IEEE Robotics & Automation Magazine - March 2017 - 44
Maximum Torque Needed for 30° Failure
3
Torque (N.m)
2.5
2
(a)
1.5
1
180° Test (N = 10)
90° Test (N = 10)
0.5
0-180
0-180
Frapped
0-180
FrappedBacked
Joint Type
0-360
Frapped
Angle
Figure 4. The failure torques by joint type and testing angle
(blue: 180°; red: 90°; N = 10 for each boxplot). The results show
the added benefit of frapping and backing operations. Note
that the joints with a 180° range are most durable in the 180°
position, whereas the 360° joint and a 90-270° joint (results are
not shown) were most durable in the 90° position.
Time
(a)
(b)
Figure 5. The repeated load-testing rig. (a) We held joint samples
(white, center) with plastic clamps (black rectangles) and
commanded a servomotor (hidden behind the white indicator
dial) to torque a clamp around the axis perpendicular to the joint
axis. We incremented torques from 0 Nm by 0.06 Nm, executing
one back-and-forth cycle at each torque level and holding each
torque for 3 s to allow the joint to move to its mechanical limit.
(b) We stopped the test when the joint rotated more than 30°
off axis, defined as "joint failure" (typical trial).
readily with torsional loads. The sensitivity of the joint to such
off-axis torque is, itself, a function of its angle at the time of
loading. To compare our designs, we chose to load each joint
in torsion at bend angles of 90 and 180°.
We built N = 10 of each joint out of 7.6 -cm # 7.6 -cm
foam-board squares, which we fixed in plastic clamps
constructed of 0.64-cm acrylonitrile butadiene styrene
(ABS), 2.5 cm away from the joint edge. Each clamp had a
transition zone of thinner 0.16-cm ABS extending 1.25 cm
closer to the joint edge and reducing stress concentrations
that could tear the plates. Clamps allowed some translation
in the direction of insertion but otherwise completely constrained the samples. With one clamp stationary, the other
was torqued with a servomotor (Dynamixel MX64, Robotis,
Inc.), which also provided an angle measurement (tested
44
*
IEEE ROBOTICS & AUTOMATION MAGAZINE
*
March 2017
(b)
(c)
(d)
(e)
Figure 6. The structural members made using PARF techniques:
(a) notched prism, (b) layered plates, (c) cut-folded prism, (d)
hot-glued fins, and (e) crush-folded prism. Each was made from
a 30.5 cm # 15 cm piece of foam board.
accurate to better than 1°). Gradually increasing the max
torque of the motor, we twisted joints back and forth, maintaining each direction long enough for the joint to twist to a
stationary position (see Figure 5). We calibrated our torque
measurement using test masses of up to 1 kg hung from an
arm of length 29 cm and torqued against gravity by the servomotor until it stalled.
After applying both frapping and backing to the joints,
any additional taping appeared to have rapidly diminishing
returns. At that point, the plate material itself was the main
source of failure, limiting the joint's ability to resist torsion.
We compared the standard 0-180 frapped-backed joints
built with both types of tape to simplified joints built using only
bidirectional fiber tape, subjecting both types of joints to the test
as above (N = 30). The two-sided Kolmogorov-Smirnov test
(scipy.stats.ks_2samp SciPy 0.13.3) gave p < 0.001, showing that
samples are significantly different. Standard joints had an interquartile range 70% smaller than that of the simplified joints and
median 10% higher failure torque. Results justify the use of both
types of tape. Under repeated constant loads at 75% of
the mean failure torque, standard joints (N = 5) failed after
3,252 ± 12 (mean, standard deviation) cycles.
Structural Member Design
PARF techniques can be used to build structural members
with improved load-bearing capabilities compared to single
plates. Some structures easily built with the construction
techniques described below include layered plates, fin-stiffened plates, and prisms (see Figure 6). Note that the way in
which the shear is transferred from one plate to another
strongly affects rigidity in shell structures. All of these structures can be built with tape to transfer shear; hot melt adhesive (Surebonder All Purpose Glue Sticks) can be used to
improve results.
Layered plates are weakest structurally but most compact.
They can be either glued together across the faces or taped
together around the outside edges. Fins or stiffeners can be
used to dramatically reduce bending of a plate in a specific
direction. They are best applied by gluing onto a baseplate.
