DrJB Posted January 23, 2014 Posted January 23, 2014 Sounds like the OP is doing a tristar wheel ... Look up Lego Tristar and you'll see few interesting designs. Quote
Lipko Posted January 23, 2014 Posted January 23, 2014 Couldn't you get away with a near-perfect scalene triangle and build a totally different but more trivial frame? base length: 19L, height: 16L. Okay, the sides would only be 18,5L long, but is that a huge problem? Quote
JGW3000 Posted January 23, 2014 Posted January 23, 2014 (edited) The key is to have some adjustability to avoid misalignment and undue stress on pins, I used 90-degree blocks which allow axles to freely pass through, only now you have an irregular spacing between the connectors. .Adjust axle lengths to permit building off of, and add bushings to keep axles in place. Replacing the 2L with 3L pins on the beam ends may also prove useful. Once assembled, you can probably remove the center parts. (I was in a boring meeting and this occurred to me ) Edited January 23, 2014 by JGW3000 Quote
Blakbird Posted January 23, 2014 Posted January 23, 2014 This does not seem right. In fact, I tried building it, but could not. Looking at each of the vertices of the triangle, you cannot fit one liftarm in between two others, such that the angle between them is 30 degrees. For the middle liftarm to fit between the neighboring two, the spacing/gap must be equal to 1M. However here, we have 1.732 (=sqrt(3)) minus 1 = 0.732M ... Keep in mind that the width of a Technic liftarm is not 1M. It is narrower than that to allow space between adjacent parts. So this does stress the pins, but not nearly as much as your figure would suggest. Quote
JGW3000 Posted January 23, 2014 Posted January 23, 2014 (edited) Had another meeting, some more concepts, these maintain the 1M spacing at the points, many options on how to connect in the middle and between the legs - all are stress free. Although in the second one, the 2M axles are not fully seated in the connectors. Combinations of my previous post with this one will avoid the need for 'tri-connectors', but will involve axles with adjustments. Edited January 23, 2014 by JGW3000 Quote
DrJB Posted January 24, 2014 Posted January 24, 2014 (edited) Keep in mind that the width of a Technic liftarm is not 1M. It is narrower than that to allow space between adjacent parts. So this does stress the pins, but not nearly as much as your figure would suggest. You're absolutely Correct, I was going for 'extremes/nominal'. The ultimate test is really to try and build the actual contraption, and if you're using relatively new parts with the 3L friction pins, the contraption is difficult to snap together. One option to relieve the stress a bit would be to try the 3L smooth pins instead ... but those are rather rare in modern technic sets ... We're getting really creative here (and using 'rare' Y parts) ... nice!!! I tried LDD (on a separate monitor) on my lunch break, but somehow whenever I do that the color palette gets totally messed up on the other 2 monitors ... and I can't see anything ... I wonder if part 64566 provides the correct spacing .... though it is not 100% technic, but nonetheless can attach to straight liftarms and rather 'strong'. Edited January 24, 2014 by DrJB Quote
Saberwing40k Posted January 24, 2014 Posted January 24, 2014 Umm, I hate to say this, but having a triangle shape like this will actually impair the function of the mechanism. A tri star bogie has to have 3 radially arms, with nothing in between them. Making the assembly a full triangle could result in the frame catching on an obstacle. Quote
DrJB Posted January 24, 2014 Posted January 24, 2014 Umm, I hate to say this, but having a triangle shape like this will actually impair the function of the mechanism. A tri star bogie has to have 3 radially arms, with nothing in between them. Making the assembly a full triangle could result in the frame catching on an obstacle. Correct ... but the OP has not confirmed yet he's building a TriStar wheel, or is he? Quote
JGW3000 Posted January 24, 2014 Posted January 24, 2014 (edited) Umm, I hate to say this, but having a triangle shape like this will actually impair the function of the mechanism. A tri star bogie has to have 3 radially arms, with nothing in between them. Making the assembly a full triangle could result in the frame catching on an obstacle. We're getting really creative here (and using 'rare' Y parts) ... nice!!! OK, here is a solution with common parts and equally spaced beams, not sure how strong this will be Edited January 24, 2014 by JGW3000 Quote
