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Hexapod progress reports.
07 Nov  04
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07 Nov '04
Hexapod

The most important requirement for designing new things is an ordered mind.  I used to have one but I am getting old at 64 and the really complicated stuff I used to do is not so easy any more.  So I need to keep it simple!!

How the idea was born.  When I was writing my book on how to use single chip, self contained, microprocessors it occurred to me that one of these microprocessors might just be the ideal thing to control one leg of a multi-footed/legged walking machine.  The more I though about it the more feasible it seemed.  So I set to thinking about it and decided to do a web search on what had been posted on walking machines.  Nothing worthwhile had been done.  Lots and lots of computers and wires but nothing note worthy had been accomplished, lots of theory.  Most of the stuff really did not even work considering that tons of money had been spent. Seemed to me I could do better with less.  Less because I have only so much money (and no government grants).

So I made some notes and did some sketches which lead to the realization that I did not need a microprocessor at all.  This was a mechanical contrivance and everything that needed to be done could be done mechanically.  Oh one needed a switch here and there but it was100% a mechanical problem.

So what does a walking machine have to do.

It has to walk by lifting its feet moving them forward and putting them down in some kind of regular, repeating way.
It has to move forwards
It has to move backwards
It has to be able to turn
It as to be able to change its speed.
It has to be able to change the length of the steps.
Since there is an operator, the machine intelligence needed is minimal.

In my case it had to carry a 200 lb guy with long legs and look cool!
Since I wanted to traverse rough terrain, I decided that it had to be able to amble over a 6 inch curb, the kind one runs into in an urban environment.
I was not concerned with the smoothness of the gait at the initial design stage.

What  do I need to make all this happen.
An engine with push button start since I am getting too old to pull on starting ropes. The engine drives a hydraulic pump and all the power is derived from hydraulic cylinders.  Only three are needed. (I presently think this is accurate).  So I need the pump the starter the battery etc.  A reservoir for the gas and hydraulic fluid and the three 4 way valves to control the three cylinders.  A half a dozen switches to tell me where the cylinders are.  Some simple logic to cycle the works.

I have decided on a two lever control like on a zero turning radius mower.  Each lever controls one set of legs.  The further you move it forward, the longer the step gets.  If you pull it back, the steps go backward.  So if you push one lever forward and pull one back the hexapod turns in place just like a zero turning radius mower only it does it with steps!

When you start up, the levers are in neutral and as you increase the fluid flow the machines marks time on the same place without moving.  The more fluid released to the system, the faster it marches on the same place.  Slowly move the levers forward and move away.

A lot of neat stuff does not work the first time out of the box so I have decided to build the test platform out of slotted angles, keep machining to an absolutely minimum and use lots of nuts and bolts so things could be changed as needed. 

A the present time I am making the engine-hydraulic system and working on the design of the legs and framework.  I have a one cylinder and a two cylinder army surplus engine, 8 cubic inches and 16 cubic inches respectively. (saturnsurplus.com).  I am using the 8 inch engine right now but can shift to the 16 if need be.  The output mountings but not the bases are interchangeable.  Here's the little one.
The engine does not come with a stand or have a base it can be made to stand on so I made a simple one out of 1 by 1 angles.  The way this works, you can lift the engine off the base and that is very convenient when you have to be removing the engine again and again to weld and drill etc, on the base as you mount and unmount things to it.

10 Nov 04

I needed to crank the engine with a starter and I did not want to mess with the crankshaft extension end so I turned up a removable pulley/adapter I could bolt onto the capstan for the starting rope.  Took  me close to two hours to turn the thing.  I had a lot of material that needed turning away on the 4 inch round on my small Myford lathe.  Here it is mounted to the engine.  Also a picture of the starter that has to go onto the base some how.  This is a starter/generator for the Cub Cadet and similar mowers.  The system also needs a solenoid to start the starter and a regulator to properly keep the battery charged.  I can already see that the engine-generator-starter-hydraulics are going to be far the most expensive parts of the project.
08 Nov 04

These are my initial design sketches in Pro-E that allowed me to see what the proportions needed to be.  Top is 6 feet by 6 feet.  Frame is about a foot high.  Tubes are 2 inches by 2 inches.  The feet are 4 inch pipe cut in half.  The important thing to note is that there are very few machined parts. 
Almost the entire  thing will be welded out of standard tubes angles and flats.  No machining!!
Legs
Ideas and design Copyrighted by  H. S. Sandhu 2004.  All rights reserved worldwide
Hydraulic Pump and drive coupling will need a mounting designed and built.
Solenoid switch for starter
Starter Generator needs to have a pulley made for it
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The larger, two cylinder engine is currently mounted on my fence row mower and looks like what you see on the left.  It can be lifted right off when needed for an important  hexapod experiment!  Its really way too powerful for this mower and will be for the hexapod too (I think).

These are two really neat looking and good running Viet Nam era engines.  They start real easy and are completely waterproof and radio shielded.  Magneto ignition on both.

Available from saturnsurplus.com.  They are not expensive.  There is also a 4 cylinder (32 cubic inch) horizontally opposed version.  NEAT.  A really cute engine suitable for hovercraft.
The 4A032 engine.


Gas springs keep the legs extended.
6 ft by 6 ft
 
This pulley will be used to start the engine with the Starter/Generator
 
 
 
 
The single cylinder engine I will use
End view of the starter side
General view of where the pump goes
Head on view of the shaft to drive the pump.
 
View of the control end of things.
These two are the 1A08 engine and the 2A016 engine.