# failed coupler/keyway



## Yukon_Shane (Jul 15, 2010)

Hi folks,

I've had a failure in my coupler/keyway and I'm wondering if someone here might be able to give me some advise as to what I did wrong and how I can fix the damage.

I purchased this coupler from EVCouplerconnection a few years ago and it seemed to work well for a few years but last month it blew apart while I was trying to take off from a stoplight. You can see from the pictures that the keyway worked it's way out of the coupler and rounded off the edges of both the motor shaft keyway slot and the coupler keyway slot.

My setup is fairly peppy but it's no race machine (Solition Jr., 160V pack) so I don't think that excess power was the problem. 

Any suggestions on what I should do differently next time and how I can fix the rounded out motor shaft keyway slot?


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## electro wrks (Mar 5, 2012)

Bummer this happened. The EV DIY community has gone around and around over what's the best coupling design. All I know is, in my commercial/industrial design and fab business, I would avoid using a set screw over a key coupling design(like yours) in any piece of equipment over a few HP, with reversing loads, or in critical fail-safe applications.

Some people seem to be getting away with using the design. Having an interference(pressed-on) fit and/or a squeeze bolt on the end of the shaft seems to help. Any movement between the coupling and the shaft, over time, can cause the kind of failure shown in your pics. More pictures of your set up: adapter plate, transmission input shaft, clutch/fly wheel (if you have them) bell housing, etc. would help us. If this coupling is made of aluminum, that could be part of the problem. Even if it's made from high strength alloys, it still may be too soft and/or not have enough contact area necessary to handle the torque. 

Generally, I've found tapered bushing couplings are the way to go . They positively squeeze a coupling, sprocket, pulley, flywheel, what have you, onto the motor shaft. I've seen some tapered bushing coupling designs that work so well, the equipment manufacturers eliminated the key and keyway entirely! Some EV component suppliers have tapered bushing design couplings.

You do have to seat the tapered bushing with a soft mallet and/or re-torque the tightening screws or nuts 1 or 2 times. And, you should check the flywheel(if there is one) for run-out. You may have to move components around to index them or have a machinist do a little clean-up, scraping, and set-up work. But that's it. No more worrying about your set screw type coupling destroying your motor shaft and transmission. BTW, the centerline of all these components should be lined up within a few thousands of an inch. But that's a discussion for another day.

Also, if your motor shaft isn't chewed up too badly, you may be able to still use it with a tapered bushing. Back up the shaft with a heavy piece of hardwood or aluminum and pound the curled up edges of the keyway back into place. Hey, it's worked for me. Use a new key and a tapered bushing as a guide. Make sure the shaft is well supported by the back up piece or you will be pounding on the bearings, possibly ruining them. Check the run-out and try to adjust as before. You might get away with it.


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## Duncan (Dec 8, 2008)

I will back up Electro wrks
I was always trained to transmit power by friction
Either in a taper or directly - a key is useful to line things up but if you use it to transmit torque it will fail in the end

If you look at a flywheel - it may be doweled for location but the power loads are taken by friction between the flywheel and the crank
The bolts apply the clamping load to provide the friction

You need to change to a taper clamp system


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## dragonsgate (May 19, 2012)

Looks like a bit of slippage on shaft. Maybe to small of a key? A tight fit between shaft and coupler with tight fitting key is important as well as centering. I am not using a tapper but the fit on my coupler and shaft is snug and had no trouble for 50K miles. Is the coupler solid or is it sprung? I think the shock absorption of the springs has helped a lot.


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## Yukon_Shane (Jul 15, 2010)

I'm not familiar with the tapper lock approach. I'll have to do some research on this. 

If it relies on friction then perhaps I don't have to worry to much about the keyway being eaten up which would be nice.

Any suggestions on where to find such a coupler?

thanks for the response.


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## Yukon_Shane (Jul 15, 2010)

dragonsgate said:


> Looks like a bit of slippage on shaft. Maybe to small of a key? A tight fit between shaft and coupler with tight fitting key is important as well as centering. I am not using a tapper but the fit on my coupler and shaft is snug and had no trouble for 50K miles. Is the coupler solid or is it sprung? I think the shock absorption of the springs has helped a lot.


I'd agree, definitely looks like some slippage and I'm guessing that the slack I'd been feeling in the drivetrain for the last couple of months, that I thought was the transmission or rear end, was actually this connection. 

The key and coupler seemed to fit well but I wouldn't call it "snug", it slipped on pretty easily so perhaps the key was to small. 

The couple was clutchless but it was sprung, it used the centre spring section of the old clutch to dampen the torque a bit. I'm not much of an expert in metals but the coupler looks like aluminum to me so perhaps that was the problem. 

