Hi peachpuff and thank you for the comment. We actually have a video with real beer on the tray. Please check our channel or you can see it directly here:
View: https://youtu.be/zBNCFJx5Cnc
This was only the "Aftermath" video to show more detailed how this device was build. But you are right, this device is getting slower with a lot of weight on it. The reasons are the used components to overcome the inertia. With more stable materials and stronger motors, the device could accelerate with weight as fast as you saw it without the weight.
Best regards,
The Fedmog Challenge