BDA780’s Miniature Twin Rotor Wankel Engine project

[BDA780]

So I have finally decided to document my twin rotor Wankel engine project.

Years ago I saw the video below of the twin O.S. Wankel engined R/C tractor pull car and thought that was the coolest thing since sliced bread.

 

 

Fast forward a few years and I saw a twin rotor O.S. Wankel based engine in the YouTube thread, which has been the crux of this project. The engine build by ‘20B’ combined two O.S. Wankel PI’s together with a custom machined centre and rear housing, in addition to an oil hardened 4140 eccentric shaft.  Unfortunately the only video of it running is the one below and the project thread stagnated years ago due to a crushed bearing.

 

 

It wasn’t the only twin rotor project, as avid model engine collector Miguel de Rancougne had another O.S. Wankel PI based engine in his possession as seen below in a Christies auction handbook.

http://www.christies.com/lotfinder/lot/a-twin-rotor-wankel-engine-4223480-details.aspx?intObjectID=4223480

 

Both 20B’s and Miguel de Rancougne’s twin rotor miniature Wankel engines provided enough reason for me to attempt to make one myself.

So in March 2014 I purchased a brand new O.S. Wankel PII with the aim to build a two rotor with my friend Ben who happened to purchase a used PII from rotary mad Puerto Rico. The idea was that we would test run both engines then pull apart his engine and CAD model it. The parts required would be additively manufactured on the universities recently acquired selective laser melting machine prior to sanding smooth. To test this theory a single rotor and eccentric shaft were manufactured from a CAD model off GrabCad in AlSi10Mg aluminium alloy. With the surface finish of the parts worse than predicted and lack of a ferrous metal powder for the machine I decided to focus on building the test table for the engines.

 

 

 

[Dell'orto]

Subscribing to this thread. Would love to build something like this for a 1/8 787B replica

[EURON8]

Subscribing to this thread. Would love to build something like this for a 1/8 787B replica

Probably wouldn't run if you built it mate.

[Testament]

woah negative nelly

[BDA780]

Right, so the first step in testing the Wankel engine was to design and build a run in/test table. These are very common for R/C plane guys and there are plywood kits available but I wanted to make a table just for the Wankel project. The brief was for the table to be easy to transport, a decent working height, adaptable for multi rotor engines, able to carry all the equipment required for the engines and be adaptable for any alterations down the line (Tachometer, EGT sensors etc.).

I then decided to CAD the table and because the old boy put the thought in my mind of using aluminium I built it around readily available extrusions.

 

 

 

 

To aid transport the top is held into the main tube by pip pin allowing for it to be quickly disassembled (assuming I get a noise complaint and need to leave quick fast).  The heavy items (battery, nitro meth bottle, starter) are placed near the base as to lower the COG hahaha, while the table top holds the fuel tank, engine and throttle lever (not in image). All the required items will be held in by O-rings held by small stubs similar to those “JDM” bumper mounts.

 

Thankfully my good friend Tim welded the aluminium and did a mighty fine job at it considering the extrusions were only 1.6mm thick.

 

 

 

 

I turned and threaded some aluminium bar to make the feet caps which are threaded into the swivel foot and will be pressed into the feet tubes. The table top was cut from 18mm MDF and will be varnished after the fuel tank and throttle lever is completed.

 

 

 

 

I was also lucky to have Ross from the Uni’s work shop CNC machine an engine bracket from aluminium which will be held by some stainless fasteners.

 

 

 

The image above shows the extent of what has been done so far. Only the throttle lever, fuel tank bracket, battery bracket, nitro bottle bracket and accompanying O-ring stubs are yet to be fabricated and welded… alas, I have taken my pretty time getting this far hahaha.

[BDA780]

Since the beginning of this project O.S. decided to discontinue production of the Wankel engine, this in turn has obviously been met with an increased demand for second hand engine and parts.

As the Type II engine is the rarest on auction sites, I decided to purchase a used condition Type I (first of the PP engines) and use that as a base for the project.

The first step was to dismantle the engine to see its condition.

 

 

 

Disassembly proved quite a challenge with one main setback. Whilst removing the rotor gear the head of my 2mm hex bit broke off into the cap screw proving a pain to get out, only for me to cock it all up and loosen the rotor from the vice chipping part of the rotor where the apex seal sits. The rotor could be reused but I have since bought a replacement.

 

Unsurprisingly the engine is simple in architecture with no side seals just apex seals held in by two mini leaf springs. The beauty lies in the finish of the parts. Without side seals the rotorhousing, rotor and end plates are all surface ground to ensure the engine has compression.

 

 

 

 

As I have two generations of peripheral port O.S. Wankels I got rotorhoe to take some extra images images of the differences between generations.

 

 

From what I have read and can be seen in the image above the Type II has a machined rotor housing and rotor as well as a newer glowplug, carburettor and cap screw fasteners. The remainder of the parts carry over from the Type I.

Thus, I aim to improve the Type I where possible and encompassing some of the Type II upgrades.

[rotorhoe]

Umm you forgot the most important pic...

[Furai]

Money money money, thats rotaries.

 

Keen to hear it screammmmmmmmmmm

[Muncie]

I'm just wondering how many rotors could be stacked before the e shaft shears off from the torque. 8 rotor would super sweet for some sort of batshit crazy goped/velodrome machine.

[Kaban0ssi]

Hello

This is an old thread, but it would be interesting to know how this project turn out to be. What happened?