1. Car Jack Mast Design Update
Presented by Doug Eddy and Dr. Sundar Krishnamurty at UMass Amherst for Hoppe Tool on 7/16/10

2. Control of Scissors’ Motion
This mechanism is under constrained.

3. Potential Remedy
Theoretically, the bottom pivots far apart shortens travel and close together affects stability.

4. Alignment without Binding
Connecting links needed
between center pivots
How well will the 3
sides move together and
keep top in line with
bottom?

5. Consider an actual Car Jack Design
The screw is horizontal
and moves up and
down during lifting.

6. Consider a Conventional Scissor Lift
The shape is rectangular.
Parallel scissors are
rigidly connected at outer
pivots. Legs are made of
rectangular tubing for
strength and stability.

7. Engineering Analysis A simplified explanation is found at:
The information is verified and correct.
This reveals a design challenge with the multiscissor arrangement.
The screw force required is very large when the angle is small at the start of lifting.
The threshold power spec is 850 Watts.
Mechanical advantage with unequal scissor’s lengths is only 15-35%.

8. Engineering Calculation Results

9. Car Jack Potential Design Remedies
Longer scissors’ length
Increase retract height and scissor start angle
Longer pitch lead of screw and nut length
Must also minimize friction and consider those effects
Clevis mounted angle optimized drive pivot mount?

10. Strap Design
8m mast supporting 120kg (EW system)

11. Claims of the Belt Design
LERC S.A.
BP – SAINT AMAND LES EAUX CEDEX – France
Tel: – Fax: –
Internet:
Page 2/4
Main Advantages
• Resistance to bullet impacts: a bullet impact on a pneumatic mast
manufactured from light alloy or pultruted composite will make a hole that
will result in an air leak and in the mast collapse. It will also make a slight
crack in the matrix likely to break the tube. In a belt drive telescopic mast,
a bullet impact (see picture) will make a hole without affecting the mast
height. Moreover, the woven and crossed structure (Filament Winding -
FW) of the composite material prevents any crack in the tube.
• Height maintained at constant level when the mast is in erection for
an extended time : a pneumatic mast tends to go flat and therefore to
retract, which can result in a cutting off of the radio contact.
• Outstanding resistance to corrosion, chemical attacks and ageing ;
• Undeformability: the tube sections show no permanent deformation even after extensive use (strength
maintained, no ovalizing);
• Best ratio between deployed and retracted heights
• Lightweight and outstanding mechanical resistance
• No maintenance other than wiping or brushing to clean and for the telescopic masts, replacement of the
belt without dismounting tubes (can be performed on the field).
• Excellent resistance to environmental conditions (use of Epoxy resin and FW process): Sand, dirt,
dust, snow, ice will not cause degradation of mast performance. On mast with the new belt system, the belt
is fully inside the mast, protected against outside environment.
• No air tightness to ensure : no adjustments to make height maintained at constant level ;
• Manipulation with naked hands, even under cold or hot temperature ;
• Adaptability to the customer’s needs : the mast structure is computer designed (SAMCEF method)
• LERC proven experience: close to 60 years in the field of composite materials, 30 years in the
manufacturing of tactical masts and antennas.

12. Design Concerns with Strap Concept
Resistance of bending around small pins
Possibility of slipping at speed desired if not enough tension
Contact area on small pins
Power required increases with tension and the number of pulley contacts for simultaneous lifting.

13. Question for you?
How do you and the customers rank or weight the various features?:
Low power required
Small area, length
Low weight
High reliability and strength
Low sway and deflection, high stability
Low start height
High extended height
Low cost
High payload capability
High speed capability
High center clearance area and proximity for the cabling and basket below

14. Consider a Simple Straight Pulley Lift
Work output = mgh = 45 pound payload x 20 feet lifting height = 900 lb - ft If the total system mechanical efficiency were 64% (although not realistic , for a system lifting from underneath) Work input needed = 900 / 0.64 = 1406 lb – ft = F x d = System pull force x System pull distance This must be done within 15 seconds, Power = Work done per unit time = 1406 / 15 = ft – lbf / second 550 ft – lbf / sec = 1 Hp, so for a 93% efficiency motor / (550 *0.93) = Hp = 137 Watts