27-11-2014 15:20

asid61

Re: pic: Bit Buckets 2015 Offseason Drivetrain

Looks great! 47lbs is a very good weight with electronics on there. Electronics all seemt of it well, but you have some wasted space underneath that top plate.

I noticed that your hex axles have a deep groove cut right before the end. This will weaken the axle by a lot. Why is it there?
Pulleys also seema bit large... the belts won't intersect with anything, right?

EDIT: Out of curiosity, how does this go together? Do you make puzzle-piece edges and glue them? How do you get machine screws into joints?

27-11-2014 15:35

Ryan Dognaux

Re: pic: Bit Buckets 2015 Offseason Drivetrain

If you're talking about what I think you are, those are probably 1/4" hex head bolts going through tube shafts. My guess is he hid the outer drive plate so we could see inside.

27-11-2014 20:05

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

We'll put more of the pneumatic components under the top plate, as well as some of the electronics you don't need to get to as frequently, like the bridge power supply.

The pulleys are 42t, the same size as on the AM14U. We checked that the belts clear the belly pan.

Ryan Dognaux's explanation of the axles in the post below yours is accurate.

It's all put together with mortise and tenon joints and captive nuts, as described in this (excellent) Instructables page.

More renders, as promised:

The drive pod, showing most of the powertrain, as well as some example T-nut joints:


The gearbox, which needs a little more work on mounting holes, as well as an encoder mount (Anyone have ideas on how to attach an encoder? Could it be attached directly to a CIM shaft? The gearbox's output shaft remains in the drive module when the gearbox is removed, so the encoder can't be mounted on that.):

27-11-2014 21:25

Peyton Yeung

Re: pic: Bit Buckets 2015 Offseason Drivetrain

This might help with the encoder issue.http://www.chiefdelphi.com/forums/sh...hreadid=131034

28-11-2014 17:49

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

Thanks for the idea. Here's the gearbox with that sort of encoder mount:


Since we don't have much experience milling complex parts, I'd like to 3D print the encoder mount. I think it would be structurally sound; others have printed much more complex motor mounts.

28-11-2014 20:04

asid61

Re: pic: Bit Buckets 2015 Offseason Drivetrain

The encoder mount doesn't need to be round. You can bandsaw out some rought stock, square it up, take a couple cuts and drill a couple holes and be done. Bandsaw after to get it round. You could put it on a lathe if you wanted to, but we did something similar for our offseason project and I would not do it again. Could be good if you don't have a 3D printer.

30-11-2014 20:32

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

We cut about half of a drivetrain today as a prototype.

It generally goes together well for a first prototype, though we found some bugs we want to fix before building a full chassis (including a misalignment in the laser cutter that led to beveled edges).

30-11-2014 21:24

orangemoore

Re: pic: Bit Buckets 2015 Offseason Drivetrain

It looks like it is going good. I am interested in seeing how this turns out because we have gained access to a similar machine. It is a 4'X8' Shopbot. And being able to confidently believe a drive train out of wood will hold up would be really nice to know.

I do have a few questions

Where did you get the wood/what product is it?

Do you plan to use this for FRC next year?

How do you plan to test it? How will you know it won't break?

30-11-2014 21:41

nixiebunny

Re: pic: Bit Buckets 2015 Offseason Drivetrain

The wood is 1/4" 5-ply Baltic birch from Woodworkers Source. They sell 5x5 foot sheets, which we cut into sixths for the 29x17" laser cutter.

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.

07-12-2014 00:42

z_beeblebrox

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?

07-12-2014 00:55

asid61

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?

07-12-2014 10:33

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

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.

07-12-2014 21:59

z_beeblebrox

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.

07-12-2014 22:07

orangemoore

Re: pic: Bit Buckets 2015 Offseason Drivetrain

What is the cutting area of the laser cutter?

07-12-2014 22:12

EricH

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*

07-12-2014 22:16

nixiebunny

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.

07-12-2014 23:00

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

*throws 1.78 lbs of wooden circles*

13-12-2014 21:54

z_beeblebrox

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:

14-12-2014 23:46

nixiebunny

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!

15-12-2014 00:05

MrForbes

Re: pic: Bit Buckets 2015 Offseason Drivetrain

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

17-12-2014 13:52

philso

Re: pic: Bit Buckets 2015 Offseason Drivetrain

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

18-12-2014 00:19

z_beeblebrox

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.

18-12-2014 09:28

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

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?

