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Unread 12-26-2017, 07:50 PM
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FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

Hello Chief Delphi,

On behalf of FRC team 2168 we are happy to present our 2017 off season prototype project.

Background:
In the 2011 build season the team was faced with a decision relative to implementing a linear lift vice a telescoping arm. The decision was made to pursue a linear lift because of the team’s lack of manufacturing resources and mentoring staff. In 2013 the team built its first belt drive train based on the standard sheet metal parallel plate chassis design using the dead axle concept. Based on the 2013 success the team built a similar drive train in 2014 with two key differences; those differences being offsetting the drive train gear box from the center of the chassis and using 6061 AL for the transmission output axle. The results of those decisions caused the team to return to using #35 chain and re-assess our design methods for belt driven drive trains. In the 2015 off season the team prototyped a #35 chain based WCD and then implemented it for the 2016 game with lessons learned. In the 2017 off season the team prototyped a belt-in-tube WCD with the drive train gear box centered and then implemented it for the 2017 game with lessons learned. During the 2017 off season the team acquired a CNC router table and subsequently a project was needed to prove out/become thoroughly familiar with using the equipment prior to the 2018 build season.

Objectives:
#1 Build a telescoping arm design for both a pick and place game and a climbing end game.

#2 Build a belt-in-tube WCD using the same pulley size with larger wheels and offset gearboxes.

#3 Build a belt-in-tube WCD direct driving a wheel off of the drive train gear box.

Rationale / Basis:
#1a The telescoping arm would necessitate manufacturing that would evaluate all use cases for the CNC router table, i.e., gearboxes, tube structure, poly carbonate, other AL plate piece parts.

#1b Based on the 2018 game hint, it seems to suggest a pick and place game with stair climbing. A good design solution for this type of game would be a telescoping arm based on meeting a pick and place need, as well as keeping the robot’s CoG low for stair climbing.

#2a Common belt design knowledge dictates that the larger the wheel implemented the larger the drive pulley based on tensile loading. Given the success that was realized with the 2017 belt-tube-design which implemented 24T 5mm HTD pulleys, empirical evidence is needed to determine if 15mm HTD belt with the described pulley size would continue to produce the level of exceptional performance with 6” wheels on a non-flat playing surface.

#2b In conjunction with #2a, would offset drive train gear boxes over stress specific belt loops or would the desired performance and longevity be maintained?

#3 One of the team’s drive train design rules has been to not direct drive a drive train wheel with the drive train gear box axle based on the shock loading that would be imparted in the drive train gear box, especially for a game with a field surface like 2016. This has led to game play impacting arrangements on our robot. Given the bearing support structure that exists in common WCD drive designs and other FRC teams past implementations, is this rule an over constraint to the team’s design strategy each year?

Discussion:
Design requirements:
In order to create a test device that met the possible 2018 challenge as described in #1b in terms of scaling stairs and climbing, the team leveraged on the 2004 game platform with a slightly more aggressive stair set and slightly less aggressive pull-up bar distance (2004 = 4 steps with 1.5” rise and 3” run, prototype = 4 steps with 2.25” rise and 4” run / 2004 = 108” to the top of the pull-up bar from the middle platform surface, prototype = 84” to the top of the pull-up bar from the platform surface.
In terms of performance criteria, the team set a goal of full rotation for the arm (i.e., approximately 200 deg.) in under 2s with a 25 lb. load (less the weight of the arm/gripper) and full extension of the telescoping arm and a retraction of the arm (60” of travel) pulling a 155 lb. load in under 2s.

Summary Design Results:

Chassis: (Reused from the 2017 design with a new belly pan) 31” x 28”, 2” x 2.5” tube

Drive Train: Belt-in-tube (15mm HTD Belt, 24T 5mm HTD Pulley), 10WD (Eight 6” Pneumatic wheels + Two 4” Colsons) 2 Speed, 2CIM+1 mini WCP gear box (JVN real 15.8 ft/s high, 7.7 ft/s low)

Arm: 100” max height from the floor, telescoping gear box three 775 pro @ 95:1 / loaded retraction 2s / stall load 1294 lbs., pivot gear box 2 mini-CIM @ 360:1, loaded rotation 82.3 deg/s retracted and stall load 162 lbs., loaded rotation 55.7 deg/s fully extended and stall load 58.4 lbs.

