Richard's N.A.M.E.S. '01 Special
The Quad Ringbom
all started on Sunday afternoon March 25th when Roy called and asked
"Are we going to NAMES this year?"
"Yes, lets." I replied, knowing full well that I didn't have a new engine to take. (My wife had laid down the law some years ago - "No out-of-town trips unless you have something new to take.")
I had four and one half weeks to build an engine that hadn't been designed yet. "I guess I'd better get started" I thought to myself.
The Ringbom concept immediately came to mind. The Ringbom type of Stirling cycle engine has no mechanical linkage to actuate the displacer piston, consequently I could avoid all the time and effort associated with designing and building such linkage. I had built two Ringboms on the past, "Thumper" and the "Double Acting Ringbom". This new engine would share the same proven design parameters as "Thumper". There was no time for experimentation.
Not quite sure how a Ringbom works? Click here.
I checked my "scrap box" for parts and pieces that could be incorporated into a new engine. I found half a dozen connecting rods and a pair of gears. I also found Pyrex test tubes (Advance Scientific & Chemical, Inc.), dashpots of various sizes (Airpot Corp.), and assorted sizes of stainless steel shafting and miniature ball bearings (Nordex, Inc).
Using test tubes for displacer cylinders eliminated substantial machining time, as did using dashpots for power cylinders.
||The gears deserve special mention. I made them several years ago when I first started cutting gears with a wire EDM. They each have 40 involute teeth and a pitch diameter of 1.325. This equates to a diametral pitch of 30.1886792 - not an even number. The computer allows one to specify the center to center distance between gears as well as the number of teeth. The resulting gears however don't necessarily interchange with "standard" sizes.|
The base is made from 1" thick aluminum. A circular cavity was machined on the underside to serve as a fuel tank and then a 1/8" thick plate was welded in place to seal it up. The outside shape was machined on a CNC mill and the 1/2" radius all around the top edge was cut with a ball end mill and several thousand lines of G code.
Click on the image above for a (much) larger view.
The connecting rods attach directly to the power pistons without wrist pins. The power cylinders, therefore, must swivel or oscillate. This also necessitates the flexible tubes from each power cylinder to its displacer cylinder.
Final assembly took place on Thursday evening in my motel room in Southgate, Michigan. Friday morning, April 27th, opening day of the 2001 NAMES Exposition, the Quad Ringbom ran for the first time.
Next year I'm going to start earlier.