18-12-2014 09:38

nuclearnerd

Re: pic: Bit Buckets 2015 Offseason Drivetrain

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)

18-12-2014 12:54

s_forbes

Re: pic: Bit Buckets 2015 Offseason Drivetrain

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.

21-12-2014 12:49

orangemoore

Re: pic: Bit Buckets 2015 Offseason Drivetrain

It appears that some parts were not saved in the same place as the rest of the project and were left behind when put on grabcad. Most of these parts are spacers and things that are not important

21-12-2014 13:26

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

What parts are missing for you?

I just looked over the GrabCAD model and it looks like everything is there. I used SolidWorks Pack and Go, so it should have captured all of the parts regardless of location.

21-12-2014 13:37

orangemoore

Re: pic: Bit Buckets 2015 Offseason Drivetrain

This is the message I got. I looked through the folder and couldn't find the part.
http://1drv.ms/13s7hOI

21-12-2014 14:21

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

I re-uploaded the model; try downloading again.

21-12-2014 14:46

orangemoore

Re: pic: Bit Buckets 2015 Offseason Drivetrain

Is it just me or did the Download All button go missing. I now have to download all of the files individually.

21-12-2014 14:51

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

Missing for me too. That's odd.

21-12-2014 14:52

orangemoore

Re: pic: Bit Buckets 2015 Offseason Drivetrain

Could it be a setting in the project?

21-12-2014 14:54

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

I don't see anything.

21-12-2014 17:21

orangemoore

Re: pic: Bit Buckets 2015 Offseason Drivetrain

The Button is Back!

22-12-2014 03:11

fb39ca4

Re: pic: Bit Buckets 2015 Offseason Drivetrain

Very nice. Our team has had laser cut chassis for the past two years, but they are nowhere near as modular as yours.

22-12-2014 18:13

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

Thank you. We looked at your team's robots when we were trying to figure out whether or how a laser-cut robot would work.

Do you guys have any experience with wood gearboxes or bearing press fits? We're trying them on this robot but won't have much time to test them before build season.

23-12-2014 02:32

fb39ca4

Re: pic: Bit Buckets 2015 Offseason Drivetrain

We've never done wood gearboxes, but bearing press fits work fine, you just have to make the hole a hair smaller than the size of the bearing.

Is your chassis held together entirely with T-slots? We thought those would not be strong enough, so we use wood glue for everything. It probably helps that you are using 1/4" plywood, rather than 3/16".

23-12-2014 02:54

asid61

Re: pic: Bit Buckets 2015 Offseason Drivetrain

How small is "a hair smaller" for wood?
Press fits in metal are pretty precise. 0.001" smaller than the bearing is a light/ medium fit, whereas 0.002" is a heavy press fit, for the usual FRC bearings. Wood would be more forgiving on the size.

23-12-2014 10:03

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

Everything is held together with t-slots.

We've experimentally found that cutting the bearing holes .006" undersize compensates for kerf and gives a pretty tight fit. I imagine that this number varies with laser model and material.

23-12-2014 13:00

fb39ca4

Re: pic: Bit Buckets 2015 Offseason Drivetrain

Like z_beeblebrox was saying, the number varies due to the laser kerf, as well as the softness of the wood. If you haven't tried it before, I would cut a test piece with different sized holes in 0.001" increments to determine the ideal size. The other option is cutting holes slightly too small and sanding the inside until the bearings press fit.

23-12-2014 14:42

asid61

Re: pic: Bit Buckets 2015 Offseason Drivetrain

Thank you, I will file that away for when we use wood.

30-12-2014 16:00

z_beeblebrox

Re: pic: Bit Buckets 2015 Offseason Drivetrain

Here's the next version of the drivetrain. It maintains the same general design as the last iteration, but the CAD model has been completely redone. It is now better organized and entirely equation driven- the length, width, height and other properties can all be adjusted by changing numbers in a text file.

This model is not intended to be cut out as-is. It's intended as a base that a team can quickly and easily adapt to any game, changing the size, wheels, gearbox or anything else. As such, the gearbox mounting, which is intended as an example, is not equation-driven and the model includes no lightening or access holes, wheels or axles.

The electronics layout is also not a final design - it is simply a demonstration of how SolidWorks' blocks can be used to quickly draw an electronics board.



The gearbox included in the model is a repackaged Vex Pro Ball Shifter. Its only custom parts are the 4 wooden enclosure pieces.

SolidWorks files are available on GrabCAD here. Look in the folder "2015 Offseason Drivetrain v2 Upload".