FulanoDetailHydraulic mech
Like I said, I would 3D model a hydraulic actuated mech just in case.
Because:
- I literally could not find a single example of a voice coil and a servo motor that could output 3,000 kg of force while being compact and light.
- I also cannot find a way of predicting how the output of these electric actuators would behave. Would they be efficient? Would they be fast, but weak? Slow, but strong? I tried to ask online and essentially, when people aren’t just plainly telling me to kill myself, they explain that they cannot help me without investing a lot of time and effort on calculating/simulating the performance of these actuators.
- And to be honest, the more I burnt my brain trying to figure out how to make the electric actuators lighter, the more I wondered if it would have been best to use a hydraulic system. A central pump with a single 300 kW motor, however its weight, would still be more practical than 35 different motors that can’t even fit in the mech’s body.
- Normally, hydraulic/pneumatic actuators need to be 100% solid in order to contain its working fluid, however, if you use the highly efficient diaphragm/membrane linear actuators, you can modify the structure comfortably. The idea is that a high tensile strength tissue/cloth membrane would work as the liner inside a skeletal solid structure on the outside, using a design similar to monocoque, truss, lattice, metal foam etc.
The hydraulic actuators that I will base myself on:
Spider-leg inspires new, rotary diaphragm actuator
For the pump itself, I think I will go with a hydraulic radial diaphragm piston pump. Which is normally a hydraulic radial piston motor, but adding energy to it turns it into a pump.
Poclain Hydraulics Motor Technology
The idea is to keep the diaphragm pistons in place while applying check valves and rotate the outer undulated ring.
Since I will be working with diaphragm pistons instead of gear-pumps, it will be easier to adjust the size accordingly to the motor/engine output.
For the actuator you can still apply an undulating pattern on the outer ring similar to the 3 sine waves of the 3 phases of a brushless motor.
This way you could have rotary actuators that could work not dissimilar to the electric actuators (which the electromechanical servo controlling system) and still be really precise.
Just imagine that there are 3 different radial piston hydraulic motors with a wave outer ring with the undulation on the outer-ring being the same undulation of a phase if it was an electric motor.
You could also make the wave-plate axial instead of radial:
Learn hydraulic axial piston motor
Of course, that is not the only type of hydraulic rotary actuator:
All of these can be built using the diaphragm design, even the Helical Spline rotary actuator, which I do think is interesting.
How the Hydraulic Rotary Actuator works
You don’t need to make it as complex as the ones shown in videos etc, you could even use ball screws etc.
Source: What type of hydraulic motor is most efficient?
Now I need to find a cloth that can survive 15 to 20 MPa of pressure in order to make these membrane actuators.
… Bruh, literally anything. HDPE has 40 MPa of tensile strength, steel has 600 MPa. All I need to do is to make the membrane based on the thickness and weight of plastic ropes for towing.
I could even surpass the 15/20 MPa threshold that hydraulic systems normally use in order to save even more weight.
Observation:
Cavitation on water starts to occur at 3 m/s of linear speed, which should be the upper limit of the fluid flow in the actuators and in the pump.
Cavitation upon low-speed solid–liquid impact | Nature Communications
Cavitation Explained and Illustrated
However, it is hard to say at which exact speed cavitations start to occur at the surface of an object, which would be the major problem in a water hydraulic actuation system.
The pump must be adapted to the power source that will power the pumps, either an internal combustion engine or an electric motor, taking into consideration the maximum flow speed and pressure, it would be optimal to adapt the pump.
Since the pump will also be a diaphragm piston pump (due to efficiency and low complexity), you would need to change the diameter and stroke distance of the pistons proportionally to the speed and torque of the engine/motor.
Source: (PDF) The future of ship engines: Renewable fuels and enabling technologies for decarbonization
Magnetohydrodynamic levitation for high-performance flexible pumps | PNAS Steel Heart- Artificial Heart Prototype (these pumps works more like a heart, it may be useful)
Depending on what you power the hydraulic pump, with a combustion engine or electric motor, you could use hydrodynamic bearings. Since a combustion engine can’t be powered on and off all the time unlike electric motors, you could use the engine to power the hydrodynamic bearings while idling.
Also, let me link this here, because I will use it a lot.
