Final lift report

Department of Mechanical Engineering

Lab Report: Lift Design

Joshua Alexandre Dos Santos (080591858)

and

Tomos Porter (071455464)

Lift Design

CONTENTS

Summary............................................................................................................................................................................... 2

Introduction and design Specifications.................................................................................................................................. 3

Design alternatives and choice of solution............................................................................................................................ 4

Concept 1:......................................................................................................................................................................... 4

Concept 2:......................................................................................................................................................................... 5

Concept 3:......................................................................................................................................................................... 6

Refining mechanism.............................................................................................................................................................. 8

Calculations..................................................................................................................................................................... 11

Material selection............................................................................................................................................................. 14

General assembly drawing.................................................................................................................................................. 15

Operation............................................................................................................................................................................. 15

Conclusion........................................................................................................................................................................... 16

References.......................................................................................................................................................................... 16

2 Joshua Alexandre Dos Santos and Tomos Porter |

Lift Design

SUMMARY

Monster trucks are very big as well as their wheels. With such large tyres in a small vehicle, the pressures are very low. This can lead to punctures. Changing the wheels is a real issue given their size and weight.

Therefore, there is a need for a lifting system to assist the fitting of the wheels.

Throughout this report, various concepts of lifting devices are considered. Only one is chosen to be further developed. Calculations are made to avoid failure and make it as safe as possible. Finally, a assembly drawing is given as well as a description of the mode of operation.

INTRODUCTION AND DESIGN SPECIFICATIONS

Lifting devices may be use for various purposes. This specific device has to fulfill particular specifications:

Design considerations:

The lift must be able to create a 0.8m ground clearance below the bottom of the wheel in 12 seconds.

Tyre widths vary between 1.5 to 2.2 meters in diameter and the lift must be able to lift all sizes.

The device must fit into a transit style van. Maximum device weight is 200kg. One should be able to move the device at least 2 meters away with the tyre mounted on

dusty and rough surfaces. It may be submitted to a small incline (5 degrees). One must be able to remove or put hubs on the wheel. Factory transfer price must not exceed £400.

Assumptions:

Wheel can remain vertical and does not need to be able to rotate about its axis. Electronics are controlled using a “black box”

Other assumptions are clearly specified along the report.


Lift Design

DESIGN ALTERNATIVES AND CHOICE OF SOLUTION

In this section, explanations are given to communicate the principles each design.

CONCEPT 1:

Figure 1

Figure 2


Description:

This concept lifts the wheel by gripping it between two horizontal-sliding rollers at a fixed height above the ground. The reaction of these rollers against the underside of the wheel pushes it upwards as the rollers are pulled together by a linear actuator.

Grip Lift (Figure 2)

Advantages:

This design is very simple and compact, requiring a minimum of moving parts. It is compatible with wheels of almost any size, with no need to specifically adjust the fork distance (as this is an inherent function of operation).

Disadvantages:

This design is only able to lift the wheel as high as the rollers, and increasing the roller height to the needed 0.8m would reduce the vertical component of the reaction too much to be useful.

Grip Lift

Lift Design

CONCEPT 2:

Figure 3


Description:

Based on hay bale forks for tractors, it possesses adjustable arm width.

Advantages:

Adjustable fork width Compatible with pneumatic and electric

power source Compatible with multiple types of

transmissions. (Pulleys, chains, lead screw)

Disadvantages:

Complex Difficult to incorporate tilting mechanism

Lift Design

CONCEPT 3:

Figure 4

Choice of concept:

Concept 3 was chosen because of its simplicity and few parts. The lead screw offered security when the tyre was lifting as the friction would stop it from collapsing. Many improvements need to be added at this point.

Choice of transmission:

The pneumatic power was efficient and offered very fast lifting. But the lifting distance was not very large (only 0.8 meters), hence there was no need for a big rush.

A lead screw was chosen because it was safe and it would hold when the tyre was elevated due to the friction. The friction had a disadvantage because it means that the power transmission would be very poor due to the low efficiency. Simple calculations were made to unsure that using a lead screw would be a feasible option.


Description:Two forks are first set the required distance apart before lifting the wheel by using a screw jack.

Advantages:

Simple fork design with few parts Compatible with pneumatic or

electrical power source

Disadvantages:

Due to the lead screw friction, it could be challenging to achieve the desire altitude (0.8 meters) in the time limit of 12 seconds.

Lift Design

Basic power calculations:

A 30% overall efficiency was assumed to perform the preliminary calculations.