I didn't really like the clutchless set-up for driving so I was planning to go to a clutch set-up in my new conversion; however, this is putting a bit of a wrinkle in my plans


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## major (Apr 4, 2008)

Yukon_Shane said:


> I'm not much of an expert in metals but the coupler looks like aluminum to me so perhaps that was the problem.


Never use Aluminum for a shaft coupler or collar. Among other reasons, it has a greater coefficient of thermal expansion than does steel so it will loosen as it warms. Don't use it with a taper lock or any type of coupling system.


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## Yukon_Shane (Jul 15, 2010)

major said:


> Never use Aluminum for a shaft coupler or collar. Among other reasons, it has a greater coefficient of thermal expansion than does steel so it will loosen as it warms. Don't use it with a taper lock or any type of coupling system.


thanks major.

so it's likely that the aluminum coupler just expanded or wore down enough to loosen up the key in the keyway and mangle the sides of the motor shaft keyway.

With that in mind I wonder what the likelihood is of being able to clean up these edges a bit and use a new coupler without having to take the motor apart and have the shaft machined?

If I was going to machine the shaft would it make sense to just have the keyway widened out and use a larger key (with a different coupler of course)?


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## electro wrks (Mar 5, 2012)

If you post more pictures and give us more details, we might be of more help to you. Motor make and size, type and make of donor, adapter plate details, type of transmission, etc. would be a good start.

If you can get a micrometer on the worn vs. the unworn areas of the motor shaft, it could give us some idea of its condition. Check to see if its tapered. Are there grooves or a wear step on the shaft where the coupling was riding? Also, if you can, use a dial indicator (< $30.00 for a good enough set up at Harbor Freight), to check the shaft runout.

And seriously, try carfully peening (OK lightly pounding) the curled up areas of the keyway back into place with a small to medium sized ball peen hammer. Don't forget to back up shaft opposite where your pounding with a piece of hardwood or aluminum so not to mar the shaft or damage the bearings. By backing up the shaft I mean have the motor horizontal, and the shaft end of the motor's weight supported by the shaft on the backup piece.

In your case, the motor shaft has a large center hole(for a pilot bearing?). You should put a temporary plug in this hole to back up the keyway while it's pounded back into shape. Try out this fix. The shaft, maybe the motor will probably have to be replaced if it doesn't work.

Also, having spouted off about the benefits of tapered bushing couplings, I'm having trouble finding a supplier that has them! Does anybody make these anymore for EV conversions?


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## dragonsgate (May 19, 2012)

I was trying to word a reply how to go about some kind of a fix. Wrks said it well enough. If you don't have a dial indicator on hand you can get a rough idea of how out of round the shaft is by anchoring piece or rod to something heavy and will not move easy. Make sure the motor will not rock also. Place one end of the rod against the shaft and slowly turn it by hand. The flared bits might be a problem so you will have to find a spot with no bumps all the way around. As you turn the shaft the rod should stay in contact all the way round the shaft. This is for rough evaluation. For precision you will need a mic and an indicator.


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## major (Apr 4, 2008)

electro wrks said:


> Also, having spouted off about the benefits of tapered bushing couplings, I'm having trouble finding a supplier that has them! Does anybody make these anymore for EV conversions?


http://www.grainger.com/search?gcli...80350&ef_id=U72XdwAABXLfqz2y:20141212041036:s 

Taper lock google brings up plenty. I'd suggest he take his motor and coupler to a local machine shop and get their opinion. They may have a source for the taper lock they are accustomed to using.


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## Yabert (Feb 7, 2010)

Yukon_Shane said:


> I'm not much of an expert in metals but the coupler looks like aluminum to me so perhaps that was the problem.


The aluminum coupler and/or the bad key is probably the problem.
I've similar set up in my Smart (clutchless, centre spring section of the old clutch) without problem after 4 years despite I'm passing 1000A in my Impulse 9 (read here lot of torque at shaft). The only difference: My coupler is build from 4140 steel...

Now, as solution for your problem, I suggest you to use a B-Loc Fennerdrive Keyless bushing with new steel coupler if your motor shaft is long and big enough.

I wish you best luck.

Edit: Your motor is a Kostov 10, right? So, 113 lbs-ft of torque at 600A and a B-Loc B103 1-1/8'' can transmit 445 lbs-ft of torque (safety factor of 3,9 seem good to me).
B-Loc B112 = 675 lbs-ft of torque... Perfect if your shaft is longuer than the 1,486'' I can see on Kostov drawing.


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## Yukon_Shane (Jul 15, 2010)

Thanks for your responses guys. I think Major's right, I'll see if I can find a machine shop to take a look at this for me.