The arm uses a unique design to support both a pick and place use case as well as support the dynamic loading associated with climbing. At a high level, Stage 2 (the middle tube) is moved up/down using #35 chain driven via the telescoping GB mounted to Stage 1 (the bottom tube) and hard mounted to Stage 2. Stage 3 (the top tube) has a combination of ” diameter rope and surgical tubing connected at its bottom, routed over pulleys at the top of Stage 2 and hard mounted at the stop of Stage 3 which is used to extend Stage 3 as Stage 2 is chain driven up or as Stage 2 is passively driven up by two constant force springs. Stage 3 also contains a sliding truck internal to the tube, which on the top of the truck is connected to an extension spring, and at the bottom of the truck interfaces with a 1000 lb. pull strap routed to pulley drum connected to the output of the arm’s telescoping GB.

Conceptually this design incorporates a level of redundancy and more importantly ensures that the #35 chain will never experience the dynamic load associated with climbing for which by calculation its breaking strength would not be able withstand, ultimately creating a telescoping arm design that supports both game piece pick and place as well as climbing. The full CAD model for this prototype can be found on GrabCAD. Please enjoy our short release video on YouTube at the link below. Thanks for reading and good luck to all teams in the 2018 season!

https://grabcad.com/library/frc-2168...on-prototype-1

https://www.youtube.com/watch?v=mHT1qSmKwiY

Credits:

A huge shout out and thank you to West Coast Products (WCP) for donating the gear boxes for the prototype drive train and a portion of the gears used in the prototype arm gear boxes.

The team’s intention was to install a 2011 type gripper on the arm. As this was not our primary focus we chose to leverage 973’s 2011 gripper, however never manufactured it, so you will notice the partially completed gripper design in the CAD model.

The team leveraged FRC team 233 The PINK team’s Flickr account and what pictures could be found of the former FRC team 40 Checkmate for design arrangement inspiration.
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FRC Team 2168 - Aluminum Falcons, [2011-20xx]

FRC Team 229 - Division By Zero, [2004-2010]


"Desire is the key to motivation, but it's determination and commitment to an unrelenting pursuit of your goal - a commitment to excellence - that will enable you to attain the success you seek."

Last edited by lnex1357 : 12-26-2017 at 10:49 PM.
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Unread 12-26-2017, 11:07 PM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

Awesome write up and thank you for posting the CAD. This is a really cool design and a great way to use time in the off-season.
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Unread 12-28-2017, 07:54 AM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

This is awesome! Thanks for sharing.

The belt in tube design is very clean. I would practice changing belts with your pit crew though. We used belts in Stronghold and had some issues with stripped teeth and one break that made for stressful times in the pits If this year's game includes stairs, I would probably stick with chain.

I love the disc brake on the arm joint, and have been waiting for an opportunity to use one on our robots. How did you actuate it?

The arm looks super beefy (not necessarily a bad thing). Would it be possible to use tubes that are closer in size to each other? I'm not entirely sure I follow your description of the rope and surgical tubing used in your second stage, but this came to mind:
http://www.genuinemodels.com/images/...on_diagram.gif
We have used that concept on telescopic arms a couple times and were happy with the way it worked. You actuate the second stage, and the third one comes out automatically.
I'm curious as to how you came to the conclusion that #35 chain wouldn't be strong enough for hanging? I would have no qualms hanging a robot from it.
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Unread 12-28-2017, 08:10 AM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

Cool project.

Can you save your top model as a STEP file and upload it to grabcad for those of us who don't use Solidworks?
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Unread 12-28-2017, 09:42 AM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

Looking good Josh/Kevin!

