pic: Team 3647 West Coast Drive
 

Re: pic: Team 3647 West Coast Drive
 

Great job!

I bet the gussets could be 1/8" thick instead of 1/4" and still hold up.

I would add some kind of cross bracing connecting the two gearboxes together. This will make your whole frame more rigid and provide those gearboxes and CIMs with much needed support.

Re: pic: Team 3647 West Coast Drive
 

Ditto Chris for the transmission support. 1/8" plate, bent at the proper angles and bolted to the front of the transmission and joining at the top of the side rails may solve it.

Re: pic: Team 3647 West Coast Drive
 

Looks like a good start!

I would seriously consider riveting a belly pan made of thin sheet (0.030" aluminum or 0.040" polycarbonate maybe) to the entire bottom of the frame and omitting the bottom gussets. This will be a nice place to mount electronics and other components as well as stiffening and strengthening the frame substantially. Ditto on making the gussets thinner also.

Re: pic: Team 3647 West Coast Drive
 

Thanks for the feedback!

Slight updated version, bigger standoffs and nutted/bolted.



The gussets currently are 3/16, so 1/8th would hold up just as well?
And replacing the bottom gussets with a poly carb bell pan sounds like a good idea.
I am thinking of using this: http://www.andymark.com/product-p/am-0836.htm

Also I am debating between using eClips or threaded ends on the shafts to hold the wheels in place, would you would guys recommend?

Re: pic: Team 3647 West Coast Drive
 

One idea I would have would be to move the center sprockets to inside the transmission plates. This way the outer transmission plate could be touching the chassis which would give much more support to the gearboxes.

Re: pic: Team 3647 West Coast Drive
 

This was something I thought about but the reason why I didn't do it was because the gearboxes are fully based on the toughboxes. If I changed the layout of the gearbox (moving the sprockets inside), it would mean we would need to make custom shafts and I want to keep machining down as much as possible.

Re: pic: Team 3647 West Coast Drive
 

We were able to do this without making custom shafts by using the cluster shaft from a supershifter. the main output shaft works with a larger gap without any issues as long as you get the extended output shaft

Re: pic: Team 3647 West Coast Drive
 

Oh I will definitely look into that, thanks!

Re: pic: Team 3647 West Coast Drive
 

I notice that you have some rather serious looking fasteners going all the way though the transmission and frame tube. I would suggest making those fasteners smaller. Graded 1/4-20 bolts will be plenty strong enough, even graded 10-24 fasteners would work fine.

I would also suggest having either an insert in the frame tube to transmit clamping loads from the bolt, or have a clearance hole on the outside tube wall and have the bolt only clamp to the inside tube wall. Otherwise it becomes easy to bend or crush the tube with zealous tightening.

Re: pic: Team 3647 West Coast Drive
 

They are 1/2-13, I wasn't sure how well 1/4-20s would hold so I went big... but I guess it wasn't needed.
I will make the outsides holes, clearance holes in the next revision for sure.

Re: pic: Team 3647 West Coast Drive
 

Sounds good. A 1/2-13 bolt is serious overkill. It's proof load would be 7,800-17,000lbf depending on grade. (I know this is a somewhat arbitrary value, I intend it as an 'order of magnitude' indication of it's strength, i.e. you could comfortably hang an F350 Super Duty truck using one of these bolts).

Here is a nice chart for bolt strengths: http://www.almabolt.com/pages/catalo...oadtensile.htm

A common rule of thumb is designing to 75% of proof load.

Re: pic: Team 3647 West Coast Drive
 

After taking all the feed back, here is another go:



Gearboxes are now mounted right on the frame with AM SS shafts.
Poly Carb belly pan replaces the lower gussets.
Weighs about 33 LBS.

Re: pic: Team 3647 West Coast Drive
 

Looks very nice! To add stability between the transmissions, I'd recommend the cross hex tube from AM that comes in the kit. Extremely light and with a 1/4-20 tap they will attach right where the nuts are on the tops of the gearboxes.

