# Why aren't more bipedal (or even quadruped) robots made with joints/articulations similar with those found on atmospheric deep dive suits?

The sole reason I'm making this question is due to the fact that such joints/articulations would allow the electric motors to continuously move while the walking motion is performed, instead of the back and forward movement of our biological counterparts in which such robots were inspired.

I'm assuming that if you keep changing speed in a specific way, you could replicate the same back and forward movement of biomimetic legs without the need to force the electric engines. After all, spinning wheels are supposedly more efficient than legs.

(of course, the examples bellow are for human use in mind, unlike the robots that can be reduced to simple bearings)

The joints/articulations that I'm referring to are the leg ones on these examples:

• allow the electric motors to continuously move while the walking motion is performed ... this makes no sense, please explain what it means Aug 1, 2022 at 19:15
• @jsotola when a bipedal/quadruped leg moves backwards and forwards, the electric motors need to fight the inertia of the leg movement every time. If you let an electric engine rotating continuously, it could use less energy since it isn't fighting too much inertia. Aug 2, 2022 at 15:59
• those joints do not rotate continuously ... they move forwards and backwards Aug 2, 2022 at 16:20
• @jsotola but you can change them to be able to rotate continuously. Aug 2, 2022 at 16:57
• There's a lot more parameters to tune that drive efficiency calculation than continuous rotation. And even that is not a good proxy if you build in elasticity to a system reversing motions can be very efficient too.
– Tully
Aug 2, 2022 at 18:20

Why aren't they, you ask? Typically, it would be a worse design.

Atmospheric deep dive suits, and, for that matter, space suits, are designed to maintain constant internal volume. Otherwise the occupant would have to constantly work against external (dive) or internal (space) pressure simply in order to move.

The fancy joints seen in both kinds of suit are a design solution for the constant-volume constraint. In addition, the actuators are people, not motors, and accommodating humans adds a whole new dimension of constraint.

In contrast, robots with walking legs are designed for a thoroughly different set of constraints. Remove those of constant volume and human occupancy. Open up a vast new design space of size, power, speed, battery life, and so on. Include tradeoffs of cost and safety.

Although both applications involve legs, there is little reason to expect a design for one to carry over to the other.

The Kinova Jaco arm has some joints on a 45 degree angle.

This arm is specifically designed to aid people with disabilities. I believe they used these joints to eliminate pinch points wile still maintaining range of motion.

When I was designing a new humanoid arm I did a study on the best arrangement of joints, I looked at off-axis joints like this too. I quickly found that they are not very good. You get a lot more "bang for your buck" with orthogonal joints. i.e. more range of motion and better manipulability workspace.