How to Make an OAWR (Obstacle Avoiding Walking Robot)

This Instructable shows how to make a little walking robot which avoids obstacles (much like many commercially available options). But what's the fun in buying a toy when you can instead start with a motor, sheet of plastic and pile of bolts and proceed to build your own. Well I hope you share this attitude and please enjoy.

update - coming soon, lovely prepackaged kits from oomlout

Features:

--No difficult to source parts (no switches, relays, or IC's (everything but the motor is available at Home Depot).
--No soldering.
--Has a Mechano for grown-ups feel.
--Choice of options for cutting out pieces (scroll saw & drill, access to a laser cutter, purchasing online from Ponoko).

A quick video of the finished product walking through frame:

( A longer video of it navigating between obstacles can be found on step 7 )

Notes:

(If you would like any of the files in an editable format they can be found on a parallel Instructable here )

(Coming Soon, an Instructable on how to use a microcontroller (Arduino) to control the robot)

(I have used metric units and components in this Instructable. However those more familiar with imperial units do not despair, replacing the metric component with their nearest imperial counterpart should work (although I have yet to test this)) .

Step 1: Parts & Tools

All parts, with the exception of the motor, can be found at any Home Depot. The motor can be ordered from a number of online stores for about $10.

(there is also a pdf version of the parts list attached to this step '21-(OAWR)-Parts List.pdf')

Parts List:

Nuts and Bolts: (~$10)

• 3mm x 15mm Bolt (x20)
• 3mm x 20mm Bolt (x2)
• 3mm x 30mm Bolt (x9)
• 3mm Washer (x48)
• 3mm Nut (x45)
• 4mm Nut (x26)
• 5mm Washer (12mm OD) (x2)

Electrical:

• Various Colours of Electrical Wire (~$5)
• Crimp Wire Terminals (red 5mm ring) (x18) (~$2)
• 2 AA Battery Box (x2) (~$2)
• Motor (Tamiya twin motor gearbox (#70097) (available from many online sources) ( on froogle ) ( manufacturers site ) ( sparkfun ) (~$10)
• Crank Set (Tamiya 3 mm Diameter Shaft Set) etamiya ) (<$10)

Miscellaneous:

• Acrylic (150mm x 300mm x 3mm thick) (~$6)
• Whisker Wire (260mm x 1.6mm)(or two large paper clips) (~$1)
• Elastic Band

Tool List:

Required:

• Printer
• 5.5mm Wrench (x2)
• Screwdriver
• Pliers
• Crimp Terminal Crimpers
• Hot Glue Gun

Additional Tools Depending on Choice of Sourcing Acrylic Parts

Option 1 (Scrollsaw & Drill)

• Glue Stick
• Scroll saw
• Drill
• Drill Bits (3.2mm, 12.5mm, 16mm)

(I was going to use this option however I snagged a free shipping coupon from Ponoko so instead had my pieces laser cut)

Option 2 (Ponoko)

• A Ponoko account

(option I used)

Option 3 (Access to a Laser Cutter)

• Access to a laser cutter

Step 2: Cutting Pieces

Please chose which steps to follow based on the cutting option you have chosen.

Option 1 (Scroll saw and Drill)

• Download and print the pdf pattern (please choose the file corresponding to your paper size) -A4 size paper ( '31A-(OAWR)-Scrollsaw Pattern(A4).pdf' )-Letter size paper ( '31B-(OAWR)-Scrollsaw Pattern(Letter).pdf' )(it is important to not scale the drawing while printing)
• Measure the ruler on the printout against a ruler you trust, if they do not match the pattern has been scaled and you need to look at your printer settings before reprinting. If they do match up, onwards.
• Glue the pattern to the acrylic sheet.
• Drill holes
• Cut out pieces using a scroll saw

Option 2 (Online Digital Manufacturing; Ponoko)(this is the option I used)

• Get a Ponoko account ( Ponoko )
• Order the pieces here . (they are priced at cost ($11.47 Cutting cost + $8.28 material cost = $19.75 + Shipping (a warning Ponoko is currently only shipping from New Zealand so shipping is quite costly))

Option 3 (Access to a Laser Cutter)

• Download the laser cutter optimized pattern (pieces are placed side by side and duplicate lines are removed)-( '32-(OAWR)-Laser Cutter Outline.eps' ) (.eps format)
• Cut the file on your laser cutter.

Step 3: Whiskers

The last step before we start putting it all together.

Bending the whiskers is quite straightforward. Use pliers and a 130mm length of 1.6mm wire (actually a large paper clip will also work), using the pattern in the attached PDF ( '41-(OAWR)-Whisker Bending Guide.pdf' ).

