Hi Anton

Just when I thought you cracked it with speed, something strange happens

When dropping the block from 10m = ok = 14m/s as per calc (see model)

Move the block down to 5m => nonesense answer like 0.07... (should be 9.9m/s)

Yet move block to other elevations like 8.5m or 2.5m , seems to work ok (but I haven't checked the result against calcs (12.9, 7)

So I am completely stumped

BTW sometimes the block appears to penetrate the baseplate and slowly return to zero, could this be the reason?

Thats ruined my day

Cheers

Robin

falling block2.skp

Thank you so much Anton, I was just about to post an apology for a stoopid boy Pike moment (no smilie for Duh )

but I read the second line and it outputs frame to screen, what a numpty

You gave me some other scrip that outputs velocity, strange to note that the cube reaches a terminal velocity ca 2m/s ca halfway down - intriguing. Is there something in there that simulates viscosity?

onUpdate {

Get current velocity

cv = this.get_velocity

Output it in the note

note = sprintf("Velocity: (%.3f, %.3f, %.3f)", cv.x, cv.y, cv.z)
simulation.display_note(note)
}

Cheers

Robin

A bing moment has occured

when I # out the reset line, I just had a ontouch line only and it outputs to screen what might be some sort of final velocity m/s on impact (according to the script info)

pls see model

Now I cant yet correlate that to the calc velocity which should be 14m/s on impact from 10m
it comes out at 58 and varies with the UI sim setting of Newton update rate (currently 10)

also from dropping from 5m gives 33 (should be 9.9m/s and is 1/sqr2 - .707) whereas 33/58 is ca.57

maybe some dynamic friction in play?

Is this a worthwhile line of enquiry?

Cheers

Robin

ps the ball is in anton's examples funny little thing - and something for gamers pool table maybe?

falling block.skp

Hi SU fans
Can anyone help me make a timer to display the interval (secs) of a falling object hitting a baseplate (see model)

Faust kindly contributed this to detect the object hitting the plate - it resets on impact and I loose all the time info on screen. There is no pause or stop action to replace reset AFAIK

onTouch { |toucher, position, normal|
MSPhysics::Simulation.reset
}

I have discovered the

start_timer and stop_timer

action but don't know how to use it
Ideally the interval result should be displayed on screen or otherwise accessible, and there should be a facility to have a coeff to adjust the result to the correct answer - frig factor (1s) as I noticed the on screen timer/fps is not accurate and depends on several settings (time step, linear damping et al)

Sorry to be a Ruby newbie but trying my best
and this could be so useful for dynamic simulation validation
Cheers

Robin

falling block.skp

Well we are both struggling, blind leading the blind

FYI this timer thing is fundamental to simulating physical systems (mass speed acceleration)

The on touch is a good start, just need to time the sequence and display result on reset

opens up a whole new way of simulating mechanical systems

as fundamental say as a thermometer is to tell you the temperature - if you see my point

so I must perservere. If I get a result I will post it you

Cheers

Robin

Hi Faust

Through the Ruby Code editor, I found a start_timer and stop_timer function

Would this help?

Say put start at the top to activate when staring sim,

then stop_timer after the reset action line

then display timer?

sorry my newbie attempts at script (do you hav any recommendations on the best way to learn script for MSP - there's so much flack out there its hard to know where to start)

Cheers

Robin

@faust07 said:

Hi Robint
Put this script into your baseplate (copy the 3 lines, select the plate, open MSP UI, select "Script", paste the lines into the Script window, run MSP):

onTouch { |toucher, position, normal|
MSPhysics::Simulation.reset
}

and the simulation stops "onTouch".

Hi Faust, thanx for the tip, but not quite there yeet

the simulation resets and I lose all the time/frame data at the bottom of screen - which is what I need for this to be useful.

I tried .pause and .stop but they dont exist

Is there something else I could try?

Hi All

Not wishing to hijack this OP, but I cant see where to post otherwise
so here goes. Attached is a simple falling block assy to test the validity of accel due to gravity, ie block should fall 9.81m in 1 sec, all thing set right.

What would be nice is to have a script that stopped the sim once the bloack collided with the baseplate. In theory I should be able to read the time taken, no of frames etc on the bottom lhs of the screen, but just now I approximate this by tapping pause on eyeballing the block - not very accurate at all

Iv'e seen there is an "on touch" script with slamming doors but Im still a ruby newbie

Is there a way to stop the sim on block reaching the baseplate?

