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Two-cylinder, double-acting wobbler

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It's been far too long since I've had a good stretch of time in the shop, so I need a satisfying project that I can get done fairly quickly. After making Elmer's Fancy II a while back, I thought that it would be nice to have a double-acting wobbler. Two cylinders is also neat because then it can be self-starting.

So I sat down this morning with a cup of coffee, and whipped up the attached design in Rhino (my favorite Mac 3D software). Nothing too unusual: central column with internal intake and exhaust (I'll see if I can do a ghost view that shows them). Outlier standards will apply pressure on the cylinders via a spring (not shown in the rendering). Cylinder covers will be bolted on with screws or studs. Being double acting, it needs a gland on the top cover. I'll probably shape the crank disks. The cranks will be 90 apart on the actual model so that it self-starts. There are bronze bearings for the crank.

How does that sound? Can anyone see any problems with this design?


Here's the ghost view showing the air holes. The ports are drilled straight through, then 1/8" holes drilled up from the underside to intersect with both front ports, and both back ports. These will be plugged at the bottom. The inlet and exhaust come in horizontally from the feet of the standard.

This picture shows one immediate problem; if the pin in which the cylinders pivot goes all the way through, it will intersect with the air channels. I'll have to use a shorter pin on each side.

I *think* I've got the "wiring" right  :headscratch: *makes spinny gestures with one hand and pointy gestures with the other while trying to work out the piston motion*


Looks like an interesting and fun project. I'll be watching.
Good to see you in the shop.

--- Quote from: smfr on February 17, 2013, 06:33:29 AM ---Being double acting, it needs a gland on the top cover.

--- End quote ---

Being a newbie, I don't understand this. Help.

Regarding the interference between the port channels and the pivot pin...

This is the same/similar arrangement as the PMR Model 2A/2B. What they did to give more clearance for the pivot pin was have the channels intersect from the outside of the port rather than down the middle of the port.

Let the 0 be the port hole and the | | be the channel...
Here's yours  |0| where the port goes through the channel.
Here's theirs 0| | where the right side of the port and the left side of the channel intersect. That is, the left '|' of the channel is intersecting the port along the port's right side.

Said a different way, move the channel over a bit so it still intersect. Sorry to be so wordy.

Hope that helps.

Nice proportions on that engine. As another PMR 2 builder, I can agree with what Carl said, although I can't really see the spacing that well in the rendering. The centerline of the vertical passages can be moved almost a full port diameter to the side of the ports and still get good intersection to the ports.

Again, nice looking design.



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