I am neither a mechanical engineer or the son of a mechanical engineer but wish I were. I am working on a project in my garage were I need a device that will do the following.
Say I had a bucket on a rope and wanted to mechanically lower it to the next floor at roughly the same speed whether I had 30 lbs in the bucket or 300 lbs in the bucket. I do not want to motorize the process, however, I don't mind providing electric power to a braking or clutch system.
Use a "worm reduction" gear box to power the drum that holds the rope. .... but use chain or cable. I'd use aircraft cable.
You can purchase these from one of the commerical warehouse companies, complete with a motor, ... or even a wench rated to do that. I've seen garage door openers used this way, too. With a little creativity you can rig a stop switch at each end of the travel, and forward/reverse/stop buttons or toggles at each end.
The worm drive will not over run with more weight. ...(well not much, for the perfect answer).
You will need to select a drive that will provide the torque output to handle the max weight and the drum size you use, and the speed you want to move the load.
Provide that information and someone will direct you to the torque requirements.
I have constraints which prohibit me from using a motor. I am looking for some braking system on the shaft of the spool which maintains a constant descent speed regardless of the weight being applied. I have read about eddy current brakes but am not sure of their capabilities when is comes to varying loads. Do they automatically adjust as the load varies? What potential do magnetorheological brakes hold for such an application? Thanks for your consideration.
Ok, try an increase gear driven by the decending rope off a drum or whatever. The final shaft drives a centrifugal governor. Like used in old steam engines to control velosity. Weights are swung at a 45° or so angle and as speed increases the weights swing out to a larger diameter due to the increased centrifugal forces pushing a sliding bushing on their shaft that applies more force to a brake. .... or air paddles swing out to a larger diameter and gab more air. ...or changes the pitch of the blades on a large fan to cause it to move more air. All these ways require an increase gear (or reduction gear ran backwards) to gain the require torque braking. If you make it highly adjustable the exact torque requirements become more forgiving.
That sounds like just what I'm looking for. Can you recommend any manufactures or links where I might look at such a device.
Check places like McMasterCarr, or W W Graingers or other similar catalog sales houses for components, but you may have to custom make a few. I'd dig in the internet for old steam powered tractors, they were big on the kind of governor we have been chatting about. There are clubs all over the country full of folk that rebuild and show these wonderful machines in events.. maybe you could find one this spring and get some first hand views. Also perhaps you could see some in a museum from a link off the web about them, in your area. 'Or.. perhaps someone in one of the clubs lives near by and would allow you have a private look with some first hand exchanged knowledge about the governors as they must understand and rebuild them during restoration. This would take you to the next level, beyond my knowledge base.
Please keep us informed how it works out and what you learn, so we can keep the skills growing and alive.
what about raising the bucket? same speed control?
raising the bucket is not a concern, I am utilizing gravity only. My search is that which will maintain a constant descent speed regardless of the load. The devise would mount to the shaft of the spool and provide braking at that point.
Is you bucket pulling on a rope attached to a spool of rope or does the rope hang over a pully then hang back down forming an upside down U?
That will help to give a little better answer.
Also. I am not sure what it is called but I have seen a clutch that is activated by the rpm level of the shaft. It had weights attached to a springs. When rotated, the weights would pull outwards overcoming the spring resistance. When they moved outwards, they rubbed on the inside of a housing. The friction would help to slow things down.
The rope is attached to a spool of rope. Since speed is my concern and the clutch you mention is rpm determined, I will do a search along those lines. Thanks for the recommendation. I am also curious about the capabilities of eddy current brakes and magnetrheological brakes in such an application as mine. I have no real sense of the work they accomplish.