Good Material For Bottom of Chassis

[theCADguy]

Originally Posted by Michael Hill

Can you machine on garolite easily? I've been thinking about using it, but hear bad things like delaminatione can happen.

I'm not too sure about the machinability, but as far as I know, we haven't had any major issues as of yet.

[MrRoboSteve]

We used 1/8" polycarbonate sheet last year and it worked great. More commonly available at Home Depot, Lowes, and Menards than birch plywood, which can be somewhat of a specialty item. Polycarbonate sourced there is cheaper than the sheets that AndyMark stocks.

I would avoid using construction grade SPF plywood in a 3/8" thickness, as its quality varies widely and won't hold up as well as birch, which has more glue in it.

You'll find that acrylic sheet is also available and cheaper, but you shouldn't use it. It breaks too easily, and the broken pieces are quite sharp.

[Bryce Paputa]

We're experimenting with a custom carbon fiber composite belly pan. We're taking a thick foam core and CNC'ing grooves for strength, for a battery holder, and for mounting electrical components. Then we layer this in sheets of glass fiber and carbon fiber, epoxy it, and vacuum out the excess air while it cures. This takes more time and more planning, but has given us a much better result than the 1/16th aluminum that we used last year.

[BeardyMentor]

Plywood, polycarbonate, and sheet aluminum are all going to work well for this. Plywood and polycarbonate are a bit better than the aluminum in my opinion. The reason for this is it makes sure any electronics you mount to it are electrically isolated from the frame. Though, this is almost as easily done with double sided tape or Velcro. The take away from this is, use what ever material meets your budgetary and aesthetic needs.

One thing to note, If you want to use this as an element to stiffen up your chassis, use more screws than you would think. More smaller screws are better in this regard. One 10-24 screw every 4 inches or so around the perimeter works pretty well. Much better than just securing the corners.

[cgmv123]

Originally Posted by BeardyMentor

The reason for this is it makes sure any electronics you mount to it are electrically isolated from the frame..

The 2015- control system does not have any components with grounded cases that require isolated mountings.

[Richard Wallace]

Originally Posted by cgmv123

The 2015- control system does not have any components with grounded cases that require isolated mountings.

Even so, the frame isolation requirement (R37) is likely to return for 2015 -- it has been part of every FRC Manual that I can recall. Many instances of isolation failure that I have seen, while inspecting FRC robots, have been caused by poor wiring -- and were therefore intermittent.

Also, a non-conductive wiring substrate will not produce conductive chips when you drill it at the last minute to re-position control system components.

[Jared]

Originally Posted by cgmv123

The 2015- control system does not have any components with grounded cases that require isolated mountings.

Doesn't the axis camera have a grounded enclosure?

[cgmv123]

Originally Posted by Jared

Doesn't the axis camera have a grounded enclosure?

The 206 does, but Axis doesn't make them anymore. The M1011 and M1013 screws and enclosures are isolated.

[alicen]

My team used to mount the battery to a section of the frame and use smaller pieces of aluminum angle to make sure it couldn't move/slide. A velcro wrap was then used to secure it in the battery holder (think like a cup holder).

For most of the electronics, we would use corrugated plastic (often used for yard signs) because it was light and cheap as well as sturdy enough. Usually we had sections for different parts of the electrical system and the sections could be removed to get to specific areas of the robot. They were all held on with velcro

[s1900ahon]

Originally Posted by Bryce Paputa

We're experimenting with a custom carbon fiber composite belly pan. We're taking a thick foam core and CNC'ing grooves for strength, for a battery holder, and for mounting electrical components.

How thick is your foam?
What kind of foam? (Make, model)
Are you trying to do this in one pass? I ask this since I've found that doing wet layup in 2-3 steps is a much easier process (and less stressful). We have much less retained epoxy. Peel ply is now a good friend.

[Bryce Paputa]

Originally Posted by s1900ahon

How thick is your foam?
What kind of foam? (Make, model)
Are you trying to do this in one pass? I ask this since I've found that doing wet layup in 2-3 steps is a much easier process (and less stressful). We have much less retained epoxy. Peel ply is now a good friend.

On the most recent iteration we had a flat core (either 1/8th or 1/4th, don't know where we got it from) that we did one big lay up on. Not completely sure on the foam type, but it looks pretty similar to http://www.aircraftspruce.com/catalo.../lastafoam.php. We then made ridges separately and epoxy'd them on after the first lay up. This worked fine but doing the ridges separately took a bit of work. We haven't gotten to the CNC'd foam core quite yet, but we plan on making it with 1" foam core. We haven't had any issue with doing it in one pass, and we don't really want to have to wait for multiple lay ups to dry.

[s1900ahon]

Originally Posted by Bryce Paputa

On the most recent iteration we had a flat core (either 1/8th or 1/4th, don't know where we got it from) that we did one big lay up on. Not completely sure on the foam type, but it looks pretty similar to http://www.aircraftspruce.com/catalo.../lastafoam.php.

Thanks.

We've had good success using HDPE for a mold material and directly CNCing the mold shape (we have a router-based gantry-style CNC). Then doing a layup of carbon x3, peel ply, perforation film, breather/bleeder, and vacuum bag. After curing, the next night we did a second layup of core (1/4 nomex honeycomb), 3x carbon, etc. A carbon part in 3 days was the most efficient recipe we've developed or executed.

This recipe could be adapted to cut foam opposite to the mold, adjusting to the thickness of the first layup.

Scott

[Gdeaver]

For several years now we have been using 4mm or 1/4" Baltic birch plywood laminated with a layer off 5.7 oz plain weave carbon on both sides. The panel is a structural member of our frame. S2 glass or Kevlar cloth could be used if the conductivity of carbon bothers one. It has not been a problem for us. Last year a sponsor laser cut the panel including mounting holes. We do not laminate the practice bot panel and it does not have the durability or stiffness of the carbon panel. Each year it ensures that the team receives some experience in composite construction.

[Mr V]

1/4" plywood is what I recommend. To stiffen it up a piece or two of 1x1 angle placed on the top works well to support the battery. If you space it just slightly larger than the battery so the edges of the battery rest on it then you've got the battery constrained in one axis. Use a small piece of the 1x1 angle to make a bracket to attach it to the frame on each end.

[Christopher149]

A material 857 has used for a couple years is HDPE (high-density polyethylene). We have an absolutely enormous sheet and have been slowly working through it. Machines similarly to polycarbonate, and is opaque.

Nothing really special about it, but it's different than the other materials mentioned and has worked well for us.