3MEMS3: Launcher Update
Since the canister suffered from a blow out I haven't been able to establish a tight seal. With time of the essence and long cure times for the sealants adhesives I have access to, the canister wouldn't be ready in time for the deadline. But with the robot comfortably programmed for tackling the course, this was my sole focus.
Looking for a new gas source I first turned to balloons. Unfortunately, I found them to be somewhat tricky to work with and not really deliver the pressure how I wanted. Considering the difficulty I’ve been having converting something into a sealed pressurised vessel, I decided to stick with something that was made to be airtight. This is when I started testing a bike wheel, thankfully the height restriction was lifted so this is fully rules compliant.
As it turns out the bike wheel holds about the same volume and pressure of air as my canister does, however, the delivery of this pressure is a little more gradual due to the smaller diameter outlet.
This lead me to adapt the funnel design slightly to suit the new pressure source. I experimented with a few different concepts and fitments, including my original funnel, a tighter fitting tube and a more open cardboard support.
These designs had varying levels of success, sometimes a ball would fire, but most of the time it would either vibrate among the tube or else be lifted in the tube but not launched as seen below.
The ball gets lifted from the tube and then hovers over the outlet despite the near 120psi (~820KPa) from the bike inner tube (standard pressure for this tire). This design likely didn't work as it was too short, there is most likely a length where there is a tipping point and it reaches an effective range, however.
Some of these more intuitive designs didn't seem to work in this instance, perhaps it was the design or something not accounted for when making these parts that affected their functionality.
It was the more open designs that seemed to work better, I knew the pressure from both the canister and the bike wheel was enough to firmly blow a ball across a surface such as a table. So it seemed probable that an open design should be able to release a ball smoother, even if the ultimate range is less than a funnel or barrel design.
Force = Pressure x Area so the larger area of the open design could be leading to a greater force acting on the ball, despite the pressure loss to the surroundings.
To achieve this more open design effectively I cut away some material from the 3D printed funnel I had previously.
When coupled with the bike wheel It worked quite well at launching some balls as can be seen in the gifs below
The slightly awkward packaging of this launcher did lead to both some difficult aiming and also some more pressure losses than experienced previously with other pressure sources. Despite this, it could be put to work quite well successfully landing balls on target. Typically anywhere from 1 to 7 balls made it into the box on top of the robot, with 3 balls being most common. In most tests the balls that did not successfully land in the box came into contact with the robot as they were only marginally off target.
