Try a minimum of 1/32″ or 4-16″ maximum clearance at the end of the stroke of the displacer.
Fine shallow groove cut in the inner surfaces of the displacer discs should improve heat transfer by promoting air turbulance
I think mine was about 50%, in this video, but it was even lower in the alternator video. I made it thinner later and that did help with speed. Shortening the stroke also helped the speed. In this video it was about 1 inch and I shortened it to about 5/8 of an inch. And don’t worry about stealing my idea…it wasn’t mine, I stole it from another obscure website, I wish I could still find it to give the guy credit, because the JB weld piston works wonderful.
I’m very impressed by the speed Your engines run by.
I’m in the process of building a LTD Ringbom engine, basically from what can be found in containers. I will steal Your idea though, of using brass tubes and – not JB Weld – but after my guess a similar product, Plastic Padding Chemical metal. Thanks for the tip.
What is Your take on height of displ., versus height of displ. cylinder?
Normally 64% is recommended, but it seems that some go lower, maybe near 50%.
Regs
Thanks, also was there much tweaking of the balance spring to get the displacer to work properly? What would happen if the spring were not there??? I’m tempted to go this way with mine, though I know I will get a sure result with the mechanicaly drived displacer, I do prefer the free displacer set up its neat. Comments?
Just a technicality, but it isn’t a free piston engine, it is a ringbom engine. Free piston engines operate on tuned resonance of the displacer and piston and do not have a flywheel, hence they can usually be designed to have higher power to weight ratios. Essentially the small brass tube is just another cylinder with a piston. The displacer rod is very large, so the internal change in pressure from the piston moving up and down will have enough force to move it alternately up & down
I’m trying to get the free piston idea. Whats inside the centre brass tube beneath the spring, is there a piston in there or bush, The wire rod is so thin yet the brass centre tube is more than just a guide?
The dimensions are just what I had available to use, I used some of the information from James Senft’s book on miniature ringbom engines and LTD engines, such as having a swept displacer volume that is roughly 50 times that of the piston swept volume. For the area of the displacer rod vs the piston, I just used a 1:2 ratio.
You should try the plaster idea, it would be neat to see if that actually works. These pistons are pretty frictionless, but with any side loading they stick very easily.
Great engine!
Is it an original design, or did you get the dimensions from somewhere?
I had a similar idea to make a stirling engine with plaster pistons, that I cast into the cylinders. I thought I would coat the inside of the cylinders with graphite dust before pouring the plaster so the plaster gets a slick coating embedded in the piston.
teuf-teuf-teuf-teuf…
)
What a beautiful noise !
Big up to you !
and thanks for sharing your experience.
Try a minimum of 1/32″ or 4-16″ maximum clearance at the end of the stroke of the displacer.
Fine shallow groove cut in the inner surfaces of the displacer discs should improve heat transfer by promoting air turbulance
I think mine was about 50%, in this video, but it was even lower in the alternator video. I made it thinner later and that did help with speed. Shortening the stroke also helped the speed. In this video it was about 1 inch and I shortened it to about 5/8 of an inch. And don’t worry about stealing my idea…it wasn’t mine, I stole it from another obscure website, I wish I could still find it to give the guy credit, because the JB weld piston works wonderful.
Hi IronGoober,
I’m very impressed by the speed Your engines run by.
I’m in the process of building a LTD Ringbom engine, basically from what can be found in containers. I will steal Your idea though, of using brass tubes and – not JB Weld – but after my guess a similar product, Plastic Padding Chemical metal. Thanks for the tip.
What is Your take on height of displ., versus height of displ. cylinder?
Normally 64% is recommended, but it seems that some go lower, maybe near 50%.
Regs
Thanks, also was there much tweaking of the balance spring to get the displacer to work properly? What would happen if the spring were not there??? I’m tempted to go this way with mine, though I know I will get a sure result with the mechanicaly drived displacer, I do prefer the free displacer set up its neat. Comments?
Just a technicality, but it isn’t a free piston engine, it is a ringbom engine. Free piston engines operate on tuned resonance of the displacer and piston and do not have a flywheel, hence they can usually be designed to have higher power to weight ratios. Essentially the small brass tube is just another cylinder with a piston. The displacer rod is very large, so the internal change in pressure from the piston moving up and down will have enough force to move it alternately up & down
I’m trying to get the free piston idea. Whats inside the centre brass tube beneath the spring, is there a piston in there or bush, The wire rod is so thin yet the brass centre tube is more than just a guide?
good work!!!
The dimensions are just what I had available to use, I used some of the information from James Senft’s book on miniature ringbom engines and LTD engines, such as having a swept displacer volume that is roughly 50 times that of the piston swept volume. For the area of the displacer rod vs the piston, I just used a 1:2 ratio.
You should try the plaster idea, it would be neat to see if that actually works. These pistons are pretty frictionless, but with any side loading they stick very easily.
It’s a triple! nice work. Did you add the second top piston after as as per concept?
Great engine!
Is it an original design, or did you get the dimensions from somewhere?
I had a similar idea to make a stirling engine with plaster pistons, that I cast into the cylinders. I thought I would coat the inside of the cylinders with graphite dust before pouring the plaster so the plaster gets a slick coating embedded in the piston.
Nope. Just the brass cylinder and the sanded JB weld pistons…
Great work. Did you use any kind of lubricant for this engine?