West Coast Drive: Bellypan
 

Hello,

Can the knowledgeable Chief Delphi community shed some light on what should go into the design of the West Coast Drive Belly Pan?

Main points I feel are:
1. What material/ How thin should the material be.
2. What lightening patterns have worked best for your team? How do you achieve this pattern using solidworks? (Would it just be a matter of using the linear pattern?)
3. How do you design the tabs and mounting holes into the bellypan to ensure correct spacing when bolting in the electronics?

Any other points of interest that I have excluded would be great.

Thanks,
Adam Garcia

Re: West Coast Drive: Bellypan
 

It all depends on the construction of the frame. in many WCD's the belly pan is made out of diamond cut alum., which contributes to rigidity, which can become a problem especially in thinner or less sturdily constructed sheet metal or 1x1/ c channel frames. in the event that you have a rigid and strong frame that doesn't need the extra support, I suggest going with something as light as possible, such as our material of choice this year, verilite.

to address 2, I would just create something and linear pattern it however you want.

don't really know much about 3, we just lay out our electronics, trace them with a dry erase marker, then drill holes accordingly

Re: West Coast Drive: Bellypan
 

I am unsure whether our frame is built rigidly enough to suffice without the diamond cut aluminum. For reference, our frame is very similar to 254's design. And, since they have been using an aluminum bellypan, I feel we should do the same! Oh yes, and it adds to the overall amazing look of the drive train.

Re: West Coast Drive: Bellypan
 

Adam,

There are a lot of examples of different bellypan styles on FRC Designs. Check out the link to the Drives page below!

FRC Designs Drives: http://www.frc-designs.com/html/drives.html

Matt

Re: West Coast Drive: Bellypan
 

Thanks Matt, I will take a look at these CAD Files

Re: West Coast Drive: Bellypan
 

We used 1/8" ABS riveted to the bottom of our frame which seemed to work fine. It was a little flexy in the middle, but we added a support and then it was fine.

Re: West Coast Drive: Bellypan
 

If your gonna go plastic, I'd recommend the stuff 973 has used in the past and maybe this year?

I believe its 1/16 or 1/8" thick garolite form McMaster. Adam can provide more details.

-RC

Re: West Coast Drive: Bellypan
 

1/16th G-10/FR4 garolite. Used it 2009, 2010 and 2012. It's very strong stuff and cuts very easily with hand tools. Tensile strength is greater than most aluminum alloys, and the bellypan in tension is really the loading that matters.

Aluminum bellypans are AWESOME, but are a substantial time and resource sink. I recommend any team that isn't already building 5-star robots to focus their time and resources on something other than a pocketed aluminum bellypan. The runtime on a bellypan for a 2d sponsor can cut several gearboxes, etc...

They sure are cool though ;)

Re: West Coast Drive: Bellypan
 

I assume you're using Inventor, but if you're not, I hope this is still pretty applicable. Once you have your pocketing pattern designed and applied in CAD, layout the electronics in an assembly the way you want them in an assembly. "Edit" the bellypan without "Open"ing it. This should cause everything else to become partially transparent and not selectable. Create a sketch on one side of your bellypan, and then go to the "Project Geometry" tool. Now when you mouseover the edges of all the parts in the assembly, they will light up, and selecting them will project that edge onto your sketch. You're essentially tracing all of your electronics. From there, go ahead and draw lines where you want them, close loops so the Inventor sketch doctor doesn't complain, and then extrude your tabs/outlines/whatever you just designed to mount electronics.

Little tabs at each corner are nice, but I like making a border for the entire component. It's cooler to look at when there's nothing on it.

Re: West Coast Drive: Bellypan
 

Every time the belly pan subject comes up I have the standard reply of "composites". This is the perfect place on the robot to give students some experience with composite construction methods. A team could use G-10/FR4 sheets. I suggest that teams make their own. A piece of 1/4", 4mm or 6mm birch plywood laminated with a layer on both sides of carbon fiber s2 glass or Kevlar makes a wonderful belly pan - electronics board and provides a great learning experience for the students. Once a team can make a flat sheet other forms can be experimented with. This year we used a .06" wall tube of layed up Kevlar for our beater bar. Took tremendous abuse and is extremely light. Put some fiber in your robots diet.