Nice to have your 2018 robot completed before KO! lots of time to practice.
and looks like you succeeded in learning the new router table.

One question: Where did you source the 2" x 2.5" tubing? I have looked for it in the past and came up empty.
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Unread 12-28-2017, 11:49 AM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

Quote:
Originally Posted by Rob Stehlik View Post
This is awesome! Thanks for sharing.
The belt in tube design is very clean. I would practice changing belts with your pit crew though. We used belts in Stronghold and had some issues with stripped teeth and one break that made for stressful times in the pits If this year's game includes stairs, I would probably stick with chain.
Concur with the replacement challenge surrounding removing the belt loops specifically because the gearbox requires partial removal. We had zero issues in 2013 and last year with 15mm belt. Agree that non-flat playing surfaces change the loading dynamics and thus depending on your wheel size may require bigger pulleys. In 2016 we used #35 chain and depending on the outcome of testing with this prototype may do the same. That being said, we came across numerous teams in 2016 who used 15mm belts without a problem with 8" wheels, however they used much larger pulleys.


Quote:
Originally Posted by Rob Stehlik View Post
I love the disc brake on the arm joint, and have been waiting for an opportunity to use one on our robots. How did you actuate it?
If you slow down the release video from 0:35 - 0:41 you can see the setup. Its just a simple single acting - spring return pneumatic cylinder that actuates a lever arm pulling a cable attached to the brake caliper. The cylinder spring returns closed disengaging the caliper from the brake disc both under normal operation and in the event of loss of air.

Quote:
Originally Posted by Rob Stehlik View Post
The arm looks super beefy (not necessarily a bad thing). Would it be possible to use tubes that are closer in size to each other? I'm not entirely sure I follow your description of the rope and surgical tubing used in your second stage, but this came to mind:
http://www.genuinemodels.com/images/...on_diagram.gif
We have used that concept on telescopic arms a couple times and were happy with the way it worked. You actuate the second stage, and the third one comes out automatically.
Relative to the tube size, we have had a lot of discussion about how to make it smaller and lighter, balancing this desire against the ease of assembly and maintenance the current tube size provides will be the trade should we implement a telescoping arm in the future. Bottom line is based on sketch evaluations we have done using 0.375" OD bearings available from Vex Pro, the tube design could become as small as 1x1 (stage 3), 2x2 (stage 2), 3x3 (stage 1).

Regarding the actuation method please see the attached image.

Quote:
Originally Posted by Rob Stehlik View Post
I'm curious as to how you came to the conclusion that #35 chain wouldn't be strong enough for hanging? I would have no qualms hanging a robot from it.
The working load of #35 chain depending on what website you go to can range a lot. Using McMaster as the baseline, the working load is 190lbs. Most text books I have read suggest that working load for chain or rope by the manufacturer is about 1/5th the breaking strength. In our case this would mean the chains breaking strength is about 950lbs. Another point to remember is that the dynamics (tensile loading) seen by the chain on sprocket hard mounting to the arm vice wrapping a strap or rope around a drum driven by chain is far different. For example last year we used #25 chain to drive our 2.5" OD drum for our climbing strap with absolutely no problems.

Our telescoping gearbox stalls at 1294 lbs. When you consider the acceleration, distance traveled, and mass being moved, a strap around a winch drum provides a much more reliable method for working with the dynamic loading of climbing and then stopping (of course some of this can be overcome by the control system). While the chain would likely work throughout the season for climbing, the fatigue it would see during climbing over the season, makes it a definite failure point in a critical part of the arms functionality. In short the winch drum with the strap affords us redundancy in a critical area. One avenue we do want to investigate from performance/smooth control perspective is removing the chain (to reduce complexity and weight) and seeing how the arm performs.
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FRC Team 2168 - Aluminum Falcons, [2011-20xx]

FRC Team 229 - Division By Zero, [2004-2010]


"Desire is the key to motivation, but it's determination and commitment to an unrelenting pursuit of your goal - a commitment to excellence - that will enable you to attain the success you seek."
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Unread 12-28-2017, 11:50 AM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

Quote:
Originally Posted by Rob Stehlik View Post
This is awesome! Thanks for sharing.

