ideas to strengthen this suspension needed

[deckard9]

Hello,

I am bulding a big MOC (http://www.eurobricks.com/forum/index.php?showtopic=80259), that probably weighs around 40-50lbs. It rests on 5 solid axles, that are connected to the chassis with 5 9-stud link arms. 4 longitudinal and one cross. It turns out, that the link arms are a bit too weak and have too much play. When the tank encounters an obstacle the axle tends to swing back and to the side to avoid the obstacle instead of working in the suspension. Sometimes the steering linkage bends.

I need something more rigid then link arms.

The steering is done with actuators, which have 2 drawbacks: 1. they are slow (but its a tank thus speed is not that much of an issue), 2. they have an integrated slip clutch. When the resistance is too big, they slip and the wheels loose alignment. I then have to turn the wheels to max to re-align them. Both is not ideal.

Rack and pinion steering turned out to have too much play. Also rack and pinion - as far as I found - is too weak and less stable then the actuator setup.

Any idea to beef up the linkage is highly appreciated, because its nearly the last obstacle to completing the build.

Its hard to get a good picture, cause the thing is too heavy to flip or turn.

thank you,

deck.

[DLuders]

Nice MOC! It's hard to see exactly what's happening in the suspension, but perhaps you could substitute these parts to replace the flimsy 9L Steering Links. You could put two 6628 "Technic, Pin with Friction Ridges Lengthwise and Towball" onto the ends of a 9L Technic Liftarm:

Edited April 5, 2013 by DLuders

[Zerobricks]

Use more diagonal bracing and studded bricks!

[OleBM]

Wow! Nice Moc! As a star wars fan, I gotta say that this is very impressive!

To avoid your wheels steering and bending when hitting an object, and transforming that into a suspended action, you could add a certain degree of caster angle to your suspension. And of course, you could try to use more rigid pieces. Studless liftarms longer than 9 studs tend to be quite "woobly" when clicked together without reinforcements.

[deckard9]

Nice MOC! It's hard to see exactly what's happening in the suspension, but perhaps you could substitute these parts to replace the flimsy 9L Steering Links. You could put two 6628 "Technic, Pin with Friction Ridges Lengthwise and Towball" onto the ends of a 9L Technic Liftarm:

Which element would I use to put the towball in?

Wow! Nice Moc! As a star wars fan, I gotta say that this is very impressive!

To avoid your wheels steering and bending when hitting an object, and transforming that into a suspended action, you could add a certain degree of caster angle to your suspension. And of course, you could try to use more rigid pieces. Studless liftarms longer than 9 studs tend to be quite "woobly" when clicked together without reinforcements.

I tried working with a caster angle, but the tank is so heavy, that due to the geometrie the steering would have to lift the tank a bit everytime you turn, which simply doesn't work because of the weight.Or I would have to compensate for the caster angle in the suspension with a correction in the sold axle to get upright steering which would make the axle quite complicated and less stable, I think.

Thank you all for the input!

Edited April 5, 2013 by deckard9

[Someonenamedjon]

You just put in it the ends like a regular pin.

[deckard9]

Yes, but where does the ball go, if I want to loose the flimsy steering links? I want to get rid of the black 9L steering links, that connect the axle to the chassis... So far they where the only elements I found, that have a tow ball holder and thus offer full freedom of rotation. If i use Liftarms with towballs instead, I need something to hold the towball on the chassis...

Edited April 5, 2013 by deckard9

[Someonenamedjon]

Maybe just remove the links and put beams there.

[deckard9]

You mean the natural play of the pins would offer enough freedom for the axle to move? That might well be...

[DLuders]

This Bricklink webpage has a number of different Modified Plates that could accept the towball, like this one:

[Someonenamedjon]

You mean the natural play of the pins would offer enough freedom for the axle to move? That might well be...

Probably... Best make a small mock up of it before you put it on your model for the fear of breaking it.

[z3_2drive]

Haha watching all of you think of replacements...If you can afford to change the length of the links(I'm sure you do with such a big MOC) just place a 7l liftarm between two of these- -and connect with 2l axle+pins and there you go-stronger link with same towball connection as original 9l link, just 2 studs longer Good luck on that beast!

EDIT: other than that I'd use ideas previously stated, especially the use of studded technic beams, not studless, wherever you can.

Edited April 6, 2013 by z3_2drive

[Bzroom]

I would use what seems to be referred to as a Pendular Axle. You would basically create solid axles all the way across. Make this substructure as rigid as possible, and then fix it to the chassis with turn tables on either end to allow to tilt side to side. Attach your springs and steering would be contained within the axle substructure.

Alternatively, if you want independent suspension, i would try to make the trailing arms connect to the axle at the widest point, and taper inwards towards the chassis. This way forces on the wheel will be directly in line with the tie rod, and the tie rods will practically from a triangle which will not skew.

For steering, if you use two linear actuators they will get out of sync. I would try to come up with a very solid tie rod between the two sides, and put the linear actuators between the tie rod and the axle. Then you could use two or more LA's at that one interface, to make the steering stronger. If their clutch is overcome, it will probably happen at the same time and they will not be much out of sync. The clutches would allow them to become aligned again automatically i'd think.

Also, it does look like you have some triangulation, but you'll need it in the right places. The best example i've seen is if you take a shoe box, and grab both ends of it, and try to twist it, you will see the box is completely rigid against all forces and torques, when applies through the edges. Now, take the lid off the box and try to twist it again. It will bend to shreads very easily. This is because the space frame is no longer fully triangulated. The lid face is now allowed to skew, and triangles resist skewing. You'll want a fully enclosed triangulated frame. You can either use a triangulated, box, or a tetrahedron or really any number of faces so long as every face is fully triangulated, and connected to other fully triangulated faces.

Edited April 6, 2013 by Bzroom

[OleBM]

I know that the official set that lego released back in the day ( http://www.bricklink.com/catalogItem.asp?S=7261-2 ) had pendular axles. It also had a very simple type of steering which I don't know the word for in english, but you achieve steering to either side by simply tipping the whole model over to that respective side. This would maybe be worth looking into. The model itself don't have to be able to steer extreme curves, because after what I have read about this tank, ( http://scifipedia.wikispaces.com/Heavy+Assault+Vehicle%EF%80%A2+Wheeled+A6+Juggernaut ) steering was a bitch, and the tank was suitable for open terrain combat only

[deckard9]

Thank you! This input is great. I'll try my best and see what I can come up with. I'll give the liftarms instead of the steering links a shot and will try to add more crossmembers..

I can't use penular axles, since the weight is so big, that if I don't have some travel in the suspension, it will bend the chassis... if one wheel on a pendular axle is lifted the whole pivot is lifted. On a vehicle with 5 axles this means the only way to compensate for this is bending the chassis...

Because you all insist on studed beams instead of liftarms... is the difference in stability really that big?

Edited April 6, 2013 by deckard9

[efferman]

yes, a sandwich with two studded 16L(15 holes) beams and two plates in between is extremely stronger than a studless beam combination

[Someonenamedjon]

Well, studded beams are slightly thicker and stronger, i read a post about it somewhere where this guy put the under a weight thingy and bent them.

[Zerobricks]

Its about technique. A pair of studded beams with 2 plates bteween them are 300% more rigid than 2 studless beams with connectors between them.

[Technyk32231]

Try using 6L links, because you can put an axle through the joints. Also, for better control, you could try some version of a triangulated 4 link, but without 9L joints. Good luck building!

http://www.brickshelf.com/gallery/88high/IDEAS/4-link-suspention/dsc01271.jpg

Edited April 25, 2013 by Technyk32231