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Meccano Jay
02-05-2010, 04:38 PM
The simple Meccano walker Project, by Meccano Jay


About:
This is a simple Meccano based servo driven biped. It isn't a perfect machine by any means but it could make for a neat afternoon with the kids or even a cool science project. I thought out, designed, and built the model used for the pics as an example only. The wonderful thing about robotics is that imagination is key! This is just a basic example you may build it exact but I encourage you to modify it to your liking. I do plan to offer some basic software along with the example just to get you walking.


Project:
I set out to design and build a simple functional walking biped with as few servos as possible. I decided on this particular design based on the fact that it only requires 2 DOF to walk. I feel the base design is solid and I also feel any Meccano fan could have this up and walking in no time.
This design incorporates two standard hobby servos for movement, Hitec HS322HDs. For control we will be testing a Phidgets 1061 Advanced Servo 8 motor usb control board. Example code will be provided along with software to get you started quickly. Everything else used was Meccano (erector). The project yielded an 8 1/4 in tall walker.


Happy Building
http://viewmorepics.myspace.com/index.cfm?fuseaction=viewImage&friendID=508288277&albumID=819349&imageID=8494756

Meccano Jay
02-06-2010, 12:43 PM
Building a simple walker

Skill level: Entry level walker / first time build (my first real walking build)

Getting started:
First of all a checklist, there are a few things you will need.

2 hobby servos, I used Hitec HS322's.
1 servo controller, used Phidgets Advanced Servo 8 motor usb control board, available with servos.
1 assortment of Meccano parts and tools to include;

NOTE: this is a general parts list, based on what was available to me at the time. Your parts may differ as may your design concept. Happy Building!


2 Meccano wrenches
1 Meccano hex head driver (for bolts)
4 x 11 hole flat circular strips
2 x 3 hole double angle strip (for ankle joint)
13 x 1 hole L (4 x ankle joint)(4 x servo arm joints)(4 x servo mount)(1 x control board mount)
2 x 3 hole L (ankle joint leg joiner)
2 x 5 hole angle girder (Ankle joint pivot connecting rod mount)
4 x 9 hole flat (legs)
2 x 6 hole flat (upper leg joint support)
1 x 5 x 7 platform (base you mount everything to)
2 x 15 flat (servo linkage arms)
1 x 7 hole flat (servo arm, servo 0)
1 x 5 hole flat (servo arm, servo 1)
2 x 5 hole U (1 x servo mount/bot hanger)(1 x control board mount)
2 x 3 hole triangle flat (servo mount)
4 x 5 x 3 Flanged Plate (2 x feet)(2 x servo spacers)
50 or so assorted screws and nuts/lock nuts for joints! No lock nuts? Double nut!
2 x rubber collar (servo linkage stoppers for the foot end you will want to use a long screw for the bottom linkage arm mount to allow proper play) lock nuts may be used as an alternate.


I will spare you a pile of pics of erector sets, im sure your all familiar. lol.

Meccano Jay
02-06-2010, 12:50 PM
Right foot
Using a 5 x 3 flanged plate attach an 11 hole circular strip in the 4 5 and 6 hole position in the 3 hole flange of the 5 x 3, making sure the curve is upward, the flanged plate will be upright with flanges pointed down. Repeat for opposite side of flange with a second circular strip, note: align flat strips evenly. This should leave you a standing foot with 4 points of contact on the ground. Now attach a 3 hole double angle strip, flat side down, aligned with the center 3 holes of the foot. Leaving you a nice u bracket to serve as an ankle. The front of the foot will be the longer side of the circular strips. Attach a 5 hole angle girder along the inside edge of the top of the foot. Position flush with the back, angle pointed upward on the outside of the inner edge of the foot. Once the angle girder is in place, place a long screw through the front hole of the upper bent of the girder. Secure into position with a nut, attach a rubber stopper on the end of the screw.
(NOTE: I have found that it is a good Idea to use a couple of 90 deg. Angle brackets attached to the front toes of the walker. On the underside of these apply a stick on rubber non slip pad. This helps with traction in the kitchen, or on the lab table.)


Left foot
Repeat steps above, the only difference in the left and right foot is the placement of the angel girder, place along the inside edge of the foot.

Meccano Jay
02-10-2010, 02:04 PM
Upper servo mount
Constructed of 2 pieces of 5 x 3 flanged plate bolted together to make a height adjustable mounting box. This assembly bolts to a 7 x 5 Flanged Plate, flanges down.
To mount the upper servo, I used a 5 hole double angle, 2 long screws, 6 plastic spacers, 2 5 hole flat, and about 4 nuts. Turn your 5 hole angle upward, place a long screw downward through the holes at either end. Place 3 plastic spacers per screw. This can now be placed through the holes of the upper servo mount, use the edge holes of the servo mount. (NOTE: this will be the “front” of the bot.)Attach with nuts, leave nuts loose, this will act as a clamp mount for the servo. Simply slide your servo into position and tighten! (Tip!: a small strip of no slip rubber placed on the servo side of the 5 hole angle, and on the flange plate will dramatically increase servo stability in this mount configuration. CAUTION: do not over tighten, let the no slip rubber do its job, over tightening could lead to servo damage or failure!)

