Discussion & brainstorm topic: Reducing motor load

Hope this topic rattles up some discussion about reducing the load on (wiper) motors :

I've seen a few possible solutions pass and think this is an interesting topic to discuss and brainstorm about since an affordable solution would benefit all of us using motors.

A few things/possible solutions I've seen so far:

- BSFT style springs:
To help balancing the platfrom and to keep a continuous load on the motors to prevent wormwheel wearing iirc?

- FernVeilleux and Thahustvedt use cilinders with expansion tanks in their projects:
I have no idea about the physics and costs involved. Would be great to see the basics, needed parts and calculations for this explained in more detail

- Car trunk gas struts
read about people wanting to use them and since they go for about $ 20,- per set It could be a cheap solution.
But never seen them actually being used, so I have no idea if this would work and how much lbs they would have to be etc.

Here's some info on pneumatic cylinders. I bought mine used from Ebay for just $45, and that's not much considering how big it is. http://www.ebay.com/itm/380286002481?ss ... 500wt_1413

You can get cheap cylinders of various sizes very cheaply from chinese Ebay sellers. I haven't tried them yet, but plan to in the future. Example: http://www.ebay.com/itm/MAL-16-x-25mm-P ... 808wt_1396

The cylinder has a 32 mm bore, which means it will produce 8,04 kg of force per kg/cm² pressure (or 1,24 lbs of force per psi).

If you have a 200 mm stroke cylinder, with a 32mm bore, you have a volume of roughly 0,16 L (area of bore multiplied by the height). Lets use a 1,5 l expansion tank (soda bottle) in our example, which is ~10 times the size of the cylinde volume. If the expansion tank is pressurized to 5 kg/cm², the spring force will be approximately 40 kg. As the spring extends the volume of the system will increase by 0,16 l, to 1,66 l (not counting the volume of the unused part of the system, like the air hoses and so forth, for simplicity), and will vary the pressure by an amount proportional to the change in volume. In other words, the force in this system will vary from 40 to 44,3 kg. A larger expansion tank will result in less variation.

Another advantage to an air spring system is that the same setup can be calibrated to any force by changing the pressure, so you can achieve perfect unloading without changing anything mechanical, or replacing springs.

I have thin hoses in my system, 4mm and 6 mm internal diameter, and the air does not seem to be restricted by this. Larger tubing is better of course.

Positive:
+Nearly linear spring force.
+Adjustability.
+No restriction of the speed, unless too thin hoses are used.

Negatives:
-Complexity. It's more complex than a coil spring to install, and might need topping up after a few days with air as there will probably be a very slight leakage. I'm surprised at how well it holds air though.

Thanks a lot for your explanation Tahustvedt!

If I'm correct basically what you do is place an air cylinder with an expansion tank next to the motor and pressurize it until the platform (including driver) is easy to level and move up/down without having to apply too much force? And the bigger the expansion tank is, the more linear the cylinder responds.

Are there any basic rules to calculate the cylinder one would need for his platform?

Edit: found a pneumatic force calculator

And is a single action cylinder used:

Or does it have to be a double action one:


Just curious, the cylinder in the second link you posted only has a 25mm stroke, isn't this too little?
If I compare this to e.g. my platforms eventual max 10cm motor travel shouldn't it have a stroke approx. equal to that?

Anyone any ideas on using car trunk gas struts?

The cylinder needs to be double action for it to work as a spring. Single action cylinders usually have a spring in the opposite end to move the cylinder back when air is removed, I believe. You connect the tank to one end of the double action cylinder, and leave the other end unconnected to breathe freely.

A double action cylinder can be set up to either compress, or expand, depending on which end you apply pressure. I apply pressure so that mine wants to compress, which means there is no chance of the piston rod bending under load.

The cylinder I linked to was just an example. The first one I found on Ebay. You can find cylinders of different bores and strokes if you search.



Gas struts usually have a damper to reduce the speed of the motion, don't they? I'm sure they can be used, and are probably simple to install in comparison, but they offer far less flexibility and won't be linear.

I'm planning on using gas struts, yes you can get fast action struts with little dampening. You wont find many used on ebay you would have to buy new. They can be preloaded with a specified amount of air resistance by the manufacture or distributor, then you can release the air to your prefered amount but once you do you cant put that air back in, so it is like a one time adjustment.
I will dig out some info and edit my post when I find it.

http://www.specialty-fasteners.co.uk/up ... erview.pdf

http://en.wikipedia.org/wiki/Gas_spring

@tahustvedt

You pressurised the cylinder so it wants to compress.
Which meens it's mounted in such way that your sim (when idle) wants to expand it right?

In case of my sketch (the more common type of sim compared to yours [strike]it would have to be the other way around because the motors will have more problems pushing the platform up than pulling it down or am I mistaking there?[/strike]

Edit:

Just figured out that my statement above is wrong and most likely should be:

• Cylinders on same side as motors: Cylinders need to be pressurised so they want to expand
• Cylinders on other side of pivot as motors: Cylinders need to be pressurised so they want to compress

Right?

That sounds right.

Yes, my sim wants to extend the cylinder. I don't know how long these cylkinders last in this application, but I expect the high quality ones to last for years since they are for industrial use.

hmm, just came to think that if my above statement is right, 2 cylinders won't be enough:

if I place 2 cylinders on one side they will help push the platform up on that side (and thus sort of pull it down on the other side) but it won't help the other way around, or am I missing some logic here?

Edit: as you can see pneumatics just isn't really my thing

If the sim is balanced and teetering then the expansion tank is probably not a good idea as you will not want a linear force. A double action cylinder can spring both ways if it's pressurized on both end connectors while centered, and then the connections are closed. It will give progressively more force towards each end and the force can be adjusted by changing the pressure.

