Novatives Original Design
The project consisted in a competition or a tender in the website of Grab Cad, where one company (Novative) wanted some help finishing the design of a Hand Truck. The Hand truck was prepare to load weights of 700 Lb, and using one stabilizer Leg, the workers could move the weights without problems for the factory.
The main problem was the Suspension of the Stabilizer Leg, which had to resist the weight of the load without brake. They thought using one spring and a Shock suspensions that it wasn't enought; that's why they were asking for help and creating this contest.
The features of the original design of Novative were the following:
The first and second images is the static anaylisis of the leg suspension, while the third are the dimensions and the value of all the parameters of their problem.
After give all the parameters, they uploaded their model (handtruck and leg suspension) so we could see them in a CAD software.
the handtruck + leg suspension opened in catia
Original leg stabilizer
After take a look, analyse and done some operations, it was clear that the design they did wasn't able to resiste the weight and forces they wanted. specially with a shock spring that can resit 1200 Lb of force.
To finish the specifications, Novative comented that they wanted to maintanin as many pieces as the original, which meaned not modifying the design in excess.
My Design
The first thing was the operations. How is it possible that the design can resist that weight. weight that could be increased up to 900 Lb!!
The three options were the following:
-increase the angle between the shoch spring suspension and the stinger wheelleg welment.
-use two springs, one in the original position and add a second one that can take part or half of the force weigh
-A complete new design
The third option is the last of the three, because it could be used just in case the other two weren't possible or compatible with what the client wanted.
So I started with the first one, engaging the shock suspension in the rear part of the leg welmentl and in an upper place of the handtruck. This configuration started to be to complicated; adding many new pieces and probably having many problems when I would do the stress analysis.
Then, I decided to focus in the two springs shock suspension option. I could maintanin the leg welment (without modificatons) and I would just have to create a new braket that substitute the two semi-brakets of the original design.
With calculations done, I determined that the angles of the springs are 45º and 61º, as it can be seen in the folowing image.
sheet with some operations and the angles of the configuration selected
After the calculations, the two shock springs suspensions have to resist a 1200Lb force compression (the maximum permited) and the force of the conexion between the braket casign and the leg weldment is 1463.72Lb in the opposite direction.
The design has to be closed for when h rear leg is not necessary, so I added some pockets or guides that the pins could follow and let the system close.
Image of the hadntruck+rear strider in catia (springs removed)
Image of the handtruck+rear strider wheel in close position
Due to the high values of the force, and the design, I had to added some reinforced parts in both sdes, in the rear and at the botton, so the braket casign could resist them without braking, deformating to much or cross the plastic point.
The material selected was a steel with an E of 2e9 and a poisson ratio of 0.30.
Analysis in Abaqus cae of the braket casign stress without reinforcements
Analysis in Abaqus cae of the braket casing stress with the reinforcements
Altough is not 100% finished, the improvemets are small, and the configuration was ready to a client analysis.
My design was finally the 10 best, and altohugh I didn't get the best prize, I got one lower and the satisfaction of finishing in a good position being my first design in the professional world of the Cad engineering.
As it can be seen in this link, my design had the 10th best punctuation.
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