Solidworks Cascading Belt Slide Tutorial
This is a simple tutorial on how to constrain an assembly with a synchronous movement style cascading actuator.
The tutorial was made because of a post here on 2018 with someone asking how to, and no one had/gave an answer. Since I was making one for a project of mine, I found out how to with trial by fire.
See here for the principle video: https://www.youtube.com/watch?v=yGxCs2ka7HQ
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Step 1: Limit Distances
Firstly, this tutorial is going to be based on the user already having the core linear motion decided on, whether it be linear rails, V-Wheels, drawer slides, etc.
With that, the assembly will start with all rails in the retracted position:
Below, the purple lines show that the outer most t-slot will be fixed in place wherver your assembly attaches to. Thus, to constrain travel, a limit distance mate from #1 to #2 is made with a 0 min, and whatever max you need.
This mechanism is based around every subsequent stage being the same, so if you want 1m of travel done in 2 stages, you would have two 500mm travel stages, or you can have 4 250mm travel stages. Regardless, the process is the same: a limit distance between a pair of rails is made with the same distance of 0 min and X max.
Note that this whole design is constrained on one side, and then mirrored to the other.
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Step 2: Belting
From the video in the description, it shows how the use of belting, chains, or cable is used to make every stage of travel move in sync. To achieve this, the initial stage fixes the (belt will be used from here on) to force the next stage to move at the same rate of travel as itself.
To achieve this mechanically in Solidworks, the use of rack and pinion mates are needed; two for every stage in the assembly.
The image shows how the t-slot to the right, which in this specific case is the fixed t-slot, is the rack and the timing belt pulley is the pinion. There is no need to reverse the mate for any of these.
Below is the second rack and pinion mate with the same pinion, but the next t-slot in sequence.
This is repeated for all stages. Remember, all of these mates are to be done with the assembly fully collapsed. If not, you can suppress all R&P mates, move the assembly to the collapsed position, then un-suppress them all to allow for correct motion. If not, it will not act right at all.
If you have a pulley or something that does not have the exact pitch diameter and you know what it will be, a simple formula for timing belt pulleys is this:
(Num_Teeth * Belt Pitch) / Pi. So for the assembly of mine, (20*2)/Pi = ~13mm per the mates shown.
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Step 3: Conclusion
If all went well, you should have an assembly that moves like the initial video (23.5mm/s linear speed, 235mm travel total):
I hope this tutorial will prove useful to someone, and it should be something other CAD software can replicate.
If anyone has suggestions to improve the overall concept, feel free to post them.