Power available ∙ η=Volts ∙ Amps∙η

Energy ¿ lift=Power available∙ Lifting time

Energy ¿ lift=(mass of tyre+mass of forks frame ) ∙ g ∙ h

The fork frame mass limit was calculated using Microsoft excel (Table 1)

Tyre mass on each fork (N) 981

Height to lift (m) 0.8

Power (watts) 153.6

Energy to lift tyre (joules) 1843.2

Lifting time(seconds) 12

overall efficiency 0.32

Maximum mass of forks (kg) 34.8623853

Table 1


Lift Design

REFINING MECHANISM

Major improvements covered in this section:

Adding a tilting movement Adding a frame to stop it the forks swiveling as the lead screw is rotating. Adding brakes Adding handles Removing adjustable forks

Brakes:

The casters supporting the frame are equipped with brakes to keep the device stable during loading and unloading of the tyre. The casters are able to move to every direction.

Handles:

Handles are necessary to move the device around with the wheel mounted. The handles would be set at shoulder around shoulder high which would make the device bigger in height. Therefore, removable handles would be ideal.

Adjustable fork width:

At first, a sliding mechanism was considered so that the distance between the forks could be adjusted. But it was realized that a set fork width could pick up tyres ranging from 1.5 to 2.2 meters in diameter and up to 1.5 meters wide. The forks were set to be fixed 1.2 meters apart.

Figure 5


Lift Design

Figure 6

Figure 6 explanation: This figure illustrates the forks at its highest and lowest positions. Part 2 slides into part. Vertical dimensions are to scale. Thicknesses of the members are not to scale. When folded, the device will be just under a meter tall


Lift Design

Legs: The legs needed to be as long as the forks to prevent any offset of the center of gravity.

Member number 2 is extendable.

Tilting movement :Linear Actuator

Figure 7


A linear actuator was assumed to be able to fit inside the forks. It would push back on the frame and tilt the forks.

Calculations were made to find how powerful the electric actuator needed to be. The tyre mass was assumed to a point load in the middle of the hollow fork.

BM=(D1+D 2 ) ∙mass∙9.81=1863.9Nm

2

1

Lift Design

CALCULATIONS

Assumptions:

The tyre was assumed to be an evenly distributed load. The bending in the z direction was assumed to be negligible (Figure 8) For the bending calculations, the fork was assumed to be a cantilever (Figure 9)

Figure 8

Figure 9


Lift Design

The Bending Stresses on the forks were calculated and the graphs were plotted using Microsoft Excel.

Shear Force=−mass ∙ x

Bendingmoment=∫ Shear Force=−mass ∙ x2

2

Combinedmoments=BMc=¿

The maximum bending is attained when the tyre is picked up on the tip of the forks. (distance AB=0 on figure 9)

Iterations:

Iterations were made to verify that the hollow rectangular beam (figure 10) would take the combined stresses. The value of h1 needed to be less than 7.5 cm in order to be able to pick up tyres of diameter up to 2.2 meters.

Figure 10

I 1=Secondmoment of area=(b1∙ h1

3)12

I 2=Secondmoment of area=(b2 ∙h2

3)12

Combined secondmoment of areaof hollow section=I c=I 1−I 2

Bending Stressσ=(BM ∙ y)

I c


Lift Design

Combined Stress=[σ2+τ2]1 /2 where τ=0 because there is no torque applied

Combined Stress=σ=Bending Stress

Stress concentration factor

It is important to allow some leeway when designing something, to account for unknown variables. If the shaft were to be designed with the experience stress very close to the yield stress of the material, then if something unexpected were to happen that the designer had not considered, it could end up in a catastrophic failure. To prevent this, the allowable stress was calculated using a number of different factors.

Allowable Stress= YS(b∗c∗d∗k )

Where ‘YS’ is the yield stress, ‘b’ is the fatigue factor, ‘c’ is the shock factor, ‘d’ is the safety factor and ‘k’ is the stress concentration factor.

b=1; c=1 ; d=1.75; k=3

Figure 11


Lift Design

Conclusion from the iterations:

The hollow beams were strong enough to take the load. Heavier filled beams were not needed to be used instead.

The electric actuator could not be fitted inside the forks. They would have to be fitted on the sides of the forks.

The forks would need to be made out of mild steel and they would not be hollow anymore. Using Solid Edge, the weight of the fork frame was calculated using the density of the type of material chosen and the its volume.

