Solenoids For hydraulic Mechanical Arm of ROV

[TeamHydraROVHouston]

Greetings, My team is currently working on the design of a mechanical arm to be attached to the frame of the ROV, and want to have the entire hydraulic system onboard. The issue we are facing is that there will be two arm with each requiring 4 double-acting cylinders, and two solenoids per cylinder used, coming to a total of 16 solenoids. Is there any way to possibly reduce this number or possibly another hydraulic configuration?

 

[MikeHalloran]

Solenoid valves are pretty cheap, relative to other ways to control a cylinder, which might explain their popularity. Why do you care how many valves there are?

Have you considered servovalves or proportional valves?
Do you know what they are?

... Another hydraulic configuration? You mean, one other than the one that you haven't actually revealed? The one that is, or not, compliant with the design specification that you also haven't revealed?

What problem are you trying to solve?



Mike Halloran
Pembroke Pines, FL, USA

 

[georgeverghese]

At the outset, it would appear that a 4 way solenoid valve could also be used for each double acting cylinder?

 

[TeamHydraROVHouston]

Thanks Mike I appreciate your response. Yes, I should have first stated some of the fluid hydraulic specs we are limited to. It's a rather small scale vehicle compared to the ones we see in the industry today and is our capstone engineering project. We are designing and manufacturing it ourselves with the assistance of other companies and sponsors. For the hydraulic system, we can only have a max pressure supply of 150 psi and the pump run off 15A 115VAC outlet with a nominal voltage of 48V. I have designed an arm with 3 degrees of freedom and a gripper as well and would like to achieve a payload lift of about 10 pounds. There are three linear double-acting cylinders with a 7/16" bore that actuate the arm. For our scale of project and the purpose of trying to keep the weight of the system light, I was wondering of there was another way to actuate the arms other than using 2 solenoids per cylinder? We are also possibly looking into the "hobbying" area for this equipment due to our low pressure specs. I have not considered servo or proportional valves and will definitely look into it. I am relatively new to hydraulics and am in the learning phase. I enjoy and am interested in learning everything I can about them.

Thanks George, I have considered using a 4-way 3 position solenoid for each as well, which would reduce the number of solenoids, and would still operate the valves the same as the 3 way 2 position we have now for each, so that is def a possible route to go.

If it is helpful I can post a drawing of the arm.

 

[3DDave]

Off topic: I dislike the term 'capstone' It's the last thing put on a structure and indicates it's finished. I think education should never have a capstone.

 

[3DDave]

On topic - using springs to set the cylinder position would cut the number of solenoids as only single-acting cylinders would be required. Normally, high force is needed in only one direction. You may lose out on speed in the spring actuated direction and some force is taken to overcome the springs, but it is workable. Notice that most muscles of most animals have one side much larger than the other.

 

[TeamHydraROVHouston]

Thanks Dave, I appreciate it! I have considered using single-acting, but didn't pursue the thought, but you bring up a great point. I am going to do some analysis and consider them as an option. Have a good one.

 

[MikeHalloran]

Given the unusually low system pressure limit in the rules, you may not want to give up the pressure/force necessary to move against a spring.

Also, if you don't want to use proportional or servo valves, you could PWM regular four way valves, or even hydraulically parallel a biggish four way valve with a tiny four way valve, so you have coarse and fine control of each cylinder. Or you could put a fixed orifice in the supply to a biggish four way valve, and use a biggish on/off stop valve in hydraulic parallel with the orifice in order to provide coarse/fine control.

In either case, the multiple valves per axis could be run by a 'stepped' five position toggle, sort of similar to the 'regular/express' mode of some auto power window controls.



Mike Halloran
Pembroke Pines, FL, USA

 

[PNachtwey]

Why not move the arm directly with electric motors and small pumps like a scaled down mobile system? This way energy is not lost by pressure drops due to valves.



Peter Nachtwey
Delta Computer Systems

http://www.deltamotion.com

 

[subsearobot]

for your education, look at Hydraforce SP08-47D proportional valves. these are used as a cost effective solution for proportional hydraulic control in some subsea systems. They will not operate at the low pressure that you are using however. It is a 4way, 3 position valve that controls both directions of a cylinder (or motor).

will your pump/motor be submerged? if so, what are you going to do for a "reservoir" (we call them compensators when the entire system is submerged)?

wish I could help more- sounds like a fun project. I dont have much experience with low pressure hydraulics- industry standard is 3000psi or even 5000.

 

[georgeverghese]

Agreed, think it is the hobby application that seems to be getting in the way of enabling the typical higher hydraulic pressures required for a lighter combined weight of the hydraulically operated actuators.

 

[TeamHydraROVHouston]

Thanks everyone for the feedback, taking them all into consideration and I really appreciate it! The more I can learn the better. Been working hard balancing summer courses and work, along with the project. To answer the pump question, we'd like the pump to be submersible, and still deciding on what to use as the reservoir. I will surely update progress as we move along. Thanks.

 

[TeamHydraROVHouston]

Good Afternoon,
I was curious as to whether anyone has a suggestion for a good option for a submersible pump for the scale of application we are doing for our project. As we'd like to have all our hydraulic system be on-board. The deepest we are going to go is 75 feet and only utilize 125 psi pressure supply from the pump. We have also considered that if we do not do use a submersible pump, we can design a pressure housing to house the unit on the ROV.