29-10-2014 00:21

Christopher149

Re: pic: Concept 6W Drive Train

Any particular reason for cutting off the corners? Does it help much in giving more area for a given perimeter?

Definitely have to concur that simple is good.

29-10-2014 00:23

Munchskull

Re: pic: Concept 6W Drive Train

Looks solid.

29-10-2014 00:51

asid61

Re: pic: Concept 6W Drive Train

Looks a little too solid IMO. There's a ton of 1x1 on there.
However, 34 lbs is still pretty light for six cims (actually that's very light) so adding in a shifting gearbox would make good use of that drivetrain I think. It's only a couple pounds more, and allows for safe top speeds of 18fps+ without worrying about main breaker trips.

29-10-2014 01:00

mman1506

Re: pic: Concept 6W Drive Train

What makes this drive train better than a kitbot with nitrile treads and 6 cim gearboxes? If you want to keep it simple why not go that route?

29-10-2014 01:04

Re: pic: Concept 6W Drive Train

How is that any simpler than this?

29-10-2014 01:13

AdamHeard

Re: pic: Concept 6W Drive Train

It's not.

29-10-2014 01:21

asid61

Re: pic: Concept 6W Drive Train

Oh I just noticed:
Your main gearbox shaft is attached to the out frame member. If the outer frame becomes damaged in a collision and bends a little, it will damage the efficiency of the gearbox, and possibly render you immobile on one side.
Also, what's the reasoning behind cutting the corners? It seems like extra work to me.

29-10-2014 01:34

EricH

Re: pic: Concept 6W Drive Train

They are trying to work within their existing resources, and this is a simple design that fits within those resources. I would probably find it reasonable to assume that they don't anticipate having the funding to buy Versa, or to buy Versa and still do X, Y, and Z that they want to or need to do. Or that they're one of the teams that prefers making over buying (there are a few out there).

Is a WCD simpler? Maybe. But if you're doing all the machining for it, there are some advantages to NOT doing a WCD (like having more time!). Even if you are thinking of buying one, there could still be advantages to not doing one (dead-axle setups tend to be a trifle easier than live-axle setups in terms of manufacturing, something about no keyway or hex).

29-10-2014 01:42

Dunngeon

Re: pic: Concept 6W Drive Train

Are the gussets at the corners supposed to be seperate strips or angle iron? If they are seperate strips, it looks like a hard hit to the upper member could severely bend it inwards.

Edit: The upper 1x1 above the wheels

29-10-2014 01:44

Re: pic: Concept 6W Drive Train

A full versachassis can get expensive, I'll admit that, but just using some of the parts can greatly simplify this design and make it not only more effective, but more reliable as well. You don't need to buy an entire drivetrain setup, but using what your resources will allow can greatly simplify things.

You don't need to break bank on COTS parts to make a great drivetrain, but ignoring the cost effective resources available to teams isn't the answer either.

29-10-2014 02:02

T-Dawg

Re: pic: Concept 6W Drive Train

Is there a particular reason why the corners of the chassis are cut off?
The only reason I can think of is if you're trying to make the chassis fit within the 112 inch frame perimeter.
Otherwise, I don't see a structural benefit of cutting the corners off.

29-10-2014 02:14

Spoam

Re: pic: Concept 6W Drive Train

If I had to guess it would be that they're trying to keep all the 1x1s the same length for convenience? Then cut ends to keep it flush. Personally though if that's it then I might rather have the extra support from corners.

29-10-2014 06:32

JesseK

Re: pic: Concept 6W Drive Train

(nvm)

29-10-2014 12:45

Deke

Re: pic: Concept 6W Drive Train

It gave about 4.5" inches in perimeter back, so the frame is at 28 x 30 with ~ .5" to spare. The small increase in bumper complexity seems worth the extra 4.5".

I think you are right depending on the game, but I would like to avoid the added complexity and cost if possible. Most games don't require 18 fps imo.

Not much, it helps with bumper support and added area for mechanisms. I also like how the gear box gets packaged. We like to build as much as we can in house. The kitbot wouldn't have the students machining the components.

