Author Topic: engine mounting v 4.0  (Read 77314 times)

mobile_bob

  • Administrator
  • Hero Member
  • *****
  • Posts: 2787
    • View Profile
Re: engine mounting v 4.0
« Reply #15 on: December 22, 2006, 05:16:19 AM »
sleep?  who needs sleep?

just ask Doug :)

yur burnin daylight pilgrim, er moonlight???

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

Doug

  • Guest
Re: engine mounting v 4.0
« Reply #16 on: December 22, 2006, 06:24:48 AM »
Burning the Lime light Bob lol....

How do you figure out all this centering the forces at the crank stuff Bob?
I know it relates to the mass of the block shifting rocking elements to the crank center but how did you arive at the math to do it?

I spent the night pondering grout, blocks and machine plates....

Have a safe and happy holiday.

Doug

mobile_bob

  • Administrator
  • Hero Member
  • *****
  • Posts: 2787
    • View Profile
Re: engine mounting v 4.0
« Reply #17 on: December 23, 2006, 05:25:05 AM »
Doug:

it is not a mathematical problem but rather a geometric problem

when you consider the enormous gyro forces placed on the crankshaft and its support brgs (mains), and the flywheels, it is fairly easy
to see that we don't want the crank to move at all if possible. (If i remember correctly this is the prime concern of GuyF, in that he has concern
over movement of the crankshaft inducing stresses that might lead to failure)

so if we want to stabilize the crankshaft we have to center the rocking component at the centerline of the crankshaft, then the rocking can
rock and roll all it wants to without effect on the crankshaft, brgs or the flywheels.

if we bolt the engine down to a base that is below the crank centerline, the crankshaft will move thru and arc that has its pivot point roughly at the
center of the bottom of the case, or in a 6/1 an arc of approx 12.5 inches (at least), and perhaps alot more depending on the spacing of the subframe mounts, or the
length of the concrete block it is all mounted to (should the block be sitting on unstable earth such as damp/dry clay)

i wish i could figure how to post a diagram, i think i could explain it more clearly with a couple of pictures.

i guess i will have to learn a new skill,
maybe i can just draw a picture and take a digital pic of that and email it to someone that can post the damn thing...

what happened to blackboards anyway?


bob g

otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

Doug

  • Guest
Re: engine mounting v 4.0
« Reply #18 on: December 23, 2006, 05:43:28 AM »
Please draw me a picture I think I follow, but I'd like to see it on paper.

Doug

haganes

  • Jr. Member
  • **
  • Posts: 63
  • captain
    • View Profile
    • Haganes Cruises of Southeast Asia
Re: engine mounting v 4.0
« Reply #19 on: December 23, 2006, 06:10:31 AM »
the issue is harmonics.  a destructive harmonic can develop in any rotating device.  that frequency could be the frequency of the bolted down engine onto concrete (however, experience of thousands of these engines tells us that is not true), or a soft mount (since every mounting situation is different, an unlucky sod could accidently find this frequency).  the safest route is the bolted down engine on concrete.  Having said that, soft mounts could work as well or better.

captain steven 
B & W Alpha 404 (280 hp @ 350 rpm)
Mercedes D231 (100 hp)
Lister TS2
Lister TR1
GTC 10/1 Listeroid

Guy_Incognito

  • Sr. Member
  • ****
  • Posts: 255
  • Just a guy, incognito.
    • View Profile
Re: engine mounting v 4.0
« Reply #20 on: December 23, 2006, 06:42:27 AM »
when you consider the enormous gyro forces placed on the crankshaft and its support brgs (mains), and the flywheels, it is fairly easy
to see that we don't want the crank to move at all if possible. (If i remember correctly this is the prime concern of GuyF, in that he has concern over movement of the crankshaft inducing stresses that might lead to failure). So if we want to stabilize the crankshaft we have to center the rocking component at the centerline of the crankshaft, then the rocking can rock and roll all it wants to without effect on the crankshaft, brgs or the flywheels.

This is the bit I've always had trouble with.

For reference, I'll define my axes. Looking at listeroid side on, directly facing the flywheels with a generator off to the right, x is left and right, y is up and down, z is in and out of the image. From there, you can define planes - the x-y plane is the one looking side on at the flywheels, the x-z plane is the view from the top, the y-z plane is the view from the side. All of those can be taken as 'slices' along the missing axis, eg the x-y plane is an infinite number of slices in the z-plane. If you want to sketch out a listeroid on a bit of paper and label the axes, it'd probably help with what's to come.

So, we're all looking at the same thing? Good.