The belt in tube design is very clean. I would practice changing belts with your pit crew though. We used belts in Stronghold and had some issues with stripped teeth and one break that made for stressful times in the pits If this year's game includes stairs, I would probably stick with chain.

I love the disc brake on the arm joint, and have been waiting for an opportunity to use one on our robots. How did you actuate it?

The arm looks super beefy (not necessarily a bad thing). Would it be possible to use tubes that are closer in size to each other? I'm not entirely sure I follow your description of the rope and surgical tubing used in your second stage, but this came to mind:
http://www.genuinemodels.com/images/...on_diagram.gif
We have used that concept on telescopic arms a couple times and were happy with the way it worked. You actuate the second stage, and the third one comes out automatically.
I'm curious as to how you came to the conclusion that #35 chain wouldn't be strong enough for hanging? I would have no qualms hanging a robot from it.
Quote:
Originally Posted by EricLeifermann View Post
Cool project.

Can you save your top model as a STEP file and upload it to grabcad for those of us who don't use Solidworks?
Eric,

Absolutely. Grab CAD will be updated with STEP file on Monday.
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FRC Team 2168 - Aluminum Falcons, [2011-20xx]

FRC Team 229 - Division By Zero, [2004-2010]


"Desire is the key to motivation, but it's determination and commitment to an unrelenting pursuit of your goal - a commitment to excellence - that will enable you to attain the success you seek."
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Unread 12-28-2017, 11:53 AM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

Quote:
Originally Posted by page2067 View Post
Looking good Josh/Kevin!

Nice to have your 2018 robot completed before KO! lots of time to practice.
and looks like you succeeded in learning the new router table.

One question: Where did you source the 2" x 2.5" tubing? I have looked for it in the past and came up empty.
Thanks Rick!

Check these guys out. You have to buy 16ft. minimum lengths.
http://www.easternmetal.com/standard...t_products.htm
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FRC Team 229 - Division By Zero, [2004-2010]


"Desire is the key to motivation, but it's determination and commitment to an unrelenting pursuit of your goal - a commitment to excellence - that will enable you to attain the success you seek."
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Unread 12-28-2017, 01:56 PM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

Quote:
If you slow down the release video from 0:35 - 0:41 you can see the setup. Its just a simple single acting - spring return pneumatic cylinder that actuates a lever arm pulling a cable attached to the brake caliper. The cylinder spring returns closed disengaging the caliper from the brake disc both under normal operation and in the event of loss of air.
Cool! Looks pretty straightforward. Is this a standard disc brake I could get at any bike shop?

Quote:
Relative to the tube size, we have had a lot of discussion about how to make it smaller and lighter, balancing this desire against the ease of assembly and maintenance the current tube size provides will be the trade should we implement a telescoping arm in the future. Bottom line is based on sketch evaluations we have done using 0.375" OD bearings available from Vex Pro, the tube design could become as small as 1x1 (stage 3), 2x2 (stage 2), 3x3 (stage 1).
Agreed, ease of assembly is an important consideration. We made an arm with 2.5" > 2" > 1.5" tubes for our arm in 2016. The guide bearings were 0.5" OD from Mcmaster Carr. Assembly was a bit tricky, but not too bad.

