06Oct

Magnets? What are the forces on it?

Many people wonder how magnets can withstand accelerations of the print head.

We made a simulation with mechanical analysis software MECA3D (thanks to Mr Boulaton for his help). The trajectory the center of the print head will follow is a square of 100 mm side , rounded in the corners, the green square in the image below. The almost 400 mm long perimeter is covered in 1.2 seconds , with average speed of about 20 m/min (F20000 in the ISO code) .

It’s a little messy, but it still gives information .

The most requested are the magnets between the carriages and arms. Efforts have similar speeds for the 6 joints and similar max values . The spikes correspond to the phases of acceleration where abrupt changes in direction occur.

The blue curve below represents the axial force of the carriage on the arm to make the move. The spike correspond to the phases of acceleration when a change of direction occurs. The dotted curve represents the same component of static effort . A positive effort is a tension in the arm, so at risk of detachment of the ball. The maximum is about 0.75 N.

The radial force, which could also contribute to the separation of the magnet is very low, less than 0.1 N. This is logical given the very low mass carbon fiber arm . The most critical phases occur are those during accelerations or decelerations. The simulation was performed with an acceleration of 10.5 m/s ². In the second graph, the torque peaks at  t = 0.3 s when it reaches 1.2 N. Knowing that the maximum acceleration is about 3.5m/s ²; there is a large safety margin, in addition each Spiderbot magnet is capable of holding more than 4N.