If :

- The forces are generated from the crankshaft/reciprocating mass due to imbalance between reciprocating/rotating masses and power pulses.
- The bulk of these forces are in a plane at 90 degrees from the crankshaft, that is a plane defined by the x and y-axis.
- The forces that are parallel with the crankshaft that would cause the engine to rock outside of this plane (in the z-axis) are minimal. If your two flywheels are imbalanced with respect to each other, you'd get some. Of course, all listeroid manufacturers pride themselves on the extremely high quality and balance of their machines, so this is rarely an issue.

Then:

It doesn't matter how you mount/hang/swing that engine as it's still rotating and the forces are still present.  Gyro forces only occur when when a flywheels axis is rotated. You can move a spinning flywheel without any gyro forces in all axes. It's only when you try and rotate the axis that gyro forces occur. As long as you don't get any rotation (turning) of the flywheel axis in the y/z planes (in our scenario, you can't rotate the axis in the x plane, it's just visible edge-on as a point in that plane).

This explains to me when I was watching that video of the loveson startup - it was very slowly creeping clockwise. One of his flywheels is slightly imbalanced compared to the other, causing a rocking moment in the y-z plane and rotating the flywheel axis, creating gyro forces which try and twist the machine around.

Following from that, it's very important to note that gyro forces all come from somewhere. Grossly simplifying gyro mechanics, one can say that a gyro is a thing that will convert forces 90 degrees. Twist a spinning flywheel about it's axis and it will want to lean. Lean a spinning wheel and it will want to twist. All the forces that make a gyro move are already applied somewhere - 90 degrees on another plane. If you take the loveson startup video, the forces are a rotation of the flywheel axis in the z-plane (front on to us in the video). These forces get translated to a clockwise movement of the base on the floor. So the forces are still there - instead of trying to rock the engine, they've been shifted to try and rotate the engine.

Finally (!) from all that, seeing as the crankshaft is already rotating, it doesn't really matter if the forces are applied in one plane or another - they're 90 degrees out, but the shaft rotates continuously past both planes anyway. So the gyro forces are just forces that would have been applied 90 degrees earlier/later anyway.

There. That's the problem I have with that bit. Can anyone sort it out for me?  :D

(And a blackboard would be a really, really handy thing to have right now.)


mobile_bob

  • Administrator
  • Hero Member
  • *****
  • Posts: 2787
    • View Profile
Re: engine mounting v 4.0
« Reply #21 on: December 23, 2006, 07:01:25 AM »


GI and Doug:

send me your email, i got a jpeg image of what i am talking about
i can send it, but don't have a clue how to post it here.

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

mobile_bob

  • Administrator
  • Hero Member
  • *****
  • Posts: 2787
    • View Profile
Re: engine mounting v 4.0
« Reply #22 on: December 23, 2006, 08:18:02 AM »
i don't know if this will work, but i tried to learn how to do it in paint and then upload to a coppermine album
http://listerengine.com/coppermine/displayimage.php?album=lastup&cat=0&pos=0

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

mobile_bob

  • Administrator
  • Hero Member
  • *****
  • Posts: 2787
    • View Profile
Re: engine mounting v 4.0
« Reply #23 on: December 23, 2006, 08:21:49 AM »
hooray,,, it looks like it worked!

now at least i can get a picture to help explain what i cannot relate in words effectively :)

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

Doug

  • Guest
Re: engine mounting v 4.0
« Reply #24 on: December 23, 2006, 03:09:13 PM »
Thats what I thought you were talking about...

I was thinking about that at work last night, that and soil mechanics, weight of a cubic foot of concrete ect ect.

A lot of considerations when you build a foundation. Normaly I avoid most of the engineers where I work because they're all staff and find more work for me. Lately they avoid me because I grill them with questions about math, soil compression vibration ect ect.

Even people who have the mentall tool boxes fully equiped avoid this stuff.

Doug

Guy_Incognito

  • Sr. Member
  • ****
  • Posts: 255
  • Just a guy, incognito.
    • View Profile
Re: engine mounting v 4.0
« Reply #25 on: December 23, 2006, 03:21:30 PM »
Well ,that does help to explain it a bit!  :)

I still think the machine will try and rock around the CG as opposed to where it's mounted on the crankshaft centreline - that is , with the setup as you've drawn,  you'll get some left-right movement of the frame instead of a true rocking action. Was trying to find a good real-world example, but it's a little hard. Probably the best way is to use a ruler, and hang it vertically from a bit of string tied off-centre. Jiggle the string back and forth and you'll find the pivot is at the CG. If you want it to pivot at where you tied the bit of string, you'd need to raise the CG.