I'll update this thread with the fix I come up with. 

...so many things to learn with EV conversions...


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## electro wrks (Mar 5, 2012)

major said:


> Taper lock google brings up plenty. I'd suggest he take his motor and coupler to a local machine shop and get their opinion. They may have a source for the taper lock they are accustomed to using.


The bushings themselves are plentiful and dirt cheap on eBay. I'm referring to the semi custom housings/adapters for ICE flywheels and/or the transmission input shafts that the bushings fit in.

Canadian Electric Vehicles has gone back to the set screw design :http://www.canev.com/adapters.php

Somebody else must make them.


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## Yabert (Feb 7, 2010)

Hi Yukon

If you need help to use a Fennerdrive Keyless bushing or to design the coupler part, just let me know.
I also know Old.DSMer on this forum who used Keyless bushing with his Kostov 11. He had problem with his Tsubaki keyless bushing with incorrect installation, but, from what I know, he has success with fennerdrive unit.
http://www.diyelectriccar.com/forums/showthread.php/1995-eagle-talon-awd-kostov-11-83470p5.html


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## boekel (Nov 10, 2010)

Lots of models to choose from.
search for:
conical clamping elements

This is one of many companies:
http://www.fptgroup.com/dss/docs/689_06_Fenner_Shaft_Fixings.pdf

Good luck, it looks doable, though best is to turn the shaft clean on a lathe to prevent alignment issues.


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## Yukon_Shane (Jul 15, 2010)

Anyone have a particular gear puller they'd recommend for dississempling a warp9? I want to pull it apart before sending it to the machine shop. I don't want them welding next to the bearing.


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## Yabert (Feb 7, 2010)

Yukon_Shane said:


> ..sending it to the machine shop. I don't want them welding next to the bearing.


A bigger shaft or they only add new material before rework the shaft?
I did the rework of a shaft after I added weld with correct result few years ago.

The only point I suggest you to take care is than some regular machine shops can consider an eccentricity of 0,003" as good accuracy, but too big eccentricity can cause undesirable vibration on the motor.
If you work with a motor shop, they probably know what they do.

Good luck and keep us updated with few pictures.


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## Yukon_Shane (Jul 15, 2010)

Hi Yabert,

thanks for your response. 

I don't think I'll be able to find a motor shop here in the Yukon; however, there are a few machine shops. I'll ask around with regards to their accuracy.

What do you recommend as a good accuracy?


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## dragonsgate (May 19, 2012)

Yukon_Shane said:


> Hi Yabert,
> 
> thanks for your response.
> 
> ...


I would say dead on or better. Zero.


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## Yabert (Feb 7, 2010)

Yukon_Shane said:


> What do you recommend as a good accuracy?


That's the good question!
I think the best is to mesure the variation on your armature. They can adjust the bearing seat at 0,000'' on the lathe and verify if the steel lamination stack have some eccentricity.

In the past I had to repair the shaft of my forklift motor. On the lathe with a dial indicator, I thought that 0,002'' of eccentricity was good (0,004'' of shaft movement per turn). When I decide to see the motor shop because my motor vibrate, they said that I need to rework my shaft before they attempt to balance my motor.

Wel, all this to say that rework a motor shaft isn't very easy, despite for a machine shop.
If they can remove the motor shaft from the armature that should be fairly easy to rework, but trying to rework the entire armature is another story.... it's why I suggested you the keyless bushing solution in the first time.


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## dragonsgate (May 19, 2012)

I had some wear on one of my first couplers I built. The input shaft on the trans was right at four thousands out and I could feel it. Up to three thousand rpm it was tolerable but anywhere over and I could hear it and feel the vibration. It is hard on bearings and will eventually cause something else to break. Yabert mentioned the thing I was wondering about. How to go about working on the armature with the windings on it. In the proses something is likely to get bumped and insolation chipped at the least. The money it is going to cost to have some one do the machine work is not going to be cheap. Might it be better and at not that much more money to get another armature or a new motor?


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## z_power (Dec 17, 2011)

The idea sounds ridiculous but I'm throwing it randomly:
Mount whole motor onto big lathe's "seat" (bed? frame?) and propel the shaft with motor's own power. If armature is set parallel to lathe's main axis then in theory shaft could be cut in exact shape and spot on without eccentricity... (pls pardon my poor language)


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## Yukon_Shane (Jul 15, 2010)

Yabert said:


> That's the good question!
> I think the best is to mesure the variation on your armature. They can adjust the bearing seat at 0,000'' on the lathe and verify if the steel lamination stack have some eccentricity.
> 
> In the past I had to repair the shaft of my forklift motor. On the lathe with a dial indicator, I thought that 0,002'' of eccentricity was good (0,004'' of shaft movement per turn). When I decide to see the motor shop because my motor vibrate, they said that I need to rework my shaft before they attempt to balance my motor.
> ...


good points...so you're thinking I should just clean up the keyway and use a keyless bushing...I'll have to think about that a bit. 