Hrafn Posted January 24, 2014 Posted January 24, 2014 OK, here is a solution with common parts and equally spaced beams, not sure how strong this will be I like that you're using commonly available parts, but ultimately I think the axles are going to slip out of the connectors. To withstand tension, the assembly really needs liftarms, which can't pull apart. Quote
JGW3000 Posted January 24, 2014 Posted January 24, 2014 I like that you're using commonly available parts, but ultimately I think the axles are going to slip out of the connectors. To withstand tension, the assembly really needs liftarms, which can't pull apart. My thoughts also. How about going with 4 points (four wheels) instead of 3 - this will make the assembly much more rigid and much easier to build. Quote
JGW3000 Posted January 24, 2014 Posted January 24, 2014 Trying not to beat a dead horse here, but this is my concept for a four-wheel mechanism - may need to be strengthened where the axle 8 w/stop connects to the two gears being used as the hub. I would build this myself if I had 16 matching wheels (have 8 too small, and 10 between my 9393 and 8049, but not ready to give them up yet). Quote
DrJB Posted January 24, 2014 Posted January 24, 2014 While nice, (and your perseverance commendable) it would not work very well as a tristar wheel (assuming it is what OP wants to build) Quote
JGW3000 Posted January 24, 2014 Posted January 24, 2014 While nice, (and your perseverance commendable) it would not work very well as a tristar wheel (assuming it is what OP wants to build) DrJB, please elaborate? Assuming this part would be a replacement for a tri-star wheel, what issues do you see? Quote
SNIPE Posted January 24, 2014 Author Posted January 24, 2014 (edited) Hi, Thanks for the replies, yes its a tri-star wheel I'm after, After trying each idea I think Darsedz' idea is the best as it is the strongest and is fairly centered, so it will either be my original idea or his up to now. I think axles supporting this will be too weak as axles bend easily under load and I couldn't seem to fit a bracket with a hole in-between because the gaps on each point of the triangle is less than 1L. Philos idea looked good but it didnt line up on the last hole needed, it was simular to my original but was less offset. I heard a triangle is the strongest shape which is why girders have that pattern and for a square you'd need more motors, more wheels, more gears/chains Edited January 24, 2014 by SNIPE Quote
DrJB Posted January 24, 2014 Posted January 24, 2014 (edited) DrJB, please elaborate? Assuming this part would be a replacement for a tri-star wheel, what issues do you see? You need to look-up how the tri-star (developed by GM for some military vehicles) works. Because there are only 3 wheels, it is easy to go over obstacles and ditches. If you put 4 wheels however (or even more), such 'off-terrain' capability would strongly diminish ... especially if there is a hole/ditch and one of the wheels needs to take a dice. With 4 wheels, the 2 neighbors would prevent the center wheel from going very low in a pothole. Edited January 24, 2014 by DrJB Quote
darsedz Posted January 24, 2014 Posted January 24, 2014 .. After trying each idea I think Darsedz' idea is the best as it is the strongest and is fairly centered, so it will either be my original idea or his up to now... good news... now it's time to do the rest and show it to EB audience :) Darek Quote
JGW3000 Posted January 24, 2014 Posted January 24, 2014 (edited) Found this interesting page of a motorized MOC of the iconic LandMaster from the movie Damnation Alley http://lego.roerei.n...-landmaster.htm, by Jurrien Bijhold; it features two pairs of tri-star wheels, all 12 wheels are driven, and articulated body sections. Edited January 24, 2014 by JGW3000 Quote
Hrafn Posted January 24, 2014 Posted January 24, 2014 I suspect that some version of Zblj's "Twister" tri-star setup is going to work best. It's simple and looks pretty robust, and the arms are spaced at exactly 120 degrees. Quote
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