Gold gear vs steel gear

[tatt61880]

"Oops"

Yes, you are correct - the motor strength is multiplied with the (combined) moment of inertia of the two objects the hinge is attached to, to get the real motor torque. So as tatt pointed out, the correct unit for the motor strength should be 1/s^2 (or rad/s^2, to be precise), describing the rate of change of the angular velocity of the affected object.

The reasoning behind this choice of unit is that a machine works the same if you scale it or change the involved densities. But obviously I messed the unit up when adding it to the GUI (much later).

Now that that has been cleared out - the obvious question is, would Nm be a better choice of unit? For some things, yes. But I'm betting there will be people who are gonna be irritated that their machines no longer works the same when scaled.

What do you think? Keep the current strength (rad/s^2, i.e. angular acceleration), and only fix the unit displayed in the menus? Or change to Nm? And then when scaling, also scale the Nm strength as to keep constant angular acceleration (as now)?

Thank you very much for your good explaining. =)

But I'm betting there will be people who are gonna be irritated that their machines no longer works the same when scaled.

Current system also has weakness in scaling, doesn't it?

When you scale geometries twice as large, the moment of inertia will become 16 times larger than the original.
This fact means the torque which motor outputs becomes 16 times larger than original system.
However, the torque should be 8 times larger than original system for working the same (because the mass and the length become 4 times and twice larger than before scaling, respectively).
So, when scaled twice as large, the motorTorque should become 1/2 of original to keep working well.

Seeing is believing.
[scene]45009[/scene]

What do you think? Keep the current strength (rad/s^2, i.e. angular acceleration), and only fix the unit displayed in the menus? Or change to Nm? And then when scaling, also scale the Nm strength as to keep constant angular acceleration (as now)?

I'll take another solution.
Keep the current motor strength(=motorTorque) and add the variable for real motor torque, just similar with "mass and density".
And save current motorTorque into scene data and do not save realMotorTorque. (density is saved and mass is not saved).
"motorTorque" is not good name. However for forward compatibility, the name shouldn't be changed...

I want to ask a question below to Phun/Algodoo's engineer.
* When scaling, should motorTorque also be scaled automatically for keeping to work well?

[Kilinich]

"Oops"

What do you think? Keep the current strength (rad/s^2, i.e. angular acceleration), and only fix the unit displayed in the menus? Or change to Nm? And then when scaling, also scale the Nm strength as to keep constant angular acceleration (as now)?

IMHO best way is make physically correct strength (not affected by geom density/size) and scale it with motor(hinge) size.
That will also fix "small gear vs big gear motor" incorrect behavior.

[kilebantick]

I actually agree with Kilinich, this would not only solve a few problems, but it could actually make it slightly more realistic.

[tatt61880]

How about my solution?

motorTorque_and_realMotorTorque.PNG

(44.04 KiB) Not downloaded yet

I'll take another solution.
Keep the current motor strength(=motorTorque) and add the variable for real motor torque, just similar with "mass and density".
And save current motorTorque into scene data and do not save realMotorTorque. (density is saved and mass is not saved).
"motorTorque" is not good name. However for forward compatibility, the name shouldn't be changed...

[kilebantick]

!!! Very nice idea indeed!
I suggest to only let that be visible in advanced mode, otherwise we'll get a lot of posts from new users asking what it is!
Nice idea Tatt

Although: I seem to have been severely mis-informed. I didn't know Rads was a measurement for how much force a motor has applied to the object it's attached to, i thought it was how many rads a second it spins in a 0 resistance enviroment

Someone care to explain, just so i can understand for the future?

[emilk]

I seem to have been severely mis-informed. I didn't know Rads was a measurement for how much force a motor has applied to the object it's attached to, i thought it was how many rads a second it spins in a 0 resistance enviroment

Someone care to explain, just so i can understand for the future?

"rad" means radian, and is by itself a measurement of angle (2*pi radians == 360°). rad/s is then the change of angle over time, i.e. angular velocity. And rad/s² is the change of angular velocity over time, i.e. "angular acceleration" (not a commonly used term I think...). For a motor this means the change of angular velocity every second for a 0 resistant environment. You can visualize this by making a motor attached to a geometry and plot the angular velocity (rad/s) of the geometry. You will see a straight line, the slope (derivate) of which will be what is given as motor strength (rad/s²).

I hope that makes it a bit more clear.

(PS: the derivate will be easier to calculate in 1.7.5...)

[kilebantick]

Thanks for clearing that up!

[tatt61880]

For a motor this means the change of angular velocity every second for a 0 resistant environment. You can visualize this by making a motor attached to a geometry and plot the angular velocity (rad/s) of the geometry. You will see a straight line, the slope (derivate) of which will be what is given as motor strength (rad/s²).

Good explanation, but I can add explanation for reducing misunderstanding.
* The slope equals to motor strength when motor is on the center of gravity of the geoms.
* The slope is proportional to motor strength even when motor isn't on the center of gravity of the geoms.