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  #16   Spotlight this post!  
Unread 14-06-2007, 23:24
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Re: Unibody/Monocoque Construction

To Follow up on Woody's note above:
Team #33 has used a Structural Sheet Metal chassis design on several of our robots. Not exactly a monocoque, but similar. Like elaborated above by other teams; this is the strongest and lightest way to make many elements of a Robot. Our structural Chassis module is under 9 lbs including axles, motor mounts and battery tray, and it is very strong and very rigid. It has easily survived over 13 FIRST events of other teams relentlessly pounding on us and I have yet to have a failure of any kind. This design is a mix of .063", .050" and .040" T6 6061 Aluminum. We use 5/32 Alum/Alum Rivets for most of the jointery any use 10-24 screws with Jnuts for the wheel enclosure in case we want to go in an service the chains. We plan to post the complete set of CAD models, shop drawings and Assembly instructions to our team website later this summer (www.killerbees33.com)
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  #17   Spotlight this post!  
Unread 14-06-2007, 23:56
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Re: Unibody/Monocoque Construction

Quote:
Originally Posted by Jim Zondag View Post
To Follow up on Woody's note above:
Team #33 has used a Structural Sheet Metal chassis design on several of our robots. Not exactly a monocoque, but similar. Like elaborated above by other teams; this is the strongest and lightest way to make many elements of a Robot. Our structural Chassis module is under 9 lbs including axles, motor mounts and battery tray, and it is very strong and very rigid. It has easily survived over 13 FIRST events of other teams relentlessly pounding on us and I have yet to have a failure of any kind. This design is a mix of .063", .050" and .040" T6 6061 Aluminum. We use 5/32 Alum/Alum Rivets for most of the jointery any use 10-24 screws with Jnuts for the wheel enclosure in case we want to go in an service the chains. We plan to post the complete set of CAD models, shop drawings and Assembly instructions to our team website later this summer (www.killerbees33.com)
Wow, that is beautiful... It's hard to imagine that whole frame weighs less than my 12lb battlebot.

Are the wheels sheet Al as well? How much do they weigh?
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Unread 15-06-2007, 00:06
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Re: Unibody/Monocoque Construction

The entire frame was chromoly and consists of two main pieces - a main "tower" and a "trolley" that rolls up and down the tower. These two pieces together are about 25lbs with the rollers and bearings. The lifting platforms (aka - wings) used monocoque construction (mostly .040" 6061 T6). These were made just like aircraft wings - skin over two main spars made from sandwiched aluminum. The actual wing pivots are made out of 0.1" thick chromoly plate - these plates ARE heavy, but very strong. The first set of wings were 17lbs each, I believe. I think the lightened wings were about 15lbs each (you may have seen us frantically finishing these in our pit in Atlanta). Other than these main parts, of course we had our control panel (monocoque box), monocoque battery box and pnuematics panel, two outriggers also made of chromoly (2-3lb each, not included in the 25lb), transmissions, wheels, etc... I'll have to let one of the other team members post some good pictures of the frame.

If we were doing a more standard base, we would have used monocoque. We used entirely monocoque the two previous years - frame and manipulator/shooter. It goes together much quicker and is plenty strong if you have a "normal" shape. To accomplish our design goals last year, we needed a large part of our robot to move 12" and it needed to support large internal forces (upwards of 1000lbs) from the wings and it needed to have a big hole through the middle of it. This could have been done with monocoque given enough analysis and design time, but it just wasn't practical to do in 6 weeks. The tube structure was much easier to design and is more durable than monocoque would be in this application. The chromoly tubing is tougher than mild steel, so thinner wall tubing tubing can be used most places which keeps the weight down.

Monocoque is ideal for distributed loads - like the areodynamic loading of an aircraft wing. The rolling trolley in this robot concentrates very large forces on just a few points (the rollers). Using monocoque, these points would require some fairly thick material along the roller tracks to distribute the point loads. We may have saved a few pounds using monocoque for the lift bot, but it would have taken a lot more design effort and for the same weight, the tube structure is a lot stiffer.

