# Would a human-powered small mecha by using a mechanical lever system and Basic Hydraulics/Hydrostatic Transmission be physically possible?

Well, of course, I know that the question in the title is a bit too brand for the site, but will simplify it down the text so I hope it is more specific to answer. And yes, I know that histories don't need to be an "1:1 ratio" of realism, and need only to sound convincing, but I like to check reality first.

## The simplified question:

So, for this question I will put the supposed informations of this contraption:

• The Mecha would be more or less the size of a human, like a fat power armor.
• The materials that would be used to build this thing (structure, cylinders etc) could be aluminium, steel or even carbon fiber.
• You can imagine that the entire system is a series of steps in the ground in sequence (like the lever, cylinders etc. So that it is easier to stipulate.
1. First, a class-1 lever where the load would be a hydraulic/hydrostatic cylinder, and the force would be the hand/legs of a person.
2. Second, I don't know much about these subjects myself, so I hope I don't make incorrect assumptions: Option 1 would to make a larger and shorter piston at the end of the lever that would impulsionate a longer but thinner cylinder, the option 2 would be the reverse.
3. At the end of this thinner cylinder would be the final load, which, if wasn't a simple system laying on the ground, would be the weight of the mecha, the human and the cargo. Which I would put at worst at 300 kg in total.

## The basic principles to this question:

In basic hydraulics, it is said that a small weight can lift a heavier weight by increasing the surface where the force is applied (and sacrificing distance in which work is done) as shown in the picture bellow:

Of course, this also resembles a little of the physical principles of lever mechanics, in which you distributes the force of a load all over a lever cable, sacrificing the distance the object is risen, as shown in the picture bellow:

Well, I don't know much about hydrostatics myself, but what I know is that hydrostatic transmission can be used both for vehicles (like a forklift) and for human-powered "animatronics", as used by Disney in this paper:

## The idea:

Hyphothetically, if you had a 40km+ long indestructible lever on a indestructible fulcrum, you could lift the Eifel Tower with only your body weight.

With this in mind, the idea is to use these same principles (hydraulics/hydrostatics and levers) in order to increase the distribution of force without needing a 40km lever so a human pilot can power the legs and/or the arms to carry the system itself, themselves and up to 100 kg of cargo.

Yes, I would be "increasing" the "length" where the load is, but I would also increase the "length" where the force is being applied, increasing the distance in which the first move. If made any sense.

## So, the simplified system would be like this:

• First, a class-1 lever where the load would be a hydraulic/hydrostatic cylinder, and the force would be the hand/legs of a person.
• Second, I don't know much about these subjects myself: Option 1 would to make a larger and shorter piston at the end of the lever that would impulsionate a longer but thinner cylinder.
• At the end of this thinner cylinder would be the final load, which, if wasn't a simple system laying on the ground, would be the weight of the mecha, the human and the cargo. Which I would put at worst at 300 kg in total.

Of course, the idea would be to add more levers and cylinders to move the upper part of limbs, like the thighs and the forearms. The hands and feet would be too complex and/or delicate to actually scale up.

• A few years ago Raytheon had X0S 2 exoskeleton that used hydraulics, I think it allowed the soldier to lift about 200 pounds for long periods. To save space and energy hydraulics were an important part of the suit. DARPA also has had several exoskeleton programs that I think also use hydraulics. While not a true Mecha, I think you can find several examples that might help you figure out how you want to do the engineering. Jun 10, 2022 at 0:00
• A human body produces, at peak, about 2kw. A car engine puts out 20-200kw. I don't see many car-engine powered mechs...... Jun 10, 2022 at 8:01
• Are you deliberately excluding an electronic control system?
– user86462
Jun 10, 2022 at 10:53

You've missed a point about force multiplication

Yes, you can use pullies or hydraulic/pneumatic pistons or levers to make it easier to move something — but you're forgetting that the force needed to move something doesn't change.

If you have a force multiplication factor of 1:10, what that means is that you need to pull on the rope for 10X the distance to lift that heavy object that could have been lifted in 1X the distance if you had the strength. Or that you have to pump the hydraulics ten times because you don't have the strength to simply push the brakes to stop your car quickly. In other words, force multiplication doesn't make the item you're trying to move lighter, it just breaks the work up into small units to make it manageable. And it has a price.

The consequence is that your mecha will move at a snail's pace (and I'd expect the human powering it will become exhausted long before anything akin to traditional mecha results will be seen).

So, while the technical answer is "yes," the practical answer is "no."

If you're knee-jerk reaction is to disbelieve that, hop on your bicycle and ride it up a hill. You can gear down to bring the job of going up the hill into the realm of human practicality — but the bicycle slows down to make it happen. In the end, all the force needed to move the object is still required to move the object. The phrase "force multiplication" would be better expressed "the-trade-off-between-chopping-up-the-force-into-consumable-bites-and-how-much-things-slow-down-to-make-that-happen."

• Exactly, work = force * distance; you can lift 20 times more....one 20th the distance.
– user86462
Jun 10, 2022 at 10:54

Yes but....

A good first approach to any engineering problem is to approximate the energy requirements. The energy requirements tell you how big-er an engine you need to drive a mechanical system.

What do I mean by energy requirements? Well, a normal human can use a high-lift jack to lever a 4wd vehicle off the ground. With nothing other than some mechanical advantage a human can lift 2000-3000kg. Of course, this increase in strength isn't free. It comes at the expense of speed. Each pump of a high-lift-jack amplifies the users force 100 times, but it also makes the motion 100 times smaller. The humans arms move 0.5m, the car moves 0.5cm. And so it takes a longer time to lift the car.

The same applies for your mech-suit. The human is your power source, and so everything is a tradeoff.

• A human can run at 20kph, but if you double his mass, his speed will halve (approximately - A human carrying 100x his body weight may not be be 100x slower, he may be squashed).

• a human being can dead-lift 100kg. If you use mechanical advantage to increase his strength to be able to lift 1000kg, it'll take him 10x as long to lift it the same distance.

Mechanical advantage is no free lunch. If the only source of energy is the human body, then you are limited by the 2kw peak output of the human body - regardless of the complexity of the system you surround him with.

The relationship between force and time may not ve clear, so we'll take a brief look at Energy Per Second, otherwise known as ... Watts.

1 watt is equal to 1 joule of energy in one second. 1 joule is the energy to lift 100g through 1 meter.

So a human beings peak energy output of 2000W is enough to lift approximately 200kg through 1m in one second. Sounds unrealistic? Watch a deadlifting contest. Or the human can move approximately 1kg through 200m in one second. Sounds unrealistic? Watch some javelin throwing.

So if you strap a human into a 300kg mech suit, you can expect a perfectly-tuned-mech-suit to be ~3-4x slower at running than said unaided human. Chuck on another 100kg of cargo, and it'll be ~4-6x slower than a human at running.

I can put on a 30kg backpack in about 3 seconds. It'll take your mech-suit-human about 9 seconds to lift 90kg of cargo onto his back.

You may notice I haven't mentioned hydraulics or levers or anything about how the suit is built. And that's because energy analysis doesn't require the detail of these things - one reason why it's so useful. No matter what your system is built with, the above constraints will still apply.