TDM's setting being what it is, we might as well gather inspiration from real 15th century military inventions or proposals of such inventions. People were making them decades before Leonardo da Vinci started speculating and drawing. If you've ever heard of Hans Talhoffer's famous 1459 Fechtbuch, you'll know it's not just about various kinds of melee combat (in itself interesting for anyone into HEMA), but also features interesting military contraptions for defence, attack and general siege stuff.
One of the more unusual inventions depicted is the "crayfish". It's a little, mechanical, armoured "robot" with an asymmetrical design, vaguely resembling a steel crayfish. It has various steel blades sticking out of it, at different lengths, on all sides, and these move as the crayfish is propelled back and forth. It is a device powered purely by pulleys, and its undercarriage is mounted in a shallow channel built into the cobblestones of an access road, e.g. a road leading to a gate or gatehouse. Operated from inside by defenders, turning winches and pulling pulleys, the crayfish goes to one wall, then to the other wall, then back again, etc. As it moves, the blades are also operated, and they can deliver nasty cuts to the ankles of enemy infantry. With enough stone channels built into the road, close enough together, and these crayfish going back and forth and their blades cutting into the air like wild, enemy infantry can be slowed down or deterred, lending the defenders some time. This invention is detailed in this publication about the Fechtbuch, on page 325. Well worth the read. A very good TV documentary about the Fechtbuch was made several years ago, with the cooperation of several historians, specialist, and the Medieval Centre technology museum in Denmark. The crayfish is detailed around the middle of that 45 minute docu. I think it's well worth at least a single watch.
Challenge: Build a working "siege crayfish" trap for some fortification-related mission for TDM. Or any other type of location that could fit, really.
There's also a design for a 15th century diving suit from Talhoffer's book. The helmet, with the air hose attached, was derived from a repurposed tournament helmet. Remarkably, a replica was tested during the making of that documentary I link to above. Though they were concerned it would be dangerous, surprisingly enough, It worked fine. Obviously, you needed a team of three volunteers, pumping air dilligently to the diver, via a system powered by period blacksmith bellows. But it worked. The experiment is seen in the finale of the docu.
Challenge: A harbour or waterway based mission for TDM, where some of this archaic diving suit is being put to use. Maybe Bridgeport has some divers in the services of the city, helping to clean up muck down in the docks, and so on ?
If we're talking medieval lasers, maybe we could also have ones that don't immediately set off a trap, but merely play some warning music or warning monologue from steampunk loudspeakers. Sort of like in this scene from a recent Westworld episode, where a guest is running away from a Bengal tiger after the robots went nuts, and she reaches the edge of the resort, near what appears to be a hydroelectric dam. As she and the tiger bypass the border between resorts, they run through a laser beam and that sets off a warning to the effect of "Attention, you have reached the boundary. You are not authorised to go further. Please turn back.".