15-10-2014 17:19

Tyler2517

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

That looks like you have a lot of extra weight in motors and gear box's are you sure you will need that much power in your drive train.
Why the 4 independent gear boxes?

15-10-2014 17:28

nathannfm

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

The only way I could see using 4 separate gearboxes (assuming you want all those motors) is if they were fully COTS. If you are making your own plates you might as well optimize it.

Also, if that frame outside the wheels is not supporting the axles you could replace it with standoffs between the wheels (to comply with bumper rules) and move the drive rails out almost an inch on each side.

15-10-2014 18:15

waialua359

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

I'm with you on this. With a smaller footprint the last 2 years, you could acquire more space to work with inside the drive rails area. Because our drive base is modulated using standoffs and plates, we were able to run our chain inside to add even more space AND have the access to the chain, sprockets, etc.


I like the hexagon shape. I'm assuming its to "help" get out of T-bone situations, if necessary?

15-10-2014 19:29

Sohaib

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Are you sure you have enough power?

15-10-2014 20:10

Oblarg

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Not so sure what I think about the 8-motor, 4-gearbox setup. Looks really heavy - what benefits are there, specifically, over a two-gearbox 6-CIM setup? Keep in mind that you'll also need more air and more tubing and more failure modes to shift with this gearbox arrangement.

15-10-2014 20:39

TikiTech

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

True more space could be had, though not as much as you think. We did the stand off to bumpers on last years WCD 6 wheel robot.. Was very robust.

http://www.chiefdelphi.com/media/img...9ae90ccd_l.jpg

http://www.youtube.com/watch?v=LfKh6wgLArM

But we still didn't like the bumpers. We used 2 "C" shaped bumpers and was strong but was not to our liking. The idea is to have a one piece bumper drop over and lock on.

Yes this hex frame was done with "Tbone" in mind. Though last year with the 6 cim 2 speed low gear layout we had not many issues with that. Though it should help with getting pinched against a wall..

This is an off season project to try out some odd ideas thought up. The transmissions were done separately so that they can be used in other areas beside just drive.

We like the idea of putting the motor weight over the main drive wheels with the battery centered. Even though this looks like less space it has more internal space than last years robot. The outer frame is 2x1 while the drive tubes are 1.5x3". Gives a great exterior edge for LED ground effects.. FRC Swag!

We were so underweight last year.. Was strange to have to add weight, so we were not concerned with that on this prototype.

The idea is to have the electronics tray nested with the pneumatic shifters and run a plate above all of that level with the top of the frame for a clean deck almost the entire size of the robot. We will have the battery and electronics orientated flat at that time. The vertical battery was added to check the COG. which at the moment is centered on the robot at 4" off the ground.

Not knowing the game this platform leaves a lot to play with.

Of course as soon as the game is released all will change.

If desired I can put up some other views of the drive. There are some newer revisions done and can put up some of those pictures if desired.

Thanks for the comments, keep them coming.

Aloha!

15-10-2014 20:43

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

My hex drivetrain is about 28 lbs. How much does this weigh? It looks overkill heavy, and a lot of your custom solutions seem to be poorly thought out. Could you detail your thought process behind the major details of the design?

15-10-2014 20:51

TikiTech

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

More power!!

LOL

yes offset by weight.

The idea is to have two driven axels.. and a bit more power with added traction of 8 wheels

We are currently working on a single transmission plate that has two driven axels. We are waiting on our CNC to arrive that will allow us to make the larger more complicated plates. These current plates are done by hand on our small lathe / mill. That is the biggest reason they were separated. That and there was thinking of being able to run front and rear at different speeds. No clue personally why, maybe climbing? Sometime we build off ideas just to do so.

15-10-2014 21:33

Abhishek R

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

With the chain in the tube, how are you managing to turn with the drive, wouldn't there be a large amount of wheel scrub? Maybe a plan to lathe the Colsons on the outside to be slightly smaller?

I like the hexagon shape. Interesting idea to be able to run the front and rear wheels at different speeds, I wonder what applications you could have with that setup.

15-10-2014 21:37

TikiTech

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Poorly thought out is not very helpful..

What do you think is poorly thought out?

Current weight without the battery is 25lbs including electronics shown.

This is our first attempt at a hex frame. Most of this design was based on what materials we have or can get locally. Being in Hawaii, shipping stock material to prototype with is very expensive, so we have to be creative with what is on hand and available. There is nothing here but Lowes and Home Depot. No real machine shops or metal vendors or the like here.

Being a 4th year team we always enjoy learning different ideas, constructively..

Mahalo!