Interactive Nomogram for Sizing of Hydraulic Hoses
The recommended velocity for pressure delivery hoses varies from source to source, example:
Flow Capacities of Hose Assemblies
How to determine fluid velocity & hose ID
HYDRAULIC HOSE SIZING NOMOGRAM
Line Sizing And Fluid Velocity In Hydraulic Systems | Flodraulic Group
It would be interesting to have integrated impact absorber/dampener/air spring on the actuator for compliant motion and/or safety.
How Mono vs Twin Tube Shock Absorbers Work
To Be honest, I don’t really know what is the difference between the two, since in both you use pneumatic pressure to protect the system from impacts. But while searching on the subject, it was heavily advised to use both of them on car suspensions.
I received an answer on Quora:
“Firstly; forget the term “shock absorber”, because it’s misleading and wrong. The term is normally used as a synonym for “damper”, but actually the shock absorber in a suspension system is the spring. The damper is a completely different thing. With that out of the way, I can explain:
An air spring is an inflatable bladder that acts just like a spring. It’s like a balloon basically. Like a spring, after it absorbs the initial shock, it’ll bounce around a lot, so it needs controlling…
A damper is what controls the motion of a spring and stops it bouncing around after impact. Bouncing is caused by the spring releasing the initial shock that it’s absorbed back into the system as it uncoils. A perfect damper allows the spring to absorb the initial shock and then arrests the recoil movement instantly once the spring has recovered to its static length. It does this by being a piston in a tube with valving that affects its resistance to movement. Perfection is rarely achieved, mainly because each bump is different and the mass of a car will change with fuel load, passengers etc. The damper invariably affects the initial shock absorption too, which makes tuning dampers really difficult. Parameters you can change for the valving are normally bump, compression and rebound, for fast and slow bumps.”
HAC(Hydraulic Actuator Controller) v2.0
Automatic Control System for an Oil-Hydraulic Actuator of a Scissor Lift
These are the only compliant hydraulic actuators that I could’ve found.
(Why always solid metals? Why not trusses, lattices, polymers, composites etc? It is always so unnecessarily heavy…)
And since we are already here, why not make it a telescopic diaphragm acuator?
This time I won’t even attempt to make it double acting, specially because it really isn’t that practical. The return motion of the hydraulic cylinder will always be weaker because the rod always takes space inside of the actuator, and since pneumatic/hydraulic actuators work based on the pressure applied on the cross-sectional area, you really can’t avoid it.
Unless you use a rope as the shaft, but that would only allow for a pulling action.
But in the end, the telescopic one would either be the stewart platform mech or a base line for every actuator on the system.
Now I need to think about the hydraulic connectors/fittings and the hydraulic hoses.
Q.Safe Flat Face Quick Coupling - The Gold Standard
Oleocon Hydraulic Quick Coupling
Flat-Face Screw-to-Connect Couplings in Detail
Stucchi Quick Couplings - Flat Face Screw: VEP-HD Series
Which Is Better - Poppets Or Flat Face Hydraulic Quick Connect Couplers?
Tractor Basics - Hydraulic Couplers 101
Rectus Quick coupling series 25KB how it works
Rectus Quick coupling series 87KF how it works
How Do Rotary Unions Work? (it is the hydraulic counterpart to the slip ring)
It would be dangerous to have quick fittings during active pumping, so it would be interesting to only allow the hydraulic fluid to flow with a simple open-close valve.
Again, it will be a problem to make every hose and fitting by hand…
Hydraulic Fittings | 3D CAD Model Library | GrabCAD
Hydraulic Fittings, ORB, JIC, NPT, SAE | 3D CAD Model Library | GrabCAD
The servo-valves as well…
Again, the best option for these would be to buy off the shelf, but since they are obscenely expensive, we will need to make a compromise with cost, precision etc. Just like any other part of this mech.