You are correct with how we are thinking. I would argue once you add bumper support and interfaces for mechanisms to a WCD, it is more complex. This structure immediately supports the bumpers and provides a little better locations for mechanisms imo. We also try to build as much as we can in house. We are fortunate enough to use the manual lathes and manual mills in the school to build.

With the bumper outside of the frames protecting them, I am not to worried about it. The dead axles also act as cross members supporting the outside lower beam. If the upper beam needs more support, cross members could be easily added. The corners being removed reduces the frame perimeter, allowing more length or width to be added.

Using angle pieces to connect the beams, the corners have no structural benefit as they carry no load. Now if top and bottom gussets were used, then additional structural support would be provided. The statics and solid mechanics of the structure make the corners the strongest part. Angle pieces are susceptible to torsional loads, but the internal beams stiffen any torsional loading the structure would take. If you draw up a free body diagram it becomes clearer.



I can't take much credit for this, I just copied it from 469 with a few tweaks. I would say it worked pretty well for them, world championship and such things. Not sure any one was questioning the reliability of their drive train, hats off to them, they are an inspiration to all teams.

29-10-2014 13:42

AdamHeard

Re: pic: Concept 6W Drive Train

We mill our WCD siderails on a manual mill for reference.

Also, bumper support on a WCD doesn't need to be complicated.

As for interfacing to mechanisms, how is it more difficult with a WCD?

29-10-2014 13:57

Oblarg

Re: pic: Concept 6W Drive Train

Are there really no problems with only having a bumper support that low off the ground? As far as I can tell, that's going to be contacting the bumper well below-center.

29-10-2014 14:00

AdamHeard

Re: pic: Concept 6W Drive Train

No problems at all.

We make one piece bumpers with strong corners. Any moment trying to bend the bumper over is reacted by the adjacent section.

29-10-2014 14:12

AdamHeard

Re: pic: Concept 6W Drive Train

Here is a good exercise...

Design a few drivetrains, give them all a good honest effort (otherwise you're just wasting your own time and lying to yourself).

While designing, do your best to optimize all the variants for your resources. Publicly post them for review. Invite BRUTAL commentary, take this in stride and incorporate the feedback that makes sense. If you have enough experienced students, mentors and possible sponsors that can offer review, the public part could be skipped.

At the end do a fair comparison of the different options on the criteria that matter to you; fab time, difficulty, cost, etc...

Going into nearly every season we have designed a swerve, west coast, plate sandwich drive and the last few years butterfly/octonum. We constantly reassess them to better suit our ever changing resources, and compare them on the merits we care about.

It's unreasonable to anecdotally link it to a drive a good team ran. Using that logic ANY drive can be proven to be the best.

29-10-2014 14:20

Oblarg

Re: pic: Concept 6W Drive Train

Ah. We've never done one-piece bumpers. We probably should try it out, it seems. Thanks.

Edit: Out of curiosity, how do you do the corners on your bumpers?

29-10-2014 15:53

Deke

Re: pic: Concept 6W Drive Train

We ran bumper supports similar to that and milled the rails manually. Our wc drive performed awesome last year, no issues. By the end of the season the bumpers were all smashed in at the top from no framing support and became more difficult to install, that's my beef with it. It also took a bit to get framing supported for mechanisms, there just isn't alot of framing on a wcd. Most of the framing required alot of attention throughout competitions. It's all fairly minor complaints, i don't have an issue doing a wcd again but i think a different approach could free up resources for us.

I'm confused who this information is for, isn't this the exercise we are going through? I enjoy the commentary and feedback, I am hoping it helps. I'd prefer feedback on pros and cons/strengths and weaknesses, versus design process rhetoric.

29-10-2014 16:02

AdamHeard

Re: pic: Concept 6W Drive Train

Can you post your frame and bumper setup from season?


It's for anyone willing to read it. Is this the only drive you are developing this fall, or are you also re-designing your WCD to have something to compare to?

Maybe look at vexpro drive in a day, and modifications (or stock) you could do there. I know 558 was really happy with, and just posted about it.

