[sifawangiaEV]

Hi everyone,

I'm in the process of choosing a coupler to mate my Warp9 DC motor with my Mini Cooper manual transmission and I've come across a couple of options. I'm browsing grainger.com and their Rigid Couplers here and I've come across a few coupling types that I think will work for my conversion. Here are the different types (on the grainger.com website):

I've heard that these types of couplings have been successful in EV conversions so I thought I might give one a try. I'm leaning towards using either the 1-piece clamp rigid shaft coupling with a 1.125 inch bore diameter:

Link (https://www.grainger.com/product/RULAND-MANUFACTURING-Rigid-Shaft-Coupling-1-1-8-2ALJ3?Pid=search)

Or using the 1-piece set screw rigid shaft coupling with a 1.125 inch bore diameter:

Link (Rigid Shaft Coupling: 1 1/8 in Bore Dia., Steel, 1 7/8 in Outside Dia.)

Are their any benefits/drawbacks to using one coupling over the other? I'm thinking of having a machine shop cut and weld my clutch plate onto the transmission side of the coupling. What does everyone think of this? What coupling do you recommend?

 

[sifawangiaEV]

if you make it rigid then your alignment needs to be absolutely perfect and you need to 'clock' the shafts to each other first by putting a DTI on one shaft and rotating it around the other in several places to ensure it is both parallel and concentric. This is not an easy task if your coupling lives hidden inside a bellhousing and even harder if you don't have a shimming/adjustment system. The jaw couplings allow easy assembly plus have a stated acceptable misalignment amount. Any misalignment in the shaft that is forced into alignment by tightening a rigid coupling will cause extra stresses and lead to something failing.

What kind of coupler would you recommend?

 

[sifawangiaEV]

I already sent you a link on the other thread

Yeah I commented on it but Pete didn't seem to think it would be reliable. Are you using it in your conversion? If so, how did it turn out?

 

[sifawangiaEV]

Ok, I think I'll give it a shot based on what you've told me.

I will be purchasing the coupling that is specified in these stats (link) with a 1-1/8" bore diameter. Will I need to purchase two steel hubs to make a complete set (versus one) as well as the spider and the steel spider cover, totaling out to: 2(61.13) + 25.58 + 38.45 = $186.29?

 

[sifawangiaEV]

I'm pretty set on buying this part but I would like if anyone could approve or disapprove buying this part so I could feel more confident of my purchase if you know what I mean

 

[sifawangiaEV]

Ah, didn't realise he was using a clutch too so yea, those little metal tabs on the periphery of the disc inside of the lining are the flexible coupling. In fact having a flex coupling and a disc would not be a good idea. Otoh, two separate items with average alignment ability joined by a rigid coupling ends in damage eventually.

As soon as you release the clutch pedal, a traditional clutch setup is also a rigid coupling. The alignment of the coupler is reset every time you push and release the pedal, and that's okay because the engine and transmission are properly aligned, and in a traditional setup the short transmission input shaft is supported and aligned on the engine end by a pilot bushing or bearing.

Sorry if I didn't make this clear before but I'm going clutchless so I won't be using my clutch pedal or a clutch at all. I just want to connect the motor shaft to the transmission shaft with a coupling. Would the McMaster Carr coupling work fine for this application?

 

[sifawangiaEV]

Sorry everyone if I've been all over the place but I've decided to go with a rigid coupling because it would be the longest lasting for my conversion and I'm willing to do the extra tough work to make it work. I just dropped it off at the machine shop with my clutch plate to be welded together, when I realized something not so good...the torque of the rigid coupling wasn't as high as I thought it was. Here's the spec sheet:

I could've sworn that when I bought the item, it said that it had a torque rating of 2,400 in-lb. I'm thinking there might be a glitch on the website but I'm not certain because there is a chance that I somehow read it wrong. What do you all think? Does this rating look right for this coupling or does it seem like a glitch? Should I be considering a new coupling?