Alternatively, notches can be cut into the plates and taped
together. Triangular prisms are particularly good at resisting
both torsion and bending. They can be made by folding or
cutting notches in the plates. Plates can be folded in two ways:
Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - March 2017
IEEE Robotics & Automation Magazine - March 2017 - Cover1
IEEE Robotics & Automation Magazine - March 2017 - Cover2
IEEE Robotics & Automation Magazine - March 2017 - 1
IEEE Robotics & Automation Magazine - March 2017 - 2
IEEE Robotics & Automation Magazine - March 2017 - 3
IEEE Robotics & Automation Magazine - March 2017 - 4
IEEE Robotics & Automation Magazine - March 2017 - 5
IEEE Robotics & Automation Magazine - March 2017 - 6
IEEE Robotics & Automation Magazine - March 2017 - 7
IEEE Robotics & Automation Magazine - March 2017 - 8
IEEE Robotics & Automation Magazine - March 2017 - 9
IEEE Robotics & Automation Magazine - March 2017 - 10
IEEE Robotics & Automation Magazine - March 2017 - 11
IEEE Robotics & Automation Magazine - March 2017 - 12
IEEE Robotics & Automation Magazine - March 2017 - 13
IEEE Robotics & Automation Magazine - March 2017 - 14
IEEE Robotics & Automation Magazine - March 2017 - 15
IEEE Robotics & Automation Magazine - March 2017 - 16
IEEE Robotics & Automation Magazine - March 2017 - 17
IEEE Robotics & Automation Magazine - March 2017 - 18
IEEE Robotics & Automation Magazine - March 2017 - 19
IEEE Robotics & Automation Magazine - March 2017 - 20
IEEE Robotics & Automation Magazine - March 2017 - 21
IEEE Robotics & Automation Magazine - March 2017 - 22
IEEE Robotics & Automation Magazine - March 2017 - 23
IEEE Robotics & Automation Magazine - March 2017 - 24
IEEE Robotics & Automation Magazine - March 2017 - 25
IEEE Robotics & Automation Magazine - March 2017 - 26
IEEE Robotics & Automation Magazine - March 2017 - 27
IEEE Robotics & Automation Magazine - March 2017 - 28
IEEE Robotics & Automation Magazine - March 2017 - 29
IEEE Robotics & Automation Magazine - March 2017 - 30
IEEE Robotics & Automation Magazine - March 2017 - 31
IEEE Robotics & Automation Magazine - March 2017 - 32
IEEE Robotics & Automation Magazine - March 2017 - 33
IEEE Robotics & Automation Magazine - March 2017 - 34
IEEE Robotics & Automation Magazine - March 2017 - 35
IEEE Robotics & Automation Magazine - March 2017 - 36
IEEE Robotics & Automation Magazine - March 2017 - 37
IEEE Robotics & Automation Magazine - March 2017 - 38
IEEE Robotics & Automation Magazine - March 2017 - 39
IEEE Robotics & Automation Magazine - March 2017 - 40
IEEE Robotics & Automation Magazine - March 2017 - 41
IEEE Robotics & Automation Magazine - March 2017 - 42
IEEE Robotics & Automation Magazine - March 2017 - 43
IEEE Robotics & Automation Magazine - March 2017 - 44
IEEE Robotics & Automation Magazine - March 2017 - 45
IEEE Robotics & Automation Magazine - March 2017 - 46
IEEE Robotics & Automation Magazine - March 2017 - 47
IEEE Robotics & Automation Magazine - March 2017 - 48
IEEE Robotics & Automation Magazine - March 2017 - 49
IEEE Robotics & Automation Magazine - March 2017 - 50
IEEE Robotics & Automation Magazine - March 2017 - 51
IEEE Robotics & Automation Magazine - March 2017 - 52
IEEE Robotics & Automation Magazine - March 2017 - 53
IEEE Robotics & Automation Magazine - March 2017 - 54
IEEE Robotics & Automation Magazine - March 2017 - 55
IEEE Robotics & Automation Magazine - March 2017 - 56
IEEE Robotics & Automation Magazine - March 2017 - 57
IEEE Robotics & Automation Magazine - March 2017 - 58
IEEE Robotics & Automation Magazine - March 2017 - 59
IEEE Robotics & Automation Magazine - March 2017 - 60
IEEE Robotics & Automation Magazine - March 2017 - 61
IEEE Robotics & Automation Magazine - March 2017 - 62
IEEE Robotics & Automation Magazine - March 2017 - 63
IEEE Robotics & Automation Magazine - March 2017 - 64
IEEE Robotics & Automation Magazine - March 2017 - 65
IEEE Robotics & Automation Magazine - March 2017 - 66
IEEE Robotics & Automation Magazine - March 2017 - 67
IEEE Robotics & Automation Magazine - March 2017 - 68
IEEE Robotics & Automation Magazine - March 2017 - 69
IEEE Robotics & Automation Magazine - March 2017 - 70
IEEE Robotics & Automation Magazine - March 2017 - 71
IEEE Robotics & Automation Magazine - March 2017 - 72
IEEE Robotics & Automation Magazine - March 2017 - 73
IEEE Robotics & Automation Magazine - March 2017 - 74
IEEE Robotics & Automation Magazine - March 2017 - 75
IEEE Robotics & Automation Magazine - March 2017 - 76
IEEE Robotics & Automation Magazine - March 2017 - 77
IEEE Robotics & Automation Magazine - March 2017 - 78
IEEE Robotics & Automation Magazine - March 2017 - 79
IEEE Robotics & Automation Magazine - March 2017 - 80
IEEE Robotics & Automation Magazine - March 2017 - 81
IEEE Robotics & Automation Magazine - March 2017 - 82
IEEE Robotics & Automation Magazine - March 2017 - 83
IEEE Robotics & Automation Magazine - March 2017 - 84
IEEE Robotics & Automation Magazine - March 2017 - 85
