VTR1000 Dynamic Engine Simulation
 

I've been tossing it around for a while now - years actually.

I have started a detailed dynamic model of a Super Hawk 90 degree V-twin engine. I just have to get a grasp on how it all works from a motion/force/acceleration standpoint.

If anybody is interested, I will post details of the development and give insight to how this type of modelling is done and graphs showing forces torques, acceleration, imbalance, etc.

Most people have no idea how this is done, since it requires an ME background, but it is quite interesting. I will do my best to develop the necessary background as to how motion is described and force is calculated. I'm developing it for my own interest, but also to show my son how it works.

Maybe I can stimulate someone to pursue a career in engineering. We need more engineers and fewer investment bankers, IMO.

Anybody interested?

Sounds pretty cool!

sweet

Can anyone tell me an easy way to display graphics on the board (diagrams, etc)? Can I upload PDFs?

So far, I have the equations of motion (position, velocity and acceleration) for the crank, rods and pistons. I'll have to give some background before I can present them in a way that is comprehensible.

pdf's are listed in the upload files of type so go for it!

sounds awesome :)

should be interesting. I get lost once you guys start talking about harmonic and orders of vibrations etc. So I look forward to learning something - good luck.

That sounds like a great project! I'd love to contribute to your efforts. I happen to be a gearhead turned ME, so I could provide technical input, write-ups, ITR (Independent Technical Review), etc. I also have a couple Superhawk engine cores that could be opened for photos. My free time is limited, but I'm always available for a good cause. PM me if there is anything I can do to help you out.

Awesome! Another ME here. Please post details!!!! :D

I want to start with a basic description of the motion of a piston. Everything builds from there, and yes, there will be graphics later.

Let's start with one piston. It travels from ene end of the stroke to the other. It is only free to move along it's stroke path. It's motion is restricted in all other directions by the fact that it is contained in a cylinder. (Obvious, but necessary to describe the motion).

Next, I'll define some motion concepts of linear motion:
d = delta, which I will define as "the change in"
p = position - Where the piston is at a given time (t).
v = velocity - the rate of change of the position with time = dp/dt
a = acceleration - the rate of change of velocity with time = dv/dt

For ease of description, position, velocity and acceleration can be in either direction, and maximum can mean maximum, or minimum, interchangably.

As the piston reaches the end of the stroke (either end), it slows to a stop (v=0), then changes direction and accelerates in the other direction. At midstroke, the velocity reaches a maximum, then the piston accelerates in the other direction until it reaches the other end of the stroke maximum postion, and velocity is again 0.

So when position (p) is maximum, velocity (v) is 0 and acceleration (a) is maximum in the opposite direction. When velocity is maximum, position and acceleration are zero.

Hold that thought. It will be important later. Next I'll talk about rotation.

Your homework:

Look up sine wave in Wikipedia.

im a future ME. I live for this stuff. I wonder if we can calculate rod stretch when a piston is at TDC at max rpm. would be interesting.

he said rod stretch lol

Once you have the dynamics, you can calculate stress and strain on the components. The rod stretch would involve taking the tensile force, integrating the over the varying cross-section of the rod. I'll leave that exercise to you, once I give you the tensile force :).

But first, we have some more things to define. My wife couldn't believe I was doing this last night. She asked me who would be interested. I said "motorcycle people". she said "Oh my God" and went to bed.



*Attachment moved*

And here's a graphical representation of sinusoidal motion:

http://i35.tinypic.com/21nl1mb.jpg

what the hell is that??? It looks like the mole on my back !!

So let me get this straight___ this ultimatley means more throttle twist means you go faster through the twisties over less time and then k over m with a red dot???

Awsome

Very interesting. Looking forward to more.

Nice write up and I think I'm actually ready to solve some equations, but you may have to give us a math refresher too:)
RC

LOL! You didn't do your homework, did you!

Actually, the crank pushes and pulls on the piston in the same way a spring does. It may not seem like it, but the math is the same. So think of the sine wave as the piston moving back and forth, with a pen attached, writing on a piece of paper that is moving by at a constant speed, creating a "time axis".

Oh, and please - no photos.

Thanks.
All in good time...

More stuff for you to chew on...

Equations of motion:

*Moved* RC

Oops, will Excel handle this or will I need to dig out my old scientific calculator:)
RC

I don't think you'd want to try it in excel. But I'm not that good at modelling in Excel. You won't like doing it with a calculator

You'll need an iterative equation solver. Start with a known initial condition, such as 1 piston at top dead center, the other at midstroke, and define the known lengths and angles, then step through a full revolution in small angle increments of the crankshaft.
If you use a constant crankshaft speed, you can just solve the velocity and position equations.

I'm going to use Matlab, or EES. I'd like to use EES, but Im not sure I can get the graphical output I want to present. I'm too busy right now. This is a project that will take shape over several months. I hope to have the motions done this week.

Ultimately, I want to solve the balance problem. When I was building my engine, I put lighter pistons in and wanted to figure out how much material to remove from the crank, to rebalance. But then the riding season was coming, and I was advised not to worry about it, so I put it together and rode the piss out of it!

I have most of the weight measurements, and a solid model of the crank that I developed back then.

Here's a picture of the test setup I used to calculate the moment of inertia of the crankshaft, based on the oscillation frequency. I set the journal on small gauge pins and measured with a stop watch.

I don't think I ever got very good agreement with the solid model, and it was time to put it back in the engine. I still have the numbers, so I'll try to figure it out.

http://i34.tinypic.com/rkpnw7.jpg

Wow, so this is what motorcycle riding ME's do in the winter to cure cabin fever?
















:mrgreen: Nice writeup.

You know... I'm considered a complete nut amongst my friends... I tear apart everything to have a look inside... And I will model some small portions if I need it to figure out stuff (quite familiar with Matlab)... But this is a bit more impressive...

I will however do the same to about any electronics I come across... (Anybody have a need for a component list for the main curcuits in the VTR? or a schematic? I can provide them...)

Oh come now Hawkrider... You have your ways to cure it... Me... I tear apart stuff and rebuild them... some measure them first...:D

Yeah, you got me. I do fork revalves.

I think there's a few of us here with that gene.

Thanks, but it's not that impressive, at least I can't claim to have invented it. The slider-crank model of a piston and crank are a classical dynamics problem.

My interest in providing the description was to show how easy it is, if you have the right approach. Nothing magic. Just a practical application of math that most people never see. Cool problem, though. And once we have the model developed, we can try all kinds of things.

Don't you need the moment of inertia about the center of rotation and not the rod journal? It doesn't do you much good to model the system about an axis that it does not rotate about.

Your picture of sinusoidal motion is misleading, all that you need is sin(t). The model you are suggesting should not take into effect the flexibility of parts and therefore the spring constant would be zero or infinity depending on the situation.

The moment of inertia can be translated to the center of rotation, if you know the distance between the swing axis and the actual rotation axis. I'll present the simple mathematics when I get around to it.

There is no spring. A mass on a spring exhibits simple harmoninc motion. A rotating shaft does too, but in two dimensions.

It has to be sin(omega)t. If you don't know the frequency, you can't calcualate y at time (t). I only used that diagram because it was the first example of simple harmonic motion I found.

The motion of a piston is not simple harmonic motion because the position varies with crank angle and connecting rod angle.

No need. I'm also a BSME and have been doing analyses like this for almost 20 years now. I was just wondering why you would bother do experimentally measure it one way just to have to translate it. Why you would not measure it about the main journals confuses me.