Re: West Coast Drive: Bellypan
 

My experience with G10 Garolite was not as favorable. I found it difficult to cut and that it puts a lot of wear on cutting tools, and I'm not particularly fond of the dust from cutting it. The reason we went with 1/8" ABS was so we could tap it, then use Nylon screws and cut the screws flush with the bottom of the robot, for a totally smooth underside. The ABS is a little soft though, and requires care when tapping.

The garolite is nice and strong though, I'll give it that.

Re: West Coast Drive: Bellypan
 

Generally, what size nylon screws do you use? And you get enough thread-bite at 1/8"?! THANKS!

Re: West Coast Drive: Bellypan
 

I completely agree. I am still unsure whether we are going to create the WCD custom Bellypan or just use a sheet of garolite or ABS. Do you know the densities of each? I cannot seem to find those numbers.

Re: West Coast Drive: Bellypan
 

This was very helpful. If we decide to create our own custom bellypan this summer, then I will be sure to employ these methods. This is actually along the lines of what I was thinking, but it was helpful since you gave a more in depth description of what to do.

Thanks!

Re: West Coast Drive: Bellypan
 

Gdeaver, why use plywood for that? That thickness plywood is already almost overkill for strength, why not use foam as the web of the composite?

Dave, the garolite cuts easily on a waterjet, tablesaw, and with hand tools. We have only ever specifically used g-10/fr4 so I can't comment on how g-10 cuts.

I highly recommend you do not do a custom aluminum bellypan, the time and resources used on it would be much better in other areas.



A large factor in the decision is whether or not the bellypan is part of the frame. I believe a bellypan should be an integral frame member (connecting corner to corner in tension) for maximum weight and strength efficiency. If this is not the case, the material selection is far easier. If you want a structural bellypan, the suggestions in this thread are good.

Re: West Coast Drive: Bellypan
 

The best tool for cutting G10 and other fiberglass is a Fein tool. Since Fein's patents recently expired, you can now get similar oscillating cutting tools from other manufacturers like Bosch, Ryobi, and Dremel. Home Depot has a nice selection.

The semicircular metal blades with small triangular teeth work best, and won't break skin if you accidentally bump the tool while in operation.

The dust is a very serious concern! Breathing in the dust from cutting fiberglass can cause silicosis. This is another reason to use an oscillating cutter, rather than a rotozip or dremmel tool. The oscillating tool doesn't throw the dust very far (an inch or so for the majority of the dust). Easy to clean up, and not airborne.

-- Len

Re: West Coast Drive: Bellypan
 

Be mindfull and take care when using this method as you are creating cross part geometry and dependence. This can be no problem at all, but if the referenced part is modified or removed your very likely to encouter difficulties with constraints and missing reference geometry.

I would reccomend a more time consuming, but more stable method in which you do not project geometry and instead insert the tabs and thru holes for mounting in a seperate sketch from the truss pattern. In this sketch either measure or look up the mounting hole patterns and geometry for the hardware you're including and manually set the spacing for your holes with a dimensioned sketch.

Re: West Coast Drive: Bellypan
 

We've used everything fron 6-32 for Victors up through 1/4-20 for the PDB. As long as you are careful while tapping to keep it straight and get it in one shot (use a cordless drill), you do get enough thread engagement to hold, so long as you don't over-torque the fastener.

Re: West Coast Drive: Bellypan
 

Does anybody know if a sheet of garolite is heavier or lighter compared to polycarbonate of the same thickness?

Re: West Coast Drive: Bellypan
 

G-10/FR4 is .067 lb/in^3 and polycarbonate is ~.044 lb/in^3.

