I'm trying to come up with some print designs and I wanna do a series on ancient siege equipment. I wanted to start with the onager but the more research I do the more I begin to doubt the depictions I find. Mainly, I find images like this but this seems to be more indicative of a Mangonel or just a traditional depiction of a Catapult. The drawing on the actual wiki or the one depicted here seem more accurate to Ammianus' account of the machine.

I'm aware the design surely changed over time and may have varied in different theatres, using a sling as opposed to a bucket for example, but the frame is something that will give is a distinct silhouette and I'm a stickler for accuracy so any help would be greatly appreciated.