I figured that this thread will be the best thread to update everyone on our build season. So updates will be posted here instead of flooding the recent threads with Aperture like crazy (we don’t want you all to hate us after all!)
But I guess I might as well get started for the first “update”
Cody has moved! And is still getting situated! We are working on converging more but its a little bit harder now that he has moved Literally ALL the way across Orlando in relation to my house!
But we converged yesterday and spat out ideas for the Hand of God that we needed to talk about since we haven’t for a while.
We discussed many different features that we have both been considering for a while. First on our list was using all 12 motors for the arm giving us maximum power for the control and movement of our arm! However this left us with only one option for the rotation on the arm. Pneumatics! As some of you may have figured out by now I LOVE Pneumatics!!! So much so I came up with many different ways to control this turntable with them. One of these we posted with this picture :
This is a kind of turn table that they use in industry for limited rotation applications. In this case the maximum it will rotate is ~180 degrees. I figured that if the robot were to rotate only that distance the arm can flip in and out as it pleases from each side. However this design served one problem, Means of control was VERY VERY difficult! Stopping the cylinders mid-stoke was something I was not prepared to spend money on to build this robot. So we threw that out Very quickly.
The next approach to turning the arm was a Pneumatic “engine” or crankshaft. We never got to the CAD stage with this one, however the design would have been inspired on another college teams engineering feats with this video:
We wanted to attempt to improve upon this engine to take less air than the current model in the view took. This was a problem because what the video states is that the accumulator got 660 RPM with the tank and well over 1000 with the air tank constantly replenishing it. Now… The VEX website states “45 Strokes from 100 psi to 25 psi” This kind of scared me (yes given thats one tank, Ill do real calculations later when I get all the numbers) Even if we stacked accumulators on the bot we would be using ALOT of air very. VERY. Quickly to even turn the arm. That wasn’t the only problem though, again the control aspect came up and as we thought a previous demo my Dad had done drew inspiration to something quite elegant.
On an RC Jet plane you have quite a bit of forward propulsion… How do you stop this if you ever wanted to get your plane back? Well there is option 1. Let it run out of gas… (not ideal) or option 2. Brakes!
Brakes on some Model RC Jets are actually pneumatic believe it or not! (See why I love them now?) What happens is a special O-ring rides inside the wheels but doesn’t actually touch until the computer tells the system to pump air into the ring. What this does is it expands the ring allowing it to create friction to stop the model aircraft! Now some of you might be asking “How would we do this in VEX?” Well Say hello to my next best friend! Surgical Tubing!!! I had realized that Surgical tubing and Pneumatics tubing had the same OD and they might be able to be interchangeable inside the fittings! (NOTE: This was never tested the idea was thrown our fairly quickly) This would allow us to essentially use the surgical tubing as a brake inside of one of the turntables that we would be using. Again we were worried about being able to control everything simultaneously and the idea was thrown out.
The next design saddened me because there was only one measly pneumatic cylinder in the design and this was in our claw! However what this design consist of was the following
1 Motor for the turret
4 393 Motors for the bottom joint on the first stage of the 4-Bar
2 Motors for the second joint of the 4-Bar
2 Motors for the Telescoping Pivot
2 Motors for the Telescoping Extend/Retract
1 Moto for the claw shoulder
and 1 single action cylinder for the tripod claw.
The early phases of this design were posted here:[https://vexforum.com/showpost.php?p=188995&postcount=75
You can see the Double 4-Bar mechanism that would allow us to get both height and length out of the arm allowing us to reach our over all goal of 8 feet.
Don’t worry I’m almost done here!
However when we finally got together and had a meeting we did some mobility analysis of the current design. Trying to see what we could do better. The first thing under the gun was the very first joint of the double 4 bar. We know its going to have ALOT of stress at those points and Im sure there is a gear ratio that will be able to handle it somewhere, However for the sake of design we have decided to not power the entire bottom stage. Heres why.
While the arm is in movement there will be only so many joints moving at once. And movement of multiple joints will create some really fun reverse kinematic problems. Now we figured that once the bottom joint was at its point, it would more than likely stay at that point for the entirety of the match creating problems with motors overheating and all that jazz!!! So, What is our solution?
If you said pneumatics you guess right! And now Im happy again with pneumatics usage!!! We will be putting a total of 4 double acting cylinders onto the first 4-bar. This will allow us to “prop” the first stage off at its 45 degree angle once the match starts. This would get us the most height and distance out of the arm that we can.
Now what happens if this portion of the arm needs to move at all. Well this next part hasn’t been discussed yet but its a relatively new idea. Well. I just thought of it really!
If we were to mount the pistons onto pistons (sounds crazy I know) we would be able to have a larger range of motion out of the arm. Instead of just two positions we could have four combinations of positions the arm could be at at any given time. It could have over extended reach meaning more height or under extended meaning more distance. Might be something interesting to try out for the first stage since its entirely Pneumatic already.
Any CAD’s regarding the first stage will be updated soon! I need to find the clevis dimensions or CAD files to go any further!!! Otherwise I’m going to start making my own (might not be a bad idea…)
Anyway thats all I can think of for now!!!
Its 2 AM and I probably should be heading to bed now…