Designing PSRU'S

The whole world is using relatively small prop shafts as large diameter ball and roller bearings do not like to rotate at high speed. the trouble where conventional gearboxes is they require small diameter bearings. large diameter bearings do not rotate at high RPM. the small balls get going too fast so it would be a good idea if we could increase the diameter of the shaft and then choose a diameter somewhere near the bolt circle diameter of a prop hub. also it doesn't make sense to use a 6 inch diameter planent carrier and reduce it down to a 2 inch diameter prop shaft. it makes more sense to increase the size of a prop shaft to about 4 inches and bolt the planet carrier directly to the end of the shaft. and men of old be propped up directly to the end other and of the shaft I may want to use longer shafts for the planets in the integral planet prop shaft because it is alum rather than steel. Which material is best for this purpose? Tool steel is widely available and can be ground to size. The original shafts may work fine as they do in the alum planet cages currently in use; but those I have seen have larger shafts, up to nearly .700", while the steel version uses only .4155. Ed Carver Paul, If the idea of making a new shaft mount and contained planetary,is going to happen, might I suggest a second gear set mounted backwards. A new sun or two modified to make one could eliminate the end thrust. A poor mans herringbone gear. Bill Jepson On Feb 2, 2012 11:36 AM, "rotaryeng" wrote: This looks real simple. It might be easier than I first thought. Getting the roll pins out with Jean's bigger hammer goes a long way towards making this viable. Here is the cut a way. I'm ready to cut the integral planet/prop shaft to length and do some machining. Some of your rhino images show the planet end set inside the housing about 2 inches. How far should it be set into the shaft? And how far should it extend beyond the prop end of the tube housing? For my Cozy4 I can have the prop flange be 12.5" behind the bell. I have a 12" long housing tube. I'm going to try to use the part I saw in your box full of planet parts, I think it is called the overdrive ring gear shaft. Part #420 slauson. It fits into the front drum spline tracy uses on his damper plate, the same one I have and Jean is using. I want to weld a couple 4130 tubes to it. One for the id of the sun, and the other for the od of the sun gear. After machining the teeth from the od of the sun gear, the tube will fit over it. Using tube like this means I can extend the length to whatever I desire. It also means the pins used to hold the sun gear from spinning will then need to shear at 4 points instead of two. We can also run an oil seal on the surface of it and perhaps eliminate the need to use thrust washers on the inside of the housing for the sun gear. Good idea. That way we keep all the gear box parts the same and just change the input shaft. Our lathes can handle that. Also one is dealing with only 200 foot pounds of torque. AC spruce might have tube for the ID, but they only have a thinner wall for the od. I haven't looked around for tube yet, there is probably something available somewhere. We need 1.5x1" for id and about 1.8x2.25 for the od. AC Spruce has 1.5 inch OD .188 wall 4130 which will slip inside the the sun gear. The spline part cut down with minor machining will fit inside the tube. The tube can extend outside the front of the sun gear to act as a pilot in the aft end of the prop shaft. That will be seriously rigid. That will work great. I guess we will need some sort of low speed bearing for that. The prop shaft will be turning 3x slower than the sun, but in relative terms, the speed difference between the two is rather low. Won't that eliminate most of the rest of the chatter, as it holds things closely in line? Ed Carver I would not hold my breath on the chatter elimination. The only likely problems I can see at the moment is the surface speed of the 1.5 inch ID seal and needle thrust bearings. at 8000 RPM and 1.5 inches the surface speed is 3,142 feet per minute. Getting kind of high for PTFE so we should go to Graph-Reinforced PTFE seals at about $61. The larger OD size will better accommodate a slight run out. We are right out there on the RPM limit for a single 40 mm needle thrust bearing so we will need three back to back to get any life out of them. Mounting them back to back cuts the RPM by 1/3rd. We might as well build in a torque meter while we are at it as all gas turbines have them. This will give one a torque which can then be used to calculate the HP knowing the engine RPM. This uses the same principle the gas turbines use and that is measuring the helical gear thrust. No need to dyno your engine. The gear box will do it all the time the engine is running. These can be bought off the shelf if you use an annular hydraulic clutch throw out bearing. Then you will have to pay me a royalty as I invented it years ago and it is now sold by my former company. Renamed from Lamar Engineering to Tilton Engineering. :) The tube sizes I have in mind to create the 4130 input shaft are 1.5"od x 1" id 0.25 wall for the inner tube 2.25"od x 1.75" id 0.25 wall for the outer tube. Both sizes available online costing roughly $120 for a two foot length of each size. AC spruce does not stock the 1/4 wall for either piece, and nothing that will work at all for the OD piece. The wall thickness of the of the turned down sun gear will be about 0.200" and has a 1.387 id. A bit over kill but no big penalty weight wise. http://www.engineeringtoolbox.**com/torsion-shafts-d_947.html I may have missed a message with a Rhino illustration, but I am having a hard time envisioning what Ed is doing with the 4130 tubes on the input shaft. Do you have a drawing that illustrates what is going on? It is basically what Tracy has done but Ed wants a longer box for his Cozy.

I had an idea of cutting the planet cage onto one end of the prop shaft. Can't think of any good reason why we should not do that. I think the od of the 7075 shaft material we intended to use for the steel planet may be slightly too small.The only added issue is the potential need for longer planet shafts to give them greater depth in the alum cage/shaft. I guess that means I can use the 6 planet gears from the unit forget about doing the edm or finding special bolts. The center shaft (pn#675 Makco) could be used for the link to the modified forward drum. This will make getting parts simple because they all come from the same source. What we might do is machine the teeth down to our preferred od of the small end of the sun gear in order to slip a steel tube over it, and use a smaller tube to slip into the id of the same sun gear. This way the sun gear is slipped in between the two tubes thereby doubling the shear strength of the hold pins; while also lowering weight. The two tubes would be welded to the trimmed end of the modified center shaft.

So far all the front planets I have all have the same .440 shafts more or less. There is room for a 5/16 EDM. The area of a 5/16th bolt is .0767 so max clamping load per bolt is 7,670 pounds. 46,020 pounds total for six. Using Murray's statement about the clamping load doing all the coupling and figuring a coeff. of friction of only .1. the outer 1/2 inch width of the planet 4 inch diameter carrier is about six square inches. That would give a torque of about 4,600 x 2 or 9200 inch pounds or 766 foot pounds. No help from bolt shear. Steel on steel coef. of friction is actually higher than .1. As I recall for locomotives it is about .7 so we might be looking at as much as 5360 foot pounds. In addition Grade 8 bolts have a proof load of 120,000 psi and not 100,000 so there is another 20%. No help from bolt shear.

I've sort of assumed we would use grade 12 or better. I believe rod bolts are at least that. If I have any worry about bolting, it is preventing them from backing out, or pulling the alum threads out. I can see using the nord lock fastening system to solve that problem, and wiring with loctite, plus maybe thread inserts in the alum shaft. A lot depends on how hot it will all get. Ed Carver Drilled heads and safety wire. If you can find shafts and afford an integral aluminum planet carrier that would be a real cool solution. We need to figure out how to retain the shafts without the roll pins so it can be repaired.

Ed, I just figured out two good reasons to not do an integral planet carrier. When Ford went to six pinions they also went to a steel planet carrier. The problem with an aluminum planet carrier is the planet gears get closer to the steel ring gear and further away from the steel sun gear with higher temperatures. The other downside is the 5/16th bolts now lock the back bearing to the prop shaft. The back bearing will then take all the prop thrust load.