# Motor Bearing Life



## major (Apr 4, 2008)

TooQik said:


> Hi,
> 
> I've been reading this forum for a while now researching as much as possible before I start a conversion of my own.
> 
> ...


Most of the motors used by EV DIYers have high quality sealed and permanently lubed ball bearings which last the life of the motor. It is rare to see or hear of a bearing failure.


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## TooQik (May 4, 2013)

Thanks major.

My biggest concern was shortening motor bearing life by using a heavy duty clutch.

I did actually manage to find another post on this topic in these forums from 2 years ago a few hours after posting my questions...isn't that always the way.


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## Karter2 (Nov 17, 2011)

> ... how much would/does retaining a clutch setup decrease the motor bearing life expectance given the increase in axial load on the motor bearing?


A clutch should not exert any axial loading on the motor shaft, or make any difference to bearing life,.. assuming it is well balanced.
Clutch forces are contained between the flywheel, pressure plate and the clutch spring housing , which is bolted to the flywheel.


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## Duncan (Dec 8, 2008)

Hi Karter

_A clutch should not exert any axial loading on the motor shaft, or make any difference to bearing life,.. assuming it is well balanced.
Clutch forces are contained between the flywheel, pressure plate and the clutch spring housing , which is bolted to the flywheel._

Only when the clutch is engaged - when the clutch is released (clutch pedal depressed) the axial loads are from the clutch release arm to the motor(engine) bearings


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## EVfun (Mar 14, 2010)

If there is any balance issue the flywheel and clutch will exert relentless load on the motor end bearing. Do not run an EV with a flywheel vibration as that has damaged a number of parts on different EVs. A clutch will exert some axial load on the bearings, just try and push in the release ring by hand (won't budge.) I don't know if it is significant. I know the VW guys lament heavy clutch discs because they have been known the bust the clutch cable tube loose inside the frame (and that's a PITA to fix.) If the flywheel and clutch is being retained many recommend the flywheel be shaved down to a minimum weight, for performance and balance. 

I ditched my clutch and didn't look back. Some transmissions do not shift well cluchless, while others don't mind. It is much easier than shifting clutchless with a flywheel attached, but the armature is more load on the syncros than just the clutch disc. It will always be slower than shifting with a clutch, so the EV racers either retain the clutch or ditch the transmission.


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## electro wrks (Mar 5, 2012)

Karter2 said:


> A clutch should not exert any axial loading on the motor shaft, or make any difference to bearing life,.. assuming it is well balanced.
> Clutch forces are contained between the flywheel, pressure plate and the clutch spring housing , which is bolted to the flywheel.


 You are correct about the clutch disk gripping forces. However, when the clutch pedal is depressed, the force exerted by your foot is applied through the release bearing, pressure plate, clutch, and flywheel to the motor shaft and bearings. Multiplied by mechanical and/or hydraulic advantage, this force can be several hundred pounds or more. It should be confirmed that the bearings normally supplied with the motor can handle this thrust force. 

Angular contact bearings can sometimes be substituted to handle the combination of radial and thrust forces.


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## major (Apr 4, 2008)

electro wrks said:


> ....when the clutch pedal is depressed,....


Which you rarely do in an EV


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## dougingraham (Jul 26, 2011)

TooQik said:


> My biggest concern was shortening motor bearing life by using a heavy duty clutch.


I was concerned about using the stock clutch on my Rx-7 conversion project because the original peak torque spec on the motor was 104 ftlbs and with a Warp9 and 1000 amps it would be about 277. I ended up deciding to keep using the clutch because it was still in good condition. What I found is I don't have nearly enough tires to make even the original clutch slip. The tires lose traction first. And since with an EV you never have to slip the clutch to start there just isn't much wear. Heck, around town I just leave it in 3rd gear and only shift into 5th when I go on the highway. If you were racing I suppose there might be some advantage to running it up to redline and storing a bunch of energy in the flywheel and then dumping it into the drive train with the clutch but that is a different scenario and in that situation stuff is going to wear out and break. Because you are concerned with bearing life I am guessing that is not how you are planning on using your EV.