Re: pic: Team 3647 West Coast Drive
 

I think we do have a few of those shafts left over, sounds like a good idea.
Now all there is left is building it...

Re: pic: Team 3647 West Coast Drive
 

I always like seeing a quality base come together, especially with someone so willing and immediate at/to implement suggested changes.

The corner gussets could be 1/16" if you wanted to save some weight, but 1/8" certainly isn't too heavy and is easier to sell to doubting team members.

Definitly change the bolts on those gussets to rivets.

Incorporate from the get go a very rigid bellypan (as you have no internal crossmembers). Metal is nice but can be heavy unless very thing or heavily pocketed. I'd reccomend g-10/fr4 garolite from mcmaster for a VERY strong and light material that also happens to come in glossy black.

I like the changes you made to the gearbox mounting.

Can we get a close up and/or section view of the outer wheel/shaft/bearing block setup? There is a LOT that can be done right/wrong there that really make or break such a system.

On the same note, what are your plans for tensioning?

The reason the gearboxes are somewhat weakly mounted is if you view them completely from the front/back of the robot. They create a moment tryign to peel them off from teh frame, and you only have bolts at one elevation to react this. You really want bolts at two different heights (it deosn't have to be much) to react this. Our bolts are only .75" apart vertically and hold up just fine.

Ditto earlier comments about #10-32's being adequate, our entire drive uses nothing but.

Keep working guys! Very exciting to see, and you're on your way to a very nice drive.

Re: pic: Team 3647 West Coast Drive
 

The key to making a six wheel drive work properly is the stiffness of the frame.
I echo the belly pan idea...if you have access to a waterjet it can be done very nicely...

In the absence of a belly pan you might consider cross members... but remember the frame must be really rigid... in all directions.

Another option to help your frame stay rigid is utilizing the bumpers as part of your rigidity... you might as well use them if you have to have them.
By engineering them into the frame...you can gain rigidity ...

take a look at the drive base we posted last week
(1983 is the team number)
We utilize a double side rail.. ours is not a West Coast drive like yours...
We also incorporated the bumpers and their mounting into the frame...legally.

I think too many teams don't think of the bumpers as part of the frame/drive base...rather they think of them as an add-on...

Think of them as integral from the beginning and you can lighten in other areas...

Nice looking CAD work!!

Re: pic: Team 3647 West Coast Drive
 

I've heard others recommend this stuff too. Any particular thickness that you use? It looks spendy, but if it's worthwhile then it might be worth an order.

Re: pic: Team 3647 West Coast Drive
 

We like 1/16th. Runs like $60 per robot and you get a LOT left over for other parts. Mcmaster btw.

Re: pic: Team 3647 West Coast Drive
 

Why rivets over bolts?
I have currently a 1/8 sheet of poly carb in place as the belly pan, is that not stiff enough?

For chain tension, there are pockets for the bolts/shaft in the bearing blocks to allow them to side .25inch.
I will get a photo of the bearing block step up later.

Re: pic: Team 3647 West Coast Drive
 

Rivets are a lot lighter and are a set and forget operation.

Re: pic: Team 3647 West Coast Drive
 

You could probably move all the outer wheels a couple inches further out. They appear to be at least 8 inches inside the frame. Also, if the bumpers have to be all the way around the robot as in the last several years the need for the chassis extensions infront of the wheels diminishes except for as a bumper mount. Eliminating that and using the bumpers themselves solidly connected in the corners (such as a single piece bumper) allows you to place your wheels even further out.

Very nice looking chassis, Bryan

Re: pic: Team 3647 West Coast Drive
 

I do not like the look of those gussets. The fact that the frame has no internal bracing and the gussets are so small and have so few holes I think might make it really structurally weak. I would definitely increase the number of holes in each gusset and make them longer so that there is more bracing in each corner. Also, I would recommend another member somewhere in the center.

Re: pic: Team 3647 West Coast Drive
 

Also important to this design - rivets are better in shear than bolts.

Re: pic: Team 3647 West Coast Drive
 

How big of a rivet? And I assume pop rivet?

