Upon the request of R Secret Designs to find the "ultimate magic fabric" for their FlexStar, a multiple armed flexible throwing toy. The purpose of our project was to find an abrasion resistant fabric, which would be flexible at the same time. Due to the nature of the toy it needs to withstand multiple skidding on surfaces such as asphalt and concrete. We continued to do this by exploring different assembly methods as well as different fabric constructions.
The first step we took in the process was to take apart one
of the toys to be able to get the existing pattern to work with.
While we were waiting for samples of the real oxford nylon cloth
used, we assembled a prototype out of coated polyester. The prototype
was flexible, but it was so soft that it did not fly very well.
Also the fabric did not have enough stiffness to help support
the flex star during flight. By this, we mean that the arms of
the toy twisted during flight. This fabric was obiously not the
first choice but it would be good to test different assembly methods.
This process helped us in learning what the problems were during
the construction. Our first conclusion was that the pods at the
end of the arms were puckering due to the shape. (curved) We vowed
to get rid of them to improve the abrasion of these pods. The
points created by the puckering of the pods are the first part
to wear out during skidding, if we eliminate them then we will
make the toy much more resistant.
We believed that by moving the stitches away from the edge of
the pod, the puckering would be reduced. We planned to move the
stitches to the sides of the pod. With a little help of the Apparel
School we asystem for making one have a larger diameter than the
other. Having the smaller piece sowed on the other side would
cause the stitches to be pulled away from the edge. We used tabs
in order to help us sew the two un even pieces together. These
tabs would be folded to make up for the differnece in circumference
when sown together. The result were the following: First the two
pieces were almost impossible to sew together, the process wasalso
too laborious. Second the construction method did not achieve
what we had hoped for. In reality it was the exact opposite.
After deciding that the construction method used by R. Secret
Designs was the best, we decided to fill the pods with polyester
beads. We got on the phone that very day, and ordered some from
a contact the school had. The idea for using them came about because
the beads are weather resistant,washable, and they will not swell
up if the toy lands in a puddle. They are also round which will
give the pods a better packing order. They are made out of recyclable
polyester, which is very friendly for the environment. Lastly
they are not expensive and that was also a big issue. Unfortunately
to this day we have not received them, so we have not been able
to run experiments comparing rice to polyester.
Our next idea was to make the pod out of a knit structure. In
this way we would be able to remove the stitches from the sides,
and therefore remover the puckering all together. This would reduce
the different costs of the stitching process such as labour, sewing
thread, etc. Then went to the knit lab, we needed to use a small
needle gauge, 10 cut, so that the stitches would not catch and
snag on the asphalt. Before building a fully fashioned version
of the pod, we made a few yards of fabric so that we could do
some abrasion tests. The tests were a success in most cases, the
knit fabric was made from a 72 tex, 3-ply nylon yarn (Nylon 6.6
was used). The abrasion more than tripled in comparison to the
oxford cloth used previously, for most cases. The exception was
the inflated diaphragm test.
Then we proceeded to make a fully fashioned sample; however, we
soon realized that without the appropriate equipment we would
never be able to construct sample this way. The equipment we were
missing was a knitting machine with presser feet, which would
keep uniform tension throught the sample during knitting. We did
on the other hand, make more of the fabric such as the one we
tested, in order to build our models. We sewed them together following
the original procedure used for the woven flexstar.
When they were constructed, we found that the 420 nylon parapack
fabric worked the best. The stiff woven boddy and the new knit
outside pods were the perfect combination. We think that it is
even easier to throw than the original. We took the flex star
apart and weighed all the peices individually. After that we made
the proper adjustments to make sure that the weights of the original
and the improved flex stars were the same.
The improvments we observed with the knitted outer pods were the
following. Fisrt, we noticed the toy openned up faster after being
released (see following figures). Second, it was easier to throw
because of the way the knit fabric reacts to the centripetal forces
when being thrown. The loops in the knit structure stretch allowing
the toy to have more of an even circumference when in flight.
Figure 1. Picture of woven Flexstar in flight. Note that righthand spar is twisted, affecting aerodynamic response.
Figure 2. Picture of knitted Flexstar in flight. Note that spars are flat. This was observed repeatedly during flight testing.
The following tests were performed on the knit fabric, a single jersey, and the woven Oxford, 210,420, 730 denier nylon:
| Test Results | ||||
|---|---|---|---|---|
| Fabric | ABRESER | WYZENBEECK | INFLATED DIAPHRAGM | DRILL TEST |
| No. of Cycles | No. of Oscillations | No. of Cycles | No. of Seconds | |
| 210 Nylon Oxford | 400 | 425 | 4000 * | 45 |
| 420 Nylon Parapack | 1700 | <<>> | <<>> | <<>> |
| Nylon 82 tex (S. Jersey) | 3500 | 750 | 2870 | 300 * |
ABRESER: Model 503 Standard Abrasion Tester. Abrasion Test Wheels # H-22 (Calibrade).
INFLATED DIAPHRAGM: Universal Wear Tester. Pressure of 3 psi Weight of 3 lb. on head.
The results on our knit fabric were better than we expected. We new that we would have some problems with snagging, so we used a 10 gauge knitting machine. This means that there are ten needles to an inch. This made the loops small enough that snagging was not a factor. The knit fabric had a much softer hand as compared to the woven fabric, even though we were not able to make them without the seems. We expect it to be better with this improvement. Significant improvement was in the flying time of the Flex-Star, because of the knitted structures, the beads were allowed to expand inside each pod, and as a result of that, the force distribution was even on each arm of the Flex-Star. Because of this uniformity, the air resistance was equal on each arm, and that improve the over-all flying properties of the Flex-Star. These results were reached by throwing the Flex-Star over 50 times in the air. The only negative test was inflated cylinder. The reasons for the failure of the fabric under these conditions were the single jersey structure. The pressure and abrasion on the fabric was applied only on a small area of fabric. Under these conditions one loop broke, and cause failure in the fabric due to the laddering effect. These are typical results for a single jersey fabric, but under normal conditions the toy will not be exposed to as high tensions as in this test.
Yarn = $9.5/lb. for 100 lb. of yarn.
That is $20.90/kg.
The price for a 7 gram pod would then be $0.146
If the Shima glove machine is used. (cost between $8,000 new and
$6,000 for used)
We estimate that the machine would knit five pods in about 4 minutes.
Annual production of the machine at 85% efficiency, 50 weeks a
year, on 2 shifts, five days a week, would be 25,500 of each the
five and the three point toys.
If they are sold for $11.99 and $9.99 respectively.
Therefore total retail annually would be $561,000 a year, and
the utility would be $465,931 annually.
Note: These prices are using estimates of both labor and manufacturing
costs. Real prices were used when ever possible.