15-10-2014 21:42

TikiTech

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

The drivetrain is set up as a WCD with the outer wheels offset (1/8" above the center).

We never had any scrubbing issues with our 6 wheel WCD. The center wheels are 7" apart and should not see much scrubbing. We do have some Omni wheels for the front/rear if tests proves it to be an issue.

Just working on crazy ideas, never know what it could accomplish...

Thanks!

15-10-2014 22:05

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

I use the term "poorly thought out" very loosely. It's just part of the vocabulary. What I mean to say is I can't tell your train of thought in this design, and there are many design choices I question because I do not understand the reasoning behind them (hence why I asked about your thought process behind it).

What I see when looking at this frame immediately is the large quantity of gearboxes, and the large quantity of CIM motors. I understand earlier you said you made the decision of the 8 motors for the sake of "more power", but doing the math on my end shows marginal improvements in usefulness that do not seem worth the extra weight nor the risk of blowing the breaker. So I'm wondering what was the in-depth reasoning behind your choices for 8 motors, as well as the initial reasoning for 4 different gearboxes (I know you said you're planning on a new gearbox, but I'm curious about why you thought 4 different ones was the best solution initially).

Also, your frame layout with the 2x1 making the hex on the sides makes me question if you will be able to take your wheels off. For a true WCD the ability to easily remove your wheels is invaluable at times, and it appears like you're sacrificing this ability to shape your frame in this method. Out of all the ways to make a hex shape, why did you choose this one?

Speaking of framing, your 2x1 appears to be 1/8" thick - the more common style for a WCD - so with all of your tubing non-lightened, 8 motors, 4 gearboxes, and colson wheels, I really have a hard time believing that this drive system even without the electronics is 25 lbs. You have almost 20 lbs solely in drive motors, let alone solid 2x1x1/8 aluminum tubing and 4 large gearboxes, and then the added electronics makes it impossible for me to believe this is 25 lbs.

Your constructive iteration is the key to success - I just try to restrain from constructive criticism until I understand the thought process behind the design, so that I can better focus my advice towards the design and the designers.

15-10-2014 22:05

Abhishek R

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Oh, I didn't realize there was a drop. I faintly remember team 118 having to use different sized wheels because they could not enough space in the tube to have a big enough drop with the sprockets and chain. Did you have a solution to that problem or did everything seem to fit inside the tube just fine?

15-10-2014 22:26

Gregor

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Not sure how poorly thought out can mean anything other than poorly thought out?

15-10-2014 22:56

asid61

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

If you could consolidate your gearboxes into two 3 cim gearboxes, you could save a ton of weight and motors. I don't see the point in adding the power above 6 cims, unless you're planning on hitting 20 fps+ with 0.01s less time(not really math, just an order of magnitude calculation).

15-10-2014 23:16

Aren Siekmeier

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

As others have pointed out, there isn't much reason to go with 8 motors over 6, or even 4.

But even if you insist on 8, or at least having the option to mount more motors, you can still save a considerable amount of weight and improve performance by combining 4 on a side into a single transmission, with two output shafts. You can still do so with the WCP DS components.

Duplicating the shifting mechanism on both sides adds quite a bit of weight and cost and means that shifting may not be synchronized. Separating powertrains between front and back means that you could lose half your power if you're wedged or tipped up on your back four wheels. And there's more friction and inertia with all those stages.

Also, mounting the encoder on the input cluster like you've shown will introduce quite a bit more backlash between the encoder and your wheels, and will require knowledge of the precise shift state to schedule gains properly. Combining everything into one gearbox should give you some options to keep the encoder on the gearbox if you need to, while putting it much closer to the wheel, preferably downstream from the shift mechanism.

16-10-2014 02:08

Michael Corsetto

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Apparently, hex/octagonal, chain-in-tube, CIM-over-center-wheel WCD is the new fad in DT Design.

Don't miss the forest for the trees here people.

This is coming from a team that rocked an octo-WCD in 2014.

Consider performing a honest and thorough weighted design table to determine if some of the innovations you are proposing actually outweigh the costs.

I would encourage all teams to practice this evaluation method in the pre-season. Just like there is no better time to learn CAD and DT Design, there's no better time to learn how to objectively evaluate designs based off a set list of requirements/criteria (trust me, this is no easy task. It is arguably harder than actually designing the mechanism!)

Beyond big-picture, love the effort being put forward. Winners are made in the off-season!

