FRC 6328 Mechanical Advantage 2020-2021 Build Thread

Congratulations! Your documentation log is so organized and easy to follow–thank you for sharing!

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We’re a little bummed it’s so warm! We were looking forward to skating the canal on Friday night!

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I was actually looking at the pictures you sent me on slack lead milk mentor

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wow first post was a good one! Since you’re here do you want to post up some pictures of the new intake prototype and geometry? :slight_smile:

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Alright, yeah! So after our first event, we looked at the intake performance and saw that during matchplay, some balls would get driven over due to the intake rollers spinning at a relatively low speed. Additionally, we noticed that after being intaked, many balls would pop up and over the sides of the intake. Also, when our intake was in the ‘up’ position, we noticed a pinch point for the balls at the edges of the intake plates and the front shafts of the hopper. We sat down and considered these points and decided that we had to make some changes to address these issues. 1) We decided that adding a third roller would be beneficial in containing the balls better in our hopper 2) Instead of a drop-down intake, we agreed upon a four bar mechanism (Credit to team Dave, 3683) that would work similarly to the drop down using pistons, but the intake travel would be more linear as opposed to vertical 3) To address the ‘pinching’ issue, we decided upon moving from continuous rollers to using mecanum wheels and 50A durometer stealth wheels on all three rollers to funnel balls towards our hopper more efficiently 4) Our three rollers are now in a circular path (in a collinear roller path, there would be far too much compression at the middle roller and it would cause balls to slow down significantly when they reached the top of the bumper) We’re working on finalizing the CAD and are working towards beginning manufacturing so we can have this on the robot for Robottowa!





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Four-bar intake is dope af, thanks for posting this update!

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What’s the compression between the intake and the bumper? Our team has also run into issues with our intake being too slow/unreliable.

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Yeah! For this intake, we have 0.875 inches of compression (6.125 inches from the bottom of the roller to the ground), here’s a screenshot of the 2d sketch


For the compression from the middle roller to the bumper, it’s approximately 6.165 inches (8.29 inches center to center from roller to bumper, (8.29-(1+1.125)) ).
Ignore the messiness :grimacing:

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Unfortunately FirstCanada has cancelled all events for week three cancelling Carleton. Hopefully this virus passes away soon.

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This is truly devastating for our team, we had a meeting last night to discuss the cancellation, our team had decided to pull the plug on the trip prior to the announcement of cancellation for the obvious fear that someone on our team could potentially bring Convid-19 with them to Ottawa. Ottawa has relatively few cases right now, but unfortunately the Boston area is quickly becoming a hotspot. We felt it was our social obligation to avoid risking this. I feel for our students but am proud of how well they took the news, we are still motivated to continue work on the robot to get it to be as good as we know it can be.

On the note of all this, I’d just like to take a minute to express our gratefulness being able to get one play in. There are many teams robot that wont touch the field this year and I feel for them.

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Thank you for your teams contribution to #openalliance this year, it’s helped out our team a bunch. I hope y’all consider doing it again next year, I’ll join you.

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Where’s the milk?

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Bumping this to ask how these gearboxes held up. Did you experience any problems with bending or cracking with the 3DP plates? Also, what is the gearing on your drive train?

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Just a side note: If you’re interested in doing 3d printed plates for a gearbox for a competition robot, I definitely would not design it the same as an aluminum plate gearbox. I think 6328 printed these plates as-designed (for 2D Aluminum) just to see what would happen. If you are starting with the idea of 3D printing a gearbox, there’s no need for through-hole lightening at all - consider more deliberate webbing inside a solid shell.

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They actually held up very well. We probably have around 50 hours on them on our practice robot and they’re only just starting to have issues with teeth slipping in the second stage of the gearbox.

I would very much not recommend using these in a competition robot, lightening holes or not. I’m sure there’s ways to redesign them to make them last the comp season but we want our drivetrain to be bulletproof, so isn’t worth it for us when we can just make metal ones and not have to worry. After a while of stresses the oynx will plastically deform and you lose all tolerances. It was a cool test to do, once I get back into the shop I’ll pop the gearboxes off the robot and take some pictures to post here for you!