Re: pic: Team 3647 West Coast Drive
 

We use 3/16" pop rivets. These are awesome because they go perfectly in a No.7 hole(clearance for a 10-32). The gussets seem OK in size just as long as your using a good belly pan. It might just be me but it looks like your using 1/8" wall end-rails, 1/16" is plenty strong there.

One thing that will keep your gearbox clean is getting rid of all unnecessary bolts. For instance the same bolt that holds the top of the motor in can also go through the top standoff. If your making these plates with a cnc or water-jet, you can round the corners and try doing some pocketing. If you go the cnc rout then making the plates identical will keep your (cnc)sponsers happy.

Re: pic: Team 3647 West Coast Drive
 

Would something like this for a belly pan be okay? http://www.andymark.com/product-p/am-0836.htm

Re: pic: Team 3647 West Coast Drive
 

How do you feel about plywood, yeah it is ugly but it is cheap. How effective do you feel it would be? I know that 1114's Kitbot on Steroids uses 3/4" plywood for their electronics mount.

Re: pic: Team 3647 West Coast Drive
 

If you just put some paint on your plywood than it looks almost beautiful. It's a good material for stiffness and weight, especially at 1/2" and 1/4", and most teams that build field elements have some leftovers for things like electronics. You do have to worry about warping, though.

Re: pic: Team 3647 West Coast Drive
 

Care to elaborate on that? For example, I'd find it very hard to believe that a 1/4" pop rivet (steel or aluminum) is better in shear than the shank on a graded 1/4-20 bolt.

A properly designed and setup bolted joint can sustain more shear loading than the bolts themselves alone. The friction between the two parts, as generated by the clamping load of the threaded fastener, carries a substantial amount of load in addition to the bolts. Can the same be said for rivets?

Team 95 likes to use 1/2" or 3/8" high quality birch plywood. It is plenty strong enough and is lighter and more visually appealing that 3/4" construction grade plywood.

Re: pic: Team 3647 West Coast Drive
 

Looks really good and I am excited to see how it turns out and how successful it is.

Re: pic: Team 3647 West Coast Drive
 

I don't have a link handy, but I recall seeing a recommendation to use thin plywood with fiberglass cloth bonded to it with resin.

Re: pic: Team 3647 West Coast Drive
 

I remember that too, somewhere. It might have been Baltic Birch though, which is a bit lighter than plywood and commonly comes in multiples of 1/4" thickness.

Re: pic: Team 3647 West Coast Drive
 

Yes, I think you're right.

Re: pic: Team 3647 West Coast Drive
 

The belly pan is the perfect place to use composites. Very rigid, very light, usually very thin and also non-conductive. I highly recommend a fiberglass or carbon fiber belly pan.

Making a composite panel yourself is also something just about any team with a vacuum pump can do.

-Brando

Re: pic: Team 3647 West Coast Drive
 

Just make sure that if you use fiberglass for your bellypan that you're not 816 and have it end up being 8 pounds, un-lightened. :p

Re: pic: Team 3647 West Coast Drive
 

Was 8 pounds lightened, bro. 3/8" Thick Fiberglass Sheet Was Overkill for a bellypan, but you can't beat free.

(Until you're trying to figure out where you have 5lbs of weight that shouldn't be there.)

Re: pic: Team 3647 West Coast Drive
 

Just a couple of days ago, too!

This is in the thread discussing honeycomb material.

330's used various bellypan material; I believe we used 1/4" Baltic Birch in 2005 and built areas that weren't running under structural frame members up to 1/2" with glue. In 2007, using plywood, a pattern was traced on the bottom to allow electronics to be supported and have extra material around screws, then the whole thing was routed out. From the top, it looked solid because we didn't go all the way through.

Re: pic: Team 3647 West Coast Drive
 

How have I not heard of this monster bellypan before??

A nice think piece of birch wood wrapped in fiber, soaked in resin, and vacuumed should give a VERY rigid, VERY light belly pan.

Re: pic: Team 3647 West Coast Drive
 

That's actually what we'll be doing this year at Boeing's composites lab and autoclave. If the composite bellypan works out, we will also be making other structural members using other composites. Having so many Boeing structural engineers has its perks. :D

Re: pic: Team 3647 West Coast Drive
 

To expand on this a little...

