A trailer which turns into a stage. This is a custom creations for a french company which asked me for building a replica of its product.

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Next to a contest organized at fanabriques 2012 on the theme “build a stage trailer”, the company StageMaster SAS contacted me in September to build a replica of a Folding Stage Trailer SM70. After discussing about bill of specifications, I have started the design process and the quotation. After 4 month of work, the trailer is finished and it has been delivered to the customer.

Bill of specifications

The aim was to have a reproduction of a stage trailer SM70 with following motorized functions :

  • 4 pneumatic stabilizers
  • Folding right and left panels with a motor
  • Folding upper panels with a motor
  • raising roof with a motor

Next to that, the following specifications has been introduced regarding the design and deadline :

  • color : Black frame, black roof and floor, black panel, gray upper structure
  • dimensions : around 60cm long
  • can yoke to a truck
  • deadline : February, 2013

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Design process

The first thing I have done is to build a rough frame to test different types of functions. I have started to build with linear actuators, and pneumatic cylinders but none of them were adequate. The actuators were too big for the scale, and if I have increased the scale, I would have had a very big trailer with lot of weight problem. This scale is a compromise with the functions and the scale. Finally, I have decided to use the internal space of the frame to make the folding functions. That is why I have developed next the system of axle driven. The axle of rotation of each panel are consequently directly driven by a motor and high gear reduction (8/24, 8/24, Worm/24, 20/20 bevel gear). This system enables me to have smaller slider beams.

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The second point was to come up with a solution for the raising roof. In dead, on the real model, the main functions were piloted by many hydraulic cylinders. Especially the roof which is elevated by a 3-section telescopic hydraulic cylinder, which is impossible to reproduce in lego. I have therefore tested many systems with 3 sections actuator based on 8421 crane and rack system but none of them were adequate.  Either the clearance was too small, or the stiffness was too low. I have thus developed the final solution : a 2-section slider for the rigidity and a system of winch for the raising force. This solution was very stiff and compact because all driven devices are located in the frame. A M  motor drives a worm screw on a 24-tooth gear which winches two axle with two strings. Then the strings roll on a pulley, reach the top of the slider beam and are attached to the moving parts of the sliders.

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The last problem I had to deals with was the weight. The panels are completely recovered of black plate, I had to now the global weight and the consequence on the functioning. That is why I have first of all calculate the mechanical power on the axle of rotation depending of the motor, the gears and the efficiency and compare with the needed force for raising the panels. By applying a safety factor I have modified the gearing to have enough force. I have made the same thing for the elevation of the roof by comparing the force of the winch with the needed force using winchtools.

After that, I have completely modeling the model of SR3D builder, in order to create the bill of material. In total, there are 1575 parts for the trailer and 600 for the truck. After receiving the whole parts from 5 bricklink sellers, I have built the trailer and check the functioning. After 4 months of work, I am satisfied by the result, It adds a success to my industrial references.

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Gallery

You can watch the two videos, the first was made with my parts to check the functions and present the concept to the customer. The second is the final version with all the parts.

The pictures during the building :

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