Servo Valve (Directional Control Valve) | 3D CAD Model Library | GrabCAD
Snow Mackenzie | CAD Models | GrabCAD
Oil cooler,Design hydraulic stations | 3D CAD Model Library | GrabCAD
Rotating valve to create a sinusoidal movement | 3D CAD Model Library | GrabCAD
Circle Turn (Rotary Distributor) Hydraulic Valve Animation - No Audio . Volvo / Champion Grader
Proportional hydraulics, proportional valve, servo valve - how it works - Technical animation
[EN] Directional high-response cartridge valve WRC-4X: explanation & function
Proportional Directional Valves: Fun With Electro-Hydraulics
Sliding and Rotary Spool Valve Animation | Directional Control Valve
Direct Acting vs Pilot Operated Relief Valve Animation | Hydraulics
LS pressure flows through the LS circuit to the LS valve group in main control valve for #kyb #valve
Directional Control Sliding Spool Valve Working | Hydraulic Valves
how rotary directional valves work
Hyvair Solenoid Operated Directional Valves
Diaphragm Valve Working Animation Diaphragm Manufacturer Donjoy Technology
Eccentric Rotary Plug Control Valve | Valtek Sulamericana | EXL Series
Mucon USA Iris Diaphragm Valve (Being honest, I really like this valve design, but I don’t know if it would be useful for high pressure systems)
IRIS VALVE FROM NACHI VALVE THAILAND (there are mechanical iris valves that are way more solid and robust)
Four Types of Valve Work #valve #machinery #industrial #pipelines
MITSUMI Iris Valve "Choke Valve" demonstration @ iPBS2016 show
DIAFRAGMA MECANICO by MARIANOSANTOS - Thingiverse
Iris diaphragm (v2) with non-overlapping blades (parametric) by dkcode - Thingiverse
Iris diaphragm with non-overlapping blades (parametric) by dkcode - Thingiverse
Mucon ED 12 (írisz valve) | 3D CAD Model Library | GrabCAD
Iris Aperture Mechanism | 3D CAD Model Library | GrabCAD
Shutter Mechanism | 3D CAD Model Library | GrabCAD
Optical Iris Diaphragm | 3D CAD Model Library | GrabCAD
https://www.thingiverse.com/thing:5372788
Iris Mechanism | 3D CAD Model Library | GrabCAD
Aperture Box by BrienAllison - Thingiverse
EGGER - IRIS Control Valves | Australia & New Zealand | www.pumpsystems.co.nz
Counter Balance Valve Working Video in Hydraulic System
MITSUMI Iris Valve "Choke Valve" demonstration @ iPBS2016 show
Series 5200 Control Pinch Valve
Flowrox Pinch Valve Functioning
Type A Air Operated Pinch Valve
Mitsumi Iris Valve : Choke Valve Made in Japan
Flow Control Valves in Hydraulics - Full lecture with animation
Pneumatic Needle Valves by | Good Supplier's
Flow Control Valve Animation for Industrial Valve Company
#crane #excavator #automobile #Lifting equipment#Remote Control Proportional Valve
Arduino and hydraulics/oleodynamics proportional valve - Project Guidance
DIY Two Sizes RC Hydraulic Valve with 9g Mini Servo and 25kg Servo Motor
How to make RC hydraulic valve only with minilathe [no cnc there] step by step [plans included]
Direct Driven Ball Valve 1/4 NPT by flour4 - Thingiverse
Servo Valve by ericinventor - Thingiverse
Servo Driven Ball Valve 1/4 in Female NPT by Finch - Thingiverse
Servo Valve by VincentGroenhuis - Thingiverse
Servo Valve from Ball Valve + Hobby Servo by senorjp - Thingiverse
I was looking for manual valves for 200 bars/atms (20 MPa) of pressure, most of the diagrams are like the one above, where they don’t specify in which unit it is being written. I asked BingGPT (because it is the only chatbot that you can send pictures without a premium account) and it said it is in millimeters, but the diameters are in inches.
But, as you can see, it can handle up to 400 bars/atms (40 MPa) of pressure.
Also, a curiosity about the subject: valve torque.
I was wondering how much torque it would be required to rotate high pressure valves, and although I could find any solid answer, it seems it highly depends on the diameter of the hose and thus, the valve blocking element.
According to a few websites, valves for 10,000 psi (1,000 bar/atm or 100 MPa) would need a maximum 15 newton meter of torque (or 1,5 kilogram meter of torque).
