Algodoo

It would have been perfect if it wasn't for those little velocity dips in each corner. Just curious, did you try to straighten out those dips?

BTW - I worked for an industrial laser manufacturer 25 years ago, and making perfect right angle translations on a CNC for a high power laser cutter caused us a lot of grief. And so I understand how challenging it can be especially when driving a large massive load.

Q: Did you try to straighten out those dips?
A: Yes, by varying the spring force, constant, and damping. In the end I just tried to hide them by setting Smoothing to 50 on the Plotting widget.

"In the end I just tried to hide them" --
(I do stuff like that too when the need arises.)

9.9/10
From the first glance at thumbnail I wasn't sure how you will get same velocity, but now I see that you change RPM of motor as it go around
But what about making it change speed accordingly to length of spring, instead of angle of arm? That way you could change the shape (or rotate that square 45°) and it would keep working... i think

JakubKubo ,
I like the way you think. I will try your idea.

I found that reducing the Restitution to zero for all four of those blue rails helps a bit too.

Xray,

I found that the higher restitution results in a smaller unsmoothed blip. Also, I still get the blip upon removing the frame, so I think the blip is mostly associated with the mechanism inside the frame.

Agree. Those blips seen in the plot are just an artifact of the control system making abrupt direction changes. e.g., In a corner translating from the x direction to the y direction, x has to suddenly stop moving with virtually infinite deceleration, and y has to start moving with virtually infinite acceleration. That is impossible to do without an artifact showing up in the velocity plot. Just a fact of life!