Chassis Connections

[Katie_UPS]

So, I'm on a team that does a lot of welding. And by a lot, I mean that every robot since I've been on the team has been welded- the arms, the frames and -the title of the thread- the chassis. The other three robots that our team has made have been kit frames. So, to incite your responses:

How do you keep your 'bot -but more specifically, your chassis- together?

[blayde5]

From as far back as any of the mentors and alumni have remembered, we've used Bosch-Rexroth's 3-way gussets and 2-way gussets to keep the chassis together. We used to be able to weld part of it but our welder got stolen 5 years or so back. Usually we don't find any problems with these and our chassis never really fails.

[Billfred]

Most of the robots I've had a hand in were held together with bolts--then again, most of those robots have used the kit frame.

What 1618 did in 2008 (and 2815/1398 in 2010) was use rivets. 1618 used the IFI kit frame that year and simply substituted a rivet in each place where a bolt was used originally. The result (click for the big image) was rock-solid, with no problems the entire Chesapeake Regional. (Bumpers likely aided that.)

2815 and 1398 used a custom sheetmetal frame, which naturally I can't find a good photo of this morning. (The next best thing is this photo.) We had about five 3/16" rivets on each edge of the frames, along with support from running dead axles. There was then a back plate and a belly pan, also riveted together. While I wasn't in the pits as much this year, I can't think of a single report of frame trouble across two teams and five events. And just as a bonus, we were able to rip apart both drivetrains to shake out drivetrain bugs by drilling out ten rivets and undoing three bolts holding the axles in place. (Okay, fixing the drivetrain issues didn't really seem like a bonus at the time...)

I wouldn't consider rivets an automatic decision on the frame, but they're certainly a strong choice each year.

[Brandon Holley]

In the past couple of years I've developed a pretty cool method for putting our frames (chassis) together.

Basically we have our own gussets made out of ~.060" aluminum and make them in two varieties, 'T' or 'L' (this is usually done by waterjet, and we can get the parts for around ~$1/piece). The Ts have 4, 1/8" holes and are 3" long while being 2" tall. The Ls are 3 holed around 2" X 2".

We pretty much use 1" box beam for all of our framing needs. This then allows us to put a simple hole pattern of 1/8" holes 1" apart, and 1/2" from any edge to rivet our frames together. For most applications the riveted frame is strong enough as is. However, the nice thing about doing it this way is that you have created a welding jig once riveted. If you then want to go back and beef up certain or all joints, you simply just start welding. The gussets will hold the frame extremely square, especially if you put the holes in the frame members on a bridgeport or mill.

I'll try to dig up some pictures to make life easier, but in the meantime if you have any questions feel free to ask.

EDIT: Picture found




-Brando

[Jon Stratis]

We welded a custom chassis in our second year, but have stuck with the kit-bot frame bolted together ever since. For us, welding the frame together ended up taking too long and was too mentor-intensive (and less student participation) than we want.

[JamesCH95]

My team has used bolt-together frames, typically plywood with angle-aluminum brackets or the kit frame. For 2010 we welded the kit frame together (saves several pounds of weight over fasteners) with some custom wheel brackets. Took 1 mentor (me) less than two hours to do at work (we had no welder at our work space). We then bolted on everything else, including some 3/8" plywood for a deck.

I would highly recommend welding the kit-frame together for the weight lost and stiffness/strength gained. It's 5052 aluminum, so it has no temper to lose through welding. If you are just welding the kit frame together it should take less than 1 hour to assemble, prep, and weld. The kit hardware holds it in place very nicely.

[548swimmer]

Our team uses bolts. What we have is a "modular" system of cross supports and drive "modules."

http://www.chiefdelphi.com/forums/sh...ad.php?t=85712

Each of the side plates is .188 aluminum (6061 T6 I believe) despite my best efforts to use .125...

The round spacers between the side plates are half inch aluminum round stock tapped with 1/4-20 on each end and secured with 3/4 inch panheads.

The square tubes run from outside plate to outside plate and are 1/8 wall (I keep pushing for 1/16...) with 2 inch long inserts tapped one inch deep 1/4-20 and secured with 3/4 inch panheads.

We have found this system to be fairly lightweight, especially if you use your spacers for axles. In addition to weight, the outermost module can be quickly detached from the rest of the chassis by removing the bolts in square tubes. For wheel/chain repairs, you can simply remove the outermost side plate.

[Hawiian Cadder]

we have always used the pancake design with aluminum plate. typically this takes around 150 metal screws. however when designing the robot this year we didn't really do the math and ended up with around 1400 holes. the box of screws, (2000 8-32 5/8 long button head) weighed almost 10 LBS. lock tight application for the whole robot took 5 people around 10 hours.

due to this, we are going for angle gussets with 1 inch box tube this year, hopefully it will be easier.