My sense with the keyless bushing is that there is a lot of margin for error in installation and if it doesn't run properly it'll be hard to tell whether or not I just installed it wrong or if the shaft is damaged enough that it needs to be reworked anyway.

I'm trying to get some information form the local machine shops to see if they are able to make this repair but obviously this isn't the best time of the year to be doing this so I'm not having much luck.

I'll keep hunting.

thanks again for the feedback guys.


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## Yabert (Feb 7, 2010)

Yukon_Shane said:


> so you're thinking I should just clean up the keyway and use a keyless bushing...


Right!
I suggest you to download the FennerDrives B-Loc catalogue and understand the installation instruction.

http://www.fennerdrives.com/b-loc/
http://www.fennerdrives.com/install/


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## dillond666 (Dec 27, 2010)

I guess this thread is a bit old but I'll tell you how I'd proceed anyway 

The armature needs to come out and have the bearings removed. Then it needs to go into a lathe with a four jaw chuck on the shaft at the commutator end (with aluminium packing) and a revolving centre on the damaged end. The armature should be clocked up perfectly on both bearing journals by adjusting the chuck and perhaps shimming the revolving centre with paper. The shaft can then be carefully machined, just enough to restore the surface.

Remove from lathe and have the keyway milled true and slightly oversize.

A new non standard key and coupling will need to be made from steel with a 0.0005" to 0.001" interference fit. Rebuild and use heat to fit the coupling. There is no substitute for accurate machining.


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## Yukon_Shane (Jul 15, 2010)

Hi folks,

just to close the book on this: I brought the motor to a few machine shops in my area. Most of them didn't want to have anything to do with it unless I took the motor completely apparent and handed them the drive shaft to work with (which was disappointing). I did find one shop that seamed to understanding that taking the motor completely apart was a monumental task and agreed to work on it if I took the armature section and bearings off. So that's what I did.

They welded in the messed up keyway and cut a new one. Cost me $200 which seamed reasonable. Of course I had to figure out how to take the motor apart and put it back together but that wasn't really a big deal and kind of a fun experience really. 

I've attached a picture of the finished product below. I think they did a pretty good job but I'm really not an expert in this area so we'll see how it holds up. 

I have learned my lesson and will not be using an aluminum coupler again. I've purchased a new coupler for CanEV that looks significantly stronger then the one I got from "EVCouplerConnection". The guy who runs EVCouplerConnection seems very nice and helpful but after this experience I can't say I'd recommend using his products.

While I had the motor apart I noticed some pretty significant oil leakage from the two bearings so I replaced those. This oil leaking may not be a big deal but for all the time and money it cost I figured I might as well.

anyway, thanks for all of you assistance with this. 

cheers,

Shane


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## major (Apr 4, 2008)

Hi Yuk,

I suggest you still use a taper lock on the repaired shaft. The rebuilt keyway may not be as strong/hard as the original and result in trouble relying on a key to hold torque. Also, bearings used in these DC motors are typically sealed & lubed for life. Make sure you get good quality bearings with high temperature seals (not shields) and high temperature grease. Bearings should always be replaced after removal from the shaft press fit. Reassembly needs to press on the inner race with a sleeve or you'll damage the new bearing. 

major


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## Yukon_Shane (Jul 15, 2010)

major said:


> Hi Yuk,
> 
> I suggest you still use a taper lock on the repaired shaft. The rebuilt keyway may not be as strong/hard as the original and result in trouble relying on a key to hold torque. Also, bearings used in these DC motors are typically sealed & lubed for life. Make sure you get good quality bearings with high temperature seals (not shields) and high temperature grease. Bearings should always be replaced after removal from the shaft press fit. Reassembly needs to press on the inner race with a sleeve or you'll damage the new bearing.
> 
> major


Hey major,

Thanks for the advice. Because I've already purchased the conventional coupler I think I'll risk it. My car isn't a serious race machine and I'm cautiously optimistic that it'll hold together but if not I'll update this thread so you can say "I told you so"

I shopped around a bit to find decent replacement bearings and think I did a decent job but if you have a specific recommendation for bearings I'd be inclined to follow your lead as I'm not entirely sure what the specks for these should be.

I did use a sleeve to press these back on; however I heated the bearings up first as well so they really didn't need much force at all to go on. One of them slipped on without even a tap.

All and all it was a pretty simple procedure...these motors seem beautifully simple.


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