how to model a rubber track ?

[Guest]

the question is:


should the track be an assembly or a single part in Sw?


If it should be an assembly of dozen of same parts, then how to fix that problem that the part appears quite differentat the position on the horizontal surface and that on the flange due to deformation? see the pic. enclosed


The track shown in the pic is created as a single part, and I think it is actually impossible to make it move, 'cause the motion of it should be along its outline, and I have no idea at all how can a part like that moves along its own outline.


Any idea? Pls say out your opinion -- you don't have to be with the solution.

 

[Guest]

sorry , I fail to unload the picture although it is only 11KB...

 

[Angstboy]

Well...in the absence of a picture or diagram or even a web link of any sort showing how this situation is so very different from the previous problem of modeling a tank track that none of that advice applies...I am going to take the path that usually leads to disaster, namely the path where one just makes blind assumptions and stumbles onward - otherwise known as the infamous 'ready, fire, aim' scenario...


From the way you word your description, it sounds to me like you are confused because you have a track made up of multiple track blocks and there appears to be a case of 'impossible geometry'. Now this is where I am not quite sure I understand your question. The track block that is horizontal and static appears to be geometrically different from the track block that is engaged by the driving sprocket - I think because somehow you are STRETCHING the block like a rubber band? Am I following you correctly? The track block engaging the sprocket is deforming by stretching due to it's being made of rubber and that is what you are confused about?


If this is indeed the case...if it was me, I would model the track as if the blocks were solid and not made of rubber. Assume they will NOT stretch and deform, leave them rigid. Then the track will move - trust me, it will because they are rigid on a real tank and it moves quite well. What I would also do is build tension adjustment into the belt/track so that the slack/stretch of the beltcan be taken up when the vehicle is constructed in real life.


I think you are going to drive yourself absolutely crazytrying to show eachrubber track block deforming by stretching as it goesthrough or around a certain portion of the path. I am not even sure if Solidworks even has the power to do that in such detail. Solidworks can animate a chain with rigid links. So make the tank tracks with rigid links and you can make a nice animation that is a good APPROXIMATION of what will happen. It will get the idea across, which is why the animation package is really included as a part of Solidworks.

 

[Guest]

thanks a lot


Sorry for not making it clear.


In modeling the track, it is exactly the deformation driving me crazy. IF I draw the track as a single part, which means I creat a single block and then use the Arc Array function to make the whole track with this basic block. With this method, the block which locates above the flange automatically appears deformed -- its originally even surface are then deformed to be an arc surface in order to fit the outline of the wheel. HOWEVER, in the way, I have no idea how to make it move since the track is just a single part which is supposed to move along its own outline.


Then I tried to create the track as an assembly, then the question turns out to be how to create all those track blocks? Cause some of them, are undeformed, with even surfaces, while the others, above the flanges of the wheel, should be deformed to fit the outlines. AND once the track moves, which means all these basic blocks move along the outline of the track, then the undeformed one are going to deformed while the deformed ones are going back to normal....

Cause the mass budget is reall critical, so I can only choose rubber track, and even for a metal chain, although deformation can be advoided, however, the relative position of the blocks and the blocket and the grips also change in the movement.


Cheers!

 

[Angstboy]

Take a lesson by observing how things behave in real life. If I am reading you correctly, you are assuming that the track blocks MUST deform into an arc as each one passes over the idler roller in the front. In my earlier description of how a tank track on a real tank moves, this would be the idler 'sprocket' in the upper left position.


It doesn't happen. The track blocks stay rigid. The blocks are free to rotate as they are being carried along by the connecting blocks on their ends - those are the ones that actually engage the driving sprocket and carry power. The blocks/pads themselves have a tanget contact with the idler wheel. As several wrap around it, all that changes is the angle of attack of that tangent. I am sure that Solidworks can keep a 'tanget' mate between two rotating parts. So all the track blocks stay identical- none have to 'deform' into an arc.


Yes, you and I know that in this model with the track being rubber there will be some stretching. But is it really going to make that much difference in the animation? I don't think so.


Yes, you do have to make a lot of blocks in order to make a tank track. That is just the nature of the beast. But once you do one, thank goodness CAD lets you copy them. You do not have to make each one from scratch.

 

[Guest]

cheers!


I will try to follow your way and see what happens


It will probably be a problem cause my track are quite short and each block is rather big therefore I quite doubt whether it can work to neglect the deformation...


many thanks -- be back soon

 

[Angstboy]

If modeling the track as a CHAIN does not work....perhaps treating the track as a very odd BELT might be in order. That might be something to consider....

 

[Guest]

cheers


I did consider to treat it as a belt in the simulation... BUT there should be someway to make a more real track move, AND I just would like to find it out...


The last hour I have been drawing the new track, which is an assembly rather than a single part. THEN I've got NEW questions -- HOW to assemble a track?


