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Unread 29-10-2014, 12:45
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Re: pic: Concept 6W Drive Train

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Originally Posted by Christopher149 View Post
Any particular reason for cutting off the corners? Does it help much in giving more area for a given perimeter?
It gave about 4.5" inches in perimeter back, so the frame is at 28 x 30 with ~ .5" to spare. The small increase in bumper complexity seems worth the extra 4.5".

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Originally Posted by asid61 View Post
However, 34 lbs is still pretty light for six cims (actually that's very light) so adding in a shifting gearbox would make good use of that drivetrain I think. It's only a couple pounds more, and allows for safe top speeds of 18fps+ without worrying about main breaker trips.
I think you are right depending on the game, but I would like to avoid the added complexity and cost if possible. Most games don't require 18 fps imo.

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Originally Posted by mman1506 View Post
What makes this drive train better than a kitbot with nitrile treads and 6 cim gearboxes? If you want to keep it simple why not go that route?
Not much, it helps with bumper support and added area for mechanisms. I also like how the gear box gets packaged. We like to build as much as we can in house. The kitbot wouldn't have the students machining the components.

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Originally Posted by EricH View Post
They are trying to work within their existing resources, and this is a simple design that fits within those resources. I would probably find it reasonable to assume that they don't anticipate having the funding to buy Versa, or to buy Versa and still do X, Y, and Z that they want to or need to do. Or that they're one of the teams that prefers making over buying (there are a few out there).

Is a WCD simpler? Maybe. But if you're doing all the machining for it, there are some advantages to NOT doing a WCD (like having more time!). Even if you are thinking of buying one, there could still be advantages to not doing one (dead-axle setups tend to be a trifle easier than live-axle setups in terms of manufacturing, something about no keyway or hex).
You are correct with how we are thinking. I would argue once you add bumper support and interfaces for mechanisms to a WCD, it is more complex. This structure immediately supports the bumpers and provides a little better locations for mechanisms imo. We also try to build as much as we can in house. We are fortunate enough to use the manual lathes and manual mills in the school to build.

Quote:
Originally Posted by asid61 View Post
Oh I just noticed:
Your main gearbox shaft is attached to the out frame member. If the outer frame becomes damaged in a collision and bends a little, it will damage the efficiency of the gearbox, and possibly render you immobile on one side.
Also, what's the reasoning behind cutting the corners? It seems like extra work to me.
With the bumper outside of the frames protecting them, I am not to worried about it. The dead axles also act as cross members supporting the outside lower beam. If the upper beam needs more support, cross members could be easily added. The corners being removed reduces the frame perimeter, allowing more length or width to be added.

Quote:
Originally Posted by T-Dawg View Post
Is there a particular reason why the corners of the chassis are cut off?
The only reason I can think of is if you're trying to make the chassis fit within the 112 inch frame perimeter.
Otherwise, I don't see a structural benefit of cutting the corners off.
Using angle pieces to connect the beams, the corners have no structural benefit as they carry no load. Now if top and bottom gussets were used, then additional structural support would be provided. The statics and solid mechanics of the structure make the corners the strongest part. Angle pieces are susceptible to torsional loads, but the internal beams stiffen any torsional loading the structure would take. If you draw up a free body diagram it becomes clearer.



I can't take much credit for this, I just copied it from 469 with a few tweaks. I would say it worked pretty well for them, world championship and such things. Not sure any one was questioning the reliability of their drive train, hats off to them, they are an inspiration to all teams.
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Unread 29-10-2014, 13:42
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Re: pic: Concept 6W Drive Train

Quote:
Originally Posted by Infinity2718 View Post
You are correct with how we are thinking. I would argue once you add bumper support and interfaces for mechanisms to a WCD, it is more complex. This structure immediately supports the bumpers and provides a little better locations for mechanisms imo. We also try to build as much as we can in house. We are fortunate enough to use the manual lathes and manual mills in the school to build.
We mill our WCD siderails on a manual mill for reference.

Also, bumper support on a WCD doesn't need to be complicated.

As for interfacing to mechanisms, how is it more difficult with a WCD?
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Unread 29-10-2014, 13:57
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Re: pic: Concept 6W Drive Train

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Originally Posted by AdamHeard View Post
Also, bumper support on a WCD doesn't need to be complicated.
Are there really no problems with only having a bumper support that low off the ground? As far as I can tell, that's going to be contacting the bumper well below-center.
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Unread 29-10-2014, 14:00
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Re: pic: Concept 6W Drive Train

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Originally Posted by Oblarg View Post
Are there really no problems with only having a bumper support that low off the ground? As far as I can tell, that's going to be contacting the bumper well below-center.
No problems at all.

We make one piece bumpers with strong corners. Any moment trying to bend the bumper over is reacted by the adjacent section.
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Unread 29-10-2014, 22:25
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Re: pic: Concept 6W Drive Train

In recenty memory, there have been:
2010: Giant bumps made moving fast only possible in the individual sections
2011: Open space for driving. Very fast driving was useful.
2012: Open space for driving, except when passing over the low barrier.
2013: Open space barring the pyramids.
2014: Totally open space. 1678 was geared for 22fps according to their website.
If you feel that the cost/complexity is beyond the team's scope, sigle speed is more than fine. But when running 6 cims, be prepared to add in some kind of anti-breaker tripping code anyway just in case.
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Unread 30-10-2014, 01:17
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Re: pic: Concept 6W Drive Train

You may want to consider what would happen if this chassis is used in a game that allowed high speed and hard hitting, like this years. There is the possibility that the vertical angle pieces in the corners deform when hit on that corner causing the two outermost side tubes to move backward. Since it looks like your axles are supported by the lower side tube, they may bind in the bearing blocks and/or cause the robot to not drive straight.
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Unread 30-10-2014, 07:14
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Re: pic: Concept 6W Drive Train

Shafts were 7075 1/2 hex.

Sloppy is probably the wrong description, more flexible than anything. The top of the side plates had some decent flex in direction changes.

I like the suggestion for removing the upper inner support, ithink that could easily change depending on the game and mechanisms required.

Quote:
Originally Posted by philso View Post
You may want to consider what would happen if this chassis is used in a game that allowed high speed and hard hitting, like this years. There is the possibility that the vertical angle pieces in the corners deform when hit on that corner causing the two outermost side tubes to move backward. Since it looks like your axles are supported by the lower side tube, they may bind in the bearing blocks and/or cause the robot to not drive straight.
That's a good point, it would help to add some reinforcement to support the lower beam alignment.
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