The garolite is unquestionably far stronger in this application however. Although commonly used as panels by teams, it is a very poor choice for a structural bellypan (some people will disagree on the basis that they've done it and it works, but it's very inefficient for the same strength).

Re: West Coast Drive: Bellypan
 

Yeah, cross-part references can get pretty tricky. I put each component (or type of component) in a separate sketch and extrusion feature so that if I change something, it's easier to deal with. You can also break the adaptivity and make it a normal part so you don't need to worry about it.

Re: West Coast Drive: Bellypan
 

Garolite G10: http://www.matweb.com/search/DataShe... d5f85&ckck=1

G10-FR4 may be slightly different because the "FR4" stands for "Fire Retardant" (implying a different chemical composition for the resin), as explained in the notes section of that link.

Polycarbonate: http://www.matweb.com/search/DataShe...5030fc9 84f35

The polycarbonate link is 1 result from a search that returned over 1000 polycarbonate types, so consider it a generic estimate. For example, the "Unreinforced Polycarbonate" result lists a density of up to twice what the generic one lists, but is a range of densities rather than a specific density. Who knows what the polycarbonate from McMaster is :confused:

Re: West Coast Drive: Bellypan
 

I think you wanted this PC, not PC/ABS or PC/acrylic 'alloys'

Re: West Coast Drive: Bellypan
 

Quite true. I would recommend projecting the geometry of the motor controllers, tabs, etc. in a first sketch and extruding. Then, add the lightening pattern to the back side. Sometimes, I like to dimension the pockets/cheese holes/lightening pattern from the projected geometry of the motor controllers. This way, if you change the arrangement of the electronic components, the mounting holes will not suddenly disappear into one of your lightening holes.

However you decide to do it, I would highly recommend keeping any mounting holes and lightening holes as different features, with the lightening holes farther down the tree.

Re: West Coast Drive: Bellypan
 

I suggested birch ply as the core material for several reasons. It's cheap, available and easy to use. We do not do west coast drives. On some of our robots the belly pan is a structural member and carries significant loads. Foam core has point impact issues. There are many options for core materials. I suggest a team start with plywood and then move on to more advanced composite methods. This year our beater bar was made of a round tube of kevlar cloth and epoxy. Very light and very strong. There are many places on the bot for team made and purchased composites. I feel the most important thing is to expose students to their use.

Re: West Coast Drive: Bellypan
 

We have done a 254 style bellypan the past couple seasons. Aluminum or not, we like our bellypans to be cut without a bunch of manual operations like laying out the electronics, drilling the holes, etc. This would lead us to some sort of router/waterjet method of fabrication. Since we're already using waterjet, it makes sense to just go for the aluminum version.

We layout all the electronics in CAD, and place the mounting holes into the CAD for the bellypan. If you are designing in SolidWorks, the "Vent" tool is your best friend in the world. It saves a lot of modeling time, and is quite powerful for this type of operation.

We get to anodize our bellypan with the rest of our parts too, so it looks extra cool.




-Brando

Re: West Coast Drive: Bellypan
 

For the record, credit for the waterjet bellypan should go to 233 not 254. In 2009, Mike D convinced us to give it a try and we haven't looked back since.

Re: West Coast Drive: Bellypan
 

Could you please explain why 254 uses a bellypan? Why haven't you looked back and what did you do before 2009?

Thanks,
Bryan

Re: West Coast Drive: Bellypan
 

In 2004-2005, we had a ~1/2" sheet of plywood.
In 2006-2008, we had a 1/4" sheet of ABS. It was nice to be able to physically lay out all of the components and just drill/tap holes wherever for mounting & zipties.

The bellypan is of comparable (or less) weight to our previous solutions and acts as a structural member of the frame, stiffening it substantially. Furthermore, when the frame tubes are riveted to it, it acts as a welding jig and holds the frame tubes nice and square. It helps make the competition and practice bots closer to identical. Although it does look good ;), it is really just a luxury and I wouldn't say having the waterjet baseplate has improved our on-field performance or made our wiring any nicer.

