rgl::plot3d(): plot size is too small when scale is changed


I just start to use Rshiny and get stuck on this issue:

I am trying to use plot3d to draw a 3D plot. The y axis is duration, with unit = day or week. In the panel, I created a radiobutton. Basically users can select which unit they prefer. In the original data, the unit is day, however, if they select week, then the data would be re-scaled. You can image the data range would be smaller once week is selected. Data for other axes keep the same and the width/height are set to 800 in the mainpanel. The plot looks perfectly fine when day is selected. The problem is when week is selected, the plot turns to be very small and I have to zoom out it every time. It kind of makes sense to me because when the scale decreases, the plot would be smaller. But I don't know how to fix it. I keep searching on line for few days and get no luck. I hope I've described the issue clearly and any help would be highly appreciated.