Discussion & brainstorm topic: Reducing motor load

And suddenly the construction gets a lot more complicated for someone who has only a bench press with a cross table to his disposal

Sorry, but that's a bit out of my league

How about the option of using cylinders with a shorter stroke positioned half way the pivot and motors? 32mm bore with a 10mm rod at 7kg/cm² results in approx 50kg max if I'm correct.

Edit: or I could use two of these (one for each cylinder) combined with u-joint

But I'd have to be sure they have enough angle and it would add another $ 40 to the budget

Sorry it's more easy for me in Dutch
Hoi Floris ik weet niet precies wat je nu van plan bent,maar als je een dubbelwerkende cilinder aan 2 kanten wil vullen zonder expansievat.
Dan zal de druk snel boven de maximaal toegestaane druk van 10 bar komen als je begint met een voordruk van 7 bar en sloop je de cilinder.
Je hebt dan een cilinder met een veel langere slag nodig om buffer te maken.
gr.Ad

@ad: I already took that into account.

You said that 18 degrees of angle (my platform's max) results in 1/5 of the total weight rests on the motors, in my case approx. 25kg.

So at the lowest or highest position the pressure in a 32mm bore cylinder has to be approx 3,5kg/cm² to carry those 25 kg's completely. In which case the starting pressure will be a lot lower than 7kg/cm².

The cylinders are 14cm longer than their stroke so I reckon they have a 5cm buffer on each side approx.

P.s. Np on the dutch, some technical stuff simply is easier in your own language!

For those who followed this topic:

Since budgetwise it would cost more than I expected to do it right, I've decided to forget about cylinders for now and buy 4 adjustable trunk lid springs to see how much difference they make


If my budget allows I might decide to go for 3DOF (with only a slight vertical travel of e.g.100mm to keep it compact) in the future in which case I'll start looking into cylinders some more.

Thanks all that replied and shed some light on this topic, learned a lot from you so far!

Now those springs would be good. I will have a gawk around to see if I can find something locally.
Cheers, David.

If you don't mind waiting a while: on ebay they are priced with free shipping (from china):

http://www.ebay.com/sch/i.html?_from=R4 ... unk+spring

For those interested: the springs arrived today:
(the ruler is in cm/mm)

They are a lot bigger and, more important, stronger than I thought. (I can barely stretch them by hand).

So I reckon I have to place them closer to the pivot point than I intended.

Since these are the plates my pivot will end up in between:

(the steel plates are 30x30cm)

I reckon I'll just place them in between the top and bottom adjustment rails.

Edit: a quick calculation learns that at that point the springs have to stretch in and out approx 25 to 30mm (so 50 to 60mm in total). Guess I need to test it to see if they will.