What I would like to achieve is a 2dof balanced platform with a center pivot which (when motors aren't attached) can be tilted with the tip of a finger, stays that way and can be tilted back with the tip of a finger and stays that way.

That way the motors will only have to apply a little bit of force to move the platform and keep it in place.

Don't know if that's possible though.

Indeed good balance helps most to reduce the load on the motors! After doing some calculations I'm currently changing my platform so that the rotation axes go through the centre of gravity. Otherwise the torque is just prohibitively high
In case you are using a universal joint (cardan), you have to add additional weight underneath the platform (→ with the drawback that inertia will increase!), because otherwise the gravity centre is above the pivot point and your motors will still have to work too much.

And that's exactly what this topic is about:

Figuring out a way to reduce the motor load by using: springs/gas struts or cylinders on this type of sims.

It's just that I lack the pneumatics knowledge to figure this out

De formules voor pneumatische cilinders zijn simpel.
Kracht=oppervlakte van zuiger maal druk.
1 atm/bar=1kg/cm2 en 3 bar=3kg/cm2 druk
bij het drukvat met 10 liter inhoud zit met 1,5 bar 15 liter lucht en bij 6 bar 60 liter
De maten van pneumatische cilinders zijn standaard :zuiger grote X slag en dan heb je nog de grote van de aansluitnippels.
Verder is het volume verplaatsing bereken.
Werken met een grote cilinder en lage druk gaat langer mee dan een kleine cilinder met hogere druk (met de zelfde kracht)
Voor het drukvat kun je hoge druk pvc buis en lijmkappen gebruiken(zwarte pvc kap en buis)Deze kan geen 3 maar 8 bar/atm. aan
Je heb wel een dubbel werkende cilinder nodig,aan welke kant je de slang aansluit bepaald of de cilinder uitzet of inkrimpt.
zet op de ongebruikte nippel een filter zodat er geen vuil in de cilinder komt(levens verlengend)
gr.Ad

Thx for your explanation ad!

Now the question is how we can use this to reduce the motor load in the below platform type where the center of gravity is above the pivot:

Do we need to put a cylinder with expansion tank on each corner, just 2 corners or......

if you can put a tank on all for corners, this will help. I reckon anyway, but then again, what do I know :rofl:
For reducing load on motors, its like this. The best spot to connect motors is at shoulder height behind the seat. The second best spot would be near the feet end, to act like a wheelbarrow effect. The second idea I have done and am currently using. The first idea I am going to personally test, but others have proved it is the better way.
However, dont get me wrong, motors under the frame work well, they just have to work a bit harder. I have put motors in several spots and they all work.
Then again, just to add some confusion, so motors still work hard regardless, so I have found.
Probably doesn't help, but there's my bit.

Hoi Floris
Ik zou pas aan gewicht compensatie gaan denken bij een dof 3 met lift optie.
Zoals ik begrepen heb wil jij deriy's simulator na bouwen, hier heb je geen gewicht compensatie bij nodig.
De krachten bij een seatmover en deriy's simulator blijven gelijk (het draait namelijk om de afstand tussen kruiskoppeling en aktuator)als hij goed uit gebalaseerd is.
welk compensatie systeem je ook gebruikt het gaat tegen werken bij deriy's setup.
de krachten worden groter als je verder van zijn balans punt af gaat en werken als volgt: uit gebalanceerd 0kg en op 90 graden van balans punt het volle gewicht
hier tussen word het verdeeld bijv. op 30 graden 1/3 van volle gewicht 45 graden 1/2 van volle gewicht op 60 graden 2/3 van volle gewicht.
Aangezien je bij deriy's setup niet zo veel bewegings vrijheid hebt blijven de krachten ook binnen de perken.
Als je later een dof 3 wil maken zet je de cilinder onder de kruiskoppeling.
gr.Ad

English please so the rest of us can understand

Failing that
I would will think compensation just of weight at dof 3 with lift option.
Such as I have understood want you deriy's simulator after build, here need you no weight compensation at.
The strengths at seatmover and deriy's simulator remain right (it twists, as it happens, for the distance between cross link and aktuator) if he is well gebalaseerd.
which compensation system you also use it go against work at deriy's setup.
strengths become larger if you go further of its assessment point finished and work as follows: from balanced 0kg and on 90 degrees of assessment point the full weight
here between is divided it for example. on 30 degrees 1/3 of full weight 45 degrees 1/2 of full weight on 60 degrees 2/3 of full weight.
Since you at deriy's setup not this way much movement freedom the strengths within the perken have also remained.
If your later dof 3 want make put you the cylinder under the cross link.
gr. Ad

Hoi Floris
.Volgens mij hoeft het toch niet tegen te werken bij deriy's setup,als je met een dubbelwerkende cilinder werkt met 2 apparte drukvaten en slangen op beide cilinder nippels.
Op deze manier kun je beide kanten van de cilinder op druk zetten, en komt de trek/duw stang in het midden te staan,en kan met een bepaalde kracht 2kanten op geduwd worden.

So Ad, basically what you are saying is that due to my max pitch of 14° and roll of 18° the most weight my motors will have to deal with is approx. 1/5 of the total weight? (about 125/5=25kg)

Personally I think that's still a lot and would love to reduce that.

Will adding double action cylinders with an expansion tank on both connections take care of that? (so 2 cylinders and 4 tanks in total)

Edit:

If I'm correct more pressure results in the platform re-centering more easily but the motors having to work harder to tilt the platform? And are the expansions tanks actually needed in that case?

Basically in that case the cylinder is working like a spring right? So using springs would be easier, but not adjustable?

Hi Floris
I made a mistake 2 vessels upon one cylinder will not work sorry.
If expansiontanks are needed, depends on pressure
Yes the cylinder and vessel become one adjustable spring