Graupner Flex Coupler

[himmelman]

Hey,

I've recently converted a Proboat LLumar to run electric with a speed 700 motor. Everything is great except for one thing: my Graupner coupler (5mm to 4mm) wobbles excessively at high rpm, whipping back and forth inside the hull (travels about half inch side to side). Is there anything that can be done to remedy this? It would be difficult to resort to a solid coupler because of the distance between the flex cable and motor - I don't know of a solid coupler that long.

Thanks,

Greg

 

[TRUCKPULL]

Hello Creg

what length of exposed flex cable do you have????

1/4" is MAX.

Where in Ontatio are you???

Larry

St. Catharines Ont.

 

[Propjockey]

Is your Graupner unit the U-joint type? If so, you're asking for trouble. A U-joint coupled to a flex shaft is a bad combination.

Got any pics?

 

[himmelman]

Thanks Guys,

Its a little difficult to explain but the coupler itself has the flex cable in it. Graupner has a couple of couplers that are flexible (hobby-lobby website) They have a small solid area on both ends that contain the screws to attach to the motor and the flexible drive shaft leading to the strut but the centre section of the coupler itself is flexed.

I just found a picture - hope I attached it right.

View attachment 4265

 

[Jeff Shriver]

A U-joint coupled to a flex shaft is a bad combination.

I have this in my LSH boat. It works perfectly. LSH isn't a high rpm class, but I haven't had any problems thus far. I have a 3 inch flex cable U joint which attaches to a SS straight shaft. I wonder if one of your couplers is drilled off-center causing the piece to wobble.

How the heck do you attach a picture? It says on my screen I only have 3.64K global space left for attachments. 3.64K??? That is miniscule.

 

[Jeff Shriver]

I got it now.

 

[Jim Caldwell]

These couplers are designed for motor to non-flexable straight shafts ONLY.

You need to install a new flex shaft that goes all the way to the motor and use a non flexable coupler there.

DO NOT RUN UNTIL YOU CHANGE IT- it will rip the shaft and motor bearing out!

 

[Pagemaster]

Jim is correct. These are made to help the angle with a straight shaft.

Also these graupner flex couplers are not well built from the start. We started selling them and had many failures. Some were drilled off center, some were poorly glued. We now have someone build them for us.

 

[Propjockey]

Yup, I see trouble in the making. If there is enough slop in the flex, you run the risk of ripping out the whole stuffing tube. (ask how I know... <_< )

I have a 3 inch flex cable U joint which attaches to a SS straight shaft.

You have the right set-up Jeff. A flex coupler connecting the motor to a solid shaft. Himmelman is using a flex coupler to connect the motor to a flex shaft.

Another thing to consider Himmelman...how much of the flex shaft is exposed? Like Truckpull said, the more flex shaft you have hanging out of the stuffing tube, the greater the chance of something leaving your boat at a most inopportune time.

 

[himmelman]

Thanks again for the help guys, I should be able to make everything work now. I made the mistake of trying to work with what I had on hand - I'll have to get some new stuff. I wish I could atttach a video of the vibrating flex coupler - its pretty scary.

Hopefully everything else should be OK, I'm using mostly stock stuff except for the prop which is an Octura X637.

The motor to drive shaft alignment is almost dead on. I may be able to attach two couplers together with a solid shaft in between. It will take some experimenting.

Thanks again,

Gregory Himmelman

 

[charles maley]

i used u join units from a traxxas outdrive on my llumar converted

but i first epoxy a ball bering that fit snugly on the flex shaft

onto the front wood bulkhead and then i used the coupler

i have had no problem with vibration