Woohoo, now this is how you ask Questions! Here are some answers:
Quote:
Originally Posted by JesseK
That latch! Wow! How hard was it to balance the push-up force from below versus the cylinder's resistance, only to need to use the retraction stroke to then lift the entire stack in order to set it down? Was this accomplished via specific prototyping, calculations, a bit of both?
I also see an axle linking the front/rear latches on either side. Were there any issues with the left/right sets not firing at the same time, and if so what eventually solved it?
What are the 2 pieces hanging off the bottom of the claw for?
The long skinny horizontal cylinders that run front-back didn't seem to import correctly. Are they for pushing the tote stack out of the bot?
There are some really great nuggets of wisdom in the details of this CAD - from the nifty sheet metal carriage all the way down to the idler sprocket assembly design. I dunno how I would approach a rear-leaning tower without sheet metal though. It's a really neat design.
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I was not a part of the design team for the latches or indexer but I can tell you how I would have done the calculations. First I would find out the least amount of force the motors can exert through our gearing with a full stack of Totes, this way it is lifting all 5 totes (The 6th is never pulled up). Once I find that I would need the amount of force from the cylinders on the latches. I would draw a Free Body Diagram of the latch system, and calculate the force pushing the latch open (Totes pushing up), and the force pushing the latch closed (Cylinder Extending force). The force of the latches being closed would have to be less than the force pushing up.
Regarding the latches pushing the stack up, it never does. Originally the latches had slants on them, so we could pull the latches back easily without having to do anything else. However after GTR Central (We dropped a stack in the finals 1 match I believe) we changed this. We then made them have flats on them so the totes cannot come loose. However, since the cylinder could not push the stack up we had to make the indexer pick up the stack ½ an inch so the latches could be pulled back. We made a “Drop Sequence” Button on the driver’s controller. When we dropped a stack the indexer would pick up the stack a bit, pull back the latches, open the intakes to can pick up position (about 2 inches outwards from normal position) and then the driver would back up.
Regarding the axle across the two latches: No we never used cylinders on our prototype because we only had it going up (not dropping a stack). Instead we used pieced of wood screwed to a 2x4 and an elastic to pull it in. Simple and very affective. I know we talked about possibly removing a cylinder, and having only one on each side, and having this was a possibility. Also we knew that if only one of the two cylinders retracted (Shouldn’t be possible anyways) it would be bad, and we would drop the stack.
Reagarding the two pieces of Angle Iron on the bottom of the claw. Mike Marandola was not correct actually (See quote below). These pieces were so that the claw could sit in the back latches. If you look in the CAD model the claw does not sit on the back latches. Instead we had to add these so it would sit on them for when we picked up a can. The angle iron needed to sit around the top tote, maybe it helped to keep them from flying out, but that is not the original reason.
Quote:
Originally Posted by Mike Marandola
They for capturing the top of the stack.
I was given one of your worn out BB wheels at IRI and it's broached for 3/4" with a hex sleeve put in it. Why is that? Was it not originally 1/2" hex, did the plastic start rounding, or something else?
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The 1/2inch jhex broached wheels were out of stock, so we bought the ¾ Outside to ½ insde Hex extrusion from Mcmaster-Carr and glued them inside of the wheel. We had 1/2inch also, wear and tear wasn’t the reason though.
Quote:
Originally Posted by cxcad
Do you guys have any analysis that was done on your parts that you can share with us? I'm particularly interested in how you guys ensured that your robot was designed to play a full season of matches and practices for your practice bot. How do you train students up to that level of design (if you're doing analysis with the students)? That's pretty high level for most of FRC. I would assume it's the mentors doing it (ok by me), because most students don't have that type of knowledge just yet.
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If you are talking about Stress analysis and Fatigue Analysis on the Robot CAD, I do not remember ever doing any or seeing it done by any member. We try and over build things (while staying light enough). If it is sticking outside of the robot (the intakes) they will be very strong, because we assume someone will hit them. You can see in the CAD that all of the sheet metal is 1/8 inch thick, and when built it is very strong, and would be very difficult to bend/break. The only thing I can see someone doing some real stress analysis on is something that has a very large force on it (a catapult?). Even then you should just try and over built it. To make everything work for a full season, we have spares. If you go to our pits you can see we sometimes will have full replacements built for the robot, such as assembles intakes etc. If we notice something on the practice robot is warping, breaking, or something is going wrong, we improve it on that robot first and then at competition we fix the competition robot.
Quote:
Originally Posted by CJ_Elliott
Did 1114 test any other sorts of wheels or is there some resource that you can see which wheels would be best for this function, obviously banebots worked really well but if there is a way to speed up the process of selecting wheels...
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You can look at my past post
here for the answer
Quote:
Originally Posted by marshall
At the risk of derailing this thread, making that assumption about any team is something no one in FRC should do. Believe me when I tell you that the students of 1114 are passionate, dedicated, and an amazing and one of a kind group. Their mentors are ok too. 
I haven't had a chance to look at this CAD yet. Did the harpoon designs get released? |
Quote:
Originally Posted by cxcad
Of course the students are passionate. I'm not questioning that. It's just that most students can't perform meaningful analysis without some help.
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On 1114 we may do things differently than a lot of other teams. While I was on my other team it was different then 1114. It seemed like the mentors would just tell the students to go design the robot, go build the robot, and go program the robot. On Simbotics it is more like Let me help you design the robot, let me show you how you can calculate what part we need for this, let me show you how I would build the robot/let me help you build the robot, or can I show you how I would machine that part and show you how you can program the robot. This is basically what Big Simbot/Little Simbot program is.
For an example: Last year the driver and I designed the intakes. What ended up happening was me sitting next to him directing what he should change, what parts we should/could use, and then me just adding the parts he made to the assembly. He did most of the design work, and I just pushed him along and helped him learn new CAD techniques. We even touched on how to design “In-Context” assemblies. He really seemed to learn more about CAD and enjoyed it more too. He is now applying to university for Mechanical Engineering next year.
Finally, regarding the harpoons, we have not released the CAD yet, but yes we are planning on releasing it, should be up within a week or two.
Go with what you know will work, and try a little less if you are feeling brave. That is my rule of thumb. - sanddrag [more] 
07-12-2015, 23:40
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