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  #106   Spotlight this post!  
Unread 02-04-2018, 11:38 AM
Christopher149 Christopher149 is offline
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Re: FRC 95 2018 Build Thread

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Originally Posted by JamesCH95 View Post
This gives us ~30lbs to play with for ramps, which I think will be plenty.
Not sure what your design is, but I'd be happy if we kept our ramps within 38 lbs.
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Unread 02-04-2018, 11:47 AM
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Re: FRC 95 2018 Build Thread

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Originally Posted by Christopher149 View Post
Not sure what your design is, but I'd be happy if we kept our ramps within 38 lbs.
38lbs?!

We're building with sheet metal, thin polycarbonate, and one active mechanism to release them.
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Unread 02-04-2018, 12:08 PM
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Re: FRC 95 2018 Build Thread

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Originally Posted by JamesCH95 View Post
38lbs?!

We're building with sheet metal, thin polycarbonate, and one active mechanism to release them.
The difference between passive and active ramps...
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Unread 02-05-2018, 07:36 AM
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Ramps!

Amid the storm on Week 4 Teasers, here's something not too teaser-y.



We've settled on ramp geometry. We used the AM14U Long configuration as a benchmark and have two ramps of comparable geometry but different construction to choose from. The tubular design, on the right, is a bit lighter but includes 21 built parts per assembly. The sheet metal version, on the left, is a little heavier, but is only 5 built parts. I'm not including OTS components like hinges, air springs, and standoffs in those counts, they are the same in each case and require little or no effort to acquire. Not pictured: polycarbonate deck panels, gripping material for wheel traction, and release mechanism.

The specs:

~21 approach angle
152 break-over angle
10.9in deck height
18.75in deck length, 20.75in from our leading frame perimeter
32in wide approach, with clearance for adjacent bumpers

Ostensibly any 6WD comparable to the AM14U can drive up 'heavy' end first and tip into a 'climbed' position.
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Unread 02-05-2018, 09:23 AM
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Re: Ramps!

Quote:
Originally Posted by JamesCH95 View Post
Amid the storm on Week 4 Teasers, here's something not too teaser-y.

The specs:

~21 approach angle
152 break-over angle
10.9in deck height
18.75in deck length, 20.75in from our leading frame perimeter
32in wide approach, with clearance for adjacent bumpers

Ostensibly any 6WD comparable to the AM14U can drive up 'heavy' end first and tip into a 'climbed' position.
I like the design, but does that geometry work? The AM14U in the long configuration is around 38.5" with bumpers. I suppose the deck would be around 5" from the outrigger wall (your bumpers + the 2" rung wall offset). It might just work.
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Unread 02-05-2018, 09:31 AM
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Re: Ramps!

Quote:
Originally Posted by apm4242 View Post
I like the design, but does that geometry work? The AM14U in the long configuration is around 38.5" with bumpers. I suppose the deck would be around 5" from the outrigger wall (your bumpers + the 2" rung wall offset). It might just work.
The front of the AM14U frame is ~16.1in from the center axle. The deck extends ~20.75in from the front of our frame. So, assuming both robots' bumpers hit the same thing, we'll have ~4.6in of extra deck space.

Edit: your comment reminded us of the 2in offset from the tower, a very important detail that we overlooked the first time through! Thanks! We'll be relocating everything rearwards by ~2in to compensate.
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Last edited by JamesCH95 : 02-05-2018 at 09:42 AM.
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Unread 02-05-2018, 10:58 AM
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Re: FRC 95 2018 Build Thread

How does your CG look before and after adding the ramps? That was one of my biggest hang ups with doing ramps since raised bumpers with a high cg is a pretty scary combination.
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Unread 02-05-2018, 01:34 PM
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Re: FRC 95 2018 Build Thread

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Originally Posted by Electronica1 View Post
How does your CG look before and after adding the ramps? That was one of my biggest hang ups with doing ramps since raised bumpers with a high cg is a pretty scary combination.
I'm not sure.

We intend to check through testing. We're looking at 2x assemblies at ~10lbs each with their own CGs about 27in off the ground.