It's easier to jiggle the string back and forth than to try and introduce a rocking action off-centre on the ruler. It's the same thing, just looking at it from the other way. If you move the string down the ruler until the rocking action stops, you've found the CG. At that point, if you rock the ruler back and forth, there's no movement of the pivot point.


mobile_bob

  • Administrator
  • Hero Member
  • *****
  • Posts: 2787
    • View Profile
Re: engine mounting v 4.0
« Reply #26 on: December 23, 2006, 04:52:02 PM »
Gi:

one of the largest origins of the rocking component is from torque and antitorque, and that is centered not
at the center gravity, but at the crankshaft c/l

i have to go make some money right now (work)

but i was up half the night and have come up with more on this subject, that likely will raise more questions than it will answer
for some folks

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

Guy_Incognito

  • Sr. Member
  • ****
  • Posts: 255
  • Just a guy, incognito.
    • View Profile
Re: engine mounting v 4.0
« Reply #27 on: December 23, 2006, 05:17:28 PM »
Quote
one of the largest origins of the rocking component is from torque and antitorque, and that is centered not
at the center gravity, but at the crankshaft c/l

Hmmm. Let me think about that for a bit.

If the CG is lower than the c/l, the extra mass below the c/l will be accelerated less from the torque/antitorque forces trying to rotate it compared to the lesser mass above the centreline. So the upper half of the engine will be accelerated more than the lower half (F=MA, as Guy_F is so fond of saying), making the top half move further than the bottom half in the same time frame, making the crankshaft want to move back and forth sort of horizontally a bit.

Quote
but i was up half the night and have come up with more on this subject, that likely will raise more questions than it will answer

Well I've been up ALL night - it's 3:15 am now (sigh) - but I haven't been thinking about this too much.  Too many broken machines to keep me from thinking about anything much except for, "What time is it, and can I go home yet?"  :D

(And after reading over my posts in this thread, I don't want them to sound like I'm attacking your ideas as such, I'm just trying to get a handle on it.)

mobile_bob

  • Administrator
  • Hero Member
  • *****
  • Posts: 2787
    • View Profile
Re: engine mounting v 4.0
« Reply #28 on: December 23, 2006, 05:36:57 PM »
i have never felt attacked here, i invite critical thought.


to further explain my thinking:

if the engine rocking motion had it origins external to the engine, i think i would agree about going with the
center or gravity or the center of mass, and i would design accordingly, but

we are dealing with forces that center in the crank centerline, and
we want to limit the movement of the crankshaft in each of the 3 planes if possible by design,
and where we cannot limit the movement in a plane, we want to lmit its effect on the crankshaft/fywheel.

quite frankly i don't care if the valve cover moves +/- .25" or more, just as i dont really care whether the bottom of the crankcase does some part of the same.
at least personally :)

what i would like to limit though is the relative movement of the crankshaft

now for the fun part, that being the other forces or vibrations

i have seen reference here to 660 lbs of force being directed in a downward vector, presumably from ignition
and this force apparently provides for the up and down motion,,,, i disagree

i don't believe we have any down force from igntion or the power stroke, we have torque and antitorque, and we have the
transmission of the sound wave being vectored straight down into the mount, but not an actual 660 lb force.

so all we need is a donut style mount that islolates the transmission of sound from the engine thru the subframe,(rubber here) to the main frame
if the engine is fairly well balanced the mount will isolate the noise/sound vibration to the floor.

with a short profile donut style mount, there is more than sufficient surface contact to limit the for and aft movement in that plane, so i am not particuarly
concerned with movement here, likely be very small.

bob g

otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

jtodd

  • Full Member
  • ***
  • Posts: 190
    • View Profile
Re: engine mounting v 4.0
« Reply #29 on: December 23, 2006, 05:50:48 PM »

I will preface this comment with the statement that "I haven't tried this yet." and in prior discussions elsewhere on the board various people have said it will/won't work but nobody has actually tried it.  I tend to believe my own experiences as the canonical results of experiments, so I figure I'll try it and find out.  It will be at least two months before I get a chance to spin them up, so anyone else having tested this method is welcome to chime in with actual results.

I have purchased two dynamic balance rings for truck tires from Centramatic.  I purchased the heaviest versions available, which IIRC gives me about 8 pounds of mass which will automatically rotate to the position with least downward force (in other words, balancing out any imbalances in the rotational field.)  I've had mounting plates made for installation directly on the crank.  However, it may not work at all - the people at Centramatic simply said "Maybe, maybe not." for it to function in the way that I expect.  The bad news might be that I discover my engine doesn't even require balancing.  As soon as the chassis is complete, I'll let everyone know how that goes. 

http://www.centramatic.com/

JT