pic: 1885 Drive Train 2010

[JesseK]

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[dtengineering]

I'll be interested to see how the prototyping pans out, but wood is great for whipping up some models to test on the bump.

We have an 8 wd mock up that we tested in both wide and long orientations before deciding to give up on the wide orientation.

It looked good on the computer... but having something physical to manipulate made all the difference.

Jason

[Raul]

Are you planning on actively articulating the wheel pods or just letting them conform to the ramp?

[hipsterjr]

My, that frame looks familar

[JesseK]

Originally Posted by Raul

Are you planning on actively articulating the wheel pods or just letting them conform to the ramp?

The current plan is to let them conform to the ramp. If there are a few pounds left over at the end of build season, we may add some sort of simple tension system to put a traction bias on the inner 4 wheels, yet all 8 wheels would still stay on the ground.

The chassis is based off of this concept that was thought of before the C-Base towers and Toughbox Nano's came out. That concept was based off of this concept of a natural terrain-hugging suspension.

[MrForbes]

It's a neat design. I wonder about the turning ability though...we are working feverishly to get our 8wd prototype running (hopefully today) so we can drive it around on carpet and on the bump. We are keeping the wheels fixed, but with spacing kind of like what you have--not evenly spaced, center wheels further apart longitudinally than the end wheels. With the end wheels raised just a bit.

We really like how 6wd robots drive, but were concerned about the bump, and we think the irregularly spaced, drop center wheel 8wd might be a good compromise between all the designs.

[scott]

HEY! I've seen this before...somewhere...

[CHapstack]

We made pretty much this same prototype last week. We figured that the main difference between this and a 4wd like the kit bot is that the fulcrum at each corner stays closer to the ground than the axle in a 4wd would when going over the bump (so the robot doesn't tilt as much). If you spread the 2 wheels at each corner apart more, the fulcrum will stay even closer to the ground.

[artdutra04]

If you are planning on using a free-spinningn tri-wheel design (all three wheels are powered, with the carrier automatically rotating over obstacles), make sure the input shaft and wheels rotate in the same direction and make sure the sun gear is significantly larger than the planetary gears (e.g. gear the wheels faster than the input shaft).

This means you will have to gear the carrier input slower (only to gear it faster at the wheels, I know it's an ugly solution), but the torque exerted on the individual wheels needs to be less than the torque needed to rotate the entire tri-wheel carrier assembly. If this is inverted (small sun, large planetary), the robot won't go anywhere with the tri-wheel carriers just rolling over themselves.

[Madison]

Originally Posted by JesseK

The current plan is to let them conform to the ramp. If there are a few pounds left over at the end of build season, we may add some sort of simple tension system to put a traction bias on the inner 4 wheels, yet all 8 wheels would still stay on the ground.

The chassis is based off of this concept that was thought of before the C-Base towers and Toughbox Nano's came out. That concept was based off of this concept of a natural terrain-hugging suspension.

If you're confident that the innermost wheelbase is short enough to allow unfettered turning, you might consider putting omniwheels in all of the outermost locations instead of developing the tension system you're talking about.

It's largely a trade off between time and money, I guess.

[MrForbes]

I was thinking about using slick wheels on the outer ones, but omnis are a better solution.

[Madison]

Originally Posted by squirrel

I was thinking about using slick wheels on the outer ones, but omnis are a better solution.

In your case, however, be careful with liberal application of omniwheels. If y'all are using a fixed 8WD and if climbing the bump is your thing, you'll have some circumstances where only omniwheels are contacting the ground.

[acidrain2012]

looks like someone else had almost exactly the same idea we did

[MrForbes]

Originally Posted by Madison

In your case, however, be careful with liberal application of omniwheels. If y'all are using a fixed 8WD and if climbing the bump is your thing, you'll have some circumstances where only omniwheels are contacting the ground.

That's true. In our case we have the end wheels raised up (which you can't do very easily with the articulated design) so traction wheels all around is best.

[Tom Line]

A word of caution. If, during a pushing match etc, the torque of your wheels causes them to rotate the assembly and lift your bot up an inch or two, your bumpers will be out of the legal zone. This may be deemed illegal and you may be DSQ'd (if someone decides to protest). You may want to look at some sort of active actuation to prevent it.