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Thanks for the info! We got a Mark 2 over the fall and are trying to test it’s limits. We didn’t plan on putting these in our drivetrain, we like ours to be bulletproof like you. We did print our bearing blocks for our climber out of onyx, never got a chance to test its limits fully but it operated smoothly in practice and testing.

We’ve noticed that the face plate of the NEO is what gets hot first during use, do you think that was the reason for the slippage? Or the natural flexibility of the nylon in onyx?

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It was probably a combination of those two factors. During practice sessions the plates did become more flexible as the NEOs heated up. It also had the negative effect of not helping cool the NEOs like an aluminum gearbox would. Overall they held up better than I expected. It might be worth pursuing printed gearboxes if your design was actually intended for printing and not just two 1/4" plates, but the heating of the NEOs does still worry me for extended use.

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If you’re really considering printed gearboxes I would suggest looking at a PC-based material. Nylons (polyamides) have a relatively low glass transition temperature aka T_g. This is a temperature at which the elastic modulus of the material drops precipitously, which can cause all sorts of gross deformations and damage. When people heat-bend plastics they are exceeding the T_g to make the plastic much softer to bend.

image

See how the elastic modulus (stiffness) totally tanks right around T_g? That’s REALLY bad for gearboxes and other stiffness-dependent parts. Onyx is noted has having a “145°C Heat Deflection Temperature” but I do not think that this really captures the behavior we’re interested in for a gearbox. It’s a short-term test and involves bulk material at a low stress. In a gearbox we’re interested in longer-term deflection under higher stresses.

Nylons can vary in T_g in the 40-70°C range, Onyx notes it at 45-50°C. A hot drive motor will likely match or exceed that temperature, making your gearbox plates less rigid than you might need.

Polycarbonate (PC) has a T_g around 145°C. If your motors are that hot you’ve got bigger problems! ABS has a T_g around 105°C, also a big improvement over Nylon and more readily available with fiber additives I believe. Both of these would likely serve you better than Nylons in the quest to make a printed gearbox part.

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I started a sappy 2019 offseason recap video in the fall and never finished it because FLL took over my existence (woops). I decided to merge it with a 2020 season recap video, as a celebration of all our team accomplished in both the 2019 offseason and the 2020 season. We are grateful to have been able to compete Week 1, and I am truly so sorry from the bottom of my heart to all the teams that didn’t get to do so this year. Hopefully this video helps remind anyone who is struggling with that loss that the impact and difference you make on your FIRST teams goes so far beyond the machines. Even if it doesn’t feel right in the place of past season successes, don’t forget to celebrate all you did do this season, because even just attempting a crazy challenge like FRC is nothing short of incredible.

Here’s to hoping some order is restored to the world soon and that the 2020 offseason is straight flames :fire:

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Hi all, two updates!

DCMP Chairman’s! Shout out to the outreach and Chairman’s team for doing an incredible job this year putting everything together. It was a rough year, but this feels like a proper nice end to the season.

My next update is slightly sad but also very exciting for me. Over the last few months my girlfriend and I had been presented a few different opportunities in terms of career moves. Her having finished up her Masters and me closing out my Bachelors, we decided there’s no better time than now than to chase some dreams and move out to the great country of California. I am extremely excited to say as of last week I signed a job offer to work with an incredible company right outside of Sacramento in Davis, but saddened to say this means I will need to end my time as Lead Technical Mentor for 6328.

My time with the team was truly some of the best of my life. Surrounded by a great group, I learned more and pushed myself beyond what I imagined I could do. Thank you to all the mentors and students for the great times, I will miss you all tremendously.

I share this news because I regularly still receive messages asking questions about the build and robot. I would like to formally pass this off to a few other mentors who will be continuing the work with 6328. For all further questions, feel free to message @Maximillian who will be able to either answer the questions or connect you with the right team member.

Lastly, thank you to the community for engaging with us over the last season, it was an incredible experience and I am very grateful I had the chance to share it with everyone.

Stay safe,
Dave

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