Chassis Material/Construction

[Matt Reiland]

We noticed some NASA teams that pre-made connectors (like tinker toy ends) that hold tubing at different angles in the off season. THe keys here is build your 'proto-type' out of BOSCH then make the final out of tube by quickly rebuilding straight tube sections fitted into the pre-made connectors and giving it a little weld, which is much faster than making the custom ends on each piece when time is an issue. We will probably do this for 2003.

Bosch is great stuff, it just weighs alot, we did find we could 'remove' some excess material from sides we weren't attaching to for weight savings and it still was pretty strong stuff.
30x30mm

[Gary Dillard]

We've been using polycarbonate for several years now - I don't think anyone would accuse us of being fragile. This year our front frame was aluminum tubing and center pan was aluminum sheet, but most of the rest of the chassis (including the gearbox housings) were Lexan. It's easy to machine and assemble - it taps very easily for individual brackets and we use self tapping drywall screws for general assembly. A couple lessons learned - grease the screws and don't use locktite - it will shatter the laminate when it heats and cures. A key thing to remember in battle is that low spring rate materials will absorb impact energy better than stiff materials and lexan does a great job.

[Greg Perkins]

wheelman already said what we use


Badjokeguy

[Elgin Clock]

God Bless 80-20! SEE IT HERE! We usually go for the 1"x1" extruded 80-20 with 1/4 inch aluminum plate for the body. And also some 2"X 2" as well.

see example here and here

[sanddrag]

Yeah, we got some free samples of that stuff.

Could you explain a little about the "castors and one wheel on each side of your robot thing" I see in the picture?

[sidewinder]

I represent team 66. We build the sturdiest drive chassies i've ever seen, and can rarely be beaten. It is a little know fact that our robot for this last year was actually meant to handle balls. we only had one problem, a 95 lb drive chassy. We are big fans of the 1" extrusion but in my pit scouting for the last few years i have noticed something, The robots built for first don;t have enough power to bend 1" extrusion with any kind of blow.

I beleive that 20 mm extrusion, very light by comparison to its big brothers, has more than enough strength for our purposes.

As for polymers in construction, i haven;t seen many good examples of structural framing comming from it but have seen it in many good low impact uses (33's ball carrier a prime example. But after seeing the plastic bot of, i believe, 49 fall over at grand rapids last year and loose its arm, i have been weary of plastics use for robots.

[Matt Adams]

Originally Posted by sidewinder

We are big fans of the 1" extrusion but in my pit scouting for the last few years i have noticed something, The robots built for first don;t have enough power to bend 1" extrusion with any kind of blow.

I beleive that 20 mm extrusion, very light by comparison to its big brothers, has more than enough strength for our purposes.

20mm extrusion is something that we've looked into too, and I think that's definitely a possibility to reduce weight, though rough calculations would show the moment of intertia would drop to about HALF that of 1" 80-20 just by reducing the overall width and height (and presumably weight) to roughly 80% (20 mm / 25.4 mm/in) . That's the one reason that we haven't made that switch. Has 20 mm been used by your team in the past?

To keep with the thread:

In the past two years we're always using 80/20, 1010 (1" x 1")... and here's why:

The moment of inertia of 80/20 1010, which is 1" x 1", is .04413 in^4
The moment of interia of 1" x 1" x 1/8 thick box is 0.0570 in^4

The weight of 80/20 1010 is 0.495 lbs / ft
The weight of 1" x 1" x 1/8 aluminum box is 0.511 lbs / ft

So.. for those of you trying to save weight, look again!

Check it out at:
http://www.8020.net/pdf/Fractional/0...%20(31-62).pdf

Obviously though, it's more expensive than box aluminum. We were purchasing it at around $2.50 a foot. Box aluminum is about $1.50 a foot off of www.onlinemetals.com

People tend to make assumptions... crunch some numbers and you'll be surprised what you find!

In addition, the ability to actually CHANGE your frame around makes 80-20 great stuff. You can buy a 100 pack of t-nuts for $.08 each and go to town. Where 80-20 makes all their money is on those brackets and corner squares at $18 each. We make our own and come out just fine.

Matt

[Madison]

Though the 8020 extrusion itself may be lighter per foot than box aluminum, don't forget to factor in the weight of the additional fasteners and joining plates required to make it all stay together. If a team has access to aluminum welding equipment, it's probably lighter to weld a frame together from box aluminum than to make it from extrusion -- depending on its design, somewhat.

[Matt Adams]

Originally Posted by M. Krass

Though the 8020 extrusion itself may be lighter per foot than box aluminum, don't forget to factor in the weight of the additional fasteners and joining plates required to make it all stay together. If a team has access to aluminum welding equipment, it's probably lighter to weld a frame together from box aluminum than to make it from extrusion -- depending on its design, somewhat.

Let's see.

If you're using say 25 feet of 1" 80-20 for your frame, you'll save about .4 lbs over box.

40 1/4-20 bolts at 5/8" long, 8 of those corner fasteners (about .025 lbs each) and prolly about a foot and a half of 1" x .125" angle (at .2742 lbs / ft) gives you fasterner weight total of about .752 lbs...