Weig ht of t he fork fr ame=80kg

Total weigh t ¿be lifted=Tyremass+Forks framemass

Total weigh t ¿be lifted=200+80=280kg

MATERIAL SELECTION

Leadscrew selection:

The leadscrew was chosen in the ZIMM catalogue. In this catalogue, one goes through a process of choosing different parameters.

At first, based on the force that was needed to be applied to lift the wheel and the forks (303*9.8), we selected a leadscrew drive. Then, using formulas provided by the manufacturer, we calculated the minimum spindle diameter to resist buckling, and the maximum length to avoid whirling at high speed. The initially selected jack had suitable values, so it was chosen for the final design. It was also decided to use a layout with two lead screws instead of one, in order to keep the mechanism parallel as it was raised. Both lead screws would be powered by a single motor through a simple bevel gearbox.

Motor selection:

The leadscrew catalogue specified the required torque needed. The motor was selected to deliver this torque keeping in mind that the maximum power available was (24 volts x 20 amps) .

The motor selected is a 400W DC motor manufactured by Lenze.

Not much noise was generated because it’s an electric motor.

GENERAL ASSEMBLY DRAWING


Lift Design

----------------------------------------- See attached pages ----------------------------------------------

OPERATION

Description of mode of operation:

This device can be operated indoors or outdoors.

Simply turn on the motor to start lifting the forks. You can change the motor speed to raise it faster. Do drive the forks down, invert the motor.

A second pair of actuators is provided to tilt the forks forward and backward by up to 5 degrees.

All of the functions are controlled electronically using a simple control box with switches for ‘raise’, ‘lower’ and ‘tilt’ movements.

Operation reliability and Safety:

Special care needs to be taken when lifting the tyre. It is desirable to avoid picking up the wheels on the tips of the forks to avoid putting too much stress onto the forks. No sharp edges were left out to ensure safety of the operators.

This device is to be used by a minimum of 3 operators. Hardly any assembly problems arise when using screw jacks in mechanical engineering

because the surfaces being processed are machined. However, frequent geometric faults may occur in welded frames despite accurate working in steel construction. The interaction between different components can also cause alignment issues. Therefore the following must be considered: Spindles and guides must be parallel to each (figure 12) other otherwise the equipment can seize up during operation. All mounting surfaces for the gearboxes must be exactly at right angles to the guides otherwise interference can occur. This accelerates wear and/or severe damage can occur. Squeaking noises can also occur.

Figure 12


Lift Design

Temperature and operating period

Screw jacks are generally not designed for continuous operation. Operating temperatures should not exceed 80 degrees.

Inspection and maintenance:

Regular inspection and maintenance are prerequisites to ensure long life. During regular inspection, check for optical state and wear on the trapezoid thread and the level of lubrification.

CONCLUSION

The design as presented will achieve the stated aim of lifting a monster truck wheel 0.8m from the ground to fit it to the truck. However there are some areas where the brief was not met.

The device is 50kg heavier than the brief specified, due to the need to use thicker steel section on the forks to give the necessary strength.

Due to the weight of the forks, the lift will not be able to reach its maximum height in 12 seconds if fully loaded. This is a limitation of the power supply available.

The device is relatively compact, and achieves the aim of being able to fit inside a normal Transit type van.

We were not able to obtain quotes for all of the parts used, so cannot currently say whether the specified price point was met.

REFERENCES

http://www.zimm.at/media/kataloge/2008_catalogue_en.pdf

Wheel lifts

A G Equipment Wheel Lift - good design, not high enough liftEagle SMF TBE-56 Terra - not portableBlue Point Wheel Lift Assist - good design, light dutyCorghi Tyre Changers - Not portableRanger RWL-350 - too light duty, can't put wheel on the ground

Agricultural bale handling equipment

KeelAgri Bale Handler - ideal gripper, needs vertical lift and safety chain

Tanco D692 Round Bale Handler - As above

Cashel's Hydraulic Bale Handler - Very similar to Tanco

Cashel's Telescopic Bale Stacker with Duck's Foot lifter - Inc. Lift mechanism, different gripper

Culverwell's Bale Handler - As Tanco


http://www.zimm.at/media/kataloge/2008_catalogue_en.pdf

Lift Design

Fleming BBSTAC Round Bale Stacker

Parts

DADCO - pneumatic cylinders

SITEMA - Cylinder safety locksDC Linear actuatorsBCAE - How linear actuators work

http://www.zimm.at/en/screw_jacks ZIMM screw jacks

TEA HG10 actuator


Documents

Final lift report