Direct Drive: Mechanical issues

Technical discussion on converting internal combustion to electric
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EV2Go
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Direct Drive: Mechanical issues

Post by EV2Go » Wed, 18 Feb 2009, 18:46

Was thinking about this last night because I am facing a similar quandary. I want to hook a diff directly to a motor, but if you brace both of them together like we are talking about here, how do you make adjustments to the coupling???

My first thoughts would be to create some kind of slip joint over the motor output shaft, that way you merely pull the gearbox extension housing over the motor output shaft and bolt it up against the motor. But like you say if you want a more solid coupling you would want better access to do it up...

So depending on how you want to couple it, I might be inclined to maybe weld 5.5 out of the 6 sides. 4 sides of say 10mm alloy welded all sides to give it strength, top plate welded on as well but with one or two decent sized square access holes which could be covered with say 3 or 5mm alloy plate bolted down with homemade gasket. Round front plate welded on to strengthen, back plate optionally welded, could be bolted. True up bearing face and motor face so they are parallel, machine bearing hole after all welding is done.

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Direct Drive: Mechanical issues

Post by weber » Thu, 19 Feb 2009, 04:05

Here's my best effort so far:
Image

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Post by gttool » Thu, 19 Feb 2009, 05:11

that would work , you would need to be careful when you weld the output shaft actually when i think about it you may have trouble with the coupling as you shouldnt use rubber in the oil may need to make a splined coupling which would mostprobably starting to get a little to expensive why dont you use a flange as i did on Mals ute and a two peice tailshaft,or build an extension housing from tube which you can fit a short tailshaft in basically
Geoff

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Post by Johny » Thu, 19 Feb 2009, 05:27

gttool. Where did you get the slip-yoke for Mal's ute? (I've been trying to find one).
How is it lubricated? His pics don't quite let me see the whole thing.

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Post by weber » Thu, 19 Feb 2009, 05:45

gttool wrote: that would work , you would need to be careful when you weld the output shaft actually when i think about it you may have trouble with the coupling as you shouldnt use rubber in the oil may need to make a splined coupling which would mostprobably starting to get a little to expensive why dont you use a flange as i did on Mals ute and a two peice tailshaft,or build an extension housing from tube which you can fit a short tailshaft in basically

Geoff

Thanks Geoff,

I didn't intend for there to be any welding, or any rubber. Where do you see it needing welding and where rubber?

I imagined the coupling to be either:
(a) a two-piece clamp coupling with a keyway. That would requires the SOGOS to have a keyway machined in it, and it would require the coupling to be stepped if the motor shaft and gearbox output shaft were different diameters. Or
(b) a double cone compression ("shrink disc") type coupling which would require the motor shaft to have a half key and nothing done to the SOGOS except perhaps turned down to a standard size. Again it would have to be stepped if the two shafts were different diameters.

You can see the keyed two-piece clamp couplings here:
http://www.ruland.com/ps_couplings_rigid_mspc.asp

and the compression coupling on pages 28-29 of:
http://www.conbear.com/dc/file/MAV_Standard_Series.pdf

My sketch was supposed to represent the compression type.

Both are rigid and so must be precise. Also the tail housing bush would have to be precisely centered over the output shaft spline.

[Edit: Fixed broken link to compression couplings]
Last edited by weber on Mon, 16 Jul 2012, 17:44, edited 1 time in total.
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Post by Johny » Thu, 19 Feb 2009, 14:58

I see it weber. With a rigid coupling you don't need a rear bearing on the SOGOS. So you bolt the adapter plate to the motor, fit the coupling and SOGOS then pull the extension housing up over the lot and bolt it to the adapter plate (similarly to how you would have fitted the extension housing to the original gearbox).

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Post by weber » Thu, 19 Feb 2009, 16:22

EV2Go wrote: The purpose of the bush is not to provide a bearing surface, but rather to stop the yoke from getting too much sideways movement on the output shaft. ... The purpose of the bush was not to provide a bearing surface but rather limit the amount of slip yoke sideways movement on the output shaft. The slip yoke doesn’t even touch the bush there is a thin film of oil that sits between them, without that oil present the because the bush is static it will chew out very quickly.