Also to keep in mind, cutting a baseplate like this has some disadvantages including requiring significant advance planning and a solid grasp on how the wires and hoses connect all of the components. Furthermore, it takes a ton of waterjet time and we're lucky to have the resources to be able to do this. For 90% of the teams in FIRST, a waterjet baseplate is probably not worth it. There are better ways to use design and machining resources to move your robot into that top 10%. However, for teams who have the time and the resources, it is a nice thing to be able to do.

Re: West Coast Drive: Bellypan
 

Interesting, our analysis suggests that it is actually quite inefficient as a structural member. What you are saying pretty much corresponds with where my head was on bellypans: they are nice, but not mandatory. At least in our sheet metal construction, another well placed cross-member is probably a more effective use of weight. I do really like the use of the bellypan as a welding jig though, that makes perfect sense for a stick construction method.

Thanks for the info!
Regards, Bryan

Re: West Coast Drive: Bellypan
 

They are very good at connecting the frames corner to corner in tension. Most other types of loading are handled pretty well with "West Coast Drive" frames.

Re: West Coast Drive: Bellypan
 

While it certainly keeps the robot square I still think that a similar or more effective result could be achieved with some triagular corner brackets and perhaps even corner to corner cables in tension. There is definatly a good deal of bellypan that isn't actually doing much and I would still contend that as a structural piece it is not as efficient as it could be. We built a west coast drive in 2011 and like you said, it handles most types of loading very well. I think if I were to do a west coast drive again I would use a 1/16 waterjeted bellypan to use as a jig when welding and a low electronics mounting point. Because, as you said, the stick frame handles the tortional loads 1/16 should be fine for corner to corner in tension (try pulling apart a piece of sheetmetal, it can be bent, but not stretched or compressed without bending.) As a bonus, lighter material means less pocketing and less machining time.

In any case, it's only my opinion, take it with a grain of salt.
Regards, Bryan

Re: West Coast Drive: Bellypan
 

I hadn't thought of doing this for welded assemblies, but I really like the idea. Often we end up adding gusset straps to butt joint welds anyway. Why not put them in place before the welding begins in order to hold everything true.

Re: West Coast Drive: Bellypan
 

Here are a couple shots of our belly pan. We used the belly pan as the main design element to hold the frame together. We use rivets to join the pieces together and once joined the frame is lightweight, very stiff and strong. The material we used was .090" 5052 aluminum. The frame is 12 lbs total. No welding required.

We used a CNC punch press to cut the metal. Notice the basic shapes circle and square. The punched frame takes only minutes to produce but requires a bit of up front programming. The tolerances for the frame are very high. Hole to hole tolerance is +-.010" . We used a staggered perforation pattern to lighten the belly pan. A staggered pattern can reduce the weight by 50%-60%.

We laid out our electronics prior to punching. By taking the CAD model of the the electronics and extrude the mounting holes through the belly pan we come up with all the mounting holes. We used a 10-32 .250 thk. Pem standoff, a plastic isolator and a nylon screw to mount the electronics. Once installed we cut off the remaining thread and makesthe bottom surface smooth.

The proper use of the belly pan can reduce your build cycle considerably. It can be used to fixture other parts of your frame. It can be used to mount electronics. It can be used to strengthen and stiffen your frame. It can be bent up in the front and rear to allow the wheels to climb over field elements.

https://picasaweb.google.com/1045493...18089428878706


https://picasaweb.google.com/1045493...18315802523202

Re: West Coast Drive: Bellypan
 

Thank you to everybody who commented.

Our team has decided that we will buy a sheet of Garolyte for the time being. We did not know that fabricating the bellypan would be such a time/resource sink.

I fully agree that there are other parts of the drivetrain to improve upon first.

By the end of this summer, we will have a solid drive train, and will start the iterative process of improvement. I'm not yet sure when we will get to the custom bellypan, but that's the beauty of having another season to improve.