Underactuated robotics are so cool. In the hobby BattleBots community, there is a design where the whole robot only has a single motor, but it's able to move in any direction and damage the opponent, all just by controlling the single motor's speed.
Most robots have at least three motors, two drive sides and a weapon motor. The trick to getting away with one is integrating an impactor into the chassis of your bot, using the single wheel to spin up to ~3k RPM, then by tracking the rotation angle of the bot as it spins, you speed up a little while the wheel is pointing where you want to go, and slow it down a little when it's pointing the other direction.
Can highly recommend this course https://underactuated.csail.mit.edu/ Russ Tedrake is an amazing lecturer (and researcher)
Well not just battlebots, real life 6th gen fighters now all lack the vertical stabilizer so they have to rely on very sensitive real-time software control of the elevator/spoilerons to do banks and yaws. Not sure if it counts as under-actuated but they are tremendously difficult to steer without computer control.
You're referencing the fact that it's dynamically unstable, and thus needs to be stabilized with a computer. That's a different thing.
You can also have aircraft which are under-actuated yet are dynamically stable. One example is a parafoil, which achieves controlled flight using only two actuators (pull lines).
I'm not super familiar with heavy equipment like dozers and such, but some of them may also have a single motor to pressurize hydraulic fluid and valves to articulate the various pistons. So may be able to make the argument there too
In that case, the valves/pistons pairs are all independent actuators. The hydraulic motor is more a constant power source for all of them.
Yeah, the analogy for drones is hydraulic piston -> electric motor and hydraulic pump -> battery
That is common and you can't run two different cylinders at the same time. Depends on how the pump and valves are plumbed of course. Sometimes you can run more than one but you split power.
That sounds like it could be solved with more valves.
it's not that easy.
You can run your cylinders in parallel, however that means whichever cylinder has its easiest time moving is going to capture a proportion more share of the power. If things are not perfectly balanced, which in reality they're never going to be, that means the cylinder that needs to work the hardest is going to work the least. And so it's going to take a huge amount of effort to control.
Alternatively, you can run your cylinders in series, however that means that if you're trying to feather one to move slow, all the others are going to have to move slower too.
You end up needing multiple pumps in order to make this work well, but pumps are rather expensive and so that's going to bring your costs up. Plus, multiple pumps mean that you're going to potentially want more power than your motor can deliver.
All the above can be solved with careful engineering. However, engineering is expensive too in order to get this right and it's going to take a lot of work.
Almost everything can be improved by making it cost more.
Or more power ;)
Is there a way to track what's going on in the battle bots community? It was pretty cliche, but battle bots was fun to watch in the 90s/2000s.
It was brought back by Discovery and videos are also published on YouTube: https://www.youtube.com/channel/UCxNDM5ZhvDa_Z1qTUap7IRw
> but they are tremendously difficult to steer without computer control.
they are not humanly pilotable without computers. they are inherently unstable.