Recommended Torque | High Pressure Company
Accordingly to ChatGPT, the speed of hydraulic servo valves should be:
“While there is no one-size-fits-all answer, aiming for a valve opening speed that is 2 to 20 times the actuator speed can be a good starting point. Ultimately, testing and tuning within the specific application context will yield the best results.”
If you assume that the valves operate with 15Nm and 1000 RPM maximum (10 times the maximum speed of the rotary actuator [100 rpm]), the servo motors would need to actuate with a maximum 1500 watts or 2 Horsepower. 2 x 35 actuators = 70 horsepower or 52,500 watts.
Not gud.
A way of circumventing that would be to either make my own proportional servo valve (super difficult) or use a similar approach to the reed-relays.
Where the hydraulic solenoid valves would be open proportionally to the output desired.
Well, I can throw this idea in the trash can too, because it wouldn’t be practical. Look at this 200 bar/20 MPa solenoid valve:
Now what the hell do I do?
Servo driven rotary valves it is…
Or maybe not.
The progressive servo valve is said to use the hydraulic pressure itself to move the sliding bar, the electric actuator is used simply to change the balance of the pressure itself.
Maybe you could replicate the same thing electrically or even mechanically.
“Circular notches provide a gradual opening but it is not linear with respect to spool displacement. They are primarily used in lower quality or manual valves because they are relatively cheap to produce with a single cutting tool. Triangulated notches provide a more linear opening characteristic but require more machining work to make them. The third example shows a chamfered notch as used on a high-performance proportional valves to give the most linear performance and faster opening speeds.”
Source: Advanced servo and proportional Valve Training
I do think that a simpler way of doing these valves would be by separating each channel with its own individual progressive notch.
I say this because you would need really high precision for a single single spool, a precision which I cannot make with a DIY servo valve made from scrap.
(PDF) A Review of Electro-Hydraulic Servovalve Research and Development
I do wonder, however, if there is the possibility of using another fluid. Hydraulics can work with whatever fluid, oils, greases, water, etc.
But you need a balance between cost and danger.
Water is the only liquid I can think of which you can find anywhere pretty cheaply.
In either way, you can use additives on the fluid, such as antifoams, lubricants, anti-oxidant, demulsifiers, dispersants, rust inhibitor, viscosity modifier, anti wear agents, dispersants, antifreeze etc.
Hydraulic oil science. Base oils & Additives.
I could only find videos about oil additives, not water additives.
But searching online, there are a lot of additives for water. You have to find one for each type.
If you want a DIY version instead of buying bottle after bottle of whatever chemical, I asked ChatGPT for help:
“1. Antifoams
Vegetable oil or mineral oil: A few drops can help reduce foaming.
Silicone-based Antifoams: These can be found in some household products and can effectively reduce foam.
2. Lubricants
Soap Solutions: Mixing soap with water can create a lubricating effect, though it may not be as effective as traditional oils.
Glycerin: This is a common ingredient in many household products and can provide lubrication.
Vegetable glycerin: It is non-toxic, biodegradable, and can help reduce friction in the system.
3. Antioxidants
Vitamin E Oil: This is a natural antioxidant that can help prevent oxidation in water-based fluids.
Rosemary Extract: This is another natural antioxidant that can be used in small quantities.
Citric acid: It can help prevent rust and corrosion. Use about 1-2 ounces per gallon of water.
4. Demulsifiers
Surfactants: Common household surfactants like dishwashing liquid can help separate water from oil.
Dish soap: A few drops can help break up oil and water emulsions.
Polyethylene Glycol (PEG): This can be found in some personal care products and can act as a demulsifier.
5. Dispersants
Detergents: Common laundry detergents can help keep particulates suspended in water.
Polymeric Dispersants: These can be sourced from craft stores or online and can help prevent agglomeration of particles.
Baking soda: It can help dissolve and remove deposits in the system. Use about 1 tablespoon per gallon of water.
6. Rust Inhibitors
Sodium Nitrite: This can be found in some food preservation products and can help prevent rust.
Boric Acid: This is often used in household cleaning products and can act as a rust inhibitor.
Sodium phosphate: It can help prevent rust and corrosion. Use about 2-3 ounces per gallon of water.