Carbon fiber is conductive, so be careful when mounting electronics on or near it. A member of my FSAE team thought a carbon fiber battery cover would be awesome, right up until the battery got set the cover on fire!

Decent composite panels can also be made with a clean, flat surface, a clean flat plate, and some weights. Though a proper vacuum setup is the way to go. You can also get mixed fiber composites to add a nice flair of color to your robot.

Re: pic: Team 3647 West Coast Drive
 

Thank you for the clarification- I did reply too quickly.

Listen to James advice on this one!

Re: pic: Team 3647 West Coast Drive
 

I looked it up: Pop Rivets vs. Bolts

These are two kind of arbitrary sources, but it shows that while rivets are not quite as strong, they're comparable. The steel 1/4" rivet (shear: 2750 lbs.) beats Grade 2 1/4" bolts (shear:~2200 lbs.). However, the higher grades outmatch the rivets by a lot.

Re: pic: Team 3647 West Coast Drive
 

3/4" plywood would work just fine, but would be quite a bit thicker/heavier.

For a small wheeled west coast drive like this, a thin bellypan would be better.

Re: pic: Team 3647 West Coast Drive
 

You can be extremely aggressive with lightening in fiberglass and still retain your structure, because it's just so rigid. Holes with as little as 1/8" - 1/4" of material left around them are possible.

Re: pic: Team 3647 West Coast Drive
 

Someone asked for a photo of the bearing block, here it is.
Two 500 Hex Bearings press fit into 1/4 alum plates.
Bolt holes are pocketed so it slides about .25inch to allow for tensioning.

Re: pic: Team 3647 West Coast Drive
 

I assume they did a straight shear-strength calculation, which is good, but doesn't describe the whole situation.

Friction matters a lot, especially when clamping aluminum to aluminum. The static coefficient of friction is generally over 1, sometimes well over. You'd be looking at (to use my own numbers) 75%*1750lbf (proof load GR2 1/4-20) * 1.2 (coefficient of friction Al-Al) = 1575lb, so it would require 1575 lb of force to overcome the friction generated by the bolt's clamping force before the bolt sees a single pound of shear force, assuming the bolt was properly torqued.

Edit: I looked at the bearing strength of aluminum, assuming 6061 T6 it is 56ksi. Doing the math on an 1/4" diameter hole in an 1/8" thick plate says that anything over 1750lbf will start to yield the material around the fastener, so the excess strength of the rivet over a grade 2 bolt is meaningless because that will not be the mode of failure. The bolt's clamping force now makes it a clear winner.

Re: pic: Team 3647 West Coast Drive
 

Neat design. How do you keep the two plates aligned with each other and the shaft perpendicular to the frame?

Re: pic: Team 3647 West Coast Drive
 

With 2 bolts and a shaft going though the blocks, they will be aligned when the bolts are tightened. I have seen this type of design before and it seems to work pretty well.

Re: pic: Team 3647 West Coast Drive
 

I've got my doubts about the two separate plates being able to adequately support the shaft. It would probably work, but it's going to put unnecessary excess load on the bearings and possibly deflect more.

The bearings shouldn't count on the shaft for alignment.

I know 254, 1538, 968 and our bearing blocks all are complete and rigid assemblies.

Re: pic: Team 3647 West Coast Drive
 

We take a weight penalty by doing this, but this is why we just drill through a 1/8" extrusion and mount our bearings in a stationary manner. Precision milling multiple solid parts like the Poofs do and making them concentric is harder for us with our resources, so maybe it would be easier to do that and add floating tensioners or idlers.

To make up for the inefficiency of not necessarily being able to get a perfect chain tension, we switched to belts. This line of thought ultimately led to how we decided to make our "west coast" (east coast?) drive.

Re: pic: Team 3647 West Coast Drive
 

The assumption that the bearing blocks must be difficult to make is flawed. They can be dlne really simple and easy.