29-10-2014 17:42

Deke

Re: pic: Concept 6W Drive Train

Not really redesigning last year, just adding it to the considerations.

I do like the layout of the day in a drive, and actually all of the cots drives are pretty good. Our team prefers to build as much as we can, and would like some flexibility for perimeter changes.

I did read the 558 beyond the inspection when it came out, and they did say they wished they had more bracing to make the chassis more rigid.

29-10-2014 17:52

BrendanB

Re: pic: Concept 6W Drive Train

I smell no bias here. Nope.

WCD and even the Versachassis is not the answer for every team.

29-10-2014 18:18

AdamHeard

Re: pic: Concept 6W Drive Train

What didn't work out well on the framing for bumpers on this?

Hard to tell from just a top down picture, but assuming the supports between the wheels were at the correct height to support the bottom of the bumpers this should've worked out decent.

Was it a mounting issue? Did they have too much slop/play? Was it a once piece bumper?

Were you happy with the drive otherwise, and are just trying to solve the bumper issue?

29-10-2014 18:39

z_beeblebrox

Re: pic: Concept 6W Drive Train

AdamHeard, where can I find good pictures or descriptions of the bumper and bumper mount design that you guys use?

29-10-2014 18:46

Deke

Re: pic: Concept 6W Drive Train

The mounting could have been better, we used wing nuts with bolts through the bumper. It was a one piece bumper.

I have a handful of minor complaints: center live axle getting bent and wobbly a few times (took a while to replace, the dead axles performed better imo), bearing block plates hard to get at to loosen, gear box cantilevering off a few bolts seemed sloppy (, tensioners added construction and wheel maintenance time, if we got tipped the drive would sit on its frame edge and lose traction. Other than that and other things noted in this thread, it was pretty sexy.

29-10-2014 22:25

asid61

Re: pic: Concept 6W Drive Train

In recenty memory, there have been:
2010: Giant bumps made moving fast only possible in the individual sections
2011: Open space for driving. Very fast driving was useful.
2012: Open space for driving, except when passing over the low barrier.
2013: Open space barring the pyramids.
2014: Totally open space. 1678 was geared for 22fps according to their website.
If you feel that the cost/complexity is beyond the team's scope, sigle speed is more than fine. But when running 6 cims, be prepared to add in some kind of anti-breaker tripping code anyway just in case.

29-10-2014 23:53

Brandon_L

Re: pic: Concept 6W Drive Train

Usually you'd use a high strength aluminum alloy here or even steel, what did your team use?

This seems to be a result of where you're running your chains from. On most of the WCDs I've seen the chain runs are actually on the inside of the robot with the chains coming off a sprocket inside of the gearbox itself. Of course you can really do it any way you want, but as a result of sprockets on the outside yes your plates will be more difficult to get to.

What about it seemed sloppy?

With all that being said, 1x1 drives are perfectly valid. The only thing I would comment on is that some of your upper structure seems unnecessary. Maybe you're using the outer upper level for bumper supports, which is fine, but the inner upper level that holds up the gearbox could probably be replaced with something like this. Depends on what you were trying to achieve with it.

Also, I'm not sure if I would trust those vertical gussets you have going on with impacts. But I could be wrong. Who knows.

30-10-2014 01:17

philso

Re: pic: Concept 6W Drive Train

You may want to consider what would happen if this chassis is used in a game that allowed high speed and hard hitting, like this years. There is the possibility that the vertical angle pieces in the corners deform when hit on that corner causing the two outermost side tubes to move backward. Since it looks like your axles are supported by the lower side tube, they may bind in the bearing blocks and/or cause the robot to not drive straight.

30-10-2014 07:14

Deke

Re: pic: Concept 6W Drive Train

Shafts were 7075 1/2 hex.

Sloppy is probably the wrong description, more flexible than anything. The top of the side plates had some decent flex in direction changes.

I like the suggestion for removing the upper inner support, ithink that could easily change depending on the game and mechanisms required.

That's a good point, it would help to add some reinforcement to support the lower beam alignment.