Slow Moving Objects Over a Period of Time

Hello wjhyde,

Is the design and build of this motor to be a learning experience for you or others too?

Hi bwire, The motor/mechanicals will be enclosed. I do not need to show or describe how the objects move. It is not a display of mechanics, only of the objects moving over time. I imagine the electrical cords to come out of the top and plug into the ceiling outlets (if i need electricity, maybe I do not...?) I hope this answers your inquiry. Thank you, wjhyde

Hi wjhyde,

We will need some more information:

1. What is the distance the objects need to move in the 3-week timeframe?
2. How many objects will there be at any given time?
3. What is the spacing between the objects?
4. What is the weight of an object?
5. I know you said "continuously", but could the train of objects be moved a little at a time? For example, could the line be moved a half inch, stop, wait for an hour, then move another half inch, and so on?

Let us know.

Mike

*8' wide x 12' high x 24" deep*

Which side will face the earth? Or does it not matter?

Thank you all, Here I have more info: - The 2 objects will be in an environmentally controlled building, so weather proofing is n/a. - The floor is finished hardwood and very smooth. - The objects will be touching each other when they begin, then the final distance will be 12 feet apart (space between them) - I did not attempt to calculate the weight yet because I am flexible about the materials. - To better describe the objects they are like boxes on wheels only tall so the bottom (side facing the earth would be the 24inch x 8 feet) - I really do need them to be continuously moving. I really appreciate and Thank you !!

Hello Wendy,

Artistically, you could use a clockwork mechanism and that would be "real cool".

Practically you could use small electric motors with necessary gearing to achieve your "desired speed". Given the size and volume conditions described you may be able to complete the task using a battery system. Depending on the lighting, you might incorporate a solar panel into the design surfaces to top up the battery.

I'm presuming that you are after an "artisitc effect". I wish you well.

Selecting suitable reduction gears will be your challenge and when you start the trial. Some of the gears will have significant strain on them.

If you do choose to connect to the mains, then you could achieve "apparent" continuous movement by using a stepper motor and only moving on one mains pulse every second instead of every cycle (for instance).

Thank you Just an Engineer, Clockwork sounds great but I was trying for concept of momentum, sorry I did not put that in until just now... Something to signify a catastrophism. So "it" could have a beginning. Thank you

Wjhyde,

Sounds like you intend an artistic piece to be built in some fashion, but with your nebulous answer that's purely a guess on my part. If I'm correct you may want to have somebody familiar with theater stage craft assist you in this endeavour. I would guess also that these things will be less than 50 kg in mass each. Before you contact him/her there will be several details you will need to clarify for anyone to help you.

• How many axes of motion will these objects move?
• How will the rotational motion of the motors be translated to this movement? Possibilities are cable pull, belt drive, conveyor, wheel motion?
• Will each object move independently or will all be part of one assembly?
• How far will these things move?

Certainly more questions will be asked to complete this task. I do have one suggestion though, because the motion velocity you mentioned has a time basis that is quite long, I expect you will have to do some considerable gear reduction to get such a slow speed.

"momentum" that's a horse of a different color.

Bell shaped curve comes to mind.

Thank you all so very much, I have a lot to go on now. The next time I hope to post link to image and design. This really is a great place with great people, Thank you !

Does it not look a bit too slow?

Let us go this way - requirement of 12' over 3 weeks translates to be approx 10 micron per minute.

If I take a wheel base dia of say 200mm (sorry habituated of metrics)

Then the periphery = 628mm.

This wheel should have a speed of 1.6 x 10^-5 RPM.

If I take the base motor to have a speed of 60 RPM then the gear will need a reduction ratio of 3740226 (ie 3.74 million:1)

This reduction ratio looks a bit too high Let us say each stage at the extreme we go to 100x1 then four stage reductions? size? weight?

Looks a bit too complex.

Yes this is a dramatically slow movement, but don't forget many old mechanical clocks would have a mechanism that showed the phase of the moon. So this much mechanical gear reduction is not just possible, it was done long ago.

You know here the problem is not that - it has to have a power transmission good enough to drive that big black (for us) box.

Otherwise it could have been much simpler. In fact it may be much simpler than that- Let us use electronics+mechanical

Let us take a pulse of 1 sec and a stepper of 60 teeth

so each minute it makes one revolution

in 3 weeks it makes 3*7*24*60 = 30240 rev

If I assume the wheel dia = 0.5ft (ie periphery = 1.57 ft)

then it would travel 1.57*30240 = 47500 ft

but limit is 12 ft so reduction ratio = 47500/12 = 3958 : 1

a two stage worm reduction of 1:63 can do the trick

Else we can slow down the clock

With a pulse of 1 /minute, it will be a single stage reduction of 1:66

and to be light and compact of course epicyclic (multistage planetaries can be thought of - these are even available in plastic gears too to be light weight)

But all these cost is not going to be low.