-Mike

16-10-2014 02:30

themccannman

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

I detect a serious lack of power and weight in this drivetrain. Far too little power, you'll get pushed all over the place, and not nearly enough material, your robot will float away in a light breeze. I would also certainly increase your gear count, you can never have enough reductions, efficiency can be dangerous. Additional gears certainly help your weight situation too, 4 individual gearboxes certainly capitalizes on this.

16-10-2014 03:52

nathannfm

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

He says in the previous image that EACH gearbox weighs 15lb. Something is very wrong somewhere with weights in this CAD model as the WCP 3 CIM shifter this looks similar to would weigh 8.5lb with 1 CIM and 1 MiniCIM. I suppose the 15lb could be referring to each SIDE of the drive, ie. 2 of these put together, that gives a much more reasonable number. Still thats 30lb in just gearboxes, so, going under the stretch assumption that 25lb is this drive WITHOUT gearboxes thats a 55lb drive, which sounds much more reasonable.

All of that is a moot point though because OP has stated that the only reasons that there are 2 gearboxes per side is because they don't currently have the ability to make large enough plates to combine them, and that they want to be able to use the gearboxes elsewhere when the project is done.
A side note to that, MOE has had some success making plates that are larger than the travel distance of our mill by splitting the drawing into 2 parts with 1 shared hole. The shared hole is used to align the second drawing to the plate. You will also need 2 flat reference sides. This may not be possible in your situation and it may not be accurate enough for gear spacing but it worked well for chain.

16-10-2014 05:10

TikiTech

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Ok my bad. I am new to the iProperties thing.

This should have been caught by me, knowing that the CIMs together weigh about 5lbs.

There is no way that transmission weighs 9 lbs!!! More like 3.

The transmission is basically a hybrid of a WCP 2 CIM DS, 2.15lbs. and 3 CIM DS, 3.5lbs. Weight will be between that since it is basically a stretched DS if you will. A 2CIM DS with one extra idler. We went with an idler gear instead of belts. Much easier for us, we had it on hand.

The entire transmission was designed using the existing gears from our 3CIM DS making it easy to test by just replacing the frames. Future orders of different gear ratios from WCP will just work.

Last year we used the WCP 3CIM DS and are extremely happy with it. Never had any issues with breakers tripping on our 6 wheel WCD but space was tight.

We wanted a stretched 2 CIM DS, if you will. That was set up for in-frame chain setup and over the frame motor orientation. (see hex frame).

Being able to orientate the motors in either direction and a quick and easy encoder placement was the goal.

Our competition bots have always had a post tapped into the front or rear axle that the encoder used. Not always pretty..

Something different for us..

16-10-2014 11:12

Brian Selle

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

I think the difference is that 118 used a 1x2 tube so there no room for wheel drop. The 3880 prototype uses 1.5x3 tube so they have plenty of space.

16-10-2014 14:19

Abhishek R

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Makes sense, didn't realize it was 1.5x3.

16-10-2014 21:02

asid61

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Ah, ok, that makes sense. A 9lb transmission would be ridiculous.
However, that being said, I still higly recommend you consolidate your side gearboxes into one gearx each. There is no purpose to having 4 IMO.

18-10-2014 21:33

thinker&planner

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Anyone ever hear of battery voltage drop causing cRIO to restart? ;p

I say this partly jokingly, but partly practically. Even with 6 CIM WCD we were dropping out consistently during offseason when we changed our ratio to about 9fps.
We are looking into limiting acceleration/deceleration, current limiting code, etc.

19-10-2014 17:59

nathannfm

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

See if you can check your driver station logs for the voltage graph during your matches, that sounds like you might have some bad batteries.

26-10-2014 18:50

Cash4587

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Where might I find CAD models of the colson performa wheels? I am looking for a variety of them but don't know where to look. But what you have pictured is 4x1.5 and 4x2 if I am not mistaken and would be a good starting place for me. Any help is appreciated. I have checked 3dcontentcentral with no luck. Also google hasn't come up with a match yet.

Edit:
After more looking I found what I needed. Thanks.

26-10-2014 21:07

Tyler2517

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

It can also be a CAN brown out.

26-10-2014 23:23

Munchskull

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Over kill, much?

27-10-2014 09:32

JesseK

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Where did you find them?

I wind up making a generic gray-colored cylinder with rounded edges for my models.

27-10-2014 13:35

Oblarg

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

Someone posted a full CAD archive of Colson wheels on Chief Delphi some years back. Let me see if I can dig it up...

Ah, yes, here it is: https://drive.google.com/folderview?...&usp=sha ring

27-10-2014 13:51

Electronica1

Re: pic: FRC3880 - Tiki Techs - 2015 Prototype Drive

My team usually searches around in this.