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Car Jack Mast Design Update

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Presentation on theme: "Car Jack Mast Design Update"— Presentation transcript:

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

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