Mike
  #19   Spotlight this post!  
Unread 15-06-2007, 16:38
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Re: Unibody/Monocoque Construction

Thank you all for sharing your design tips and techniques--there is a lot of great information here, showing off some quality work.
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  #20   Spotlight this post!  
Unread 15-06-2007, 17:19
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Re: Unibody/Monocoque Construction

Quote:
Originally Posted by Chris_Elston View Post
It's not as heavy as you think. Our whole tube frame was somewhere around 36 lbs I think. I am not for sure on that. But I was very impressed. The biggest down fall of the tubing was the welding. We had one mentor and two students that could weld it, the process was a bit slower than 10 guys with rivets guns for sure, but I can't complain, the end result was amazing to me.

I am not an M.E. I am a Controls Engineer. About the extend of my cad is AutoCad Electrical 2008 (<<<--use to be VIA, until AutoDesk bought them out) and I like Google Sketchup. I like Sketchup and have been learning the concept of 3-D drawing, maybe that will carry over to Inventor, if I ever have a need to use it. So far, drawings electrical prints in 3D some how doesn't fit into my schedule so far :-)

Although I wonder if the electricans would freak out if I gave them a 3D wiring diagram???? hmmm.....
For the past 4 years we have used chromoly steel (.035 thick) tubing for our robot frame. It is slightly heavier than aluminum and is 3 times as strong.

Pics:
04: http://www.cooneyrobotics.com/photos/2006/100_0277.JPG
05: http://www.cooneyrobotics.com/photos/2004/2004-7.jpg
06: http://www.chiefdelphi.com/media/photos/23825
07: http://www.chiefdelphi.com/media/photos/28616

Where we buy it:http://www.aircraftspruce.com/catalo...4130square.php
(Correct me if I'm wrong Ricky)

The frame you see for the 07 bot weighs around 12.5lbs
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Last edited by AndyB : 15-06-2007 at 17:21.
  #21   Spotlight this post!  
Unread 15-06-2007, 20:27
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Re: Unibody/Monocoque Construction

Quote:
Originally Posted by AdamHeard View Post
Wow, that is beautiful... It's hard to imagine that whole frame weighs less than my 12lb battlebot.

Are the wheels sheet Al as well? How much do they weigh?
We used the standard 8 x 1 inch IFI wheels with great success. I'm not sure on the exact weight, though.
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  #22   Spotlight this post!  
Unread 16-06-2007, 17:30
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Re: Unibody/Monocoque Construction

A couple of weeks back we had a chicken BBQ fundraiser. We also brought out or robots to show the public. We used our 4H fair parade float to showcase them.
When we got the float to the parking lot we discovered that the light (from 2006) on top of our goal was loose. We did not have a ladder or any chairs for me to stand on. I had the idea of standing on top of 2007 lifter frame. It held me (cough cough 220 cough lbs cough) with no flexing or rotating. It was a very stable tower.
Also, if you want to see how we do monocoque, e-mail me. I have over 500 pictures of the 2006 (Scorpion) robot. They go from day one of build season to ship day.
I also have a lot of pictures of Sidewinder II. Just not sure how many.
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  #23   Spotlight this post!  
Unread 16-06-2007, 18:44
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Re: Unibody/Monocoque Construction

thanks for the information guys, lot's of interesting stuff in here.
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  #24   Spotlight this post!  
Unread 17-06-2007, 16:18
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Re: Unibody/Monocoque Construction

Always wanted to do a monocoque chassis, at least in aluminum. I guess our first year robot made from plywood was more or less that
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  #25   Spotlight this post!  
Unread 18-06-2007, 13:15
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Re: Unibody/Monocoque Construction

Monocoque is very strong and reliable. When we were trying to figure out how to lose weight on our robot, I was surprised when the said that hole in the wings would only make it stronger, if done right. And remember, curves are stronger than flat surfaces.
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Unread 18-06-2007, 14:51
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Re: Unibody/Monocoque Construction

I'm suprised no one has mentioned 217 yet.

I have studied their 04-07 bots in detail and there are amazingly well done w/ sheet metal. very impressive.
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Unread 18-06-2007, 15:09
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Re: Unibody/Monocoque Construction


Here's one of their pics.
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