I threw this together today:
- 6 wheel drive
- Polycarbonate outer rails
- 6" Wheels
- ~ 24lbs (no fasteners, motors, or battery)
I plan to design custom gearboxes for about 12fps, but that depends on our team’s budget. Questions? Comments? Concerns?
I threw this together today:
It looks like a great concept, though I see a few structural flaws.
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It looks like your round spacer between the lexan and aluminium are tangent to the support material surrounding them. This is very weak and I would personally reccomend at lease .25 material around all contact points.
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Move the round spacers down the same distance as their diameter, this will improve their supporting ability.
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Your square tube spacers should run from outer plate to outer plate because they provide much more structural integrity that way.
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The rearmost upper square spacer appears to be floating there (see number 1)
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Lexan will need some bottom supports so it doesn’t bow in.
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Tubes are very light as is and provide excellent mounting points. For this reason I would consider not lightening them unless you absolutely have to, and then with smaller diameter holes (see number 1).
How thick is the inner aluminum plate?
Are the wheels offset so that it is a rocker drive?
How thick is the inner aluminum plate?
The plate is 3/16" thick.
Are the wheels offset so that it is a rocker drive?
The wheels aren’t offset as of yet. I’m still debating on that one.
Thanks for the advice, I’ll implement as much as I can tomorrow. Extending the supports sounds like a good idea.
Yeah, I made that mistake my on my first drivetrain. I thought “Oh! Extra material! We don’t need this since there are all these othe spacers!” turns out you actually do…
If possible down-gauge the 3/16 to 1/8. It’s an instant 33% weight reduction. If you actually make this, DO NOT CUT LIGHTENING HOLES ON THE FIRST BUILD PLATE!!! It’s rather difficult to mount a random plate for something if there’s a big triangular hole right where you need to put a bolt. That was another mistake I made.
As for the wheels, I think they have to have some rock to turn in this configuration.
This is good advice, and if you get a couple of those extrusion supports to go all the way to the outer rail, you should have no problems at all with strength.
There is no reason to debate this at all. They wheels need to be offset or your robot will not turn. Or it might turn, but you’ll noice considerable hopping as your bot attempts to overcome the extreme friction beween your wheels and the carpet.
My team tried a simple 4WD with tracion wheels on all four axles, and that they hopped. Without a dropped middle wheel, your problem would be significantly worse.
The 6wd thing isn’t ALWAYS true. 25 does a 6wd without dropping them but I don’t know how. He can also do some other tricks to simulate the drop such as using a thicker tread. Personally I would drop the wheels.
I would also suggest you use some triangular bracing (look http://www.chiefdelphi.com/media/photos/31597 for an example) The cross members look like 1/8", how big are they? I would use 1/16" 1x1 and not lighten it.
Be prepared to change the tread on those back wheels a lot. with the battery and 4 cims back there your CG should be behind your middle wheel.
I like it.
IMHO getting your rotational inertia as low as possible would be a good thing. I assume maneuverability is very important to you if you’re aiming for 12FPS top speed, and getting the most massive components towards the center axle (which should be dropped) would improve the responsiveness of the robot.
Really? That’s interesting. In essence, is the point of contact between the ground and one of the wheels lower than the others or is it not dropped at all?