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get cargo into robot
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@Jack Chapman set the channel purpose: get cargo into robot
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I did some sketching tonight, thinking about the desire to use the intake to pull the climbing robot onto the L3 platform, which I suspect means extending the intake wheels down to drivetrain wheel level. I think geometry something like this might work well.
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The more I look at team 971's intake from 2016, the more I think it is a design worth borrowing from. Check out their tech doc: http://frc971.org/files/2016-TechnicalDocumentation-971.pdf Here's a picture of their prototype as well. Notice how they built their prototype using extrusion that allows adjustment during testing. Another thing to potentially borrow.
We have those extrusions parts . Has anyone looked at our Aries robot for cargo intake testing ?
One more geometry sketch - I think this might be better than the one from yesterday. It sticks out less far, and I think that would make it less at risk and also the risk of accidentally controlling 2 balls at once would be less.
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@Jack Scheiderman Regarding CAD, what are next steps? It seems like there are parts you could start pulling into an F360 project, like the 4" Vex mecanum wheels, the compliant wheels, the hex shaft, spacers, hex collars, bearings, maybe some placeholder pneumatic parts for the 3-position system, etc. @Kate Treviño-Yoson might be able to help with a start at bill of materials for the pneumatics. Plus, you have the step file of the arm Paul designed. Let the rest of us on the team know what support you need.
Unfortunately, @Chris Rininger, I won't be at the meeting tomorrow due to other plans but I can make sure to look into that on the Wednesday meeting.
https://www.vexrobotics.com/vexpro/motion/gearboxes/vp-180.html Paul says we need these for fitting transmission with other robot elements. Suggest we order 3 of them unless we have inventory.
4 have been ordered.
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Checklist of things to still figure out. Need to determine how to sequence & distribute these within our mechanism team, and what help we may need from Paul, the team's pneumatics experts, & others. It seems to me 1 & 2 can be lumped together & assigned to some folks, and 3 thru 5 can be lumped together & assigned to different folks, with work proceeding on the two work streams in parallel.
1. Specifically how & where the arms / pivot point will mount to the chassis
2. Intake wheel power transmission design. From conversations, it seems like the plan is to power a toothed-belt pulley at each arm's pivot point with a 775pro motor+VPgearbox, and then use one or two belts & more pulleys to get power to the shaft with the intake wheels.
3. The two-pneumatic-piston solution that will enable the up, cargo acquire, and climb assist positions of the intake. Numerous things to figure out here, and we'll need help from pneumatics people.
4. How/where the two-pneumatic-piston solution is anchored to the robot chassis or other static structure.
5. How/where the two-pneumatic-piston solution is attached to the intake (e.g. is there an extra rod across the intake arms?)
To me, the most critical / at risk thing on the list is #4. @Jack Scheiderman @Kenneth Wiersema @Paul Vibrans help wanted with #4 on the list. 3 & 5 are dependent on 4. 1 & 2, while not trivial, are going to be doable.
Here's a try at a layout for the pulleys & belts on the arm. I added up each line & approximate partial circumference to get an approximate length of ~32 inches, which is ~816 mm, which in turn is ~163 teeth @5mm between teeth, so (assuming that approach is valid) it seems like a 160-170 tooth belt might work. It seems like someone could get scrap wood, trace the arm onto it, and then get some pulleys & belts from inventory and try to come up with a layout.
I understand how the calculator works for a 2-pulley system, but not for a more complicated system with 3 pulleys plus and idler/tensioner or two. If we use two belts and three 24 tooth pulleys (one double width one in the middle) instead, then the belt sizes according to the calculator are 150-160 teeth for the longer belt (12.6" between pulley centers) and 80-90 teeth for the shorter belt (5.6" between pulley centers).
I was assuming with a single-belt system like I illustrated (you'll have to click on it to see it all) that one would devise a layout shape, approximate the belt size via a technique similar to what I used, identify the two belt sizes closest to fitting, work up a physical layout on a board (use clamps maybe?), and then as part of that tweak the positions of the idlers to get the tension where it needs to be.