That sounds like the definition of a bearing to me -- allowing something to rotate and/or slide axially while limiting radial movement. And we're talking about limiting it to a hundred microns or so here, it doesn't exactly bounce around inside that bush.

In the actual MX-5 gearbox (and presumably others) there is no bearing directly supporting the rear of the output shaft, near the spline. This would be a bad idea in any case, since with 3 bearings on a rigid shaft the slightest misalignment of any bearing will cause enormous load on them all. The spline is about 300 mm to the rear of the rearmost ball or roller bearing on that shaft. A spline can be a rigid coupling or a flexible coupling, depending on the clearance between male and female. I suspect in this case it has sufficient clearance so the bushing takes the sideways loads. Or else the spline is tight but that part of the output shaft between rear bearing and spline is sufficiently flexible so the bushing takes the greater proportion of the sideways loads.

I think we're both right, in that it's a bushing in form and a plain-bearing in function. See
http://www.nationmaster.com/encyclopedia/Bushing

Or perhaps more pedantically, the plain bearing consists of the polished hardened steel surface of the slip-yoke, the oil, and the bushing (probably of bronze or Babbitt metal).

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Post by woody » Thu, 19 Feb 2009, 17:17

Just taking a step back, this seems like a lot of work to avoid making a longer tailshaft with integral slip-yoke or even a ball and trunnion (like an early valiant) and working something else out for the speedo.

I think lengthening tailshafts should be cleaner than this.

For the speedo, I was thinking a period tacho with a speedo face.

Odometer is hard though.

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Direct Drive: Mechanical issues

Post by EV2Go » Thu, 19 Feb 2009, 17:25

Weber I can see where your thinking is at, but there is little point in putting the bearings so close together. Really the coupling needs to be between the 2 bearing for it to be advantageous, otherwise all the weight is being carried by a bearing that is almost at the motor. Also any side load and weight will be acting on the coupling which compromises it running true.

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Post by Johny » Thu, 19 Feb 2009, 17:40

Hi EV2Go. There is no bearing in weber's disgram. He is using the front ACIM bearing as one end of the SOGOS support - the rigid coupling being the trick.
woody. I tend to agree but it's worth examining if the engineering works out simpler using the gearbox extension housing. The external slip-yoke as used by gttool on Mal's ute looks good but how does it cope with dust and rubbish on the sliding bit?

Edit: Corrected "duct and rubbisj"
Last edited by Johny on Thu, 19 Mar 2009, 09:04, edited 1 time in total.

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Post by gttool » Thu, 19 Feb 2009, 17:44

have a look on most 4wds they have a slip Joint on the front

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Post by fuzzy-hair-man » Thu, 19 Feb 2009, 18:23

Weber: that's more like what I was thinking earlier less the coupling but with some sort of motor to shaft join in it's place.

However the precision coupling would have to have a slide in sort of joint I'd think other wise I can't see how you'd be able to do the coupling up. Image unless you are able to slide the rear gearbox housing over the shaft??? so you do the coupling up then slide the gearbox housing over the top...
woody wrote: Just taking a step back, this seems like a lot of work to avoid making a longer tailshaft with integral slip-yoke or even a ball and trunnion (like an early valiant) and working something else out for the speedo.

I think lengthening tailshafts should be cleaner than this.

For the speedo, I was thinking a period tacho with a speedo face.

Odometer is hard though.
Ah that explains Mal's setup a bit more perhaps, presumably the integrated slip joint still needs to run in oil? does it store a bit inside a section of the prop/tail shaft? I guess it might need checking / replacing occasionally ? is there like a grub screw or something to fill / drain?

ball and trunnion joints look similar in ways to the inside workings of a CV joint as these need to allow an amount of forwards / backwards movement (not sure how much though), CV joints are possibly another option... Image

Is an odometer a legal requirement? just wondering, practically there's probably little use for it if with an electric motor all you have to do is change diff / gearbox oil you could just do this every 3 -4 years? rather than X number of kms, any battery type servicing and you will be alerted by the BMS wouldn't you?

