LifeCat 1.0/Research Development/Previous Design Analysis

Overview

Here is some analysis of the LifeTrac III from community members.

Forum Comments

OSE Europe Lifetrac Design Safety Discussion

Here is the link to the full forum discussion.

Summary

• Frame
  • No engineering analysis done on any components of the frame for the loads encountered
  • When the machines tracks rotate in opposite directions this turns the machine but the load is transferred to the frame. Because the wheels have a gap between them the force is not equally distributed along the bottom of the frame. The force travels through each wheel, to the corners of the base frame square, from there it is transmitted up the vertical frame and along the top square frame, all of the force meets in the center of the top frame along two parallel lines. Here you have placed a very large hole which the loader attaches to. From the top centre of the frame the force from the wheels is then transmitted to the centre of the base frame.
    • Comment: Conventional machines which use tracks transfer the load from the track through a series of gears which span the entire length of the track and base frame. A conventional skid loader has the hydraulic lifter attached to a separate frame from the drivers cabin, this improves operator safety from moving parts, improves stability over the entire machine and increases load bearing capacity from the chassis I.e. it doesn't snap in half. The machine is most likely to snap in the middle of the bottom and top struts on which the wheels and loader are mounted. So two sets of forces are meeting at one point. This is the force from the wheels and the force from the loader.
  • The construction using tubes bolted through the center is not good for dynamic loading as the bolts need to be sufficiently pre-stressed during assembly. This is not possible with thin-walled square tubing
    • Comment: What are the proper forces/torques required in pre-stressing the bolts during assembly? From this we can calculate the required material thickness for square tubing to ensure no deformation during tightening.
  • Considerable forces on the frame introduce bending moments on bolts which they are not designed to take
  • Questionable engineering practice to place the longitudinal and cross-support members on different planes as it generates additional stress in the design as torsion and bending moments
  • Potential Frame Solutions
    • Welding the frame members together
    • Welding a plate to both frame members to they can be bolted together with several bolts
    • Using U-profiles instead of square tubes, You could
      • weld them
      • weld a head-plate to the crosswise frame members and bolt it to the longitudinal frame parts
    • Place frame members all in the same plane

• Wheel Motor Coupling
  • Alignment between the motor, coupler, shaft and wheel needs to be precise to prevent failure with time due to the high forces involved.

• Safety
  • No roll-over protection
  • No floor, side walls, roof, or restraining devices (Note: These should be getting addressed in LifeTrac IV)
  • No independent brake in case of hydraulic pressure loss.

• General Comments
  • Trying to have the LifeTrac be both a skid steer and tractor is a hard esign