Another problem to solve is figuring out how fast we need to spin the intake wheels, then determining what overall gear reduction to the 2 775pros that implies (assuming some amount of resistance). And we also need to consider the implications of the climb assist on that choice. Here are some initial thoughts & calculations:
- Our robot's approximate top speed is 11 feet per second or 121 inches per second
- I think there is little chance the robot will be going top speed when acquiring balls... 7 feet per second feels like a better number to use, so that is 84 inches per second.
- FRC rule of thumb is intake speed should be about twice robot speed, so that's 168 inches per second
- Circumference of a 4" wheel is around 12.6"
- Revs per second = 168/12.6 = ~13.4
- Plugging numbers into the MechanismRatio tab on the latest (v3.3) AMB Design Spreadsheet, assuming there is 1 to 5 lbs of resistance in the system, a gear reduction of around 20:1 seems like it could work. (Other assumptions: 11v & 80% gearing efficiency)
Here's a screen shot of the spreadsheet tool I used: https://1drv.ms/u/s!AikCDwtdoW5LxVP80V44lfNu579b. And here's a link in case you'd like to play with it yourself: https://www.chiefdelphi.com/t/paper-amb-design-spreadsheet-v3/335629/13 (scroll down to v3.3). The Projectile tab in particular is fun to experiment with.
Even if 20:1 is a good choice, that doesn't mean go build two 20:1 versaplanetary gearboxes just yet. Some of the gear reduction could occur from different sized pulleys needing to be used. And also, as mentioned, we need to think about the other task the wheels need to do: helping the robot get onto the L3 platform. So we need to consult the climbing team.
@Ethan Rininger and , I will not be there at the start of the meeting today, and I will miss the Friday meeting. So I've put some thoughts into a document about how to proceed with finishing design, identifying parts needed, ordering parts not in inventory, etc. I would consult mech captains and Paul to make sure they aren't doing things that overlap/conflict with this, in order to avoid wasting time duplicating efforts. Here's a link to the doc - hopefully see you today at around 6:30. https://docs.google.com/document/d/1fH5y00psw5XvcoEM0M7cMPTC7oE187ty1yVF9njc/edit?usp=sharing
A single belt solution is more time consuming to design than a two belt system because of having to design the tensioner and idler roller positions and mountings.
Agreed - I recommended 2 belt system to team this morning
Few things: 1) Did someone confirm we have enough Versaplanetary housings & gear kits? Including for the intake? 2) Mark drafted an engineering spec for the chute, and it would be good for our cargo intake team to do the same. 3) We talked about using the CNC at BARN to cut out all the arm pieces (need 8 + spares). Will someone please discuss with Mark or Chris Stanley if he’s there tomorrow? 4) In general, I recommending double checking our list of COTS parts needed for the solution & confirming we have inventory or need to order. If we have just enough in inventory, then order more because we need spares.
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@Paul Vibrans @Jack Scheiderman @Kenneth Wiersema Are you all on the same page on the intake arm redesign including the extra roller further back.
I was aware. Paul has changed the geometry of the arm as well.
@Ethan Rininger & team, we have a lot to do the next few meetings. How will we stay on track to finish on time? (Some sort of list and assignments?)
Since the side plates for the arms have not been made just yet, nobody should be influenced by the changes to correct for pulley center distance errors and the addition of another roller. I will have the updated arm assembly drawing at tomorrow's meeting unless someone needs it right now. It is really hard to tell the difference in size and shape.
Jack & Paul, thanks for the responses.
@Ethan Rininger Here are a few things for "the list":
- Overall, make sure everyone understands the design changes, including the extra bar and extra pulleys that spin the bar. I believe Paul said the belt sizes have not changed, but good to double check.
- Once the mecanum's arrive, work out how they will be mounted to the 1/2-inch hex. It is possible 1/2-inch hex will not be the best/fastest choice anymore. It's also possible that a hub design could be created & 3D printed that will allow us to proceed with the 1/2-inch hex.
