Hello I am kicking around an idea in my head. And needing some thoughts on how to pull off a particular feat.

Suppose I have a motor mounted to a table, and on the end of the motor I have a cable wrapped around the shaft. This cable goes to the ceiling and gets looped through a hook and then back down to the table.

The free end of the cable can be attatched or detached to different weights. If you want to lift a 1 lb weight off the table say 1 foot, you would select one setting that is calibrated to only lift one pound (no more).

If you wanted to lift a 2lb weight off the table 1' you would use another setting. What ever weight, say up to 5lb you could hook up and it would lift it 1' off the table without burning out the motor. (pull the weight up and hold) Hopefully in the hold mode, it is not consuming lots of electricity??

I need this device (stepper motor?????) to be able to kick in, lift and hold with minimum amount of electricity and on my wish list is it runs on DC.
I do not want the 5lb setting to be used every time, each setting has a maximum amount it can lift.

This example may not make sense because it is a super sensitive invention I am working on in my mind. In reality I am not trying to lift something off a table with a motor, but I figure if I could tackle this feat then it would transfer over to my invention.

Anyway thank you for any comments, input, or direction you can suggest so I can start my research.

Thanks again

 

What you are looking for is a GEAR REDUCTION unit.

The principal is simple. One trades off distance traveled for force applied.

A motor that could lift one pound only, could lift two pounds with a 2:1 reduction gearing. It would take you two times as long to move the distance.

You could lift 10 pounds the same way, but would take ten times as long.

Metal working/mechanical schemes are simpler to devise but sometimes more difficult to manufacture for a home based hobbiest/individual.

Ask how they would move the weights @ this place

www.homemodelenginemachinist.com

 

Another approach would be a motor (and gears perhaps) that will lift anything you want, controlled by electronics. Could the weight sensing be on the table, and not part of the lifting? I think that would simplify things, although you could also hang the ceiling pulley from a load cell. Anyway, you just need a control scheme whereby no movement happens unless the weight meets your criteria. A microprocessor and knowhow to use it would simplify this but I think brute force linear methods could be devised.
A bit more detail would help, including what your skill level is.

 

Which is more critical:

Low current usage
Lifting an object exactly 12" and holding

A stepper motor would be the best for lifting an exact distance, but holding current is there.

A motor with wormgear reduction would have no holding current, but lifting it to an exact height is problematic without feedback.

 

Low current is right at the top of my list, if I could get a small low current DC stepper motor that could be powered by batteries and could last an hour or more I would be set. It don't need to be ran 24/7 or anything like that. I would need to some how calibrate it to step through different settings. Back to my awful table analogy. Step to hold 1lb, slide a switch and step to hold 2lb, slide switch etc..

Thanks for your input guys. It is sort of hard to discuss something without giving away alot of specifics and expect to find the best answer. I started electronics in 1986 and then got a BASEET degree in 1992. I worked 10 years in electronics as a technician. Most of my work has been done on a bench as a technician - far from an engineer. I stopped that field about 10 years ago. I just bought Tina (an electronic simulation program). And am trying to get back into the swing of things. I worked for a two compainies as an electronic tech, one made electronic controls for printing presses. My other job I worked with HeNe lasers and worked as an electronic tech there also. Saying that, I am very rusty on alot of areas. Once you get into the field as an electronic tech you get good at what ever product you are manufacturing and stay in your box.
So with my back ground stated. I also spent three years in auto/diesel mechanics in 1983.

I have tried to lay some different ground rules, maybe put the table analogy aside. I will swich gears and ask my question in this fashion if I wanted to accomplish these three goals do you have any suggestions.

1)first I would turn on the switch and the motor starts to slowly spin
2)ideally I would like to monitor and control the motor by watching how much current it is drawing and put it into a holding pattern when it reaches a certain level.
3)Motor has to run on DC and it has to be pretty strong probably lift 5-8lbs if needed. And use as little electricity as possible.


I may have led the group astray with my table and motor analogy. It is the closest I can come up with at the moment to transfer over to my idea. My invention does use a DC motor. Ideally it would sense current draw of the motor something like that and the motor would stop when it reaches a preset point and hold.

You ask if the weight sensing could be on the table and not part of the lifting. Do you mean like it monitors the current to the motor or something. Yes it absolutely could. When the motor has a certain amount of torque felt it goes into a hold mode.

I am really sorry I have not told you enough to give me the best advice you are able to, I am just looking for some rough ideas, some direction to go to try to accomplish my "secret" goal. I realize good questions in most of the time = good advice out. So I will keep thinking of anther analogy that may help serve me better.

I just found this forum last year and it is such a cool place and I certainly thank everyone for the time you take out of your life to help. thanks again

 

1)first I would turn on the switch and the motor starts to slowly spin

Can the rate be constant, or do you need variable speed?

2)ideally I would like to monitor and control the motor by watching how much current it is drawing and put it into a holding pattern when it reaches a certain level.

Level, as in elevation or distance travelled, or level of current? I think the current will only rise appreciably as the motor stalls.

3)Motor has to run on DC and it has to be pretty strong probably lift 5-8lbs if needed. And use as little electricity as possible.

The weight isn't a problem - it's the time you have to lift it. That's what defines the power you need. A very small motor with a gear reduction unit could lift and hold a weight, but not quickly.

You ask if the weight sensing could be on the table and not part of the lifting. Do you mean like it monitors the current to the motor or something.

