Questions on Ross's EG33 Subie RV-10, Marcotte Drive

[Rotary10-RV]

Originally Posted by Rotary10-RV

George,
Your question about which drive is better is much like the "which engine is best?" question. That is the question is open to dispute. Perhaps a better question is, "What PSRU is safe and durable." The answer to that is, several are.
Let's list the PSRU types so that people will know what we are talking about.
1) Marcotte; internal helical gear type. The drive gear has the teeth cut on the inside and the pinion is placed inside. Ross already mentioned the characteristics so I won't re-list. Small offset about 1-3/4 - 2 inches
1a) PowerSport; Also internal gear type, Spur gear (straight cut) otherwise very similar to the Marcotte. Both are around 45-50 pounds.
Positives: Strong, compact, Small offset which is usually a benefit. Gear drive which is totally proven. rotation is not reversed, for "normal" prop rotation.
Negitives Fairly heavy, strong coupling but requires lash which can cause TV problems. Requires an expensive internal ring gear be custom manufactured.

2) Eggenfellner; GenIII Helical gear external gear w/lay shaft. All external gearing. Egg uses a inline (no offset) crank to prop. power comes out of the Crankshaft, over to the layshaft, back to the propshaft.
Positives: Compact, External gear drive which is more available. Double reduction allows more ratio choices. Using the layshaft keeps the rotation the same for standard prop rotation. Most gears, bearings can be off the shelf, and therefore cheaper.
Negitives: Double reduction, wait wasn't that a positive? Yes but the additional gearset requires another mesh to be controlled making it harder to ensure equal lash in both gearsets. Layshaft requires case to be stronger to positively locate layshaft and bearings. Two gear lashes means more angular lash and TV control.

3) Planetary: Tracy Crooks and others. Typically requires a premade gearset be available for affordability. (Mistral uses a planetary, an excellent one of their own design, bring $$$) The planetary is possibly an excellent and lightweight design. The key being that there are several gear meshes. The planetary has both external and internal gears.
Positives: Compact, theroetically the strongest gearset because of multiple constant meshes. Several ratios available from a single gearset. Both reversed and standard rotations available.
Positives: Smallest package for a given horsepower. Gear drive, has limited self-centering capability. Many gearsets available from commercial automatic transmissions.
Negitives: Complex, highest parts count of all gear drives. All gears must be carefully made to have identical pitch diameters and lash. Always includes an internal gear which is expensive to make. Argueably most angular lash, though similar to the Egg layshaft approach.

This is a start, others include, chain drives, belt drives, fluid couplings, the list goes on. We must have a good background in engineering to design any of these drives. These are just a few types, I have listed these because they are now available from several suppliers. Most other drives are going to be built-to-order. EPI will build you any of these types, to order, including an external spur gear drive. Again bring $$$. These descriptions ignore how these drives are coupled to the engine. That coupling can be a source of more problems or solutions than the drive itself. Dan H has been pounding on thew need for TV issue. This is as important as the drive itself, do your homework! I'm stopping now to get back to work!
Bill Jepson

George, Ross,
I know this is old news but I wanted to post it for some of the guys that aren't familar with the drives we're talking about.
Bill

[rv6ejguy]

Thanks Bill, good summation on the different drive types.

[TSwezey]

Robinson's chain drive PSRU has been fairy reliable hasn't it?

[Rotary10-RV]

Originally Posted by TSwezey

Robinson's chain drive PSRU has been fairy reliable hasn't it?

Todd,
They seem to have been putting the hours on it in the SeeBee. I didn't mention it in the summary because the discussion was on (I thought) the geared drives. I could be wrong. (As usual!) The Hi-Vo chain can be a very reliable drive. If you can think back to the Olds Toranado they ran a big block GM/Chevy using that drive to handle all the power continously. Proper engineering is the needed thing again. You can do a thing from scratch, or you can use drives available from a manufacturer with a proven track record. You need to have a good idea of the data and apply it carefully. Gershwinder produced a nice version. The owner is retiring and wants to sell now. The add is in the front of Contact! magazine. I have never seen the inside of the Robinson drive but it has been holding up on at least 1 example!
Bill Jepson