- As a team, brainstorm the list of To Do's, then come up with priorities, sequence, & who's doing what. Get a sense for whether or not help is needed (could be design/engineering help needed or could be just that additional people are needed), and if so then ask for help.
We should have this discussion at the meeting today with our sub team and then talk to other people about what we figured out from the discussion
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@Ethan Rininger @Jack Scheiderman @Paul Vibrans I'm trying to figure out what parts of the arm assemblies still need to be made. Please take a look at this picture and confirm the disposition of these parts, plus confirm any others that need to be made/obtained. We should start arm assembly ASAP.
1. Nyliners need to be received. I not available on time, we need to machine Delrin (acetal) bushings.
2. These are aluminum rings from 1" Sch 40 pipe bored to 1.123/1.124 and cut to 0.6875 long or the same as the spacers.
3. The spacers are made
4. The shaft needs to be made. It has a cross hole tapped 1/4-28 for the pneumatic cylinder rod.
5. The down locks need to be designed and manufactured, one for each arm.
6. The shaft extensions for the intake motors need to be designed and manufactured. They are 10mm OD and attach to the threaded hole in the end of the Versaplanetary output shaft.
7. The inner intake roller needs to be designed and manufactured. It is 1" Sch 40 PVC pipe with some means of attachment between the hex stub shafts on the arms.
Thanks @Paul Vibrans. Few more follow-up questions: a) Could we 3D print bushings as substitute for the Nyliners? PLA or ABS? b) Also, are four 1/2-inch hex collars needed per arm? c) Are any shaft collars needed on that round shaft with the two diameters (it's not clear to me how that part of the assembly stays together... loctite)?
Snap rings on the round shaft.
Any plastic can replace the nyliners.
I have not counted the number of hex collars needed.
Thanks for confirming all this information, Paul; it will help the students Monday. I'm going to try 3D printing PLA bushings now in case we don't get the Nyliners in time.
@Ethan Rininger @Jack Scheiderman Please review this thread. Do we have the snap rings for the round shaft or need to make them (3D print?)? We should add hex collars into the arm assembly kit bags + the other parts as they're manufactured.
The bushings are flanged with a 0.031 inch thick flange 0.75 inches OD. The bushing ID is 0.502 inches. The bushing OD is 0.561 inches. The length through the bore, including the flange, is 0.156 inches. Best to print them solid.
@Chris Rininger When you print out the bushing could you give me the stl on Monday? I will try to print them out on the ABS printer. It would be good to test to see which material is better.
Nyliners should be here on Mon.
@Kenneth Wiersema has shipping info for Nyliners
@Jack Scheiderman sure
We have snap rings.
Too late, printed more :nerd_face:. Regarding the cross holes on those shafts, time to break out the v blocks?
@Jack Scheiderman I think they said the Nyliners will be here tomorrow, but here are the stl files for the bushings anyway. You probably want the file labeled "Paul specs". https://drive.google.com/drive/folders/1G5dCSkaoVl1EC04iNl0tl6BuSEWb5Hsq?usp=sharing
@Ethan Rininger the tapped cross holes on the round shafts have the potential to be tricky. They're similar to some parts we made at BARN this summer. I recommend consulting @Kenneth Wiersema or Chris Stanley.
Could we use a COTS latch to lock the arm down in climbing position? Example: https://www.amazon.com/dp/B0176ISBFY/ref=cmswrothapiiI9jwCb0NKZEEK
I like the idea of using a latch that we could release with a small servo (which it seems that it could be done with the one pictured). The reason being that if the "crawler" is inadvertently deployed, it would be nice to be able to unlatch and raise. Also, it may be beneficial to raise when climbing (after getting on the platform).
@Jack Scheiderman How comfortable would you be designing #6 on Paul's list?
6. The shaft extensions for the intake motors need to be designed and manufactured. They are 10mm OD and attach to the threaded hole in the end of the Versaplanetary output shaft.
My experience as an owner of one of those is they are only about 80% reliable in garden gate service. Do you have any idea where and how to mount it?
@Chris Rininger I would love to take a shot at. I would have to see the shafts on the motor just to see what I'm working with.
