[Diy_efi] Strain gauge on engine mounts

[Rod Hiorns]

OK, I'll guess a few values ...

Shear strength, G for steel is ~200MPa
Working Torque, T, 100 Nm
Length between toothed gears, L, 0.65m
External drive shaft diameter, 0.08m
Drive shaft wall thickness, say, 0.01m ?
J, for a tube, is pi/32*((ext.dia)^4-(int.dia)^4), 2.75e-6 m^4

Twist = TL/JG = (100 * 0.65)/(2.75 * 200) = 0.1 radians (~5o)

Say you choose ~60 teeth (>2*pi/0.1) to avoid "wrapping" in the
decoding timer system. So, at 7500rpm on the engine and 1:1
gear ratio selected, you'd have ~130us per tooth, and to get 1%
resolution in the torque, you'd use ~750kHz 16 bit counters.

So who's going to be first to build it?
HTH
Rod

-----Original Message-----
From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
Behalf Of niche at iinet.net.au
Sent: Wednesday, April 20, 2005 8:03 AM
To: diy_efi at diy-efi.org
Subject: [Diy_efi] RE: [offlist] Strain gauge on engine mounts


At 07:51 AM 20/04/05, you wrote:
>Not sure that is such a good idea Mike ... the rubber is non
>linear ... just like the mounts would be, and resolving the
>edges requires some very fast counters at high speed and
>quite big counters at low speed ... plus who wants that much
>slop in the drivetrain ... it's not like you can swap this
>thing in and out all that easily is it?

Interesting point, think I misread this initially too, way too
many mailboxes here...

I think it should be possible to do this without any rubber,
and avoid any drivetrain slop and be fully differential
in respect of drivetrain lateral or even axial motion... !

I mean, consider this:-

a.   Toothed ring gear (pitch to be determined) on tail shaft
      close as possible to universal joint, firmly attached

b.   Second toothed ring gear as above but at furthest other
     end so max length of tailshaft between gears

c.   Tailshaft balanced appropriately

Question arises, would there be enough twist of the tailshaft
over the most appropriate length for the dynamic range of
torque measurement needed ?

ie. At lowest extreme the tailshaft twist may be so low that
there wont be much discernible phase shift for a coarse
pitch ring gear.
At highest extreme it may well skip a cycle if too fine pitch,
so a sync method would be needed if one is interested in
wide dynamic range - which obviously is fairly easy to implement...

Any mech structural engineers here care to estimate degrees
of twist for say 100 newton metres of torque over length of say
650mm and 80mm dia... ?


>Regards from
>
>
>Mike Massen
>Perth, Western Australia
>VL Commodore Fuse Rail that wont warp or melt !
>http://niche.iinet.net.au







>Cheers
>Rod
>
>-----Original Message-----
>From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
>Behalf Of niche at iinet.net.au
>Sent: Tuesday, April 19, 2005 11:13 AM
>To: diy_efi at diy-efi.org
>Subject: RE: [Diy_efi] Strain gauge on engine mounts
>
>
>At 01:51 AM 20/04/05, you wrote:
>>Anyone ever done or considered doing a simple DIY driveshaft torque
design?
>Heavy rubber coupler with two multi-toothed rings around each end, two
>sensors mounted to display phase difference as torque increases?
>
>Now thats a good idea, far easier than the method in the link just posted,
>probably be a lot cheaper too,  makes an inherent lot of sense, use an
>all digital method  overall.
>
>There was a poster before who suggested something similar, use ABS
>type pickup, think I misread that, thinking he was using only one, but of
>course logical and clever to use two and look for phase difference.
>
>mmmm, Think I'll take a closer look under my car next chance I get
>
>Thanks for that,
>
>:o)
>
>
>
>
>
>
>
>
>>>Dealing with nonlinearities of rubber engine mounts (amoung other
>>>things) is asking for trouble (as in huge wasted time relearning
>>>whats already been arrived at), far far more direct, efficient, effective
>>>and less invasive to measure the twist of the tailshaft :o)
>>>
>>>Regards from
>>>
>>>
>>>Mike Massen
>>>Perth, Western Australia
>>>VL Commodore Fuse Rail that wont warp or melt !
>>>http://niche.iinet.net.au
>>
>>--
>>Marc Reviel
>>
>>PowerLogix
>>http://www.powerlogix.com
>>_______________________________________________
>
>_______________________________________________
>Diy_efi mailing list
>Diy_efi at diy-efi.org
>http://lists.diy-efi.org/mailman/listinfo/diy_efi

Regards from


Mike Massen
Perth, Western Australia
VL Commodore Fuse Rail that wont warp or melt !
http://niche.iinet.net.au

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