West Coast Drive: Bellypan

[Levansic]

Originally Posted by sanddrag

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 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

[Dave McLaughlin]

Originally Posted by Gray Adams

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.

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.

[sanddrag]

Originally Posted by Michael Blake

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

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.

[Chickenonastick]

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

[AdamHeard]

Originally Posted by Chickenonastick

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

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).

[Gray Adams]

Originally Posted by Dave McLaughlin

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.

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.

[JesseK]

Originally Posted by Chickenonastick

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

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

[PAR_WIG1350]

Originally Posted by JesseK

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

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

[DampRobot]

Originally Posted by Gray Adams

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.

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.

[Gdeaver]

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.

[Brandon Holley]

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

[NickE]

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.

[BJC]

Originally Posted by NickE

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.

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

Thanks,
Bryan

[NickE]

Originally Posted by BJC

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

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.

[BJC]

Originally Posted by NickE

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.

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