What I was getting at was can you just weigh the object before there is movement and never again? Like if it started on a scale on your table and was lifted off of it, so no more weight data was available. If you need continual measuring, that's very different. I'm guessing from your description that you need continual weighing, or tension or torque or whatever.

 

Music Man

Sounds to me like you need a "current limiting" circuit in your motor control circuit.

I would place a current sensor on the power in line and send that signal to one of several current limiters that would be selected with a rotory selector switch in your on/off circuit. Each current limiter would be preset to send a signal at a given current detected by the current sensor.

The signal from the current limiter would keep the motor working until a signal from a proximety sensor or limit switch would turn the circuit off, at a preset distance, engaging an automatic braking system to hold object in place.

In all likelyhood you will add to or subtract from the suggestion given, dependent upon the direction your ultimate project takes you.

williamj

 

By using a worm gearbox you won't need any power to hold at a certain point, worm gears are self locking. Worm gears are self locking due to their high mechanical advantage, they use a small power input to do a lot of work. Allowing the use of a smaller motor. They can even be used with stepper motors for precise positioning.

As far as worrying about differing loads, things like winches and cranes are engineered for a maximum load and then can be use to lift any load up to that max load. Doing this eliminates the need to control the power input. The KISS way of engineering.

 

Group you are great, you have given me a few different options to look at. I am going to print this off and go study it for a while.

Wayne, thank you for your responses, you ask.. Can the rate be constant, or do you need variable speed? I would like to use a combination constant and variable. Maybe a postion switch and then variable in between selector postions.


Wayne, for the question.. Level, as in elevation or distance travelled, or level of current? I think the current will only rise appreciably as the motor stalls.... Level of current I think would be my best option. If I set a swithch to lift say 1lb and it ended up lifting 2 lb, it would not be what I am trying to achieve. I would only want it to lift 1 lb or less and then have a selector switch for say 2lb and it would be variable in between the selector switch postions. (I feel I could use a series of voltage dividers and a varible resistor to accomplish this???) But I am still stuck on what kind of motor I should or could use that wouldn't burn out under a load and in a holding pattern.

Wayne you commented ::The weight isn't a problem - it's the time you have to lift it. That's what defines the power you need. A very small motor with a gear reduction unit could lift and hold a weight, but not quickly.... I guess I would need it to move somewhat quickly (back to the ceiling to the table analogy, maybe move say 4 inches within a couple seconds would probably be good.


WilliamJ: thank you very much for commenting. I am going to go study up on all that you wrote about the current limiting approach. This sounds like a good direction to focus my attention. I just need to figure out the best type of motor to use for such a situation.

Shortbus thank you for your suggestions... I am also going to go browse through someplace like mouser or somewhere and see what is available in small motor worm gear packages.

Group you have given me a starting place for my journey, am going to go off and do some research on some of the suggestions.

Thanks again

 

Level of current I think would be my best option.

I really doubt that, if we're talking about a DC motor. Maybe others that know more about motors can chime in, but I don't think the motor can tell you anything about what is going on, except when it stalls it'll draw more current. If you want to know weight or tension or such, you'll need a sensor to measure that.

Current drawn by an AC motor can be a useful measure of how much work the motor is doing, so maybe an AC motor is the way to go for your project.

 

As far as measuring/weighing the load - by allowing the motor/gearbox to pivot a slight amount, when the load starts to lift the amount of movement could be calibrated by that movement. A spring with a known rate and a strain gage or slide potentiometer could do the job of weighing.

I know for some reason you want to keep this project a secret but, knowing what you really want to do would make it easier to help.

 

I know for some reason you want to keep this project a secret but, knowing what you really want to do would make it easier to help.

He should read This Thread

 

Thanks for your feedback wayneh my device is portable so it needs to be DC. Maybe it is not possible, maybe I am not capable.... I believe if it is possible and if I can ask the right questions I have come to the right place to get an answer. I will keep trying to move forward. I am only mid life so I have lots of time to think about it and
to ask questions and feel in alot of blanks. But it is a fun journey to learn something you didn't know before you started. Thanks again for your thoughts.

 

The best solution would involve a motor capable of max torque, add strain gauge in-line with load. When load meets limits, stop/hold motor, or unwind, depending on if you want it to "pretend fail" at xx lb load.

 

I have enough info at the moment to get going in some direction thanks to you guys. I definately will look at strian guage, that may be just the ticket. I have had so many inventions, I have worked on in the past, searched them, made sure nothing was close and then after not acting on them for 2-4 years I see them at the store. I guess the you snooze you loose therory kicks in. It takes money to make money. Unfortanately that is where I always fall short. I prototyped this product about 5 years ago without the motor and it has just sat for in my garage. I saw it the other day and said that is still a very useful device. I should take another look at it. I know this will probably be just another idea that never makes it off the ground and in time will be brought to market by someone else, but maybe somewhere along the way something will fall into place.. Then again.. maybe not. But like I said before it is just fun to learn something different. I think I am about done with this topic for a while and I thank each and every one of you for the time and suggestions you have given me. Thanks again

 

For more ideas look into how a crane works. they have a built in load measuring system. Also conveyors to supply a mixing operation, such as a large cement/asphalt plant or something of that nature. Even a conveyor in a mining operation weighs the material as it is moving it.

This is probably on of the most helpful forums on the web. people are here to help you learn and make your project work.