FYI If I can get this to work for my students, then the next step is to simulate the viscosity experiment using a falling sphere in fluid, but I dont know if SU can simulate viscous fluid yet?

Great stuff on this page, I am truly humbled

Robin

falling block.skp

@anton_s said:

Hi, Robin,

I just revised the spring joint to base on Hooke's law. Just need to adress a few other things before its ready for the release.

Regards,
Anton

Hi Anton

It occured to me loking at the motor joint, that it would be neat to have control sliders on important coeffs, of spring rate, friction, and damping, help to speed up student experience

BTW just seen some example in Sketchucation, blown away with the talent out there

Hope my little exercises aren' t too dull

Cheers

Robin

@anton_s said:

Hi, Robin,

The block doesn't sit still probably because you disabled the friction. Enabling the friction checkbox option for the block and for the floor contacting the block will fix the wandering off behavior.

I will add an option to control accel and damp with the SI units in the upcoming release. At the moment, I figured that spring constant is roughly equals to (accel * 7 - damp), when spring joint stiffness is set to 1.0.

Edit: Ensure that both anuglar and linear damping for all bodies are set to zero. This improves the closeness.

Anton

Yes indeed, improved action, I missed the friction box

Herewith a revised model changing block mass from 0 - 0.5 kg gives a displacement of 0 - 1.0 so the spring rate is 2

spring stiff 1 (what does this do?)
Accel 1, damp 1.5 (gives critical damping approx)

changing sample rate from 1/60 to 1/240 changes the whole model performance

iterations 16 - improves stability

the plane has a mass of 0.01kg, lowest i could get without instability

So Ive actually got a spring damper that sort of behaves but it seems like the spring has inertial mass - an ideal spring should be zero mass and friction

What do you think? Anything I can do to help (ruby dummy just now)

Cheers

Robin)

V 2

Hi Anton

I'm sure I tried every way with the friction coeffs, and it didnt seem to help much, unless Im doing something wrong. If you could get real SI units into the spring damper model this would be fantastic. Classic maths leaves everything in normalised units which is really hard for students to translate into the real world - thats what MS physics is about. I try to encourage my student to abandon th suck-it-and-see approach in favour of understanding what is really happening and calculating the effect. I know that math is a real turn off for most users, but I try

cheers Robin

@anton_s said:

Hi, Robin,

I'm glad I could help.

Best regards,
Anton

I made a simple mass/spring damper system as per model, but I get some odd results not like the damped sinusoid

Am I on the right track or have I made some basic errors

Also the block doesn't sit still on the plane but wanders off

I am also having difficulty tying in the UI with real values of spring rate N/m and damping c*velocity Ns/m

Any advice, most appreciated

Cheers
Robin

BTW I looked at the Ruby docs but couldnt tie up real units to the constants

classic spring damper

Thank you so much Anton, thats given me some homework!

BTW I didn't wish to imply you were overwriting the previous SP. MSP is of course entirely yours started from scratch - brilliant stuff

I'll be glad to pass any useful models I can generate back to you to pass around to other interested parties and perhaps help generate other instructional models

Cheers

Robin

Hi Anton
Congrats on your great work resurecting old SP for a new version. I played with SP some years ago and amazed myself by getting a caterpillar track chain to work

May I ask if it is possible, in your version, to assign real physical values to objects, eg mass in kg, spring rate m/kg, damping kg/m^2 and so on

and perhaps equivalent elements for rotating masses

Its all in aid of helping my student understand the dynamic behaviour of physical systems with different input and load conditions open loop and closed loop

If this could be done, it would be of fantastic benefit for Uni ugrads (yes there are professional - expensive suites to do this). Something tailored to fit with the unbeatable SU would be so good

It wasn't available in the original SP, only cruded dimensionless tweaks

Cheers

Robin

ps apologies if this has already been answered pls link me

Tig thanx 10^6

brilliant little tool, am using on GE to get a contour map, much less fiddly than making 100 intersecting planes method

The contour lines are a little jagged so corners need to be softened. Whats the best way to do this? Tigweld, use Bezier?

Come to think of it I haven't come across a tool that softens a 2d jagged line easily (like you can in adobe illustrator for example, any suggestions

ps Ive been player with simplfy contour and convert to polyline/fspline etc, you can only do one line at a time, its all a bit hit and miss - and with 50 odd contours this will be massively time consuming

with ca 1000+ extensions out there looking for attention, its all bewildering

Any suggestions

Cheers

Robin

Please help me see the wood for the trees.