<math skipped, have faith in my algebra>

So using 1" 80/20 for your frame is about 3.1% heavier than box aluminum, fasteners included. (13.17 lbs vs. 12.78 lbs)

Absolutely worth it IMHO.

[Elgin Clock]

Originally posted by sanddrag
Yeah, we got some free samples of that stuff.

Could you explain a little about the "castors and one wheel on each side of your robot thing" I see in the picture?

Simple, pneumatically controlled drive systems. One primary drive, and one secondary drive. The pneumatic wheels are the drive wheels hence 4 of them, two drive each configuration. The castors are just there for balance. It is a thing of beauty, no need to have a wide turning radius. We just switch drive systems and drive in a 90 degree angle from the original heading. It all worked with our I.D.A.N. System described below.

"A mini press release if you will:

The 2002 Robot

The Watertown High School Sie-H2O-Bots have created the 2002 PAL (Professionally Automated Landrover) to be a combination of simplicity and robustness. The machine uses a total of eight motors to function. These motors include three Bosch drill motors with planetary gear transmissions, one Fischer-Price motor with a custom built planetary gear transmission, two power window drive motors, one air compressor with 120 psi capacity, and one small servo motor. The final product is a durable, fast robot with good maneuverability.

The robot consists of two operating systems controlled via remote control through a computer-generated program. The two systems control the locomotion of the robot as well as a grasping system to capture and release goals. These two systems will allow the team to score points on the field by maneuvering the goals into different positions of the field.

PAL 2002 utilizes a 4-wheel drive system. The primary drive system consists of two wheels located on the east and west sides of the robot. These propel it forward and backward with tank style steering via two flight sticks in the driver’s hands. Speed is achieved with the click of a button, which activates two small air cylinders, shifting the drill motor drives from low to high range and vice versa.

The secondary drive system wheels are located on the north and south side of the robot. They are engaged when the primary drive wheels are raised off the floor and the secondary drive system is lowered. In this position, the robot moves from side to side. The tank-style steering drives are toggled by the student driver who, at his or her discretion, regulates the speed, power, and direction they deem necessary. During driver training, the ability of the robot to rotate around the goals proved to be a valuable asset. It enabled the robot under strong power to slip out of normally pinned positions with other ambitious robots.

A pneumatic system consisting of an air pump, storage tanks, regulators, valves, flow controls, and actuator cylinders is used to give the driver the luxury of switching drives instantly at the squeeze of a trigger.

The grasping systems consists of two “fork plates” that are located on the north and south side of the robot. They are ¼” aluminum plate shaped like a fork. The controls are designed to deport the fork arms by raising them vertical to horizontal from the profile of the robot, like short wings. When driven into the goal structures, the arms will automatically grab and hook the goal. The second driver controls each fork arm independently with a small control box at the driver station. Lowering the arms and driving the robot away releases the goal.

The team’s very ambitious electrical team has developed sophisticated controls, wiring, and programming to navigate the machine. The navigational system compliments the robot design very well. Important symbiotic relationships continue to develop between the electrical and mechanical systems as well as between the drivers and driver feedback systems.

The electrical team of students and engineers has created a system that would enable independent control of the machine by a visually impaired driver. Code named I.D.A.N. (Intelligent Detection, Analysis and Navigation), the system allows the robot to provide audio feedback to a laptop computer.

The cornerstone of this system is a tiny magnetic sensor that will read the earth’s magnetic field. The signal it sends out will identify the direction the robot is facing. This information also establishes the robot’s location within the five zones of the playing field. An optical switch receives a signal every time the robot moves over a line of white tape bordering each zone.

The robot has been installed with optical switches on servomotors, which allow it to “scan” for the goals and correct its path automatically. The optical switches respond to the retro-reflective properties of the tape on each goal. A pressure sensor inside the robot arms will determine that the goal is secure. The Sie-H2O-Bot team looks forward to gaining extremely valuable experience with this very sophisticated system as the season progresses.


Our experimental "Blind Drive" system won us the leadership in controls award in NYC as well."

[Joe Menassa]

wood all the way. why, because its inexpensive and does the job. We were attacked left and right this year, slamming into everything and the wood did not bugde. Our team loves it.

[Cory]

We used 1.5" Steel angle this year, because some genius thought that we would really need the extra strength. In reality our frame weighed a TON more than it should have. In the past we have used 1.5" aluminum angle, and it worked great.

[Tarzan]

bosch is good bwa-hahaha

[Jim Giacchi]

80/20 is better (And no its not because our main sponsor sells over a million dollars of it a year and gives it to use for free)

[mpking]

We've been all across the board.

96. ALL WOOD. Even the wheels!
97. Wood/Steel frame Hybrid. This bot Rocked! 2nd place in NJ
98. All Steel frame, all alumin upper chassis. 2nd in NJ again
99. again, all steel, and alumnin upper chassis
00. Aluminin Frame. Actually, the whole bot was aluminin
01. Aluminin / Bosch Hybrid
02. All Bosch. She was a tad heavy, but we have never had a bot that wasn't within a few ounces of the limit.

Another funny correlation. 96 and 02 had the same drive train, two wheels.
all the other years had skid steer. (Think like a tank)