Day 3: Extendable Arms

The trickiest part of this whole project is undeniably the arms; there are a lot of factors that actually need to be taken into account. The purpose of the extendable arms is to be able to lift the car by its wheels. Let’s get straight into what I have to think about before finalising my design and trying to build it.

There are totally four arms in one robot, two on each side. Each pair of arms is responsible for carrying one wheel off the ground; we aren’t looking to carry the car metres above, just a small ground clearance to be able to move the car. If you remember from the Day 1 blog, I referenced a video in which they don’t use scissor lifts or jack stands. They use these extendable arms to push onto the curved surface of the wheel from opposite sides to create an upward force that lifts the wheel up slightly; this is done for all four wheels simultaneously to lift the car up.

Factors taken into account: the length of the arm, the mechanism of the arm, the load the arm is capable of carrying and how to reduce friction while the arms push onto the wheels. So, in my case, the length of the arm will not matter, as I will be building DIY cars based on the size of my robot and not the other way around. The load the arm is capable of carrying will also not be a problem, as my DIY car will be based on the limitations of my robot.

For the mechanism of the arm, I had two ideas in mind; one was creating a two-axis arm, in which the arm would move in the x and y directions at will, but I ended up using the idea given in the referenced video, which is to pivot one end of the arm and use rotational motion to extend it on the other end using linear actuators. To understand when the arm has touched the wheel, I will probably be using a limit switch, although I haven’t really fully looked into it. Additionally, I will be adding rollers to the side of the arm that comes in contact with the wheel to reduce friction while applying pressure onto them. For a more stable movement of the arms, I have added a ball caster at the bottom of each arm to be able to carry the vehicle in question.

Finally, a small design update: I brought the wheel inwards, removing parts of the chassis, while the arms are as wide apart as possible. This makes the robot’s width small enough to go between the car wheels while also being able to reach the wheels with its arms. Look below at my updated design, and that’s a wrap for day 3.