Without the ramps or bumpers our drive base with elevator and cube at max height we have to drive full-stick forward to full-stick reverse in low gear to tip it over. Certainly with ramps that will get worse, but hopefully not so bad that we have to be overly careful. Our controls solution is to look at the Athena's accelerometer to chop down throttle if we're tipping if we need to.
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Unread 02-05-2018, 01:42 PM
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Re: FRC 95 2018 Build Thread

Loving the robot this year. What drove you to do this wider style of ramp over simple side-flip-out ones?
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Unread 02-05-2018, 01:51 PM
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Re: FRC 95 2018 Build Thread

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Originally Posted by asid61 View Post
Loving the robot this year. What drove you to do this wider style of ramp over simple side-flip-out ones?
Thanks!

A few things drove us that way:

-If the ramps are aimed at your superstructure (i.e. side-on) guess what an overly enthusiastic robot is going to crash into? We didn't want to roll those dice!
-Drivers approaching side-on have to deal with the scale's plates
-Drivers approaching side-on have to rely heavily on depth perception to align onto the ramp
-Drivers approaching end-on (i.e. our design) have a good visual indication of how they are aligned without depth perception
-End-on folding geometry lets us make the ramp target as wide as we have height, which is to say much wider than side-on ramps (for the same number of DoFs)
-End-on folding geometry lets us unfold everything with low-force gas springs and gravity more easily than other folding concepts we looked at
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Unread 02-05-2018, 02:14 PM
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Re: FRC 95 2018 Build Thread

Quote:
Originally Posted by JamesCH95 View Post
Thanks!

A few things drove us that way:

-If the ramps are aimed at your superstructure (i.e. side-on) guess what an overly enthusiastic robot is going to crash into? We didn't want to roll those dice!
-Drivers approaching side-on have to deal with the scale's plates
-Drivers approaching side-on have to rely heavily on depth perception to align onto the ramp
-Drivers approaching end-on (i.e. our design) have a good visual indication of how they are aligned without depth perception
-End-on folding geometry lets us make the ramp target as wide as we have height, which is to say much wider than side-on ramps (for the same number of DoFs)
-End-on folding geometry lets us unfold everything with low-force gas springs and gravity more easily than other folding concepts we looked at
Those are awesome reasons, thanks! This is making me re-evaluate our entire robot thought process...
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Unread 02-05-2018, 02:26 PM
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Re: FRC 95 2018 Build Thread

Quote:
Originally Posted by JamesCH95 View Post
-If the ramps are aimed at your superstructure (i.e. side-on) guess what an overly enthusiastic robot is going to crash into? We didn't want to roll those dice!
I feel like this is the only reason you need! :-)
Quote:
-End-on folding geometry lets us make the ramp target as wide as we have height, which is to say much wider than side-on ramps (for the same number of DoFs)
It also means the ramp target is shorter than it could be - they won't be able to drive very long into it, and it may mean teams will slide backward at the end.
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Unread 02-05-2018, 02:51 PM
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Re: FRC 95 2018 Build Thread

Quote:
Originally Posted by asid61 View Post
Those are awesome reasons, thanks! This is making me re-evaluate our entire robot thought process...
Happy to 'help'

Quote:
Originally Posted by rwodonnell View Post
I feel like this is the only reason you need! :-)

It also means the ramp target is shorter than it could be - they won't be able to drive very long into it, and it may mean teams will slide backward at the end.
This is true. However, it was within our requirements, which I alluded to earlier: work for an AM14U 6WD Long when driven on 'heavy' end first. We don't expect it to work for every robot, we're hoping that it works for a enough of the 'right' robots. Executing ramps that were nearly universal were deemed a little to complicated for us to successfully execute.
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Unread 02-05-2018, 03:03 PM
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Re: Ramps!

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Originally Posted by JamesCH95 View Post
10.9in deck height
Are you worried about teams with sagging or low bumpers?
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Unread 02-05-2018, 03:07 PM
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Re: Ramps!

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Originally Posted by Bennett548 View Post
Are you worried about teams with sagging or low bumpers?
Absolutely. Teams will poor bumpers won't be able to be considered climbed. However, we don't anticipate many teams with bumpers under 1in (because of the cable covers at 3/4in) and the AM14U chassis mounts them 2in up, giving us 0.8in of margin.

We are hoping (perhaps against hope) that other teams were/are thinking about how they might get onto ramp or lift bots and facilitate good lifting by having their bumpers towards the high end of the spec.
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