This is a spring loaded one - the gravity-only ones are less reliable according to reviews (a lot of people switch those out for these). As far as mounting, I imagined a rod coming off the side of the arm that would catch the latch, but I have not CAD'd anything. This is just an idea for a way to potentially save time (i.e. there are many, many purchasable latches out there - might be better to buy than design, manufacture, assemble our own).
@Jack Scheiderman The CADs/specs for versaplanetaries including output shaft / threaded hole are available on the Vex website. I think one of our CADs already includes the gearboxes and, if not, here's a link: https://www.vexrobotics.com/versaplanetary.html#Drawing
^^^programmatically, we discussed limiting the climb action to the last 30secs to avoid inadvertent deployments — thoughts on that welcomed
Another latch type: https://www.boatoutfitters.com/aluminum-lock-with-strap?msclkid=a10f404b5d1716fc1c041c139ae726d8&utmsource=bing&utmmedium=cpc&utmcampaign=Shopping%20-%20Desktop&utmterm=4584688610096607&utmcontent=All%20Products#215=820?utmsource=Bing&utmmedium=cse&utmterm=068-3134-10
It seems like if we are to make a custom latch (or one for each side), this location might be the place for it. The rest of the arm is outside the frame. We could redesign the arm pivot mount with the lightning holes to include a latch.
@Jack Scheiderman @Paul Vibrans @Kenneth Wiersema Looking at latest ACTUAL ROBOT CAD. It seems we've abandoned the idea of the extra roller on the arms, correct? Just the wheels on the one bar is all that fits with all the other stuff.
Also, that front hoop is outside the frame perimeter on the CAD - safe to assume it is just in the wrong place?
We still have a roller. Just no time dimension it with all of the other fires to put out. Down locks are more important now. We need to have the drive belts and pulleys installed with hex shafts of the same length that drive the shaft with the Mecanum wheels. The PVC pipe roller may need to be hold back.
yes, front hoop location is not in its final location.
@Chris Rininger I will trying to get the second roller in a complete assembly. I may not be able to if my power goes out.
@Jack Scheiderman @Paul Vibrans what is the most accurate CAD of the cargo arm? I'm trying to figure out what we have vs. don't & there are inconsistencies from CAD to CAD that I'm looking at. Thanks
There are two Cads. One is one on the robot. That one is a full assembly without the second roller. The other cad is just an arm assembly that has the second roller.
The main roller bar is now designed to be in three pieces - is this reflected in the CAD? @Jack Scheiderman It seems like we're short 1/2" wide 1/2" hex spacers BTW. My 3D printer is down currently (I need to make some adjustments), so I can't print any of the spacers. Can anyone else? Here's an STL file: https://drive.google.com/file/d/1hrGDH2RadXcIZ8n3yx0XKSlllmQDWKP/view?usp=sharing
I will try to print some this weekend
@Jack Scheiderman let me know if you're not able to do it and I'll add it to my list of things to print.
Thanks. I think we have some at school, but not for weekend outside-school assembly of the cargo arms.
Here’s latest on cargo arms after some work done at our house last night: https://docs.google.com/document/d/1AIP0lteyVlwb1rDF3VLPbLr8ruhKnyCgfJc0N9tkT8
@Chris Rininger How many Spacers do we need?
First test of the intake
I was looking at our mecanums, and it looks like AndyMark provides full CAD step files, so chances are good we can print our own replacement plastic inserts (the pieces that have been breaking)
Scroll down to documents on this page. If it works out, we can just switch to nylon/carbon as the more brittle plastic pieces break. https://www.andymark.com/products/4-in-standard-mecanum-wheel-set
If the problem with the 2nd bar flipping the ball out continues, I suggest smaller diameter pvc pipe with a raised segment in the center where we want it to pull in the ball
I imported the model into Fusion 360 and the models are of the surface and not complete. It will take some work plus physical examples of the parts to see what's missing. @Chris Rininger Did you happen to grab one of the wheels?
No. @Ethan Rininger do you by chance have one of the mecanum wheels? we're using on the intake?
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