Re: pic: Team 3647 West Coast Drive
 

If I recall, this bearing block assembly has been used by numerous teams (254, 4, 968, 1868, 60, and probably others) for many years - going back to perhaps 2004 or earlier. There must be complete drawings of the part available somewhere...

We have developed an alternative (which may be heavier, I don't know). In the past, we've taken two bearing plates and milled a grove in them above and below the bearing on the "inside". A top and bottom plate was bolted into this groove making a "box" that surrounds the chassis 1" x 2". This keeps everything square. We actually make this "oversized" to allow for adjusting the heights of the wheels as well as their fore/aft position.

- Mr. Van
Coach, Robodox

Re: pic: Team 3647 West Coast Drive
 

How? < legit question

Re: pic: Team 3647 West Coast Drive
 

I don't want to sound like a smart @ss, but a bearing block is just that, a block. Add a 1.125" hole through the middle(for the bearings), a couple of threaded holes to hold it all together and you basically have a bearing block. We add a .125" chamfer to fit in the filleted slot, and make it .010" under the width of the frame tubing to make sure it clamps. Check out our cad and you'll see what i'm talking about. Our bearing blocks can be machined on a standard mill no problem.
This is also how 60, 254,968, 1538, and many other WCD's are setup.

Re: pic: Team 3647 West Coast Drive
 

Newb question but hat does the block add over the plates I used?
Isn't the bearings taking all the weight either way?

Re: pic: Team 3647 West Coast Drive
 

254, etc.... use a much different design that is similar in functionality, but different in execution.

Our blocks are pretty much a block with the bearing hole for both bearings. This makes each face plate effectively a large, special shaped washer.

Re: pic: Team 3647 West Coast Drive
 

There isn't anything holding the bearings concentric and in plane with each other very well. This could cause the bearings to get loaded nonradially and become less efficient.

It also could be a negligable amount.

Check out one of our bases to see an example of our block, which is very simple to make.

Re: pic: Team 3647 West Coast Drive
 

Our experience has been that separate plates on either side of the rail on this type of drive do not work well. The tension in the chain tends to pull the axles at each end toward the center, creating toe on the wheels.

I'd argue that the bearing block design is the most important (and most overlooked) element in this sort of design. Plates alone probably won't cut it.

Re: pic: Team 3647 West Coast Drive
 

Well taking the feed back from above, here is take 2.



Literally a bearing block. With a pocket cut into the rail that allows it to slide about .25inch for tensioning. And two 1/8 plates that hold it in place.

Re: pic: Team 3647 West Coast Drive
 

Can we see it without the frame?

I personally prefer to tap the block and have each flange on held separately, but that's obviously up to each team to decide.

Re: pic: Team 3647 West Coast Drive
 

Here it is without the frame.

Re: pic: Team 3647 West Coast Drive
 

Is the block+plates design better than just the plates at holding the bearing axes collinear just because of the added material constraining the bolts, or is there a more complicated explanation?

Re: pic: Team 3647 West Coast Drive
 

Both bearings are partially pressed into the same piece of material.

Re: pic: Team 3647 West Coast Drive
 

The bearings are pressed into the same bore, so they are definitely coaxial.

I think that if the slots are cut in the frame rail that the plates become superfluous. Mk. 32, you may consider using flanged or heavy hex bolts and/or washers and omitting the side plates.

Re: pic: Team 3647 West Coast Drive
 

Ah, I see. Makes sense. Thank you.

Re: pic: Team 3647 West Coast Drive
 

It really is a lot cleaner with the faceplates.

Re: pic: Team 3647 West Coast Drive
 

I think you've found a good solution there. Keep up the good work.

-Brando

Re: pic: Team 3647 West Coast Drive
 

A few years ago, I had something like this bearing block fabricated for 931, courtesy of Jabba. He started with round bar stock.

Re: pic: Team 3647 West Coast Drive
 

Was that done on a manual mill?

That looks great and easy to make! Looks like you could do the bore on a manual lathe with a DRO and then the rest on a mill with DRO.