[Jeffy]

We have welded our chassis all of our years as a team. For a while our rookie year we were going to use the kit chassis, so we bolted it together, welded, then removed all the bolts. I don't remember the specific weight of the bolts and supports, but it was well over 5 lbs. We ran into trouble with the kit frame warping during the welding, so we made our own, and have done so every year so far.
If you are trying to decide what to do, I would definitely weld to save some weight. The next best option (imho) are aluminum rivets. I don't know enough about them or have enough experience to give a big recomendation, but I have seen them work very well.

[JamesCH95]

Originally Posted by Hawiian Cadder

we have always used the pancake design with aluminum plate. typically this takes around 150 metal screws. however when designing the robot this year we didn't really do the math and ended up with around 1400 holes. the box of screws, (2000 8-32 5/8 long button head) weighed almost 10 LBS. lock tight application for the whole robot took 5 people around 10 hours.

due to this, we are going for angle gussets with 1 inch box tube this year, hopefully it will be easier.

I'd love to see a picture of this "pancake design" that used 10lbs of fasteners...

[rahilm]

This year, we used lots and lots of bolts. Our whole robot was basically various sizes of aluminum angle, so we just had angle inside angle bolted together with at least 2 bolts.

In the past, we have welded (only drivetrains), used gussets and rivets, and used 80/20 extrusion.

[s_forbes]

Through the years, we have built a bolted chassis, a riveted chassis, a glued and nailed chassis, and a welded chassis. All have held up to the stress of 2+ regionals without issues.

You can build a chassis that is strong and light in countless ways if you put enough design work into it. The thing you need to ask yourself is how you can best utilize your resources to build a strong/light chassis as quickly as possible. The faster you can finish fabricating it during the build season, the better.

I would also encourage you to take a look at the big picture when you are designing your chassis. Robot functions change drastically from year to year and greatly influence the design of the drivetrain (hence why we have gone through so many different forms). Remember that you are designing and building a complete robot; the chassis and manipulators are not always independent systems.

[PAR_WIG1350]

1350 uses bolts and nyloc nuts everywhere. It makes prototyping easy since we can easily build, test, and rebuild any part (easy until you find you built an integral structural or functional component directly over the bolt head you need to get to which can't be moved since EVERYTHING is bolted onto it, but thats OK, it builds dexterity). The real issue comes when everyone is fighting to use one drill bit or wrench that is the only one of its size and happens to be the correct one for EVERY bolt on the robot.

We also like zip-ties, but not so much for the chassis.

[Chris is me]

Originally Posted by Katie_UPS

So, I'm on a team that does a lot of welding. And by a lot, I mean that every robot since I've been on the team has been welded- the arms, the frames and -the title of the thread- the chassis. The other three robots that our team has made have been kit frames. So, to incite your responses:

How do you keep your 'bot -but more specifically, your chassis- together?

This isn't strictly true. http://www.chiefdelphi.com/media/photos/24740

Anyway, Shaker used a pretty simple - if non optimized - chassis with some 1/4" AL plate, standoffs, and 80/20 extrusion to connect the two wheel modules. Standoffs were made on a lathe and secured with 1/4-20 bolts (1/2 bolts for the combination standoffs and axles), and the 80-20 was fastened by tapping the extrusion's holes and bolting them onto the chassis. It weighed a fairly reasonable weight: I think a fully driving base with compressor and everything was 65-70 pounds, with no attempts at all to reduce weight. (We wanted a low CG and we were consistently underweight the entire year)



The chassis worked just fine all year, but it really isn't that well designed. Look at the cross section and you'll see it's a lot more C-shaped than we wanted. Prechargning a pneumatic kicker caused it to noticeably deflect. We also had the electronics mounted several inches higher than we needed to which took room away from a hanger. If we did it again I would take the 80-20 structure and mount it much lower on the chassis.

[Aren Siekmeier]

2007 we used kit chassis with LOTS of loose bolts (I wasn't around then, but many alumni have memories of the robot dropping things everywhere during matches and in the pits)

2008 was a little different. We used kit chassis rails that we bent around a bunch a bunch to make a cool looking but structurally weak octagonal frame with an indent in front for the trackball, and then bolted a bunch of 80/20 up off of that. The 80/20 was quite strong, and fortunately the chassis rail didn't have any problems.

2009 (yay for the basement!) we had kitbot chassis on the bottom and then two sheets of plywood up the sides. Everything inside the bot was then bolted to this plywood, with a nice plywood roof to top it off, making for a rather sturdy setup.

2010 we welded for the first time thanks to a local prototyping company who did it for free . It was definitely the strongest we had ever made. We used the chassis for wheel mounting convenience and then aluminum box tube for a superstructure around that. Initially it was all riveted together, and then we sent it in to be welded, with gusset plates at the corners.

Attached are pictures from the years I could find.