Door access/Howard Community College/Fall2012/p2-502-cash/bracket
Mounting Bracket edit
We found out that no alterations, such as nails or screws, may be made to the door, so the entire structure must be supported by a non permanent, non damaging means. To do this, this team first tried using large suction cups with hooks. With a one KG weight attached to one of these suction cups, it fell off the door in about a day, so initial results suggest this is not a good solution. for the second attempt, this team built a mounting bracket consisting of two 2 x 4 pieces of wood held together in a "T" shape with double ended nails. To make the double ended nails, heads were cut off conventional nails with a Dremel cutting wheel and the bench grinder was used to put points where the heads had been. The reason that two pieces were used instead of one is that when one piece was tried, the weight of the linear actuator tended to turn it and pull it off the door. A piece at right angles to the direction of rotation (vertical portion in picture below) tends to resist that rotation, and also provides a surface for additional tape. Using a larger surface area of double sided tape reduces the force on any given unit of area of that tape. That is to say, the forces tending to pull the tape off are spread over more tape, so each piece of tape carries less of a load. Even tape with very little adhesive force, or stickiness, can support heavy loads if there is enough contact area between the tape and the anchoring surface.
For supporting this mounting bracket, we used single sided aluminum tape wrapped in loops to act as double sided, because that was the stickiest tape available in the lab (the aluminum tape is in the center of the picture, just under the blue painter's tape). Ideally, the next team would be able to acquire some real, very sticky (but not enough to damage the door finish) double sided tape, because that would be a lot easier than making tape loops. First we tried using large loops, because they are easier to make, but large loops tended to sag in the middle. By using many small loops, we were able to approximate true double sided tape, and the resulting mount was strong enough to hold the weight of the actuator, with the full force applied to the handle, and seemed to have a safety factor (it didn't show signs of weakening or falling off). The linear actuator as implemented did not have enough force to fully retract the door latch because the belt slipped first.
If the next team wants to continue with the printer mechanism, they will need a new, stronger spring for the idler pulley. However, they might be more successful using the Jameco gear motor included in the project bucket. Below is a drawing of one possible mounting bracket, which could be nailed or screwed directly to the T shaped mounting bracket described above.
The dimensions are:
- A: 1.3" +/- 0.1;
- B: 2.8" +/-0 .1;
- C: 0.12" dia;
- D: 0.350" dia;
- E: 0.6" +/- 0.1top edge to horizontal center line;
- F: 0.390 center to center (both sides). Size and place bottom holes to fit conditions. Material is sheet metal or plywood, not to exceed 1/4" thickness. A square piece of plywood stock that might be suitable is included in the project bucket.