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-   -   pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray (http://www.chiefdelphi.com/forums/showthread.php?t=154584)

Kevin Sevcik 01-02-2017 16:11

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Quote:

Originally Posted by EricLeifermann (Post 1639157)
I don't know what we were spinning them at accurately but it was faster than 6000. The problem wasn't that the expansion was affecting the shots, its that I wasn't comfortable safety wise with the expansion. We were also using 2in roller over a 1.5 aluminum tube, so maybe the smaller diameter doesn't expand as much was we saw with the large.

Centrifugal acceleration* = w^2 * r. More RPMs and more radius = more force expanding your tube. Since this acceleration applies to all of the tube, thickness won't matter, aside from the smaller force on the ID of the tube. The only material property that matters is some sort of ratio of density and elastic modulus, but that'd be the same since ou said it was the same stuff.

So all in all, not surprising your tube wanted to expand more than Spectrum's. Are you guys going for a longer shot to need that much more surface speed?

*Yes centrifugal. Pedants are welcome to spend 15 minutes drawing a FBD with a tangential velocity, required change in velocity to create a circular path, implied acceleration, unbalanced force to create that acceleration, etc, etc. I'm going to pretend it's a real force and get on with my life.

EricLeifermann 01-02-2017 16:14

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Quote:

Originally Posted by Kevin Sevcik (Post 1639174)
Centrifugal acceleration* = w^2 * r. More RPMs and more radius = more force expanding your tube. Since this acceleration applies to all of the tube, thickness won't matter, aside from the smaller force on the ID of the tube. The only material property that matters is some sort of ratio of density and elastic modulus, but that'd be the same since ou said it was the same stuff.

So all in all, not surprising your tube wanted to expand more than Spectrum's. Are you guys going for a longer shot to need that much more surface speed?

No just limiting the contact time and wheel size, as well as bad prototypes and the mentality that we will be able to spin slower with a properly built robot that has less friction deficiencies.

Brian Selle 01-02-2017 17:16

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Nice job 3847! What are the servo motors on the front/back of the shooter for?

fresh_prince 01-02-2017 17:21

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Quote:

Originally Posted by Brian Selle (Post 1639207)
Nice job 3847! What are the servo motors on the front/back of the shooter for?

Thanks! We'll only be using one of the two sets of three, but they're intended to be lane blockers. If we line up to the boiler and one of our side streams isn't on target, we want to be able to disable that stream instead of realigning our entire robot. We have one in the middle so that we can theoretically make a shot while our side is lined up with either the driver station or the front wall of the field.

Joy4201 02-02-2017 01:32

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
This is so amazing!
My team and I just had a few questions:
What is your shooter compression and how did you settle upon this number?
What is your intake height and how did you find this number?

AllenGregoryIV 02-02-2017 03:34

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Quote:

Originally Posted by Joy4201 (Post 1639360)
This is so amazing!
My team and I just had a few questions:
What is your shooter compression and how did you settle upon this number?

At the moment I believe it's around 4 5/8" between the drums but the tower includes two plates that can be changed to allow us to increase compression if we need too.

Quote:

What is your intake height and how did you find this number?
The height of the fixed intake roller is about 4.75" from the floor but that could also be changed by going to larger wheels. We currently have 1 5/8 compliant wheels from WCP but we could use 2" wheels if needed.

We wanted to design to the smallest amount of compression we could get to work and increase if needed. That way we start with the least load on the motors and add load as needed.

GeeTwo 02-02-2017 14:19

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Great design! Ironically, just looking at your rather complex robot, I was inspired of a way to make our gear pickup MUCH simpler (replace two motors with one belt). Thanks!

Bob Steele 02-02-2017 15:11

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Beautiful looking robot... and the CAD is nicely done.
I am looking forward to seeing how this plays on the field.

Well done!!

Joe G. 02-02-2017 15:50

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Quote:

Originally Posted by lukekaiser (Post 1639108)
Agreed

Teams need to make sure they read all rules pertaining to robot size carefully. I would hate to see a robot this well designed get to a competition and then not pass inspection.