Re: pic: Team 3647 West Coast Drive
 

Even a drill press with a DRO if you want. You don't need a mill with DRO to face the top and bottom flat.

Or maybe center punch holes using a template and then drill that way. Precision isn't terribly vital for this kind of part.

Re: pic: Team 3647 West Coast Drive
 

Flats were made using a manual mill. But the first steps were cutting blanks from the round stock (band saw) and then facing and boring them so the bearings fit square (manual lathe).

And Chris is right, there are other ways to get the same result.

Re: pic: Team 3647 West Coast Drive
 

Threads like this are one of the reasons I love this website so much.

The idea that a guy can post his designs on a website and people from across the world can pick apart his design and give their input on how to improve it, while the OP willingly changes his design accordingly is pretty darn awesome.

I hope this design sees a lot of success. It definitely has the potential.

Re: pic: Team 3647 West Coast Drive
 

McMaster # 9056K11 (or similar from a less expensive supplier) might be a good start for Richard's design.

Without a DRO, how would one check the bored diameter? Is the only way to start/stop the lathe constantly?

Re: pic: Team 3647 West Coast Drive
 

I would presume you'd drill the hole undersize and ream it.

Re: pic: Team 3647 West Coast Drive
 

Even with a DRO one would stop the late occasionally, i.e. after several passes, to check the ID of the part. Without a DRO one does the same procedure. The drive handles on the lathe will have a scale on them, something like 0.100" per revolution, typically with 0.001" accuracy. The operator would then count.

I like to take a 'skin' cut, measure the ID I just machined, subtract from the ID want to reach, and count turns/notches on the drive handles.

Edit: Chris' suggestion is also a good one. Assuming you're going to make many holes that size it is definitely worth investing in a reamer.

Re: pic: Team 3647 West Coast Drive
 

No need for a DRO. A DRO won't make the machine more accurate, just a bit easier to use.

Boring part by part is possible, but an FRC team who plans to start making custom parts should purchase the specific undersize reamer for the bearing. We really only use two size bearings on 95% of 973's robots, so it was a great investment (same for broaches, etc...).

Re: pic: Team 3647 West Coast Drive
 

Jabba ordered 9056K151. $38.69 for a one foot length of 2" o.d. 1" i.d. 6061 aluminum tube.

Jesse is right, there are cheaper sources. I change my password more frequently now, to make it more difficult for Jabba to place unauthorized McMaster orders. He prefers them because they deliver his material next day. ;)

Re: pic: Team 3647 West Coast Drive
 

For the press fit bearings, should the hole be something like .001 inch undersized? Or the same as the bearing diameter?
We have an HAAS CNC we can use, I am not sure if we have any reamers so I planed to just bore them out with a 1/2 milling bit.

Re: pic: Team 3647 West Coast Drive
 

DROs are nice, but definitely not necessary for just about everything you can do on a machine. As others have said, even with the DRO, a proper bore will require several starts and stops.

The fastest way will definitely be to get close and then ream. It will probably give you decently repeatable results as well.

We are fortunate enough to have a set of bore micrometeres at our disposal. They are extremely nice, and extremely expensive. We only allow experienced machinists to handle them and use them. They do make checking bore sizes a breeze though, and in our experience, are extremely eaccurate.

-Brando

Re: pic: Team 3647 West Coast Drive
 

is there any way of doing it with the wheels being off centered?

Re: pic: Team 3647 West Coast Drive
 

Depends on what you mean by "off centered". If you mean with the center wheel dropped, that's standard WCD configuration. If you mean the center wheels moved forwards or backwards, then you do pretty much the same thing as what is shown in the picture.

If you mean that your wheels don't have the axles in the center, well, that ought to provide some comedy to anybody watching you bounce around a lot.

Re: pic: Team 3647 West Coast Drive
 

Over on team 340, we had a similar concept... Andymark supershifters that worked great... had our chain runs inside 1.5 by 2 inch tubing (1/8 inch wall), easy to get to with the right pocket placement, and much, much safer... still had the 1/8 inch drop center, wedge top tread. We were pretty happy with our drive base this year