[Diy_efi] Strain gauge on engine mounts

Wed Apr 20 19:25:05 UTC 2005

I thought you guys wouldn't get to a possible solution but now you're
starting to get my attention!

I think the driveshaft section is the right idea.  Replace the tubular
section with a solid shaft of 1" diameter or there about.  Remember on a
typical rear axle the axle shafts are just about 1" diameter and they handle
3 times the torque of the  drive shaft.  This should give you a degree or
two of twist to work with.

The real magic is going to be on the electronic end, sensing the phase shift
and filtering it. I'm betting this has been done in the past with analog
components, filters and all for other applications not involving cars.

Keep the discussion going, very interesting!

Dan Nicoson

> -----Original Message-----
> From: diy_efi-bounces at diy-efi.org [mailto:diy_efi-bounces at diy-efi.org]On
> Behalf Of Rod Hiorns
> Sent: Wednesday, April 20, 2005 2:44 PM
> To: diy_efi at diy-efi.org
> Subject: RE: [Diy_efi] Strain gauge on engine mounts
>
>
> 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
>
> _______________________________________________
> Diy_efi mailing list
> Diy_efi at diy-efi.org
> http://lists.diy-efi.org/mailman/listinfo/diy_efi
>
> _______________________________________________
> Diy_efi mailing list
> Diy_efi at diy-efi.org
> http://lists.diy-efi.org/mailman/listinfo/diy_efi
>