IEEE Robotics & Automation Magazine - March 2017 - 86
IEEE Robotics & Automation Magazine - March 2017 - 87
IEEE Robotics & Automation Magazine - March 2017 - 88
IEEE Robotics & Automation Magazine - March 2017 - 89
IEEE Robotics & Automation Magazine - March 2017 - 90
IEEE Robotics & Automation Magazine - March 2017 - 91
IEEE Robotics & Automation Magazine - March 2017 - 92
IEEE Robotics & Automation Magazine - March 2017 - 93
IEEE Robotics & Automation Magazine - March 2017 - 94
IEEE Robotics & Automation Magazine - March 2017 - 95
IEEE Robotics & Automation Magazine - March 2017 - 96
IEEE Robotics & Automation Magazine - March 2017 - 97
IEEE Robotics & Automation Magazine - March 2017 - 98
IEEE Robotics & Automation Magazine - March 2017 - 99
IEEE Robotics & Automation Magazine - March 2017 - 100
IEEE Robotics & Automation Magazine - March 2017 - 101
IEEE Robotics & Automation Magazine - March 2017 - 102
IEEE Robotics & Automation Magazine - March 2017 - 103
IEEE Robotics & Automation Magazine - March 2017 - 104
IEEE Robotics & Automation Magazine - March 2017 - 105
IEEE Robotics & Automation Magazine - March 2017 - 106
IEEE Robotics & Automation Magazine - March 2017 - 107
IEEE Robotics & Automation Magazine - March 2017 - 108
IEEE Robotics & Automation Magazine - March 2017 - 109
IEEE Robotics & Automation Magazine - March 2017 - 110
IEEE Robotics & Automation Magazine - March 2017 - 111
IEEE Robotics & Automation Magazine - March 2017 - 112
IEEE Robotics & Automation Magazine - March 2017 - 113
IEEE Robotics & Automation Magazine - March 2017 - 114
IEEE Robotics & Automation Magazine - March 2017 - 115
IEEE Robotics & Automation Magazine - March 2017 - 116
IEEE Robotics & Automation Magazine - March 2017 - Cover3
IEEE Robotics & Automation Magazine - March 2017 - Cover4
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2023
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2023
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2023
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2023
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2022
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2022
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2022
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2022
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2021
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2021
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2021
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2021
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2020
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2020
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2020
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2020
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2019
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2019
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2019
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2019
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2018
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2018
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2018
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2018
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2017
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2017
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2017
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2017
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2016
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2016
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2016
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2016
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2015
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2015
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2015
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2015
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2014
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2014
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2014
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2014
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2013
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2013
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2013
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2013
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2012
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2012
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2012
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2012
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2011
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2011
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_june2011
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_march2011
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_december2010
https://www.nxtbook.com/nxtbooks/ieee/roboticsautomation_september2010
https://www.nxtbookmedia.com