It seems that you've made up your mind already on this, but I'll add to the comments that will hopefully prevent someone else reading this thread in the future from doing the same.
Trusses are a great invention, allowing heavy loads to be carried by the roof with minimal cost of materials. Trusses can only carry those loads when they are applied downwards on the top members of the truss. The configuration means that the forces get distributed to all the other pieces of the truss to distribute the load. If you instead hang the load from the bottom horizontal member, you've basically just got a long 2X4 suspended in a few places by pressed in truss plates (I'm assuming that you've got wooden trusses). Here's an analogy. If you're careful to apply the load evenly you can put a piece of plywood on the top of an empty soda can and load it with a couple of hundred pounds of weight before it will crush. But lay it on its side and it takes a whole lot less to do that.
The table uploaded in post #6 is not applicable to your situation. At the top it reads "maximum allowable uniform loads...". "Uniform" means a load evenly distributed along the length of the beam, which is a lot easier for the beam to carry than what you're planning - applying the entire load to the centre of the span.
Lots of people with a truss construction building without a ceiling put stuff up there as storage. I do. That's generally not a problem since it's difficult to get enough things up there to accumulate to a point where it causes a problem (and the trusses are designed to carry a small load distributed across the lower member - typically drywall and insulation). It's a completely different story when you hang a hoist underneath, though. Not only will the load probably be a lot bigger, but it's also a "point load", not an evenly distributed load. See the previous paragraph.
Your intent is to lift implements weighing half a ton, using a one ton hoist, on trusses designed to carry only a roof load. The trusses might support that, initially. If the question were posed to the truss designer he/she would say that it would fail. Sometime in the future someone will use the hoist to maximum capacity, maybe on a day when the roof is carrying a snow load, and the truss plates have worked themselves loose a bit, and the bottom chord took a hit from something earlier, and the attachment to the load slips and catches adding a dynamic load. And someone might get killed or injured.
If you're going to do this properly, which is actually easier than what you've last stated that you plan to do, the beam needs to be supported on columns at the two ends, only. Not also fastened to the trusses, as you've written that you intend to do.
The beam should be sized so that the deflection under load doesn't exceed a certain amount. There are different codes depending on the situation, but a commonly used one for gantry cranes says that the deflection should not exceed the length of the span divided by 600. So for a 10 foot span the allowable deflection under load would be 10 X 12 / 600 = 0.2 inches. The heaviest of the three beams that you proposed in your original message would deflect about half that amount over a ten foot span with a one ton load. So, just ensure that the columns supporting the beam are properly constructed to constrain both vertical and horizontal movement and leave the trusses alone.
Chris
