Telescoping Mast Design Options
Presented by
Doug Eddy, GRA and Dr. Sundar
Krishnamurty at UMass Amherst
For Hoppe Tool
Lifting Mechanism Design Alternatives
•
•
•
•
Cables on Pulleys with simultaneous lift
Roller Chain on Sprockets
Straps on Pins
Screw Driven
Other less proven risky alternatives:
• Rack and Pinion
• Linear Motors
Summary of Key Findings
• Round tubing 21% and 43% better than square for sway limitation.
• Round tubing 62% and 68% better than triangular for sway
limitation.
– Round tubing size availability for the largest section may pose a constraint.
• Manufacturable process validated for round tubing.
• Vehicle acceleration moving camera greater than 3” from rest in 1
second will exceed the 20” sway spec if the total tubing weight is
approx 132 pounds.
– This assumes there are no gaps between the tubes.
• Aluminum is recommended over stainless steel, because the tubes
can be larger with more real estate on the inside.
Concerns and Challenges
• The 300 pound camera at a fast speed imposes a high tension force on the
mechanism components.
• Can we have simultaneous lifting of all sections w/out mechanisms outside
and inside? Is the tension force too high for simultaneous lifting?
• Keeping all the mechanisms and camera wiring inside the mast poses
clearance concerns.
• Design tradeoff with the dia. size of the pulleys mounted within the bushings.
– It does not appear likely we can keep the mast weight under 150 pounds, closer to 300
pounds with internal camera wiring.
• Must keep the tension close to equal on the 2 belts or straps to prevent
binding or one side overloading.
• Maintenance access with internal components with effects of environment,
impact, etc.
Evaluation of Pulleys and Cables for Simultaneous Lift
Pros
Weights
Simultaneous lifting for all the sections
for speed
Simplicity for focus on design
optimization and root
cause of short cable life
Prototype available for preliminary
testing
6
8
Cons
Weights
Lack of free fall prevention
10
Exterior mechanisms needs revision
9
A cable life solution is still needed
8
Lack of differentiation from the prior
design
Net Weighted
Result
7
6
Similar to the Floatograph design
20
6
40
-20
Evaluation of Roller Chain Concept
Pros
Weights
More mechanically positive for
freefall
prevention if the chain
is inspected.
Less friction and better power
transmission.
10
10
Durability
10
Speed
3
Cons
Need a take up tray for the excess
chain
in one travel direction
Much more clearance gap and
protection
from debris is needed
8
4
Much larger and heavier.
8
cost
Net Weighted
Result
8
Unknown cause of binding on the
prototype.
Chain inspection is difficult and
likely
needs 2 chains for balance.
33
Weights
8
2
WillBurt has a similar design
patented
in 1993.
3
Sprockets are staggered on curved
surfaces.
3
44
-11
Evaluation of the Straps on Pins Concept
Pros
Weights
Life of strap vs. cables
10
Internal components w
compact design
10
Cons
Some free fall prevention but
less than desired
Extra bushing pin/bearing
parts
Complex details, but CNC
manufacturable
2 straps to balance loading
and add a freefall safety
feature
No apparent similar patents
so potential for differentiation
w IP protection
Weights
Net Weighted
Result
3
3
7
5
5
Strap material wear on the
take up roll at speed
7
Potential high friction / power
requirement design challenge
6
Speed capability unknown.
5
Currently designed to lift one
section at a time.
7
Temperature and other
effects on the straps is
unknown.
37
7
38
-1
Evaluation of Screw Drive Concept
Pros
Weights
Very efficient and mechanically
positive.
Cons
10
Minimal gap between the tubes.
Weights
No conceptual prototype yet.
Net Weighted Result
4
Design challenge
8
Development time
8
External cable cat trak or cable coil
is needed for camera wiring.
4
Similar to Stiletto by Will-Burt (w
Nycoil) patented in 2001.
5
Internal clearance conflict between
the mechanism and the camera
wiring.
4
The design concept of a screw
within another screw has various
design challenges.
5
Guarding is needed to protect the
cabling from the environment.
5
More difficult manufacturability.
9
10
Possibly the most fail proof and low
maintenance option.
10
Should be much faster than the
Stiletto competition.
4
Antennas use a similar design with
a flexible screw.
4
38
52
-14
Other Design Decisions
• Internal vs. External Cabling
• Tube Cross Section Shape
– Circular
– Triangular
– Square
Camera Electrical Wiring Internally
Routed Vs. Externally Routed
Internal
Pros
Better protection of the wiring from
the harsh operating environment
More compact and transportable design
Lack of options for external mechanisms
given the harsh environment.
Weights
10
8
Internal
Cons
More difficult to rapidly coil and uncoil
due to tight clearance.
Difficult challenge to ensure cabling
will never get caught in mechanisms
during the rapid retract.
Weights
Net Weighted
Result
8
10
7
Lack of real estate for a take up roll
mechanism without encroaching
on the cockpit real estate.
7
8
Loss of opportunity for a more efficient
and effective internal
mechanism design.
25
33
-8
Cross Section Analysis of Circular
Tubing vs. Square or Triangular
Circular Pros
Weights
Circular Cons
Weights
Better stiffness and strength per
weight and cost of material
8
A feature is needed to prevent
rotating motion
4
Capability of more accurate alignment
by machining bushings on a Lathe
7
Additional bushing components are
needed, but they can
be multifunctional
6
15
10
Net Weighted
Result
5
Work to be Done
• 1) Analysis of scaled down proof of design concept prototypes by the
students - completed
• 2) Evaluation of student designs and research of any other possible
options - completed
• 3) Development and/or modification for optimization
• 4) Identification of Critical Function Features & a Quality Control Plan
• 5) Design for Manufacturability and Assembly (DFMA)
• 6) Theoretical Design Validation to enable a prototype build and test at
Hoppe Tool
• 7) Provide support for life testing and subassembly testing for construction
• 8) Geometric Dimensioning and Tolerance (GD&T) analysis
• 9) Completion of prints/specifications for manufacturing at Hoppe Tool
• 10) Provide support for the first Beta Manufacturing Validation Testing
build
• 11) Refinement, modifications and improvements based on results
Project Schedule / Timeline