 

[sifawangiaEV]

I'll stick my nose in because this sort of thing was within my profession before I retired. Assuming the Mini gearbox has a conventional input shaft the first issue is that the pilot end of the input shaft must be supported just like it had been by the crankshaft. Gearboxes normally rely on this, that's why they appear somewhat loose when you wiggle the input shaft on the bench.

Then you have to transfer the torque off the keyed motor shaft to the spline without loading the spline unevenly. You rely on the involute teeth under torque for alignment.
A normal clutch disk of course is rattle-loose in the middle so that can happen freely (and cheaply).

A huge problem with a keyway-type coupling half is that the constant back and forth torque can shag out the key if the coupling is "hard", but allowing slight rotational flex will help that, which is what the rubber does, another requirement to add to the list. The clamp style coupling half (as used in the type you've identified) can help or at least delay the issue. But a far better design is what's called a taper-lock hub (see image) where there is a tapered sleeve between the motor shaft and coupling half that is drawn in by screws. These are really effective, far better than what you've chosen.

Generally engineers send the dimensional details of the two sides to the coupling manufacturer with the maximum torque and RPM and they determine the best product for the job. Hacking something together especially involving welding may work for a while but it's not a professional solution unfortunately.

One suitable design would be a rubber-based flexible coupling (see image) with both radial and bending flexibility that is configured with a taper-lock on one side and machined to match the spline on the other, allowing the pilot journal to poke through the center and locate into the end of the motor shaft - with a bushing as needed. Or the pilot support can be part of the motor side coupling half. It's only holding it centered just like a pilot bushing or bearing in a crankshaft. This would allow a radial misalignment error of perhaps 0.001 to 0.003" between the motor and gearbox, entirely practical.

If you want more assistance a useful photo would be of the two physical parts set to the locations you need.

View attachment 127751 View attachment 127753 View attachment 127752

Thank you for your input. I may try looking into this but I have already sent both the coupling and the clutch plate to the machine shop to be welded together. I think that I might just try to align the couplings the best I can to ensure the most minimal misalignment and keep it on for maybe a year or 2 before changing it.
I have pictures of the clutch plate and the rigid coupling above. Could you send links to the 2 different coupling that you recommended so I could look into it? Thanks!

 

[sifawangiaEV]

Sorry everyone if I've been all over the place but I've decided to go with a rigid coupling because it would be the longest lasting for my conversion and I'm willing to do the extra tough work to make it work. I just dropped it off at the machine shop with my clutch plate to be welded together, when I realized something not so good...the torque of the rigid coupling wasn't as high as I thought it was. Here's the spec sheet:
View attachment 127750
I could've sworn that when I bought the item, it said that it had a torque rating of 2,400 in-lb. I'm thinking there might be a glitch on the website but I'm not certain because there is a chance that I somehow read it wrong. What do you all think? Does this rating look right for this coupling or does it seem like a glitch? Should I be considering a new coupling?
View attachment 127750

Update: there was an error on the website. The torque rating is actually 4,400 in-lb.

 

[sifawangiaEV]

The machine shop that I sent my rigid coupling and clutch plate to has finished welding the two parts together. Here's the picture that they sent me:

I'm going clutchless which is why I'm just using the hub and not the clutch plate. What does everyone think of the design? If aligned properly, will it hold? Are there any modifications they should make or is it good?

 

[sifawangiaEV]

1) there is evidence of shrinkage along the middle of the weld.
2) the coupling split will cause a stress concentration where it intersects the weld. (just below the arrowhead)

That's a good point. I did notice that split and wondered if that would be an issue. What should I tell the machine shop to do to fix this issue? Should they just reweld it?

I would have welded up the coupling split on the gearbox half to stop movement at the weld. At least shim the gap tight and install some screws to limit flexing of that half.

Are you saying that the clutch bit should be inserted deeper into the coupling? Because I believe that it partially is but I'll have to see it to find out. The person at the machine shop that I was talking to mentioned using screws and a key with the transmission side spline so that the coupler can work as intended but he later decided to have some of the clutch hub part in the coupler and weld it on.