I am getting a lot of conflicting direction on this topic from different directions and its confusing me, so many extensions and sand box tools which seem to take me down roads leading to lots of work.

Surely there must be a simple way to make a contour map from and import GE map from the "add location" and "toggle terrain"

From there I want contour curves at say 50' intervals automatically then take these into an extension (say Sandbox bonus tools)

I want to be able to print out these 2d contour planes so I can make cutouts on thick card glued together to make a physical model

You would think this should be straight forward

Can anyone please help clear the mists for me

Cheers

Robin

hi all

Im posting some models that illustrate some points and queries

all comments gratefully received

Robin

[my cone n ball

rotates using a motor hinge (when will this become reversible?

Two balls used, small one falls to bottom so that larger one is off centre and crawls up the side and out otherwise just drops to bottom.

nice demo of centripetal force and a hollow solid](/uploads/imported_attachments/elvl_myconeandball1.skp)

[my lift ball

tried using lift capsule and got it working, then i moved the capsule and it all fell apart. but now i cannot recreate a lift capsul with a slider or a piston

strikes me that a slider is unnecessry as its the same as a piston but without accel and damping figures - so why bother.](/uploads/imported_attachments/E5tW_myliftball.skp)

[my rotating box

strange that the slider now makes a hinge behave like a servo
If you push tha slider to one end then the cube over turns and starts rotating in an erratic manner (like a ball running up and down a valley then gaining enough momentum to over top and run down the next valley.

before (maybe in a previous version of SP this feature would behave like a true reversible motor - now it doesnt? what happened

also if you get it going full speed one way then throw it into full speed other way, it crashes SU](/uploads/imported_attachments/wXwb_myrotatingbox1.skp)

[my spring box

cant get the spring to move at all. is it now not supported in sp3.2 ?](/uploads/imported_attachments/IRVt_myspringbox1.skp)

@gaieus said:

Well, with some little trick and using the golden section, you can make a perfect tetrahedron... But of course for us, poor SU users a real circle guide tool would be the ideal.

yes indeed you can get coords by geometrical calcs, there is a whole raft of interesting surds involving root 3

I can mail these to you if you want brain damage.

I did manage to make a perfect tatrahedron in SU but it was very tortuous

I can provide the math in pseudo code (like excel)

but I cant yet manage ruby, but from the little i know its perfectly possible and the tool would be simple to use

simply define the origin of the radii (by clicking a point or entering the coords) then enter the radii length, then display a crosshair point on the screen space, then draw in the lines to connect origins to the points and SU isn then happy

wish wish

robin

@robint said:

Hi guys

Im sure we all agree the math is the easy bit and I programmed it into Xcel to give the 3D coords - fine, but you have to input them to su to 10 decimal places to get fully coherent filled planes and accuracy - very tedious.

In case I didnt explain myself properly, just try constructing a 2D
d triangle with 3 unequal side say 1, 2 , 3

you wont manage it in SU by construction but you can calculate the point of intersection but to 10+ decimals

then go to the 3D case where you construct a tetrahedron all with unequal sides

I will look at the other stuff posted in the next couple days

cheers new year thingy

btw

this all started for me when I tried to construct a tetrahedron (12 pentagons forming a spherical shape one of the pythagoras perfect solids)

starting from a simple pentagon shape as the base, you then make 5 other equl shapes joining the base sides. Then you have to fold them upwards like a tulip until the touch their sides - try it in SU

you really do need a ruby plug in to find the points of the intersection of circles and spheres in 2 and 3D space because as we know the circle in only polygon with a lot of sides - an approximation to a circle and even with 999 sides its still not accurate enough for SU

cheers Robin

@ilovedrawing said:

I am a 13 year old boy, and a huge tank and military enthusiast.
I am very inspired by some of the work by some members of this forum. And I would really like to create my own tank. Trouble is, I'm having a very hard time creating MOVING track. How to hold the links together and for them to move with the power of my sprocket powered from the motor.
Any help would be greatly appreciated.

try this

http://forums.sketchucation.com/viewtopic.php?f=61&t=33128&p=303084#p303084

i had a problem getting a chain to revolve without flying apart. its crude but shows it can work try the model and follow the thread

you may need to wait till sp4 as its proposing to have a facility to copy complete joints (bit difficult having to set up 50 individual tank tracks with joints - take forever)

cheers robin