Quote:
Regarding the actuation method please see the attached image...
One avenue we do want to investigate from performance/smooth control perspective is removing the chain (to reduce complexity and weight) and seeing how the arm performs.
Assuming you have enough spring force to extend the arm, then I think using the winch alone would work really well. This is exactly how we did it, except we used gas springs instead of CF springs for extension. Obviously this doesn't work if you have to lift anything heavy with the arm, it would need to be powered in both directions.
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Unread 12-28-2017, 02:08 PM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

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Originally Posted by lnex1357 View Post
Hello Chief Delphi,
...
former FRC team 40 Checkmate for design arrangement inspiration.
The was the first thing I thought of when I saw this machine was that 2011 Checkmate robot. It's unfortunate that Trinity can no longer give us tremendous robot designs year after year, but it's awesome that their ideas live on to teach new students years later. Great work 2168, this thing is GORGEOUS.
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Unread 12-28-2017, 03:44 PM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

Quote:
Originally Posted by Rob Stehlik View Post
Cool! Looks pretty straightforward. Is this a standard disc brake I could get at any bike shop?
https://www.amazon.com/Avid-Brake-BB...oad+disc+brake

Quote:
Originally Posted by Rob Stehlik View Post
Agreed, ease of assembly is an important consideration. We made an arm with 2.5" > 2" > 1.5" tubes for our arm in 2016. The guide bearings were 0.5" OD from Mcmaster Carr. Assembly was a bit tricky, but not too bad.
Yes! Loved your 2016 arm (well really the whole robot), very beautifully done. Especially loved your bearing blocks, which reminded me of 67 and 1114 from years past. Would have done the same thing if not for trying to re-use in-house material. Do you remember what your total arm weight was?
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Unread 12-28-2017, 06:39 PM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

Quote:
Yes! Loved your 2016 arm (well really the whole robot), very beautifully done.
Thanks for the kind words. I liked the arm, it worked well. We had a lot of trouble with the rest of the robot

Quote:
Do you remember what your total arm weight was?
The arm weighed about 7.5 lbs, and the winch gearbox with a servo driven ratchet weighed about 5 lbs.
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Unread 12-29-2017, 07:05 AM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

Josh, looks great -- nice work!

1511 experimented with a "233-inspired" scaling arm in 2016 and was met with mixed results due to our inexperience. Unfortunately, we decided to experiment with it during the build season instead of offseason so kudos to you and your team! Some questions:

1) What did you use as bearings/guides for your telescoping segments?
2) How has the serviceability been and did you alter your design at all to accommodate this? That was one of the biggest issues we ran into.
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Unread 12-31-2017, 01:14 PM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

https://imgur.com/a/SvBkD

Here is a telescoping arm 176 used in 2016 to scale the castle. Its a 3x3->2x2->1x1 using Delrin rollers instead of bearings to allow us custom sizes to deal with tolerances of the extrusions. It uses CF springs to extend and is winched back with two 775pros through a custom worm gearbox.
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Unread 01-01-2018, 10:01 AM
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Re: FRC 2168 The Aluminum Falcons 2017 Off Season Prototype Release

Quote:
Originally Posted by EricLeifermann View Post

Can you save your top model as a STEP file and upload it to grabcad for those of us who don't use Solidworks?
STEP file is now available on GrabCAD.

Quote:
Originally Posted by Josh Goodman View Post

Some questions:

1) What did you use as bearings/guides for your telescoping segments?

We used 0.75" OD 0.25 ID bearings we had left over from a 2015 design on all three stages. Because of the dimensions we used for the tube stages and the access we need for strapping, CF springs, and rope we used 3 separate bearing blocks types as seen in the attached picture. For a competition season design, we would move a common bearing block design for all 3 stages similar to what FRC 610 or FRC 1768 implemented for their 2016 arms.

2) How has the serviceability been and did you alter your design at all to accommodate this? That was one of the biggest issues we ran into.
Serviceability is exceptionally easy by virtue of the size of the tubes and the lightning hole size/placement. We did an assembly and maintenance study in CAD before proceeding forward with manufacturing which led to some arrangement tweeks. This all comes at the cost of weight however. For example switching stage 2 and stage 1 from 3x3 and 5x5 respectively to 2x2 and 3x3 respectively would save about 5.5 lbs. in tube stock material weight alone not to mention weight savings in bearing size and pivot interfacing material. So it most certainly is a tradeoff of how reliable can you make the arm and thus keep it smaller or how easy to maintain can you make the arm and likely earn yourself some weight gain.
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