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#1
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
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We do want to use this as our competition bot design (more or less), if it works. We plan on building a few iterations now to get the hang of it. We want to make a practice robot that we can bang up to get endurance information. |
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#2
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
Since we cut the prototype last week, I've been hard at work improving the design. We'll be fabricating this iteration tomorrow.
![]() Full size here! Some information and a partial change log: -Weighs 36.7 lbs with everything shown except bumpers and battery -Contains 34 plywood parts, which weigh a total of 15.9 lbs -Gearbox removable from top or bottom with 4 bolts. Drive pod removable from side with 5 bolts -Improved gearbox with stronger design, easier mounting, more choice in ratios and a slightly increased top speed of ~12fps adjusted -Modified encoder mount for 3D printing -Revised powertrain to use wheels and pulleys from AM14U so we don't have to order more parts -Designed sturdy and easy to change bumpers -Reinforced battery mount -Added removable center belly pan section that allows access to the middle box -Revised joint layout for improved strength and easier design changes -Added lightening holes in larger wood parts We plan on sharing photos and the latest version of the CAD files tomorrow afternoon and our engineering journal at the completion of the project. Any questions or ideas? |
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#3
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
Can you swtich to COTS shifting gearboxes? A good portion of the advantage of a six cim drive is lost when using single speed, because going at any speed where the acceleration difference (between 4 and six cims) is not negligible is just asking for breaker blows.
On another note, that's a really good weight and design. The way you are fitting wodden plates together is very novel. How do you make the correct tolerances on everything? |
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#4
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
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Tolerances are largely determined by trial and error. Since laser-cut wood is so fast and cheap to make, we can make multiple iterations of a part in a day. We're cutting the slots and tabs to nominal dimensions; the laser kerf makes them a tight, but still easy-to-assemble fit. For bearing hole sizes, we're cutting a test part today with holes of slightly different sizes to see which works the best. |
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#5
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
We built it today!
A photo, as promised: ![]() Anyone want some small wood disks? ![]() We've been generally satisfied with our results. The chassis is lightweight and extremely strong and stiff; it survived being jumped on, dropped and pounded with no damage. In total, it took about 4 hours of laser time. Hopefully, we'll get it running over the next couple of weeks, as we replace a few parts on which we made mistakes and receive the stuff we ordered from Vex. However, I'll wait a little on releasing the CAD; we caught a few bugs I'd still like to fix. Edit: It's also very inexpensive to produce; each chassis takes about $30 of wood and $10 of hardware, not including powertrain components, compared to $189 for an AM14U frame or other COTS or custom options. Last edited by z_beeblebrox : 07-12-2014 at 22:07. |
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#6
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
What is the cutting area of the laser cutter?
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#7
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
If you do something similar in the future, cut the following letters into each disk:
T, U, I, and T. Add your team number, and use as giveaways. When you finally get "a round TUIT"... ![]() *ducks* |
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#8
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
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#9
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
Another meeting tomorrow, another iteration ready to fab:
![]() This version includes a significant redesign of the gearbox and its mount, allowing for a stiffer gearbox and more sensible encoder placement. New t-slot design should better retain nuts. The battery mount was enlarged and holes for a velcro strap were added. Small improvements to clearances, press fits and lightening holes were made throughout the model. This will be the last iteration of the drivetrain before build season. We received our Vex Pro and FIRST Choice orders, so will be assembling the full powertrain and wiring all the electronics on this version. Here's all of the wooden parts, laid out for the laser: ![]() |
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#10
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
We tested our last-week's robot base to destruction with a car.
http://youtu.be/kjUfTZ4KFO0 The next couple of drive-overs resulted in a flat tire on the Volvo. This week's robot is closer to working with real wheels and motors and electronics! |
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#11
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
That was what I predicted, watching the video. Poor little car.
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#12
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
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#13
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
We worked more on assembly and wiring today. Photos soon to come.
We do have two exciting documents to share: the CAD model and our engineering journal. The CAD model posted contains a few bugs that we fixed with a drill and jigsaw, but is still a basically functional drivetrain: https://grabcad.com/library/bit-buck...n-drivetrain-1 The engineering journal is a description of our process and decisions in building this project. It is not an exhaustive document, nor is it a particularly polished one, but it will contain helpful ideas for designing things with plywood: https://docs.google.com/document/d/1...it?usp=sharing Have fun and feel free to ask any questions. Last edited by z_beeblebrox : 18-12-2014 at 00:23. |
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#14
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Re: pic: Bit Buckets 2015 Offseason Drivetrain
The Trotec Speedy 300 at our build space, Xerocraft Hackerspace, has a 29" x 17" bed. We made the top and bottom in 3 pieces to let us make a 28" square robot.
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