Outrigger questions

[1974]

Hi there

I'd like some feedback on what you think is the best outrigger design?

I don't have much experience with (modern) LEGO versions as I only have the 8110 Unimog (which is perfect, but manual) and the 8069 Backhoe (don't remember that one as I bought a bunch just for parts)

Working on a large truck chassis (4x double 3739c01 wheels at the back, 4x 3739c01 steerable (<- is that a word?) at the front) which will probably weigh around 3-4 kgs. Not sure what goes on the top .. maybe a crane ...

My idea is to use brickbuild gearrack motorcontrolled outriggers for the horizontal movement and pneumatic actuators (4688c01 as I only want one inlet) for the downward movement. I will use a compressor for the pneumatics, but would an (or several) airtanks be an advantage here?

I'm wondering if four of those 4688c01 can push up 3-4 (or more) kgs?

Bad idea?

I'd luv some feedback and pointers to great MOCs that do the same or better

Also, would like to know what is regarded as the best TLG designed (manual) outriggers

I'm really only interested in outriggers that perfom well and can actually lift the vehicle. My 855 is somewhat lacking in this regard

Thank you in advance

Cheers,

Ole

[legomuppet9]

Not sure whether any outrigger design like the one you described would be able to lift 3-4kg....

[1974]

Thanks, that's what I want to hear.

I could phrase it another way, how much force can a LEGO pneumatic actuator generate? I really didn't think of that, doh. Is there a website similar to Philo's motor survey regarding pneumatics?

Edit : Found such a site :

http://www.techbricks.nl/My-pneumatic-LEGO-projects/pneumaticlegolawsphysicsii.html

But I'm afraid that went over my head

Edited June 20, 2013 by 1974

[matias bendtsen]

My mobile crane weighs about 6 kg, and lift itself wit the outriggers, but it is absolutely impossible when they are extended. :)

[Carsten Svendsen]

You might still be able to make outriggers that can lift the crane, but they wouldn't be realistic. You'd have to go with the lever principle in order to use pneumatics

My mobile crane weighs about 6 kg, and lift itself wit the outriggers, but it is absolutely impossible when they are extended. :)

True, but what good are outriggers if they're not stabilizing the crane?

Edited June 20, 2013 by Carsten Svendsen

[1974]

Thanks, DK boys

But I'd rather not use the lever principle. I'd like the outrigger to go out .. then down. If it's not possible with pneumatics (I only have the new modern versions with inlet/outlet, waiting for bunch of the old ones, so I can MOC) I'll have to use gearracks for the downward movement (doable at this scale) or LAs (would not like to) .. hmm ..

Matias, why can't it lift itself with the outriggers extended, is that a weakness in the extension? I'm planing to build rather hefty horizontal brickbuild extenders that I'm sure will not fold/stall under the weight

Where is the weak point, if I may ask? The video shows exactly what I want to do

[Blakbird]

Pneumatic actuators are not very well suited to actually lifting a heavy vehicle in a vertical orientation. When you think about it, even if they could lift the vehicle they would be useless as stabilizers because air is compressible so the vehicle would still tip as load was shifted. The best LEGO outriggers are mechanical and use an over center mechanism to lock in the deployed position at which point they can withstand and weight within the structural capabilities of ABS. If properly geared down, they can also lift vast loads. The outriggers on 8460 are a good example of this type of geometry. In terms of gearing, CP5670's annihilator uses awesome outriggers geared WAY down that lift up the vehicle.

Doing separate horizontal and vertical motion is problematic with LEGO if you actually want the outriggers to support any weight, even with LAs, because the bending stiffness of beams is just not good. To get adequate stiffness from an ABS beam cantilevered way out to an end pad, you need the cross section to be much larger than scale. So either it will look wrong or not work. The benefit of the mechanical solutions is that the supports are diagonal and therefore the ABS in in compression and can support vastly more load. The horizontal member of a real crane outrigger is usually a massive steel I-beam.

Where is the weak point, if I may ask? The video shows exactly what I want to do

See above for the answer to your question. The pneumatic actuators have adequate force output to lift the load, but the supporting outrigger beam does not have adequate stiffness to transmit that motion to the body when extended. If the actuators could extend far enough, you could still lift the body but you would see a lot of curvature in the beams (and they may even fail).

[Bricktrain]

As others have said, you can lift the crane when retracted but when extended they will only flex not support the crane. If you are only using a single acting cylinder how will you raise the feet once lowered?

[matias bendtsen]

True, but what good are outriggers if they're not stabilizing the crane?

they look as realistic as possible, and the 6 kg of crane is stability enough. its all about counterweight.

[1974]

Thank you Blackbird

I didn't think of the air compression. I'll look into the examples you've mentioned

Edit : My outriggers works pretty well vertically, they don't bend much even with a 5kg load. But I do not use beams, but a lot of bricks (which is doable on this scale), so I'll try to use the old school pneumatic actuators when the arrive. Video will follow ...

Edited June 21, 2013 by 1974