Motors, servos and hydraulics
AIman
Posts: 531
I am working on a project that will require constant pressurse to be maintained as well as applied and released quickly. Is it better to use a DC motor, a Servo or Hydraluics? This project will need to be able to hold the pressures for several hours at a time in vaying amounts and needs to be able to be applied or disconnected quickly.
What opinions are there and why do you lean that way?
What opinions are there and why do you lean that way?
Comments
Mobile, stationary? What power sources are available? Hobby application or real world? As big as a house or as big as a bread-box?
A sketch or a few more lines of explanation would REALLY help!
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Tom Sisk
http://www.siskconsult.com
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What kind of pressure are you speaking about? Are we speaking of pressure on a gripper, a hydraulic valve, some other fluid valve, a servo or a motor?
We need a few specifics here, to offer any intelligent answers.
Regards,
Bruce Bates
Post Edited (Bruce Bates) : 10/2/2006 7:15:24 PM GMT
One part is being able to control the linkage on the throttle, one to adjust the clutch (used to be pull the lever and let go but now it is slipping). And the last one is to aid with steering. We have wiring in place form the current insturment panel that will allow us to hook in a computer.
So to expand farther, the linkage needs to be controlled based off power demands, the clutch is adjusted to slow the engine - it works similar to a hydrostatic clutch. The steering is based on sensing when the steering wheel turns and then adds power to help steer.
Most of the code is in place, I am debating on what to use for adjusting these items. Motors would provide adjustments but the continued pressure is an issue. Servo's can hold the pressure but are hard to find with any sort of power. Hydraulics can apply pressure and hold it along time but I don't know how fast it applies and releases.
For emergency power down and stopping of the engine there is a 1/10 of a second window to get things going.·5 min on the long end with up to several hours in a postion.
Obviously electrical power won't be a problem.
Post Edited (AIman) : 10/3/2006 3:13:49 AM GMT
Can you tell a bit of what was originally used for each of those functions? Was it all manual or were there some controls before?
In place of a servo, you could use a small gearmotor with some positon feedback. It would give you the positioning capability of a servo but at a lower cost. The downside is many have to be powered in both directions. An emergency shutdown would have to kill the engine by another means rather than wait for the throttle motor to return to zero. Usually an ignition kill on a gas engine or the fuel rack solenoid on a diesel.
The hydraulic route can give you power and smoothness, for sure. With the right valves, speed shouldn't be an issue. The tree harvesters I work with are all hydraulic with electric control and we're dealing with thousands of pounds of logs moving at 10 meters per second then postioning them within an inch or so.
Do you have hydraulic power avialable on the machine now?
Cheers
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Tom Sisk
http://www.siskconsult.com
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They add a lot of torque, and it won't take a lot of current to 'hold' them.
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Possibly·worm gears and DC motors would work, but then how long will the motor last? Would it overheat because of applied power or would it be ok to run power constantly? My drill will overheat if it only gets enough power to hold the screws in place and starts to smell shortly after.
I suppose I could tap into the electrical and·run a pump for hydraulics. Rerouting electrical is simply a matter of using one of the open fuse slots, the only other challenge would be getting the correct valves, a smaller assembly would work better for speed and still maintain enough power.
Originally the throttle linkage was controlled with a simple internal governer. If you think of a lawn mower with the flag shaped governer, that is about how this one looked (it broke and our replacment sucks). To solve for this I ordered the sensor from Parallax that monitors RPM. This data will be feed to the computer. The computer will adjust the RPM via the linkage hookup as needed by going off the power requirements and move the throttle linkage accordingly.
The original clutch assembly was run by a lever and spring. You squeezed the handle, pulled the lever to the correct position and let go. It takes a little effort, but not much. We could manufactor something but by the time we get done with that it we may as completely rebuild and make it more user friendly.
The steering was an old form of power steering that basicly didn't do much. It helps in a full load but otherwise you couldn't really tell.·There has to be some sort of gear drive that can be worked out. A paddle boat I was on last year used hydraulics to move the boat on the river, so there is something available.
As for controllers I have the BS2, SX and Propeller chips already and an extra motherboard, laptop and computer laying around that aren't used often. Probably will hook up the laptop.
I lean towards Hydraulics more all the time, it seems to be the most reliable and easiest to monitor.
Post Edited (AIman) : 10/3/2006 1:12:07 PM GMT
The clutch was used to raise and lower the blade in the back, the brakes are non-powered and simply put steering that thing sucks! The available hydraluics were orignally meant to lift a bucket but the bucket is taken off and the power there is serious overkill. With what is there and what is available we could easily mount a small resivor behind the seat and run power from an extra fuse.
We have a small laptop in the cab that holds work to be done and stuff like that so the computer is already there.