The original coupler is designed to clamp to each shaft, but in this modification the transmission side uses a spline instead, so the clamping action won't be used at all... and is completely incompatible with the rigid splined insert welded all the way around.

Yes, the clamping wouldn't be used on the transmission side but it would be used on the motor side. I'll still be able to use a key and the screws and clamp down on the motor shaft.

@sifawangiaEV: Can you confirm if your crankshaft has a pilot bearing or not?

I don't think that it has a pilot bearing. I attached a picture of the clutch disc in my starting post so you can see that too for confirmation.

Can you get the machinist run the piece with a dial indicator, and show you how the parts were made centric for the welding? Did they put machine screws in the threads and torque them onto some properly sized rod for that portion? If you did not provide them with a runout spec or some measurable expectations then you probably cannot expect them to compensate you, but you may be able to save damage to your gearbox by stepping back and taking some time to confirm some things.

I believe that they did torque the screws to a rod, but I'll check in on Monday when the shop is open to find out what they did and if they can modify it if it needs fixing. If the part is determined to be concentric, and the split in the welding is fixed, am I in the clear?

Thanks everyone for the input. It is greatly appreciated, considered, and very very helpful.

 

[sifawangiaEV]

If the weld cracked on the first go then a second go over the top isn't the solution. They need to find out why; is it incompatible materials, incompatible filler rod, contamination, technique... That crater in the end pool looks ominous, it likely has porosity right down to the root and could initiate a crack anyway, even if that line isn't a crack.

Welding axles is an age old practice that often results in failure. Some people have the knack of it, many don't. You are doing a very similar thing to welding an axle, just less torque.

Ok, that makes a lot of sense. I'll talk to them about what the cause might be and if they can't fix it, I'll take it to a different machine shop and see if they can figure it out/do it right.

Also I cannot find the specs for this coupling that specify how much to torque the screws...Is there a general rating out there somewhere?

 

[sifawangiaEV]

I'd sure like to see photos of the actual gearbox input shaft and motor output shaft. And some idea of the spacing between them you're expecting.

The other end of the coupler that's hidden fits the motor shaft and part that's welded fits the transmission shaft. Here are the pictures:

I was suggesting welding it along the red line but you'd want to grind a "V" first so that the weld can take good hold of the parent steel.

I'm not a welder so I'm having trouble understanding what you mean. Are you saying that the coupling should fit in deeper? Or are you saying to weld through that gap for a better grip?

Next go...cut the black coupler in half to where only two cinch bolts are used and a sliver above the factory gap.

Groove the spline piece and the new baby two bolt coupler for welding HALF way around, like its amputated friend was joined.

Get it TiG welded, several passes, then chuck it in a lathe and fillet the weld so it's balanced and there are no stress points (sudden geometry changes...ridges, etc). You may need to take it to a machine shop and a competent welder vs guys who do joints on irrigation stuff.

Sorry but I don't really understand what you're telling me to do. So I cut the coupler in half and then what do I do? How will this be different from what I have already? Is the only difference a different weld (TiG vs aluminum)?

 

[sifawangiaEV]

Maybe it'd be a better shot welding the clutch spline to a stump of shaft the same diameter as the motor shaft, then tighten the coupler on both the motor and the stump shaft how it was intended to work

The problem might be that there won't be enough meat over the splines to get to motor diameter, but that just means reaming half the coupler to a larger ID...but only if they don't already stock couplers in two different ID's.

No welding needed..

So the problem with that I think is the fact that the coupler works with a key so if I used it as intended, I would need to make a keyway in the clutch hub and I don't know if that would be very reliable/practical. Is there a way where I can have the machine shop lathe the coupler to have a bigger diameter and weld the clutch hub so that it sits in there? Or would tightening the coupler around the clutch hub without a key be enough to keep it in place?
In response to remy, this coupler brand does not sell couplers with different IDs. Do you think that using this method but welding the clutch piece in instead would work fine?