You will probably want to take the flywheel and pressure plate to a shop and get them balanced together. With a reasonable design on the coupler and adaptor plates this is not going to be one of the problem areas.


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## Yabert (Feb 7, 2010)

electro wrks said:


> It should be confirmed that the bearings normally supplied with the motor can handle this thrust force.


Done!
So that represent few thousand lbs for typical motor bearing.


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## cpct (May 31, 2012)

Some time ago I stumbled upon a conversion of a Renault Espace with a BLDC motor from Golden Motor. The pressure of the clutch gradually destroyed the bearing of the motor, eventually causing the rotor to grind against the stators.

Can't find the source anymore, but it shows that it *could* be a problem. Most quality bearings can handle some axial load so it shouldn't be that bad.


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## major (Apr 4, 2008)

cpct said:


> Some time ago I stumbled upon a conversion of a Renault Espace with a BLDC motor from Golden Motor. The pressure of the clutch gradually destroyed the bearing of the motor, eventually causing the rotor to grind against the stators.
> 
> Can't find the source anymore, but it shows that it *could* be a problem. Most quality bearings can handle some axial load so it shouldn't be that bad.


It more than likely *would* show an inferior bearing used or a problem with the installation. You should not draw a global conclusion from a single incident.


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## major (Apr 4, 2008)

cpct said:


> Some time ago I stumbled upon a conversion of a Renault Espace with a BLDC motor from *Golden Motor*. The pressure of the clutch gradually destroyed the bearing of the motor, eventually causing the rotor to grind against the stators.


Hi cpct,

Are you referring to one of these motors? http://www.goldenmotor.ca/products/72-Volt-10KW-BLDC-Motor.html Used in a car with a clutch and transmission? There was more wrong with the application than the bearing 

major


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## TooQik (May 4, 2013)

Thank you to everyone who has contributed to this discussion.

I should have included in my original post the reason for wanting to retain a clutch setup - the vehicle is intended to be dual purpose as both a daily driver and hillclimb (motorsport) car. The transmission and clutch setup are primarily being retained for hillclimbing purposes.

I've had a look at the NetGain website and their parts listing for the WarP 9 motor. They list both the 6305-2RS and 6207-2RS bearings for this motor. Quick research shows these bearings have a static load rating of 12,100 and 15,300 N respectively, so halving these figures for axial load rating (assuming I've read this correctly from the SKF website) gives 6,050 and 7,650 N.

If I were to use a clutch with a clamping force of 9000 N (~2000 lbs) and assume a clutch lever ratio of 1:4, then I'm looking at approximately 2250 N of force to disengage the clutch fully. Given that this is well under the lowest figure for the bearings above, and assuming my maths is correct, then a heavy duty clutch setup with the WarP 9 engine doesn't appear to be an issue - which most of you have indicated from your posts.


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## Duncan (Dec 8, 2008)

TooQik said:


> I should have included in my original post the reason for wanting to retain a clutch setup - the vehicle is intended to be dual purpose as both a daily driver and hillclimb (motorsport) car. The transmission and clutch setup are primarily being retained for hillclimbing purposes.


I attended my first sprint for over 20 years - it was an eye opener - cars were a LOT faster than when I used to compete
My EV (Duncan' Dubious Device) was almost the slowest car there but I have built it on the cheap 
Anyway with a light car, a decent controller and decent batteries you don't need a transmission and will be faster without one

The device is 710Kg,
I have a Soliton but it is borrowed so current is set to 600amps
(I don't want to cry when I get my OpenRevolt back working)
My pack is 2P44S 16Ah Headways - 50Kg - 4.7Kwhours - max power 480amps x 100v (sagged) = 48Kw
It is not bad - faster than most cars on the road - BUT I need to double my battery pack for the track


