pic: Bit Buckets 2015 Offseason Drivetrain

[asid61]

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?

[z_beeblebrox]

Originally Posted by asid61

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?

By changing the hole pattern on the inside chassis plate and possibly the size of the clearance holes in the belly pan and top plate, we can switch to 3 CIM ball shifters. For this version, we're using single speed gearboxes because we already had most of the parts on hand and wanted to test making wood gearbox plates.

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.

[z_beeblebrox]

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.

[orangemoore]

What is the cutting area of the laser cutter?

[EricH]

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*

[z_beeblebrox]

Originally Posted by EricH

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*

*throws 1.78 lbs of wooden circles*

[z_beeblebrox]

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:

[nixiebunny]

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!

[MrForbes]

Originally Posted by nixiebunny

The next couple of drive-overs resulted in a flat tire on the Volvo.

That was what I predicted, watching the video. Poor little car.

[philso]

Originally Posted by nixiebunny

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!

Beautiful robot chassis. Beautiful car. It is a shame that either one got damaged.

[z_beeblebrox]

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.

[z_beeblebrox]

Some pictures:
http://www.chiefdelphi.com/media/photos/41024?
http://www.chiefdelphi.com/media/photos/41023?
http://www.chiefdelphi.com/media/photos/41022?
http://www.chiefdelphi.com/media/photos/41021?
http://www.chiefdelphi.com/media/photos/41020?
http://www.chiefdelphi.com/media/photos/41019?
http://www.chiefdelphi.com/media/photos/41018?

[nuclearnerd]

Pretty!

I hope you have a chance to bash this bot up in some open field defense. I'd really like to see how the plywood base holds up compared to, say, and AM14U, given that yours has much more cross-bracing. If it works OK it could be a really cheap way to design custom chassis (cheaper than laser cutting and bending aluminum anyway)

[s_forbes]

Latest iteration looks great! Get some bumpers and weight and drive it like you stole it.

I got to see the previous one (in the car crushing video) in person. It's an extremely clever design that somehow ranks high in all of the desirable categories; extremely stiff, relatively lightweight, and can literally be cut out and assembled in an afternoon out of $50 worth of material. The drop-out wheel modules are pretty neat too, I don't think I've seen something done quite like that before.

Great prototype, I can't wait to see you apply these design concepts to the rest of your robot this season. Might be my new favorite build material.

[nixiebunny]

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.