Wood Chassis vs. Kit Frame

[Chris Fultz]

Several teams are posting and discussing wood frames for their robots.

With the frame kit included in the kit of parts, i am just curious as to what is driving you to a wood frame?

(PS - I am absolutely NOT being critical of the decision at all - I am just wondering.)

[gorrilla]

its cheaper for one thing

and easier to work with(sometimes)

[Kyle Love]

Originally Posted by gorrilla

its cheaper for one thing

and easier to work with(sometimes)

You get the kit frame with your kit that you pay for, so why not use what you already paid for?

[GUI]

We are going with a wood chassis because we want a custom chassis for ease of mounting mechanisms, adaptable design (the kitbot design is not very conducive to harvester mechanisms in its standard form), strength, and modularity. We chose to us wood for the custom chassis because it is available locally (no shipping time, errors aren't as expensive), inexpensive, is great for structural applications (houses are a great example), easy to use, and very light (the baltic birch plywood we are using for our frame has a density of about .016 pounds per cubic inch). For our team, with limited funding and machinig abilities, wood is the best candidate for a lightweight custom chassis. And it builds much quicker than designs we've used in the past.

[dtengineering]

Our very first chassis (2004, prior to the introduction of the KoP frame) was made of 3/4" plywood, and... well... not particularly elegant.

Since then we've used the KoP frame each year, although never in the "out of the box" configuration. We've always chopped it, flipped it over, machined it out (slots for chain tensioning, etc.) and always, always, welded it up. You get extra stiffness and save the weight of all those bolts.

This year, though, we're thinking of going back to wood just because we've built just about everything we can out of wood (manipulators to motor mounts), except the chassis. Mind you, aluminum will still play a big part in our design, and we certainly could use the KoP frame if we wanted to, but this year we wanted to do something a bit different and show how much we've learned since that first plywood chassis.

Jason

[MrForbes]

I think we've made too many vEx robots

The kit chassis is universal, which means that it's not really "right" for any specific design. The parts are designed with primary emphasis on being able to bolt it together, rather than being strong in the directions it needs to be strong, not having extra material where it doesn't need it, etc. Many parts you want to attach to it need to be mounted with a bracket to adapt it.

With a custom designed chassis, the parts can be placed where they need to be, with strength where you want. The side rails can be made the right size to attach the transmissions and bumpers to directly. The electronics board or a mechanism anchoring part can be an integral structural part of the chassis.

It's sort of like the change in cars over the past 50 years to being unibody design, where the body and chassis are mostly one piece.

As for the choice of wood...it's relatively easy to work with if you have limited shop equipment, it's easier to find folks with woodworking tools than with metalworking tools. It's readily available, and it's inexpensive. Cutting and drilling wood takes less time because it's soft. It provides good stiffness for the weight, since it is not dense, you can use thicker pieces with the same weight as metal.

There are disadvantages, such as the low bearing load it can take, so attaching points might need to be reinforced. It will break relatively easily, instead of bending as metal would.

It's also quite a paradigm shift...we all know robots are fancy machined aluminum things, not piles of lumber!

[Kyle Love]

Originally Posted by GUI

We are going with a wood chassis because we want a custom chassis for ease of mounting mechanisms, adaptable design (the kitbot design is not very conducive to harvester mechanisms in its standard form), strength, and modularity.

I know of a certain team that is using the kit frame with an intake, and so far there has been no structural issues with the frame after altering it for the intake system. Also, there are hundreds of holes to mount to on the kit frame.

[mynameisbob]

My team has been lucky enough to have a metalworking company help modify metal and give us metal in any shape or form we may need. They have a full aluminum shop and every piece of equiptment for metalworking you can imagine. We use plywood to make a model of the design we want and they help us turn that into metal. We love these guys "Walsdorf Metal Works"

[AdamHeard]

Originally Posted by Kyle Love

I know of a certain team that is using the kit frame with an intake, and so far there has been no structural issues with the frame after altering it for the intake system. Also, there are hundreds of holes to mount to on the kit frame.

I agree with the many mounting holes being nice.

You're awesome shooter tower that scores 5 balls as second is somehow 3/4" out of the size box in the back? just scoot it forward a set of holes.

Not always as simple as that, but if you have a hole pattern on the frame, you should build around it and really take advantage of it (we like it so much, we made jigs to put .201 holes every 1/2" of any structural member).

[gorrilla]

i know that this year, the C-BASE chassis probobly wont work for us, without some modifications.... and the holes are nice and all, but they arent always what teams need(say you needed a "large" hole inbetween) which has happened to us a couple times....

[MrForbes]

Originally Posted by Kyle Love

I know of a certain team that is using the kit frame with an intake, and so far there has been no structural issues with the frame after altering it for the intake system. Also, there are hundreds of holes to mount to on the kit frame.

You can make the kit frame work, for sure! That doesn't stop all those teams from milling frames out of thick sheet aluminum

One thing I've learned over the past few years is that there are many far more important aspects of robot design, than how the chassis is made. Chassis design is a great area for teams to do things how they want to....whether it's to save money by using a kit frame, show off their CNC design abilities, try out different materials or construction methods, or whatever.

[Kiwi]

I'm not sure what my team's final decision on chassis material this year will be, but last year we used a plywood chassis because... well, have you ever tried to make those nice straight pieces of kitbot frame be round?
The wood construction was lighter than an equivalent metal frame would have been, and didn't impair the bot's driving and performance.
We use the kit frame whenever we want a more conventionally shaped robot, though.

Here's a pic from last build season of a prototype bot with basically the same construction its better-decorated descendant who played at the Oregon regional.

http://www.team847.com/uploads/image...d/DSCN0052.JPG

[GUI]

There are really two questions being debated here (one a little more so than the other), "Why use a custom chassis?" and "Why make your custom chassis out of wood?". We use a custom chassis because we can make our obot exactly how we want it, and it makes mounting everything easier for us. We use wood because it is light, inexpensive, readily available, and easy to use with the tools we have. We can also make as many mounting holes as we need in wood on the spot, or simply screw something on. A custom chassis, or a wood one at that, might not be best for your team, but with our resources and skills it is.

[ebarker]

Originally Posted by GUI

(the baltic birch plywood we are using for our frame has a density of about .016 pounds per cubic inch).

Baltic Birch is awesome,

pictures from our with Baltic Birch Aim High 2006 machine

[Matt C]

Team 173 (Rage) has used a somewhat "standard" (for them) design wood frame every year I've seen them play. Always a nice, robust chassis.