# Simulating weight through coils

#### vidin

Hello everyone,
I have a little practical question. I would like to create a weight of about 10kg-250kg. A software programm should be able to control the actual weight.

Does anybody know a good physical way to do that? I thought of coils using Lorentz but I'm not quite shure.
Any help is very appreciated. Even if just a little thought.

Thank you very much.

vidin

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#### Integral

Staff Emeritus
Gold Member
I have no idea of what you are talking about. Coils? Do you mean springs? Electrical coils?

#### vidin

I'm sorry. Probably I didn't explain very well. But let me give it another try:

For a machine, I'm trying to create a construction which can "build up" weight dynamically.
It's basically replacing a real weight with one I can control.
How heavy the actual weight at a specified time is is then being controled through a software system.
Please don't hesitate if there are still questions left.

#### Fuego

to change the weight of anything; you'd either have to change its mass, the mass of the earth, or the universal gravitational constant.

#### Integral

Staff Emeritus
Gold Member
Perhaps you could use a pneumatic cylinder, or cylinders, with input from a digital controlled pressure regulator. Check out the
Marsh-Bellofram products for regulators (I KNOW, from personal use, that they make one with good digital control up to ~170PSI.
Look to Bimba or SMC for pneumatic cylinders

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#### vidin

Thanks for the apropriate answer. (Not like Fuego who just thinks he's funny).

I will check it out!

#### vidin

Well I think I'm on the right way to describe it right. Let me now describe my problem very precise:
The module I need has a black box and a bar hanging outside. The user's task is now to pull the bar which should be about 1.5meters long. How strong it is to pull the bar depends on what the user set up on a computer system/user interface. So I have to control the force which is needed to pull the bar via software.
That's it. That's my big problem which needs to be solved. But just how? I have no clue!!!

Thank you very much for your help. I really appreciate it!!!

vidin

#### GENIERE

I can think of many ways to do it, but the easiest way I think would be…

Attach your lever to a water tank. Use your software to control a pump to add or remove water to achieve the desired weight. Feedback to the software could come from a float in the water connected to a potentiometer as the height of water can be related to the weight.

#### enigma

Staff Emeritus
Gold Member
Originally posted by vidin
(Not like Fuego who just thinks he's funny).
Well, Fuego is right. It's a language issue as far as I can see.

Weight is the force acting on an object due to gravity. You can't increase or decrease this without increasing the mass or moving the object up or down in the gravity field.

Force is the word you wanted to use.

#### vidin

The watertank idea doesn't work as it is too loud (shouldn't be heared at all when changing the force). But still thank you Geniere, I'd really love to hear your other ideas as I have none

vidin

#### Artman

I'm not too sure how accurately this can be controlled, but perhaps an electro magnet and plunger system could be controlled by varying input voltage ot amperage. I believe this could be computer controlled so that when more power is applied the magnet pulls harder on the plunger.

I think it would have to be a plunger with a rod through the coil to keep some portion of each surface in contact through the entire motion or else you would get a hard to control spring like motion.

#### vidin

@Artman: could you explain a little bit more? What kind of plunger system? It's hard for me because I actually speak German and don't know all the technical terms. A link or a description how it looks like or work would be awesome!
Thanks a lot!!!

#### GENIERE

I think Artmans concept could be made to work, but fabrication would be difficult and the current would be quite high to simulate many kilograms of weight.

Perhaps a frictional device could do the job. I may be possible to get a set of disk brakes and a rotor from a motorcycle or automobile and adapt it to be actuated by a motor driven cam. I would use a stepper motor. I don't have an easy solution to provide feed back to the software, so calibration would have to be done often.

As to my previous suggestion, the pump does not have to be located in the box and can be placed out of hearing range.

It would be helpful to know the purpose of the device.

#### Artman

Originally posted by Integral
Perhaps you could use a pneumatic cylinder, or cylinders, with input from a digital controlled pressure regulator. Check out the
Marsh-Bellofram products for regulators (I KNOW, from personal use, that they make one with good digital control up to ~170PSI.
Look to Bimba or SMC for pneumatic cylinders
This is a good idea. Sorry Integral, I didn't notice this response before.

