So I was thinking of using a pivot slide system for intake and outtake. It goes: extend → intake → retract → pivot up → extend → outtake into bucket. We would use Misumi slides and I am working on an intake that grabs the sample with a wheel. The pivot would be powered by a DC motor and would essentially be rotating a hex shaft across the midsection of the bot with the slides attached to it. I need some feedback cause my team has very little done but our mentor is pushing back on this design. What do yall think about it?
I think this can be a successful design (having done this before).
One thing to be careful with is that rotating via a hex shaft often can introduce backlash into the system (the fit between most COTS hex shafts and the mating hex feature are often a little loose for assembly reasons). Additionally, if your slides tend trend towards heavy, there is potential to twist the shaft (most notable when pivoting while extended).
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Oooh thank you for pointing out these issues with shafts. Do you have any advice on how to prevent twisting or backlash? The slides would be aluminum and the intake would be mostly printed, minus the wheel and the servo.
Generally for arms, I’ve seen using a continuous shaft between 2 uprights that the arm rotates around. This can be done by mounting a pulley, sprocket, or gear to the arm and driving that assembly instead of needing to turn the shaft. The shaft then can be hard mounted to the frame to stiffen up the structure.
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Thank you!!
Clamping mount eliminates backlash for that one interface when done correctly. Other option is to use hex as a deadaxle or zombie axle and drive the arm directly. I wouldn’t use any other method because excessive backlash will ruin your day fast. Past that, there’s the usual avoid stacking adapters, tension belts/chain to take out backlash, shim unavoidable hex/hex interfaces.
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This is quite similar to the design my team is working through with an arm pivot low and centered to the frame (5" off the floor). Two drive motors on the pivot and two more driving twin 3 x 300mm double action Misumi slides.
My team have yet to do the math in terms of weight, moment or motor specs but they had the same slide arrangement last year and were able to do a quick and dirty mock up this past weekend. They compared the pivoting arm to a fixed double reach design (straight out to pick with a handoff then straight up to score). Right now the pivot design is coming out on top because it will be much easier to reach the high accent than a set of fixed slides.
One challenge they discovered that hasn’t been pointed out yet is this design also adds in extra work for the programmers to build in extra software limits both to keep in line with the new extension limits and to keep the drivers from flipping the robot when trying to drive and extend simultaneously.
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