 

[sifawangiaEV]

Considering all that you all have said, I have two options to present to the machine shop. I will be presenting one of these options to the machine shop on Monday and ensure that the parts are concentric. I'll have the machine shop torque the screw to the rated toque for 1/4-28 screws which is about 13 ft-lb. Here are my two options:

Option 1: Remove the clutch hub from the coupler and then lathe the bore of the coupler to make it larger and also make the clutch hub diameter as small as it can be (while still maintaining its integrity, of course). Then they'll broach or mill a keyway into the clutch hub and tighten it inside the coupling, torqued to 13 ft-lb.

I really like this option and the fact that I will be using the coupler how it was intended, but in the event that things don't work out the way that they are supposed to, I may go for option two:

Option 2: I'm going to talk to the machine shop about the split in the coupler and ask what could be the possible cause of it. In the event that they figure out what caused the split and know how to fix it, I'll see if they can weld the piece back on and make it concentric. If there are no splits and the part is concentric, will this method work fine?

I will use a DTI to make sure that the part is concentric for both options. Will both options work fine? Please let me know what you think of the options.

 

[sifawangiaEV]

How much length do you have between the motor and spline, i.e. is there enough room to have a stump sticking out of the coupling with the spline inside?

There is enough room for a stump to stick out of the coupler. I'll need an adapter plate that's about 1/2" thick.

 

[sifawangiaEV]

@sifawangiaEV, Thanks for posting the photos of the actual parts. Because it's now clear that the transmission input (clutch) shaft is already fully supported within the gearbox you should use a flexible coupling that can tolerate parallel misalignment. If you use a solid coupling your alignment must be perfect. That's a tall order and not something I'd recommend trying if any sort of reliability past a few weeks is your goal. So, when I say "should" I mean like an engineer speaking politely to his manager, I really mean "must". You're shooting yourself in the foot if you try to mickey-mouse this, which is regrettably the path you are already on.

There are a number of industrial coupling types that are suitable but you also have to ensure that the type chosen will be available with appropriate shaft options. Because of the frequent torque reversals I would stick to those that use clamping methods on the shaft(s), not just a split clamp but a proper taper-lock design. There may even be one for the spline according to the literature I'm referencing below. A small amount of torsional flexibility would not be a bad thing either, but not a lot.

Because the radial misalignment could be realistically kept to within 0.5mm TIR, one option that I found quickly is the Rexnord CentaFlex. It's quite complicated to navigate the engineering selection details but it's likely that their application department will do all that for you if you supply a fully-dimensioned drawing of both sides and max torque/RPM specs. You'll need to identify the spline dimensions as well and the desired gap between the shaft ends. When you get a recommendation from them you'll need to verify that it fits within the bellhousing.

There are many other coupling manufacturers but that's up to you to research. Following this advice will provide a reliable solution but I'm going to wish you the best of luck and leave the rest up to you, as I have to move on to other things.

I called Rexnord and some of their distributors and they told me that they can’t make couplings with splines because of how precise that they have to be. So, sadly, I won’t be able to use a CentaFlex coupling for this application.
I was working with a local machine shop on making the coupling better and they were able to take off the weld and redo it. The weld that they used was TiG weld. And it has no streamline cracks. The only downside is the TIR rating of .006”. Thé machine shop said that they were getting different ratings based on where they were taking the measurements on the splined side of the coupling. They concluded that it’s most likely because the coupling is used (186 thousand miles in the car) and that it would most likely be fine since I’m putting it on the shaft that it came from and worked with.

When I tried to put the coupling on the transmission, it wouldn’t slide on all of the way. It just stopped. So basically, the coupling and the splined part shrank due to heat when it was being welded.

I decided to tap the coupling on the transmission shaft and pull it off until it was able to slide on and off easily. I’ve only gotten it to slide on a little bit more though. If this method fails, I will use a brake cylinder hone to shave down the inside diameter of the splined coupling just a little bit. I will also have to do this for the motor side because that side of the coupling shrunk as well.
My other option is to buy a new clutch plate and have the machine shop weld that clutch plate on my coupling instead (but not letting the coupling shrink). Please let me know what you all think.