_If I were to use a clutch with a clamping force of 9000 N (~2000 lbs) and assume a clutch lever ratio of 1:4, then I'm looking at approximately 2250 N of force to disengage the clutch fully. Given that this is well under the lowest figure for the bearings above, and assuming my maths is correct,_

Unfortunately the load on the bearing is the release load - 9,000N - the leverage ratio reduces the load on the clutch cable but not on the release bearing
Not that this would be much of a problem for the short times it will be depressed


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## TooQik (May 4, 2013)

Duncan said:


> Unfortunately the load on the bearing is the release load - 9,000N - the leverage ratio reduces the load on the clutch cable but not on the release bearing


Hi Duncan,

Glad to see another motorsport enthusiast.

May I ask why you're saying the full 9,000 N would be on the motor bearing? My calculation was based on the lever action on the clutch diaphragm itself, not the clutch fork. The release bearing pushes (or pulls depending on clutch type) on the diaphragm which has a pivot point to reduce required force to overcome the clamping force.


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## Duncan (Dec 8, 2008)

TooQik said:


> Hi Duncan,
> 
> May I ask why you're saying the full 9,000 N would be on the motor bearing? My calculation was based on the lever action on the clutch diaphragm itself, not the clutch fork. The release bearing pushes (or pulls depending on clutch type) on the diaphragm which has a pivot point to reduce required force to overcome the clamping force.


No you are quite correct - the diaphragm does act as a lever reducing the bearing load - my bad


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## cpct (May 31, 2012)

major said:


> Hi cpct,
> 
> Are you referring to one of these motors? http://www.goldenmotor.ca/products/72-Volt-10KW-BLDC-Motor.html Used in a car with a clutch and transmission? There was more wrong with the application than the bearing
> 
> major


Yes, I believe it was one of these. This was the source: http://www.youtube.com/watch?v=mAvXoAqif8Q
I agree on the application "mismatch" there, but to be on the safe side I put larger deep groove ball bearings from SKF in our motor.


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## Nabla_Operator (Aug 5, 2011)

Don't neglect the RADIAL load on the motor shaft as a bearing killer, engineers! This is "A" in my illustration:



It's common practise to mount the electric motor with an interface plate to the bell housing of the gear box. This interface plate should be machined with an accuracy of just a few micrometers (say: 10 micrometers), as explained in my illustration (due to the remaining tolerances and clearances on pin-hole).
The two shafts should be aligned within the clearance of the (spline + bearings) which is approx. 20 micrometer. Maybe 200 is everyhting is worn out. 
If your excentricity is close to 200, you will have rubbing surfaces inside the spline and eventually metal wear out if you do not lubricate often.
If your excentricity is close to 20, you will be fine; no vibrations occur.

Now... Let's assume you make this interface plate yourself and you obtain an accuracy of 1mm (which is difficult with DIY tools) (1mm = two shaft deflections of 0,5mm on each side), what does this do to the bearing life expectancy?

In blue I made that calculation for you: 0,5mm excentricity means 5800 Newton. This will reduce the bearing life to half a year of silent cruising in your EV.

Happy to share,

-nabla-


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## Duncan (Dec 8, 2008)

Hi Nabla

Good analysis - but you forgot one thing - 
the gearbox end is normally supported by the motor end 
(easy to check - see if the input shaft can be moved)

If it has free movement then you will NOT increase the loading on the motor


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## Karter2 (Nov 17, 2011)

And if a clutch is being used, the gbox input splines are mated to the clutch friction disc splines..so there is no direct mechanical connection between the motor shaft splines and the gearbox input.


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## Nabla_Operator (Aug 5, 2011)

You're right; I recognise now the pilot bearing between the two shafts, that takes away the radial load. As in this picture:

http://www.surplusjeep.com/MB-GPW/mb-gpw-group_2_clutch.htm


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