I´ve stuck to the colour scheme I used for the Olag Hai, animal characteristics - the pinkish Skin and troll ones , the Grey cracked Stone like Skin
Anyway, These are made up from two sets.
Set one..the "War Trolls for Catapult"..2 of them (HERE) and set two...the catapult "sledges" plus two Crews of 4 orcs in the set "Orcs Catapult" (HERE)
Either of them are a bit odd if used on thier own so you need to buy both sets.
Problems and Solutions
1. The trolls don´t attach that well to their bases. The pegs just don´t hold even with glueing or welding with a heated screwdriver. Solution? I cut the pegs off and drilled holes in the feet, made Counter sinks on the bottom of the bases and using small Wood screws, screwed the bases to the trolls.
The "sledges" have tabs underneath and the trolls have corresponding holes in thier backs. Problem ? It doesn´t fit or hold. Glue? Seeing as the plastic isn´t the glueable kit type..nope. Heat welding ?There´s too little space to do this. Solution? I cut the Tabs off and drilled holes in the trolls backs and through the "sledges" . Nails, slightly thicker than the holes were then stuck into the trolls backs. To attach I just pressed the "sledges" onto the nails.
This solution turned out to be better in that when the "sledge" is added to the Standing troll using the Tabs, the throwing arm tends to be too low so the sling with the rock hangs on the ground. By using a nail, the angle of the nail can be altered which alters the angle of the "sledge", raising the sling off the ground and giving a more or less horizontal platform for the Crew.
3. The "sledges". Seeing as they are made of non-glueable plastic, the parts need heat welding together.
The wheels on the sides ? They have (unless you look at the link below) have no visible function so I´ve added spokes so they give the Impression of being used to draw the arm down.
As actual war machines they wouldn´t work. There´s no Tension skeins of any worth to add Torsion to the throwing arm, no gearage to pull the arm down , no release System. Ok, the orc could bend Forward quickly to lob the arm Forward (in the style of a fustibalus - Stave or staff sling) but that would mean the Crew would also fly off or be putting in Claims for work related whiplash injuries.
They could be made more "realistic" like THIS but it would mean a lot of fiddly work but TBH, I like the look of them as they are.