[racket] how (animate func) works?(2htdp/universe)

how (animate func) works?(2htdp/universe)
hello~
today I tried to make the canvas that show rotating image with timer
but I can't draw image object on canvas' dc
and I can't do get-bitmap from image object

but in case of animate, it works very well
how come?
could somebody let me know how to get-bitmap from image object or draw-image
on canvas?
(for animating picture in the canvas)
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