Mini surging/accele...

Mini surging/accelerating  


Joined: 1 year ago
Posts: 1
May 14, 2020 4:48 am  

Hi there, I have had my Sisyphus for a few days now and the whole family love it.

I have a question today my sis was doing it’s normal thing on about half speed when I noticed it was making a different sound. It sounded like the motor was accelerating then returning to its normal speed, I had a look and about every five seconds you could see the balls getting faster for about half a second then going back to it’s programmed speed. 

The surges happen on both one ball and two ball mode and in all designs. 

I have put sis to sleep, woken it up, tried a couple of clearing erase tracks, and turned off the power then back on again and the problem is still happening.

The surges happen at all programmed speeds at about the same time interval.

I have captured some video to give some clarity on what is happening. 

Could you give me some ideas on how to rectify this issue. 



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Joined: 3 years ago
Posts: 374
May 14, 2020 3:03 pm  

Hi @mikewand14 - 

Glad to hear you and your family are enjoying it! I can see the periodic acceleration / deceleration in your video - but this is within what I consider "normal" Sisyphus function. There are several reasons for ball velocity to vary during track play. The primary one is that the robotic mechanism that moves the magnet(s) has mass, and therefore, the motion control software is designed to slow down before a corner so it doesn't make a knocking sound (the sharper the corner the more the decel). That is why you see it happen on the track in your video repeatedly.  I wrote this code, and it isn't perfect - when the ball is moving mostly in the rotational axis (Theta), and followed by a mostly in/out linear more (Rho), it doesn't always match the velocities perfectly. This will get tweaked in the future, and may help it look better to you. Lastly, you will notice that the ball "stutters" (wobbles) a bit at times. This is because the sand grains are not negligible in size compared to the ball, and they perturb it. This, plus the inherent flexibility of the magnetic coupling, lends itself to the ball's velocity "bouncing" a bit at certain speeds  and sand depths. Hopefully, the velocity variation you're seeing doesn't spoil the effect.


Joined: 3 years ago
Posts: 85
May 22, 2020 6:43 pm  

There is one of the twisty tracks (sorry, don't know which one) that really shows this surging behavior. It seems to be related to a combination of radial "velocity zones" and also some combination of rho versus theta movement as the ball curves through the pattern. Maybe having a formula for rho-based velocity adjustment, or at least more zones, would reduce the sudden speed changes.


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