pengaru

I've been asessing the parts that are going into my motor and it seems like the eccentric shaft is somewhat of a limitation. It's quite heavy (although it's low orbit mass, it's still relatively heavy) and the lack of a center bearing seems like the main cause of the flex experienced at high rpm. I found this site which has a 2 piece eccentric shaft that is ~2.6 lbs lighter, and includes an intermediate bearing which requires modifying the intermediate housing.

pimp eccentric shaft

Now, after discussing this mod with some friends and running it over in my head... It seems like it may even be a possibility to remove the counterweights with the intermediate housing providing a bearing for the eccentric shaft center.



Ditching those counterweights sounds damn good to me.



Anyone have any comments or info? Sources for other eccentric shafts that are hardened and/or lightened?



BTW, I've also contacted the makers of this eccentric shaft and confirmed they can perform the modifications needed to the intermediate housing so it can recieve the additional bearing for $150 USD.

jspecracer7

VERY interesting. First mod like that I've ever seen.

RX-Midget

very interesting, but I don't think you can ditch the counter weights. You will still need them to balance the rotating assembly.



The only thing that looks suspect is that it looks like they only use a single long keyway to locate the removable section of the e-shaft.

pengaru

Since the rotors are 180 degrees out of phase from one another, they should be counterweighting one another, along with the eccentric shaft lobes. I thought the counterweights were present not to balance the rotating assembly but to equalize the load across the main bearings to minimize flex/stress. Please correct me if I'm wrong. But if that is the case, wouldnt having a central main bearing cancel out the need for this? (provided the bearing has enough area and is up for the task). It looks to me the main reason the counterweights are needed is because theres just two main bearings for the eccentric shaft, at the ends. Without the counterweights I imagine flex becomes a major problem.



In a 20B or a R26B do they still only have 2 counterweights?



Also, doesnt the fact that the stationary gears clock the rotors from only one side, the far side (main bearing side also!) exaggerate the problem? At high rpm, at the far ends the rotors are not able to wander around since the stationary gear is right there (unless the stationary gear begins to give) but towards the center, there is no stationary gear support... isnt this also why people need to clearance their rotors for very high rpm operation to keep from striking the side housings? Due to the uneven stationary gear support (on one side only) ? Seems like even more reason to add a center bearing, and that problem seems like more reason to have counterweights to try keep the eccentric shaft straight. But perhaps with a center bearing one could eliminate that need. Personally it seems to me like there just needs to be stationary gears on both sides of the rotors (ideally)



BTW, I really like your midget :bigthumg:

pengaru

They want $1400 USD for the eccentric shaft, and claim the counterweights are still required... **** that. I gotta go talk to a physics guy @ fnal.gov to see about these counterweights :twisted:

RX-Midget

I'm no expert, but I don't think the counter weights are there to get rid of e-shaft flex. Here is my reason - If you use them to 'balance' the assemble at high rpm taking into account e-shaft flex, then it would vibrate like crazy at low rpm when the e-shaft is straight.



my $.02



BTW - thanks for the compliment

13BAce

Yeah, they're required for balncine the rotating assembly. My friend alsmost put together a motor with the wrong counterweights before I set him straight. The 2 piece shaft looks good, but it would be nice if they had the needle bearings for both the front and rear stationary gears. Now THAT would be a nice setup.