I’ve been getting a lot of comments lately asking about the various power options you have for exoskeletons – and they all have their merits. So let’s take a closer look.
There are Five main options.
- Servo motor
- Linear Actuator (electric)
- Mechanical Advantage
As you know, I’ve mostly been playing around with pneumatics. This is because they are cheap, flexible, fast, and easy to control. Unfortunately they don’t have much precision – typically they are ON or OFF, it’s hard to do proper positional control with these.
I’d love to work with hydraulics, but they are much more expensive, much more dangerous, and VERY powerful. They can be controlled very accurately, but will limit your flexibility because of the flow restriction due to oil. If you take the pressure off of a pneumatic cylinder, it will move quickly as it vents to atmosphere -- you can't do that with hydraulics, otherwise you'd have oil squirting everywhere!
Servo motors would be cool, but they are super expensive. Even cheap servo motors (a few hundred dollars) still only have 10-20kg-cm torque. Sounds like a lot, but if you do some basic physics… you’ll see that 20kg of torque at a distance of 1cm, equates to 0.2kg of force at 100cm – and last I checked my arms are a heck of a lot longer than 100cm. which means the exo could lift grams, not even kilograms of weight. Ha. There are ones that could work, like ones found in industrial robot arms – but I don’t have that kind of money.
Linear actuators are a cool option because they are electric, efficient, and very powerful – unfortunately, they’re also really slow. They work using a ballscrew design, not unlike how my laser cutter bed raises up and down. This allows for huge mechanical advantage – the motors in these aren’t very big or powerful, but because of the mechanism, they are! Could probably build an exo at a similar cost to the pneumatic system with linear actuators. BUT. They aren’t flexible and would have to be powered at all times – and since a battery pack is the Achilles heel of ANY exo design… not gonna work very well! When a linear actuator isn’t powered, it’s basically fixed in position. So if the exoskeleton ran out of juice, you’d be stuck in a rigid metal skeleton. Crap!
Finally we have mechanical advantage. An unpowered exoskeleton. Think about your bicycle. How fast can you ride it? How fast can you run? That’s mechanical advantage. A mechanical advantage exoskeleton would be flexible, it could enhance your strength by up to maybe 2 times, and it wouldn’t even be that expensive – but it requires a lot of engineering and design to make it work.
Here's a summary of the five main technologies:
|Exoskeleton Power Options|
|Pneumatic||Hydraulic||Electric Servo||Electric Actuator||Fully Mechanical|
So, what’s the CoD exo going to be made of? Well unfortunately since I have a very limited budget… By the way, you guys should check out my Etsy store to help support the channel! My current design is to use mechanical advantage for the lower half to maximize flexibility and reduce power draw. The upper body then will be powered allowing super human strength. Together – it’ll be a pretty versatile exoskeleton. Powering the lower half would be very difficult – good luck running! So I think this will be a happy medium which will make the exo a lot more functional.
And that’s about it! Stay tuned to my YouTube channel (Subscribe now!) for more updates!