With proper use of levers, this could easily apply hundreds of pounds of simulated weight and control of pneumatic devices is fairly precise.

#### vidin

Hi Artman&Integral,
could you please explain a little bit more as I still don't really know how to put things together.

vidin

#### Artman

There are too many unkowns to design this instrument.

1. What is the weight range? Hundreds of lbs, or just a few?

2. What is the range of motion required?

3. Should the apparent weight applied to the arm appear constant through the entire range of motion or can it change?

4. How quickly does the system have to set?

5. How quickly does it need to reset?

6. How precise do the measurements need to be?

7. What level of modulation is required for the weights? (How small do the increments need to be?)

These are just a few of the questions. I would recommend that you do a little reading on pneumatics to see what they are capable of, and see if you think they can serve your idea.

#### vidin

I will definately! Could you recommend me some books or any literature which would help me archiving that goal? Would be fantastic!

1. What is the weight range? Hundreds of lbs, or just a few?
10kg - 250kg (see above)

2. What is the range of motion required?
1-2m (see above)

3. Should the apparent weight applied to the arm appear constant through the entire range of motion or can it change?
No, need to be changeable while pulling

4. How quickly does the system have to set?
Changing the force needed to pull should be done in seconds and less.

5. How quickly does it need to reset?
Instantly.

6. How precise do the measurements need to be?
about +/- 2kg would be good

7. What level of modulation is required for the weights? (How small do the increments need to be?)
5kg each step.

Thanks for your help once again!

vidin

#### Artman

The sites that Integral posted in his response are a good starting point.

Also do some reading on the physics of leverage, to figure out the best placement of the pnuematic devices in relation to the arm.

#### Artman

I had another thought on this idea.

How about a spring attached to one end of the bar and a fulcrum that can be moved to change how much force is required to pull the bar?

#### vidin

First of all : you're awesome! I really appreciate it that you guys help me finding a solution!!!

@Artman: A special thanks to you!!!
I think I understand what you mean. But how would you control the fulcrum? Maybe installing on a pneumatic cylinder and control the cylinder? It also sounds a little bit dangerous to me because when something happens with the spring the customer could be injured.

Please let me know if you guys have any more ideas!!! I will try all out and present my solution here once it is done.

vidin

#### Integral

Staff Emeritus
Gold Member
The range of motion and forces you need is daunting. That is going to require some major machinery. Pneumatics does not do well with multi-positions, it is either on or off, so you would need to figure out some way to position your device, pneumatics could then apply a static pressure.

As for instantly, forget it, this is the real world there is going to some delays in a system of this magnitude.

#### wimms

Robotics and servo control are developed well. Seek for these things. Linear Motor, brushless synchronous motors, smooth stepper motors. I'd go for things like that.
Ever tried ForceFeedback gaming wheel? Its synchro motor controlled by pulsed modulated signal. Its effectively smooth, well dosated, and nearly instant. Bigger is more powerful ;)

#### NateTG

Homework Helper
Sorry, my German is a bit rusty.

Is there any particular geometry you had in mind for the device?
Is it supposed to be a black box with a handle sticking out, or more like a barbell/pullup bar?
Is it important to be able to set the default height?
Do you want the system to be double acting?
Does it need to respond to motion in any particular way?
Does it need to be programmable?
Based on the location of the bar?
What kind of duty cycle is this thing expected to handle?
Do you have any particular construction method in mind?
Do you intend to mass produce?

Entschuldigen sie bitte meine fehler. Ich habe seit langem kein Deutsch geschrieben.

Dachten sie an eine training Machine als sie dieses Project beschrieben? Wie w&uml;rde man dieses Ger&auml;t benutzen? zum bsp. liegend, sitzend, oder stehend?
Ist es wichtig das die Anfangsh&ouml;e eistellbar ist?
Wollen sie das Gewicht auch ziehen, oder nur heben?
Soll es auf bewegung reagieren?
Soll es programierbar sein?
Wie oft und schwer w&uuml;rde dieses ger&auml;t benutzt werden?
Wie wollen sie diese Machine herstellen?

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