Sure an odometer would be interesting especially for mileage... or should that be kilometreage Image

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Post by weber » Thu, 19 Feb 2009, 18:42

Johny has it right. There is no added bearing and the gearbox tail/extension housing just goes over the shaft and bolts to the adapter plate, exactly as it does on the original gearbox.

Woody, the speedo isn't the only reason to use the gearbox tail. As I explained at the start of this thread, there is no rear engine/gearbox mount on an MX-5. With the original ICE the rear of the engine/gearbox is only supported by the alloy truss beam (called the PPF) connecting the gearbox tail/extension housing to the diff housing.

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Post by EV2Go » Thu, 19 Feb 2009, 20:20

Must be seeing things I could have sworn I saw a bearing there before Image

Still dont like the idea of the coupling not being support though...
Last edited by EV2Go on Thu, 19 Feb 2009, 09:21, edited 1 time in total.

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Post by Johny » Thu, 19 Feb 2009, 20:28

Slip-yokes.
From reading the 4x4 forums just now it appears that driveshafts with telescopic sections and driveshafts with integrated slip-yokes are fairly common. The Ford guys mutter on about replacing the grease with teflon based stuff for extra longevity.
So you grease them!

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Post by acmotor » Sat, 21 Feb 2009, 07:15

Guys, does anyone know the low down on the line up of uni joints on the ends of telescopic drive shafts ?

Thing is, after following some of the posts above, The penny has dropped that I don't know if I have put my telescopic spline back together properly after greasing it. OK,Ok, I should have scribed it or something. It just went back together in any of about 18 different ways.

I now have a bad vibe at some revs.

Any ideas ?
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Post by woody » Sat, 21 Feb 2009, 07:37

My plan has 18 steps ... I think you can guess it.
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Post by weber » Sat, 21 Feb 2009, 07:50

acmotor wrote: Guys, does anyone know the low down on the line up of uni joints on the ends of telescopic drive shafts ?

The two yokes on opposite ends of the shaft have to line up in order to cancel out each other's non-linearities. Pictures here:
http://www.gwb-essen.de/fahrzeugbau/eng ... te_10.html

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Post by weber » Sat, 21 Feb 2009, 07:56

Got a reply from Ross Pink. He just greased the slip yoke, so there was no oil inside the gearbox tail/extension housing to bother the e-motor. But he says that isn't a good long term solution. You would at least have to add a nipple so you didn't have to take it apart to regrease. He was more concerned with proof of concept than long term use at the time.

This appears to be the solution adopted for the TransWarps. Add grease nipples.

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Post by acmotor » Sat, 21 Feb 2009, 08:08

Like in hip replacements ? Image
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Post by acmotor » Sat, 21 Feb 2009, 08:14

Thanks for the alignment weber.
Woody, I guess that brings me down to two steps !
I'll go the 12mm spanners in the morning.
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Post by Richo » Sat, 21 Feb 2009, 09:16

The BMW E30 has a 2 piece tail-shaft where the yolk is in the middle.
So the motor end has beautiful flexible coupling.
This can then be directly connected to a flange adaptor keyed to the motor shaft.
No grease - no splines.
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Post by weber » Sat, 21 Feb 2009, 09:40

Thanks to everyone for lots of helpful discussion.

The funny thing is, I'm coming back to the idea that to get the performance people naturally expect from a sports car like an MX-5/Miata, we're gunna hafta keep the _whole_ gearbox and clutch, despite using an AC induction motor and VF drive and despite the fact that it will then be a heavier car. And in that case it looks like we should use a 2-pole motor instead of the 4-pole that made sense with direct drive.

But hopefully it's been helpful to Johny and I'm sure it will be helpful to others in future.

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Post by Johny » Mon, 23 Feb 2009, 04:53

Yes. It's been a very useful discussion for me. Thanks all.

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