PS:

Sorry, the ratio should be doubled since the gap is 12 ft so each object moves by 6ft only you need a double stage reduction of 88.98:1 if you want exact 12 ft or else take 89:1 and you will miss the mark by 0.038"

PS2: Just checked up, and gear boxes (compact are available of upto 4900:1 and planetaries upto 100:1) but these are metallic, of course for you it may not matter, if you are providing uninterrupted electricity.

I fully agree with your calculations, but aren't most stepping motors 200 full steps per revolution and not 60. So by using half step driver one could easily get 400 steps for one motor revolution. Thus removing the gear reduction for speed reduction part of this problem. This will technically not be continuous motion but the increments will not be immediately discernible to the eye. This brings up a systemic problem, knowing that the system is working can become a problem. So some mechanical gear reduction may still be very useful, for behind an access panel, one could then see a slow moving motor shaft turning. At least this way one would know by looking under the access panel immediately if the electronics is producing hidden mechanical motion.

With 12 ft of motion in three weeks, that's a little more than a quarter inch an hour of travel. 12ft*12in/ft/(3wk*7d/wk*24hr/d)≈0.3 in/hr (I believe I'm repeating a calculation you already did, don't mind me. ) Likely one of the points this project is demonstrating is that constant slow motion gets you there but it's hard to see. But that will also become a problem for maintaining the project.

Another couple of points comes to my mind now. What should happen when these things eventually reach their travel limit? Do they stop, reverse, randomly change their direction of travel? How does one determine reaching their travel limit? Will there be a limit switch? Does one count steps and assume motion traveled?

I tthink the OP's show will be over (I think 3 weeks is a long time to hold an audience at one place )

But then he/she can put a limit switch as you said and trip the power / reverse the motor rotation till they clash.

Yes, the power source will be disconnected at 3 weeks. The audience can return at various times to see the changes in the space, or, if only there 1x, imagine what will happen or did happen, depending on when they are viewing. About the weight and materials - please forgive & excuse the info is not exact yet: The heaviest so far is 325 lb/each box The lightest is 120 lb/each box. Felt on bottom is ideal. Aluminum and/or nylon framing. Walls are of lightweight wool fabric. I decided on wool because it is naturally flame resistant, lightweight. Each box will house a digital projector (mitsubishi wd2000), and mac mini.

Glue felt pads to the bases of the boxes.

Attach nylon cords to the bottom of the middle of each outer edge and route the cords round via pulleys so that they both end up somewhere where they can be wound around a 1 foot diameter drum. I have shown 1 foot diameter pulleys here but they will probably be a lot smaller. Obviously you just need to get a small electric motor which you can gear down to the right speed to rotate the drum just under 2 (6/pi) full cycles in 3 weeks.

You might be able to get a chord which is less "stretchy" than nylon.

You forgot to provide any hint that would enable a responder to understand the magnitude of forces or energy involved in accomplishing the desired movement or the desired distance of travel. The physical size and construction materials of the objects are second order issues.

I suppose there is a mind reader's forum out there somewhere; but I doubt you will find that particular talent in great abundance in this engineering forum.

A lot of us here enjoy clever riddles; but if that is your objective I must say you have presented a rather dull and uninteresting example.

Ed Weldon

Feel free to return to CR4 with any future questions you may have. Please remember to post us how about the unveiling.

Wendy, If you do come back to CR4 with more questions, make sure that you cross reference: this thread in the new one, and, the new one here. That way you are guaranteed an audience from those of us already interested, plus, anyone who responds to subsequent threads.

I see that in post #21 you have said that you like the idea of felt pads on the bottom. I'm getting increasingly worried about what I think is called "stiction". In the most simple form if you were dragging the boxes with cords then the cords would gradually stretch until the force was enough to overcome the static friction, then the boxes would slide a short distance because the stretched cords would only be working against sliding friction. In other words the motion might become a bit "jerky". Felt might be quite a good choice to help avoid this problem, but, it's probably worth posting a new question in the mechanical section with stiction and felt in the threads title (maybe wait until you've made a few more design decisions). The stiction effect may even be a problem with a system with wheels driven by a long gear train. It might be worth looking at drive mechanisms designed to drive large telescopes so that they track the movement of the skies.

Wendy,

Take plenty of pictures during the construction phase and document "how you did it" as you progress.

The engineering types on here like to understand the "how it happened".

There is a member (Moose) who is expert at compiling such stories and publishing them into the forum areas. Contact him with the material.

I would certainly be interested in the "engineering" of what you finally produce.

Thank you, I'll do just that. I have already started on a small model. I'll look up Moose too. Best, Wendy

I think that this company's product line would be able to do the job. backlash free linear motion, where the speed is adjusted by the angle of the 'rolling rings' and the shaft speed. very interesting stuff. there are no gears. just the friction of the rolling rings on the bare shaft, which produces very specific motion. I used to have a vhs video of the product, which I had requested. too bad they don't have that on their website.

http://www.amacoil.com/

Chris