Lower servo mount
The lower servo mount was constructed using 4 x 90 deg angle brackets and 2 x 3 hole triangle flat pieces. Attach 2 90 deg brackets to each triangle. Use the slider side of the 90s when mounting to the triangles. Attach these to the underside of the 7 x 5 plate, mount in the center hole of the 7 sides, both outer edges. You can now mount the lower servo using its built in mounts, and 2 short Meccano screws and nuts. For this design the servo horn is in the rear.

Control board and mount
Now that we have our servos in place we need to mount the control board. I did this by utilizing a 90 deg. Angel bracket mounted in the right rear corner of the large flange plate. To this I mounted a 5 hole angle. I then used the hardware that came with my control board, and 2 rubber collars, to give the board a soft safe ride. Insert mounting screws through the board, slip a rubber collar over each screw, align screws with holes in the 5 hole angle and mount with nuts provided.

Wiring
For wire management purposes, these servo wires have been coiled around a shaft, when you pull the shaft out, the coil will usually stay put. The Lower servo will plug into the 0 location, the Upper servo into the 1 location.(Caution! Please consult your boards instructions for connection a servo.) on the Phidgets Advanced Servo 8Motor Control The ground runs the edge of the board, thus your black/ground wire always faces the outer edge.

Servo arms / linkages
For the upper servo arm I simply used a 5 hole flat. Using the stock servo horn I ran the servo horn center screw through the Meccano arm, for stability I added what I think are screws from a glasses fix it kit, Placing a screw at the 4 exposed corners. To this I added a 90 degree angle Bracket to either end of the arm, using lock nuts to allow the brackets to pivot freely. Use the round hole of the bracket when mounting to the upper servo arm. To these Brackets we add a 15 flat, one end slid over the bolt in the angle girder of the foot(secured with rubber collar) and the other mounted to the angle bracket on the servo arm, again using a lock nut to allow free movement.


For the lower servo arm, a 7 hole flat was used. Just like upper, servo horn screw through the middle supported on the outside of the horn with screws. On either end of the Lower servo arm mount 2 x 90 deg brackets. Use the slide end when mounting to the servo arm. A plastic spacer was used to attain alignment, lock nuts used for free movement. Mount the angle brackets to the legs using a lock nuts to allow free movement.

Meccano Jay
02-10-2010, 02:14 PM
For legs I chose 4 x 9 hole flat, 2 per leg. Start by placing a medium length screw through the flanged side of the large plate, position one screw in the next to last holes at either end. Slide a washer over each bolt followed by one end of the 9 hole flat. Follow with a second washer and a locking nut. (NOTE: I have found that it is necessary to add a piece of flat to the back side of the flange plate where the leg mount bolts go through. This will stiffen up the upper leg joints that were to loose before.) You should have a 9 hole flat hanging from the 2nd and 4th hole of both sides of the flanged plate when finished. At this point it is time to begin construction of the ankle joints. Using a pair of 3 hole angle girders, positioned so the round holes bot to the legs, angle on the bottom pointed outward. Attach to loose ends of the 9 hole flat with a short bolt and locking nut. I used 2 90 deg angle brackets, placing a short screw through the long hole of the bracket angle pointing downward, screw up trough the bottom into the long hole of the angle girder, one at either end. Use a regular nut to lock these into position. They will align with the double angle strip on the feet and allow you to attach the foot to the leg using 2 short or medium screws and a pair of lock nuts. (NOTE: you may want to attach the foot before locking down the angle brackets mounted to the 3 hole angle girder. This may ease the alignment process.) Repeat for opposite side and your walker should be taking shape.


This really fits between mounting the servos and the servo arms. Apologies for being a tad out of order, it seemed fitting to have the servo arm info included with the servo mount info. Also the pictures complement one another in those examples :)

Meccano Jay
02-12-2010, 02:26 PM
I have written a basic program to automate the walking process of the bot. You can download the software, VB6 Sample with code here (http://forums.trossenrobotics.com/datacenter/demos-example-code-widgets-6/phidgets-1061-the-simple-meccano-walker-vb6-studio-150/). Writing software isn't everyone's strong point, and this is no masterpiece but It will demonstrate the simple bots abilities. (NOTE: This software example is for the Phidgets Advanced Servo 8 motor Control and therefore may not work with your controller. If you are running the Phidgets please insure you have the basic driver and manager with libraries installed before installing the software.)

For those using the Phidgets, taking the first step is a simple process with the included software. Connect your bot to power and the computer, place it on a flat surface, launch Robo Studio (http://forums.trossenrobotics.com/datacenter/demos-example-code-widgets-6/phidgets-1061-the-simple-meccano-walker-vb6-studio-150/), and choose from the available options. Forward by default will take 3 full steps forward. All the directions default to 3 steps. This can be changed by typing in the number of steps you want your bot to take. Explore the software and your bot and enjoy! (NOTE: first runs aren't always successful, your bot may require some tweaking to get just right, Don't get discouraged!)

This has been a fun project that I had a great time building, Thanks for the great place to share it. I hope this has been as entertaining to read about as it was actually doing. Keep in mind this was my first bot!
jay

DresnerRobotics
02-12-2010, 10:04 PM
Great job documenting your project, and thank you much for taking the time to share not only the pictures and process, but your code as well. + Rep from me!

Meccano Jay
02-13-2010, 12:41 AM
Tyberius, Thank you for your kind words. and the rep! :)

There are alot of very skilled builders here that I take inspiration from. I hope some day to be a part of that inspiration for others so I will do my best to keep my documentation on par with that of this project. More in the works hehe!

Thank you again
Jay