped to the side of the boxes, angled towards the rear and projecting slightly below the boxes should encourage forward motion, especially on carpeted surfaces. (Another nice one, Randy!)
randofo (author)  Kiteman4 years ago
I considered doing something similar involving pivoting doorstops, but didn't feel like adding a few more steps. Brush bristles would give the same effect in one step and is actually a really great idea.
muskogee4 years ago
also could you use a 9 volt instead of 4 AA's?
randofo (author)  muskogee4 years ago
A 9V battery is 3V more which is probably a little too high for the motor.
muskogee4 years ago
Instead of using a comb... couldn't you use another ruler? Maybe a 8 inch plastic one would work.
matstermind4 years ago
this reminds me of the most useless machine ever
macrumpton4 years ago
Very cool. It occurred to me that if you had a pendulum on the joint that shifted a weight over the rear leg when you are pushing the legs apart and shifted the weight over the front leg when the legs pull together, that there would be a lot less slippage. another approach would be to use some wheels with a ratchet that allowed only turning in on direction.
Nice work, great Ible. As a kit I used to have a construction kit for an inch worm "robot" with at its "feet" wheels with a ratchet blocking any backwards movement. It moved quite fast. You could ad something similar with yours. If you want to avoid wheels (to keep a more annimal like type of propulsion) you could add something else that allows forward movement and block the forward movement. Inclined bristles should work, which would give birth to a completely new type of bristlebot.
Dr KAZ4 years ago
I agree, the ruler RULES! It can be used to (indirectly) measure mass, capacitance, resistance, magnetic flux, velocity, etc. etc. etc. and if you are very creative it can be used to measure the iron content of spinach. Trusty old ruler. Thanks for a useful, clear, fun, cheap, instructable!
inblack4 years ago
Add some grip on the boxes and it sould run faster!
WingDings4 years ago
Great idea on the comb! That's a really innovative idea. Good work on the clear instructions and photos, too.

Could you also drill a larger hole in the ruler attached to the servo horn (the size of the other side of the servo horn that fits onto the servo spline), in the centre of the four holes that the servo horn bolts go through?

That way you could affix the servo horn, in the same orientation, but with the servo horn arms on the other side of the ruler and the spline side passing through the ruler. That would make the ruler attached to the servo horn a bit closer to the servo bearings, perhaps reducing the side-loading on the servo bearings?
Lindie4 years ago
I was anticipating how you made an inch worm, till I saw it. Very nice! LOL!!!
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