I'm equally worried about teams building drive base/bumper assemblies to the maximum allowed dimension, and then regretting this decision when they realize all the cool things they could have achieved with a smaller base that enabled over-the-bumper dropdowns. In past years, iterating in new systems was just a matter of finding the space and weight, this year there are going to be a lot of teams boxed out of improving their robots and adding features like Spectrum has because they assumed bigger=better early in the process.

Chris is me 02-02-2017 16:11

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Quote:

Originally Posted by Joe G. (Post 1639589)
I'm equally worried about teams building drive base/bumper assemblies to the maximum allowed dimension, and then regretting this decision when they realize all the cool things they could have achieved with a smaller base that enabled over-the-bumper dropdowns. In past years, iterating in new systems was just a matter of finding the space and weight, this year there are going to be a lot of teams boxed out of improving their robots and adding features like Spectrum has because they assumed bigger=better early in the process.

I honestly expect the opposite to happen - teams built chasses that were too small so they could do over-the-bumper stuff, expecting a huge advantage, then realizing it was more trouble than its worth and are now sad about the substantial decrease in ball capacity they traded for that decision.

3847's robot is a good example of leaving a conservative amount of space (just an inch or three) for OTB stuff, but I bet others left way more than they should have.

Ty Tremblay 02-02-2017 17:13

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Quote:

Originally Posted by Chris is me (Post 1639598)
I honestly expect the opposite to happen - teams built chasses that were too small so they could do over-the-bumper stuff, expecting a huge advantage, then realizing it was more trouble than its worth and are now sad about the substantial decrease in ball capacity they traded for that decision.

3847's robot is a good example of leaving a conservative amount of space (just an inch or three) for OTB stuff, but I bet others left way more than they should have.

Why does a smaller frame necessarily mean a reduction in ball capacity?

ngreen 02-02-2017 17:37

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Quote:

Originally Posted by Ty Tremblay (Post 1639622)
Why does a smaller frame necessarily mean a reduction in ball capacity?

Unless you are expanding your hopper too, which they are.

I really like the design of this robot. I wish we'd have considered a gear pickup on the same side as the fuel intake because I think fuel on the floor will make it difficult to reach gears in some cases.

Chris is me 02-02-2017 23:00

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Quote:

Originally Posted by Ty Tremblay (Post 1639622)
Why does a smaller frame necessarily mean a reduction in ball capacity?

I mean, if you grow your hopper out over the top of your intake, sure. But if you grow your hopper out in that direction, isn't that just going to stick out the same distance as your over-the-bumper intake? Which then isn't sticking out farther than your robot's frame anymore? Isn't that kind of defeating the purpose then?

Ty Tremblay 02-02-2017 23:32

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Quote:

Originally Posted by Chris is me (Post 1639738)
I mean, if you grow your hopper out over the top of your intake, sure. But if you grow your hopper out in that direction, isn't that just going to stick out the same distance as your over-the-bumper intake? Which then isn't sticking out farther than your robot's frame anymore? Isn't that kind of defeating the purpose then?

I'm not 100% sure I follow. If you're extending your hopper with your collector, you negate the effects of making your frame smaller while still gaining the advantages of an over-the-bumper collector.

cadandcookies 02-02-2017 23:44

Re: pic: Spectrum 3847 - 2017 CAD Model: Gamma Ray
 
Quote:

Originally Posted by Chris is me (Post 1639738)
I mean, if you grow your hopper out over the top of your intake, sure. But if you grow your hopper out in that direction, isn't that just going to stick out the same distance as your over-the-bumper intake? Which then isn't sticking out farther than your robot's frame anymore? Isn't that kind of defeating the purpose then?

I'm not sure I follow you now. If you expand your hopper when your intake goes over the bumper, then your hopper is not constrained by your frame perimeter anymore. Thus you're minimizing the effects of lost storage space and still getting your full width over the bumper intake, at the cost of now having to designing the whole expanding hopper thing.


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