O/T - High strength/temp elastomer for Lovejoy coupling?

[Bill D]

How about a different type of coupling. Of course rpm limits what is possible. I was thinking of those kind that are two sprockets on the same axis with a length of timing chain linking them together.
Bill D

 

[CalG]

Cause instead of beating up the rubber and it flying around the whole thing would surely turn to shrapnel. As mentioned I broke several hardened S7 pins when everything was hard mounted and aligned to tenths.

Single cylinder two-strokes run rough, the graphs show the motor jumps around about +/-500 from the baseline as it's pulsing away at 450 revs per second. You need to have something there to soften the blow.

How do the gearboxes and clutch baskets ever stand the load?

 

[Terry Keeley]

The coupling issue has ben solved, proper alignment between the motor and shaft was the key.

The two uprights are perfectly aligned so I used a mic between the cradle and uprights to get it aligned horizontally and a depth mic from the cradle to the top of the uprights for vertical.

Anyone think of an easier way to do it?

 

[EmGo]

The coupling issue has ben solved, proper alignment between the motor and shaft was the key.

Anyone think of an easier way to do it?

Not to be an ass but .... not solved at all, replaced with a different problem. Now you don't have a coupling, effectively. So you have to perfectly align any engine you want to test, and 9'll getcha 10 that their mounting holes are not precision.

So. You can either do without a coupling at all and align every motor to test, or find a coupling that works.

Looking at your photo, it seems possible that you could still use cardan couplings, but two of them at 90*. There's room to move the test motor forward, looks like.

Or possibly a different type of coupling entirely which will work better.

Otherwise, resign yourself to a time-intensive alignment process for every motor. At the least, you could help that by installing some adjustment screws to the motor baseplate.

 

[Terry Keeley]

Not to be an ass but .... not solved at all, replaced with a different problem. Now you don't have a coupling, effectively. So you have to perfectly align any engine you want to test, and 9'll getcha 10 that their mounting holes are not precision.

So. You can either do without a coupling at all and align every motor to test, or find a coupling that works.

Looking at your photo, it seems possible that you could still use cardan couplings, but two of them at 90*. There's room to move the test motor forward, looks like.

Or possibly a different type of coupling entirely which will work better.

Otherwise, resign yourself to a time-intensive alignment process for every motor. At the least, you could help that by installing some adjustment screws to the motor baseplate.

Actually the motors have very accurately machined flats under the lugs (plus dowel holes) for machining at the factory so I made the cradle a snug fit...

 

[EmGo]

Actually the motors have very accurately machined flats under the lugs (plus dowel holes) for machining at the factory so I made the cradle a snug fit...

That's handy. So why are you having alignment problems then ?

 

[Spruewell]

Having the coupler so close to the engine is backwards. Put the coupler down by the flywheel and use the flexibility of the driveline to deal with alignment. The soft mounts you have supporting the engine will make perfect alignment very difficult to maintain. A solid coupler from the engine to driveline will be more reliable and allow you to more easily adapt to different engines. Put a guard over the driveline too while you are at it.

 

[Terry Keeley]

That's handy. So why are you having alignment problems then ?

Talked to my "consigliere" (toolmaker buddy) who said there's nothing to properly locate the cradle with just the spacers sitting on top of the uprights and 3/8" bolts.

One idea is to replace the spacers with drill bushings that extend maybe 1/4" out the bottom of the cradle that fit into counter-bored holes in the uprights. If the holes in the cradle and the uprights are good the only thing that would throw it off is if the rubber bushing weren't concentric, but they were turned and drilled in one go.

Might still need some shimming to get the height right but done once and it should be good.

 

[tdmidget]

EG seems to be under the impression that "coupling" means that alignment is not necessary. A coupling connects two rotating items, typically a driver and a driven elements. It does not eliminate the need for alignment at all. A Lovejoy is the least and weeniest of the coupling world. They tolerate more misalignment and transmit less power than any other. The Cardan joint requires misalignment to a degree. The shafts still must be parallel and the Cardan shaft should be at 2-3 degrees.
There ain't no such thing as a free lunch. Heinlein, numerous applications. ANY coupling needs to be aligned. More speed, more power, more need. No exceptions.

 

[EmGo]

EG seems to be under the impression that "coupling" means that alignment is not necessary.

No, he was using it in a sloppy way to emphasize that usually, couplings are designed to deal with misalignment. Obviously a simple tube that clamped tight on both shafts would still be a coupling, but for the purpose of this discussion I ignored that. Mea culpa, mea maxima culpa.

Intended point was that, with perfect alignment, lovejoy is not needed. It's not doing anything. Just use a sleeve and clamp the shafts together.

Or find a different "coupling" that will tolerate misalignment, which means Mr Keeley doesn't have to spend an hour each time he changes motors

Our boss used to run unlimited boost offies on a water dyno in the front yard. (The neighbors hated him, we thought it was cool. Nice when the run was over tho). There was a coupling in the setup, as I remember two cardan joints. It didn't cause trouble. Those engines were putting out 1,000 hp.

Should be possible to deal with 5 hp, I'd hope.

 

[tdmidget]

No, he was using it in a sloppy way to emphasize that usually, couplings are designed to deal with misalignment. Obviously a simple tube that clamped tight on both shafts would still be a coupling, but for the purpose of this discussion I ignored that. Mea culpa, mea maxima culpa.

Intended point was that, with perfect alignment, lovejoy is not needed. It's not doing anything. Just use a sleeve and clamp the shafts together.

Or find a different "coupling" that will tolerate misalignment, which means Mr Keeley doesn't have to spend an hour each time he changes motors

Our boss used to run unlimited boost offies on a water dyno in the front yard. (The neighbors hated him, we thought it was cool. Nice when the run was over tho). There was a coupling in the setup, as I remember two cardan joints. It didn't cause trouble. Those engines were putting out 1,000 hp.

Should be possible to deal with 5 hp, I'd hope.

5hp? Fuck yeah!! This ought to do it:Series 492 | GWB Drive Shaft
Note that the cardan shaft is NOT a coupling, The coupling is the flange faces which are Hirth couplings which are as near zero misalignment as can be, much like a curvic coupling. Still won't handle the speed though. Any misalignment eats horsepower. That is the source of the heat melting the polymer elements in the Lovejoy. You will never get anything near an accurate dyno number burning up your power in a misaligned joint.