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-   -   pic: Bit Buckets 2015 Offseason Drivetrain (http://www.chiefdelphi.com/forums/showthread.php?t=131268)

z_beeblebrox 27-11-2014 15:17

pic: Bit Buckets 2015 Offseason Drivetrain
 

asid61 27-11-2014 15:20

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?

Ryan Dognaux 27-11-2014 15:35

Re: pic: Bit Buckets 2015 Offseason Drivetrain
 
Quote:

Originally Posted by asid61 (Post 1410329)
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?

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.

z_beeblebrox 27-11-2014 20:05

Re: pic: Bit Buckets 2015 Offseason Drivetrain
 
Quote:

Originally Posted by asid61 (Post 1410329)
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?

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.):

Peyton Yeung 27-11-2014 21:25

Re: pic: Bit Buckets 2015 Offseason Drivetrain
 
This might help with the encoder issue.http://www.chiefdelphi.com/forums/sh...hreadid=131034

z_beeblebrox 28-11-2014 17:49

Re: pic: Bit Buckets 2015 Offseason Drivetrain
 
Quote:

Originally Posted by Peyton Yeung (Post 1410352)
This might help with the encoder issue.http://www.chiefdelphi.com/forums/sh...hreadid=131034

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.

asid61 28-11-2014 20:04

Re: pic: Bit Buckets 2015 Offseason Drivetrain
 
Quote:

Originally Posted by z_beeblebrox (Post 1410436)
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.

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.

z_beeblebrox 30-11-2014 20:32

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).

orangemoore 30-11-2014 21:24

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?

nixiebunny 30-11-2014 21:41

Re: pic: Bit Buckets 2015 Offseason Drivetrain
 
Quote:

Originally Posted by orangemoore (Post 1410801)
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?

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.

z_beeblebrox 07-12-2014 00:42

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?

asid61 07-12-2014 00:55

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?

z_beeblebrox 07-12-2014 10:33

Re: pic: Bit Buckets 2015 Offseason Drivetrain
 
Quote:

Originally Posted by asid61 (Post 1412010)
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 07-12-2014 21:59

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.

orangemoore 07-12-2014 22:07

Re: pic: Bit Buckets 2015 Offseason Drivetrain
 
What is the cutting area of the laser cutter?


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