Cause the mate types switch from each other time to time? For two adjacent blocks locating at horizontal section, they can be mated by defined a coincidence mate between their adjacent faces; HOWEVER, for the two blocks, which are above the wheels, this can't work cause their angles of attach of the tagience are not the same! And the mates between two adjacent blocks as well as the mates between the block/track and the wheels change (switch from one to the other and then repeat) in the motion of the track/wheel? How to consider this problem?


Any idea?

......thanks a lot

 

[Angstboy]

look at these sites,may give you some ideas about short track systems


[url]http://www.gatorbacktracks.com/predator_series_steel_tracks. htm[/url]


[url]http://www.rctankcombat.com/articles/track-systems/31RollerC onstruction-large.jpg[/url]


[url]http://www.rctankcombat.com/articles/track-systems/42Plastic Performance-large.jpg[/url]


For a moment, consider how a real track works on a real tank...Each track padlooks very much like a giant letter H. A section of track would then be approximated by HHHHHHHH. These track pads are not mated to each other. There are track connectors that look like an ellipse with two holes in them. Each hole slips over one of the rods of the H that is sticking up on one track pad. The other hole slips over the rod of the adjacent H. The connector block is mated to the track block by CONCENTRIC. The track block is free to rotate. The connector blocks are what keeps it in line. The connector blocks are what engage the drive sprocket also. Think about that.

 

[Guest]

thanks a lot for the websites

. The HHHHHHHH track type with track connectors mentioned is for the chain shown in


[url]http://www.rctankcombat.com/articles/track-systems/31RollerC onstruction-large.jpg[/url] (type A)


track connector does make things easier, BUT, How about a rubber track without track pad connectors? My track is much similar to this


http://www.rctankcombat.com/articles/track-systems/42Plastic Performance-large.jpg (type B)


and it is made of rubber and simpler, it is designed almost the same as that of this toy


http://www.roguerobotics.com/images/assembly/ATR/stepsix-lar ge.jpg (type C)


which has no track pad connector at all

(NOW i am considering of adding cylinder connectors )


BUT ANYWAY, I am quite curious about how to mate the individual track blocks without connectors?


Cheers
Edited by: swstudy

 

[Angstboy]

If I were doing this, two approaches come to mind. One would be to forget about the chain analogy altogether and think of this as a continuous belt with cylindrical bumps spaced along it.


The other way might be to stay with thinking of this as a chain and disregard the additional part of a 'track connector'. Make the pads themselves the connectors by altering their design. Each block would have along one side the cylindrical protrusion at 90 degrees to the belt's travel as shown in the 'type C' toy you mentioned. However, on the ends of the protrusion the pad would be recessed slightly so that the cylinder end sticks out by itself.


On the other side of the track pad you would have a corresponding female depression that mates with the cylindrical section of the next track and on the extreme ends are two male protrusions with holes in them - the holes snap on to the cylindrical ends of the next pad that stick out. Do you follow me? In this way, they interlock and the pads are allowed to move.

 

[Guest]

I guess I do follow you cause I've come up with theEXACTLYSAMEidea as your second approach this morning, and now i am on my way to prove it right

My forefeelling is that the assembly of the track would no longer be a problem, BUT how to make it move will still remain a problem. I was thinking of drag the track using contangential and conincidence mates bwteen the track and the gear wheel, but, what will happen to these mates when the pad moves out of the curve section of the wheel into the horizontal section?


I will propose my question later...


Thanks for going so long with me.


Cheers

 

[Guest]

successfully assembly the track on the wheels!!

really excited to watch the track move smoothly under my drag... tomorrow will try to assemble the whole car then find out how to make it move... sorry have to stop here today...


Cheers
Edited by: swstudy

 

[Guest]

back again'cause stuck again.


Firstly, stupid as I was, I spent a whole day to assemble the track with the new-style blocks and finally was so shamed to find the whole track then appeared as a single part in the whole vehicle's assembly. Well, then Irealized that we need to build the whole car in one assembly with every single piece of part, which means if we have got 200 pieces of track pads, we have to insert it 200 times, and if each needs three mates to settle it down, then we need to make 600 mates. Am I doing the correct thing?

Secondly, there is still a problem with the mates between the wheel and the track pads. For the first pad, one tangent mate (between the pad'sflat surface and the gear wheel's cylinderal surface) and one conincidence mate (the side surfaces of the pad and the wheel) to give it the position, and then for the succedent ones, one concentric mate and one conincident mate are set between the new pad and the former one, besides, ONE TANGENT MATE is also give to make it fix the cylideral surface of the gear-wheel. Then, The question is, these pads can move quitely well along the wheel they areinserted on and also move well on the straight section, but they CAN'T move along the idler wheel's cylinderal surface because they should be tangential to the surface of thegear-wheel.


I doubt that whether I can make myself clear. Anyway, how to mate the all these track pads and the wheels? my model only gets two wheels on each side, one gear wheel, and one idler wheel, and a track is supposed to connect them.


Helpppp! SOS