Fitness Accessory - Barbell Attachment

When the sport is religion and you are fitness addict

Yet another submission to a GrabCAD challenge for designing a fitness attachment  for Calf raise exercise. The contest was posted by 3D Technology and design requirements included:

  • The basic model should be light in weight but strong enough to support up to 1,500 pounds.
  • The design should have a locking mechanism or quick release clamp that will allow the device to lock onto a smith machine Olympic barbell (25 mm to 28 mm).
  • The locking mechanism or quick release clamp should have rubber padding that fits around a Smith Machine Olympic Barbell handle so as not to damage the barbell.
  • The locking mechanism or quick release clamp apparatus should be able to withstand 1,500 pounds.
  • The locking mechanism or quick release clamp should be able to attach and unlock from the smith machine barbell in a quick manner without any tools.
  • The lower back padding should be designed to fit comfortably on the lower back even if an excessive amount of weight is used.
  • The new design should be modern, ergonomic, durable, appealing to the eye, comfortable.

And this is what was suggested:


Donkey Calf Raise

Shape of a hyperbolic paraboloid (saddle shape) has been chosen because it is known for its ability to take on greater loads. Except for that, it would fit comfortably to any type of body of the user. The shape is clear, simple and minimalistic.


Barbell Attachment Mounting

The mechanism that attaches to the barbell is divided in two – the lower part is connected with the paraboloid with rivets, and the upper part has a handle and clipping mechanism. The mechanism is released by pushing the button that is colored in black on the left side. Just grab the handle and push the button with your thumb. The different color is to indicate which side should be pressed to release it. The mechanism is not complicated, it has simple parts that are easy to produce, and it is easy to be assembled and disassembled.

Mounting Mechanism of the Calf Raise Attachment


The body of the paraboloid and the mechanism are made of aluminum, and there is foam padding on the lower side. The mass of the attachment is about 3,5 kg.

Finite Element Analysis

The initial request was that a Finite Element Analysis should be perform to ensure that the attachment could stand 8400 pounds of compressive force. After that is was corrected to 1500 pounds, but anyway, it has been FEA tested with force of 37500 N that equals 8430 pounds, and it has no problem with that as it is seen from the images.

FEA Test - Von Mises Stress

Von Mises Stress results showed that there are only a couple of small concentrations of stress, but as a whole, the attachment is in dark blue color, which means that it could withstand even bigger load.

FEA Test - Displacement Results

Displacement results showed maximum of 3.133 mm displacement in the area where the barbell is placed. Which is not unusual, too.

Upon a request from the founder of 3D Technology the foam padding was made thicker for more comfort.

Thicker Padding Attachment

The Donkey Calf Raise attachment has been designed, rendered and FEA tested in Autodesk Inventor. The 3D model could be seen and downloaded from GrabCAD.