7. Viscosity Modifiers
Xanthan Gum or Guar Gum: These are a common thickening agent found in food products that can increase the viscosity of water.
Glycerin, Propylene Glycol and Ethylene Glycol can decrease the viscosity of water.
8. Anti-Wear Agents
Zinc Oxide: This can be found in some ointments and can provide anti-wear properties.
Graphite Powder: This can be sourced from hardware stores and can help reduce wear.
9. Antifreeze
Propylene Glycol: This is a common antifreeze agent that is less toxic than ethylene glycol and can be found in many automotive products.
Salt Solutions: Adding salt can lower the freezing point of water, though it may lead to corrosion.
10. Dispersants
Vinegar: It can help remove scale and deposits in the system. Use about 1 cup per gallon of water.
11. Additional Considerations
Biocides: If using water, consider adding a biocide to prevent microbial growth, especially if the fluid will be stored for long periods.
You could use Vinegar, Hydrogen Peroxide, Tea Tree Oil, Eucalyptus Oil, Boric Acid or Citrus Seed Extract.
When formulating your hydraulic fluid, it's essential to balance these additives to avoid negative interactions, as some can compete for the same surfaces or functions in the fluid.
The only thing that I don’t like about the hydraulic system is that you can’t really change the torque/force.
The pump needs to output 20 MPa of pressure for every actuator, and every actuator will have 20 MPa of pressure.
The only way you can reduce that pressure is by either having an individual pump for every actuator or having a hydraulic resistance in the system in order to reduce the pressure. Which as far as I could see, reduces efficiency and wastes energy. Or I am wrong?
In either way, I was thinking of having a closed loop hydraulic system to reduce weight as much as possible.
Advance Hydraulics - Open Vs Closed Loop hydraulic system
Closed Loop (Hydrostatic) Systems - Part 2
In this case, I think it could be interesting to have a pre-pressurized system in order to save energy and space. Not dissimilar to a electrohydrostatic system.
EAS-EPU Electrohydrostatic Actuation System
Well, there is also the simpler possibility of using indirect hydraulic actuators.
Just like electric motors could have screw actuators, telescopic actuators, reduction gears etc, you can do the same with hydraulic motors/actuators etc.
And although I’d prefer to have direct drive on everything, and direct drive on the electric actuators instead, I have to work with what I have.
I would bet on simple designs, but I also really want to use telescopic actuators.
Articulated Link Lift System - 002
Slip modeling and simulation of spiral zipper friction-driven prismatic actuator
Rigid chain by spiderdab - Thingiverse
Animation SPIRALIFT - modèle standard
Zip Chain Attachment for BRECOflex belts by Sam_G - Thingiverse
https://www.printables.com/model/237467-zippy-bag-clip-print-in-place-ish?lang=en
3D Printable Zipper 2 - Complete Zipper Assembly by David Naoum
3D Printed Yet Another Zipper by msadler | Pinshape
Some of them are just conventional zippers that can be 3D printed, but if the improvisation mindset of this project was ever useful, you could take these zipper mechanisms and make a telescopic actuator.
Or you could just use a conventional chain/sprocket, attach it to a telescopic tubing and push or pull.
Examples:
https://www.youtube.com/shorts/zDmhxs2CeAY?feature=share
The Smart Tricks Inside Telescopic Machines
You would need to make multiple and/or really sturdy roller chains in order to distribute the force equally through the links.
I have a terrible habit of overcomplicating everything…
Observation:
In either case, pneumatic or hydraulically driven mech, you could use twisting string actuators.
In essence, they are made of strings attached to a rotary base that rotates until the string twists so much it simulates a contraction.
I couldn’t find the exact efficiency of such an actuator, nor I am sure how to predict how fast and how strong it would need to rotate for a given force and speed of contraction.
But I found this paper which says that their twisted string actuator achieved 85% of efficiency when lubricated, the detail is that the twisted string is inside a bowden cable. So the efficiency could come really close to 90% or more.
Preliminary Study of Twisted String Actuation Through a Conduit Toward Soft and Wearable Actuation
Feedback Linearization of Variable Stiffness Joints Based on Twisted String Actuators
Another interesting aspect of it is that due to the way it works, it has a spring action/compliance action, which could increase safety around humans.
Discussions
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