(note: while initially designing this robot I experimented with many different shapes of whiskers. The pattern below is the one I found to work best, however it is quite interesting to experiment with different shapes. I was surprised how even small changes could drastically alter the navigational behavior of the robot)

Step 4: Assembling

I tried to make assembling all the pieces together as straight forward as possible. To this end I have included a Lego style assembly guide ( '51-(OAWR)-Assembly Guide.pdf' ).

A step before you begin:

• assemble the motor gearbox (I used the 58:1 ratio with output shaft exiting at hole 'A' however battery life on this setting is not great, mounting holes have been included to allow for using the 203:1 ratio with output shaft exiting at hole 'C'. If you prefer a slower longer lived version)

A step after you finish:

• add shoes to the feet of your robot (the rounded acrylic feet don't grip surfaces well). I applied a bead of hot glue to the bottom edge of each leg and performance was greatly enhanced. (But if you have access to six miniature sized running shoes that would be a much better option)

(To inspire you to assemble yours here is a 'video' of me assembling mine in about thirty seconds :) )

Step 5: Wiring

With the big pieces all together and it beginning to look pretty, the time has come to add the copper veins which will give it life. A first look at the wiring diagram ( '61-(OAWR)-Wiring Diagram.pdf' ) can be scary however if you tackle each wire individually it is quite straight forward.

Also if you are wondering how the robot operates please refer to the second image below which shows it in each of its four operating states.

Four Notes to Help You Out:

• Each wire end which connects to a connection point should have a crimp wire terminal (red 4mm ring) affixed to it (there are 18 of these points).
• The exploded view linked to each connection point illustrates whether the wire is meant to attach above or below the acrylic sheet.
• Any connection point that does not already have a bolt in it uses a 3mm x 15mm bolt and a matching 3mm nut.
• Most of all don't worry the next step is fully devoted to trouble shooting so have a go and if it's not working properly chances are you'll find your answer there.

A note of encouragement:

• You can do it.

Step 6: Troubleshooting

If you've made it this far and your robot is walking and avoiding obstacles then you may skip right over this step. However if it isn't quite working or is not working at all hopefully you'll be able to find the solution to your problem here.

(If you have a problem not addressed mention it in the comments and I'll try to help (or if you have a problem that's addressed here and have a better way to deal with it please also comment))

(I'm afraid I haven't figured out how to do tables on Instructables so this section will be formated)

Problem
Cause 1
Solution 1
Cause 2
Solution 2

Troubleshooting list:

Left legs walk backwards when they should be walking forward.
The left motor is connected backwards.
Reverse the wires from the left motor connected to connection point 'G' and connection point 'H' (ie. G<-->H & H<-->G).

Right legs walk backwards when they should be walking forward.'
The right motor is connected backwards'.'
Reverse the wires from the right motor connected to connection point 'H' and connection point 'J' (ie. H<-->J & J<-->H).

When whisker is pressed relevant leg continues walking forward.
The Reverse Battery is wired backwards.
Switch the wires from the Reverse Battery holder connected to connection point 'A' and connection point 'I' (ie. A<-->I & I<-->A).
The elastic band is too tight and not letting the switch arm swing.
Use a larger or less powerful elastic band.
The bolt holding the switch arm in place is too tight.
Loosen the bolt holding the switch arm.

In the off state when one whisker is pressed the legs begin walking.
This is unfortunately a flaw in the wiring design.
If you wish to fix this add a switch on one or both of the battery boxes or remove the batteries when not in use.

After hitting an obstacle one side continues walking in reverse after the obstacle has been cleared.
The Elastic band is not powerful enough to return the switch arm to its forward position.
Use a stronger elastic band
The bolt holding the switch arm in place is too tight.
Loosen the bolt holding the switch arm.

Batteries are in but the robot does not move.
Washer is not contacting the powered bolt.
Because the 5mm washer has a hole bigger than the 3mm bolt we use, you must center it and then tighten the screw to hold it in place. If it gets pushed off center the acrylic switch arm may be contacting the bolt in its place. To fix this loosen the whisker screw and re-center the 5mm washer.
Motors are being powered by both battery packs simultaneously resulting in a net zero voltage.
The washers on the switch arm are too big, look for washers that seem a little smaller or bend the contact bolts outwards a little.
There is too much friction in the arm links causing the motor to stall.
Loosen some of of the tighter bolts holding your legs and push arms in place.

Step 7: Finished

Congrats

I hope you have reached this point without too much frustration and you are happy with the results.

If you have any tips or suggestions on how the design or Instructable could be improved I'd love to hear them.

Also if you have finished it would be lovely if you could add a photo to the comments section or perhaps send me one so it can be added to this stage.

A video of the finished OAWR in action:

(A couple of issues still to be resolved when the legs get synced in a particular way they push against one another and almost stop the robot (thats what I was reaching in to fix), and it is still not corner proof but I'm working on it)