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    MSPhysics tests and questions

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    • F Offline
      faust07
      last edited by

      Here is an approximation of the setting of a servo joint (oscillator) with controller or script.
      The oscillation about 180° in both directions corresponds to the number pi in the script. Seems somehow to be logical ...


      Servo-Test_04.jpg


      Servo-Test_04.skp

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      • A Offline
        Anton_S
        last edited by

        Hello faust,

        Nice coding there. So, when you assign value via script, i.e some_servo.controller=, the value is assumed as some angle in radians. Whenever, you assign it via controller, the angle is assumed as the angle in preset angle units, which are by default in degrees.

        Now, instead of iterating through all servos to assign their controller, a more reliable way would be to use a variable. Control the variable through script and change servo angle via controller. Here is what I mean:

        onStart { @p3_head_osc = 30 set_var('wing', 0) } onUpdate { set_var('wing', oscillator(@p3_head_osc) * 30) }

        Paste this in the controller of a desired servo:
        get_var('wing')

        Other than that, I'm amazed by your improvement in scripting. Keep it up!

        Anton

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        • F Offline
          faust07
          last edited by

          Thanks Anton! The simple way is the best - I will try it. Here a little pengu fun with my old script solution and "Curvy Piston".


          Pengu-Test_11.gif

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          • robintR Offline
            robint
            last edited by

            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

            As one door closes another one slams in your face

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            • F Offline
              faust07
              last edited by

              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".

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              • robintR Offline
                robint
                last edited by

                @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?

                As one door closes another one slams in your face

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                • robintR Offline
                  robint
                  last edited by

                  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

                  As one door closes another one slams in your face

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                  • F Offline
                    faust07
                    last edited by

                    Hi Robin,
                    have tested to find a solution to pause simulation per script, but have nothing found until now.
                    I'm a script newbie too. For my purposes I look into scripts of models from the experts at 3D-Warehouse (AntonS & PituPhysics) or ask them in Anton's main MSP post.

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                    • robintR Offline
                      robint
                      last edited by

                      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

                      As one door closes another one slams in your face

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                      • robintR Offline
                        robint
                        last edited by

                        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

                        As one door closes another one slams in your face

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                        • A Offline
                          Anton_S
                          last edited by

                          Yes, the final velocity should be 14 m/s, and it is 14 m/s.

                          Your script in the model you posted, just outputs the frame:

                          onTouch { |toucher, position, normal, force, speed|
                            simulation.log_line("onTouch #{frame}")
                          }
                          

                          That explains why you get unrelated results.

                          To output the final velocity, you should change the code to output the speed:

                          onTouch { |toucher, position, normal, force, speed|
                            simulation.log_line("onTouch #{speed}")
                          }
                          

                          And besides, setting the linear damping of the falling box to zero will make the final velocity even more right because this will eliminate the dissipative force.

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                          • robintR Offline
                            robint
                            last edited by

                            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

                            As one door closes another one slams in your face

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                            • A Offline
                              Anton_S
                              last edited by

                              Yes, the viscosity is simulated by the linear damping. To remove the linear damping, select the desired group, open MSPhysics UI, activate the Properties tab, and set Linear Damping to 0.00. This should alter the height of terminal velocity.

                              If you meant something else, like water or buoyancy, you can add a buoyancy plane by navigating to (Menu)Extensions->MSPhysics->Create Buoyancy Plane. Although the liquid is not simulated. It's just the buoyancy force that is applied.

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                              • robintR Offline
                                robint
                                last edited by

                                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

                                As one door closes another one slams in your face

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                                • robintR Offline
                                  robint
                                  last edited by

                                  Maybe uncovered a nasty bug? Anton

                                  Here's a suggestion from your speed indicator

                                  onUpdate {

                                  Get current velocity

                                  cv = this.get_velocity

                                  Output it in the note

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

                                  When it runs, on collision it displays 0.00 as expected, the block has stopped but we lost the terminal velocity

                                  Could we say put an IF loop in the output velocity to note, only iff velocity <say .5m/s, then it should go to zero when the block stops (assuming no bounce)

                                  Just a thought, maybe a simpler approach? from a ruby newby

                                  Cheers

                                  Robin

                                  As one door closes another one slams in your face

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                                  • robintR Offline
                                    robint
                                    last edited by

                                    Sorry, Im getting tired

                                    I meant it should retain the highest last value in note when the block stops

                                    Apologies

                                    Robin

                                    As one door closes another one slams in your face

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                                    • A Offline
                                      Anton_S
                                      last edited by

                                      It's all cool 😄

                                      Here is the code for viewing maximum velocity.

                                      onStart {
                                        @max_vz = 0
                                      }
                                      
                                      onUpdate {
                                        v = this.get_velocity
                                        if v.z.abs > @max_vz
                                          @max_vz = v.z.abs
                                          simulation.display_note(sprintf("Max Speed %.3f m/s", @max_vz))
                                        end
                                      }
                                      

                                      And yes, the speed indicator in onTouch may not always work right, which is the problem of the physics engine that my wrapper is using.

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                                      • robintR Offline
                                        robint
                                        last edited by

                                        Hi Anton

                                        Installed your script, works a treat and pretty accurate 😎

                                        However I have meddled and got stuck, I cant find a way to print another result on a new line, tried everything, puts, print (can't find sprintf in docs either)

                                        As you see I want to print elapsed time as well and it works but overwrite the Max Speed result on the same line

                                        I feel really dumb getting stuck on this trivial matter, pls help 😢

                                        BTW would I be right in saying that MSP script is a subset of official Ruby 2.0 and some elements like puts and print (they dont do anything on screen or riase an error)are left out?

                                        Cheers

                                        Robin


                                        falling block3.skp

                                        As one door closes another one slams in your face

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                                        • A Offline
                                          Anton_S
                                          last edited by

                                          Here:

                                          onStart {
                                            @max_vz = 0
                                          }
                                          
                                          onUpdate {
                                            v = this.get_velocity
                                            if v.z.abs > @max_vz
                                              @max_vz = v.z.abs
                                              simulation.display_note(sprintf("Max Speed %.3f m/s\nElapsed Time; %.2f s", @max_vz, world.time))
                                            end
                                          }
                                          
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                                          • robintR Offline
                                            robint
                                            last edited by

                                            Anton, ooh that is nice

                                            from little acorns, great oaks grow

                                            So now we have a timer as well

                                            Maybe add

                                            add the x.y.z distance travelled

                                            and then I can perhaps simulate a cannon firing a cannon ball at a target

                                            and with a bit of wind and air friction, elementary gunnery for the Napoleonic War

                                            I will of course present my models to you for the consideration of others in the interest of MSP

                                            Cheers, many thanks
                                            Robin


                                            falling block4.skp

                                            As one door closes another one slams in your face

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