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LEG MECHANICS


This is the tough part. There is no way I can teach all the skillsone needs to make an effective and efficient pair of legs, but with luckand perseverance the following section should give you the right start.We are gonna concentrate on a Two motor Four legwalker which although its not the most flexible design it is theeasiest to build and its proven its reliability and capability in 35 orso existing machines.


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1: THE MOTORS

This is probably the biggest consideration in a MicroCore Walker.The level of success you have with your walker is directly related to thetype of motor used. The MicroCore itself gets an implicit feedback fromthe motors, this is what gives it the adaptively.

What to look for in a Motor....

    EFFICIENCY: This is REALLYimportant both from a power consumption standpoint (better the motors thesmaller the battery you need) and from a power to weight ratio. The betterthe motor you can get the better your likelihood of success. You shouldlook for a motor with at least a 35% efficiency rating, good cassette motorsand pager motors typically fall in this range, Mabuchi hobby motors areWAY off (typically10%). Much higher efficiencies are possible (up to 88%)but this is usually found in expensive medical grade motors like "Escap"and "MicroMo". Keep your eyes open when perusing the surpluscatalogues, these sometimes go on sale for as little as $5.

    SIZE: For the most part smaller is betterbut it's not as important as efficiency. As well you want to consider yourown skill level, don't try to work with things that a really small rightoff the bat.

    NUMBERS: Make sure you have extras.Even the best of us can really *&%# up a motor.

2: THE GEARS

You canít build a walker without them. A motor alone doesn't putout enough torque and usually runs way to fast.

What to look for in a gearbox...

    Efficiency/Size/Numbers: For all thesame reasons as above

    Compliance: This is really criticalyou should be able to grasp the output shaft with a pair of pliers andbe able to turn it and have the gears spin back to the motor. If you can'tmake the motor spin then you have a gear train that is too inefficient(most likely) or too high a ratio. Worm drives are also OUT, they onlygo one way (motor to gear and not gear to motor) and they tend to chokeunder high loads.

    Output RPM: The ideal is about 30 RPM@ 5V. More than that means that you probably won't have enough torque (andif you do the damn thing will jump around so fast it's hard to figure outwhat it's doing). A lower RPM means that the machine may be moving to slowto be of use as well the ratio may be high enough that the legs can actuallybend themselves under the torque load.

3: INTERFACING MOTOR ANDGEARS

I STRONGLY suggest you find a factory motor/gearboxcombination

If you have to build your own then bear a couple of things in mind......

    Direct gear contact:belt drives, friction drives, flexible shafts etc. all have Big problemsas far a efficiency and compliance are concerned

    Keep everything clean:Glue, Solder flux and Metal fillings are Deadly enemies to gearboxes

4: MATERIALS

Solder is our friend, and the better your materials solder the easierit will be to build a frame. Welding wire or filler rod is the best bet.Copper clad carbon steel rod 1/6" to 3/32"diameter is cheap andavailable at any welding supply place. An nice Shinny option is High Nickelfiller rod used for TIG welding cast iron but its MUCH more expensive.brass tube and wire found at most hobby shops is a good bet as well. Isuggest a solder with an Organic/water soluble flux, "Hydro X"by Multicore is my favorite.

5: BASIC FRAME LAYOUT

This is thebasic layout, you want to keep the motors and output shafts lined up frontto back and the front motor should be tilted at 30 degrees. This meansthe front motor will supply lift and push but we'll discuss that more later.You should mount the motors far enough apart to fit all your electronicsincluding batteries in between (usually about 4").

6: ADDING THE LEGS

Leg shape and configuration will vary greatly between machines. Afew things to bear in mind are:

    Contact point: This is the most importantaspect of leg design. The shape of the leg is less important as where ittouches the ground. By placing you robot on a sheet of graph paper as shownhere you can get symmetrical contact points.

    Width: Try to make the legs at least2/3 the length of your robot, this of course will depend on the availabletorque. Its also been shown that making the back legs slightly wider thanthe front helps in stability

    Connection: Make sure that your legsare connected with something structurally sound, krazy glue doesnít cutit. If you can't solder the legs directly to the output shaft then tryand find some sort of locking ring or set screw that will fit. Look forbrass gears or pulleys that have their own set screw and then you can solderthe legs directly to the brass.

    Angle: By angling the legs slightlyforward the legs will have the ability to "ratchet" over obstacles

Your legs Will changeshape several times before you are done so its best to make a set of "test"legs that are easily recoupable before you use the good materials. 12 or14 gauge household copper wire makes for effective reconfiguable "Gumby" legs.

7 MAKING IT WALK:

Gotta make a minor detour here ( you may have noticed wedon't have the MicroCore connected to anything yet ).

Interfacing the MicroCore With the Leg Motors