MIME 3300
PROJECT 1
11/16/2012
Due 11/29/2012
This project is mandatory and it counts as two homework assignments
Part I: Design a slider-crank mechanism (Fig. 1) with the following performance
criteria:
Stroke = 60 mm
Time ratio = 1.25
It is given that the ratio of the lengths of the coupling rod and the crank is 3:1.
Crank, r2
Connecting rod, r3
slider
e
Fig.1
Part II: Construction of the mechanism:
To make this mechanism, you can use everyday items that can be found in any
stationary shop and/or hardware store. You can invent your own type of
construction and procedure or use the guidelines below.
You will need a ruler, some old broken pens or thin plastic tubes, scotch tape,
cardboard, scissors, pliers, glue and some hanging wire (steel, approx. 0.05 inch
diameter… Do not use cable or other flexible wire)
Procedure:
Cut three pieces, about 1.0 inch in length of thin plastic tubes (that can be parts
of old used pens). Make sure it does not have an internal diameter of more than
2–3 times the thickness of the wire. Use two of these to make the slider as shown,
gluing one on the top of the other in the perpendicular position, Fig. 2.
Fig. 2
Using pliers, cut wire 3 inches more in length than the ruler. Straighten the wire
so that there are no bends or kinks in the wire. Insert this wire into the slider you
have already made. Wrap the ruler using this wire as shown and make sure there
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is a constant separation between the ruler and the wire throughout its length.
Ascertain that the slider can move freely throughout the length of the ruler. Use a
strong adhesive or adhesive tape to secure the wire to the ruler. This should only
be done on the under-side so that it does not interfere with the movement of the
slider, Fig.3.
Fig.3
Now cut this shape out from the cardboard (Fig.4) and glue it to the ruler as
shown in Fig.5 (slider not shown).
Fig.4
Fig.5
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Links can be made very easily from the wire. Take wire about six times the length
of crank (or 6 times r2) and insert it into the third bit of plastic tube that you cut
previously as shown in Fig.6. and construct the crank as shown. You must try to
have sharp bends in the wire for both the crank and the connecting rod.
Fig. 6
For coupling rod, take hanging wire about 3-4 inches more than the length of the
coupling rod and insert it into the slider. Bend the wire as shown in Fig. 7.
Fig. 7
Place the free end of the coupling rod on the plastic bearing on the crank and
twist both ends of the wire carefully so that the crank is joined properly to the
coupling rod (see Fig.8). Make sure that the effective length of the coupling rod is
as close to the calculated value as possible.
Fig. 8
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On the cardboard mark a point at a height equal to the offset plus the height of
the slider on each side. (This is very important because the offset is measured
from the axis passing through the center of the bearing on the slider where the
coupling rod is connected. See Fig. 9.) Then make holes at these points, just big
enough for the wire to be inserted. Carefully straighten the crank as much as it is
needed to insert it into the holes. Once the ‘U’ part of the slider remains inside the
cardboard, bend it back to its original shape.
Fig. 9
You can use scotch tape inside the bearings to reduce the clearance and also to
hold the flaps of the cardboard in place. You are done. Here’s how it looks, Fig.10.
Fig.10
Note:
1. Poorly constructed mechanisms will be returned to the students and they
must make an acceptable one to get a grade. Acceptable stroke is between
50mm and 70mm and the acceptable time ratio (a function of the
imbalance angle) is 1.09 to 1.4.
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2. You can get up to 20% additional bonus points for innovative types of
construction resulting in high quality mechanisms.
Deliverables:
For part one, submit a report showing the method you used to compute the
dimensions of the mechanism and the final results. For part two submit the
mechanism that you constructed.
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