West Coast Drive, WCD

[HarveyAce]

Hello All!
After following this thread, I was curious about what the advadntages of WCD are, and when is the optimal situations to employ such a system. I am curious because we are about to begin working on offseason training which might entail building various drive chassis and systems to get some offseason design experience. Thanks!

[sdcantrell56]

The advantages that lead us to a west coast-ish style drive were:
1) ease of maintenance
2) wider track width
3) less weight
4) protected belts

We were already planning on direct driving a wheel no matter what frame style we chose and also leaning heavily towards a live axle system since for us it is easier to fabricate the components so a west coast inspired drive fit in perfectly with what we were already leaning towards.

[ajlapp]

That's a great looking and clean chassis! Only thing I don't totally understand is why you go dead axle instead of live with the chain on the opposite side? Not really a critique just wondering what the decision making process was.

Some of the reasons:

-standard axles. we use chromoly tube to form the dead axles.....simply cut to length. this reduces machining.
-we use AM standard wheels. the plaction variety is cheaper than the performance wheel....so using a dead axle saves us having to add AM hex or key hubs back into the wheel, thus increasing the cost.
-we can service the wheels just as easy as any live axle setup i've seen. when the chain is tensioned properly it slides off the axle with the wheel as part of the assembly...no issues.
-dead axle blocks are slightly easier to manufacture....just ream an undersized hole for the axle. no precise bearing fit.
-chain on the outside of the frame rail doesn't interfere with any assembly on the inside....this makes life easier when we have to add something unplanned inside the perimeter
-we can adjust the rocker by swapping out different end blocks. live axle blocks don't allow this because there isn't enough material to machine away in the vertical direction.
-we used to use custom Dewalt planetary drive transmission....they wouldn't have worked well with a double sprocket on the inside of the chassis rail.

Note that the Super Light Chassis product can be used in either variety. The standard version is "dead" axle, but "live" axle blocks can be dropped into the outer wheel positions.

[Team 3266]

WCD sounds like it has a lot of benefits, but how do you mount a standard gearbox to the rail?

[R.C.]

Originally Posted by Team 3266

WCD sounds like it has a lot of benefits, but how do you mount a standard gearbox to the rail?

Normally if your going to all the trouble of making a custom drivetrain, you'll be making your own gearboxes as well. The only place that currently sells gearboxes integrated for a WCD is Team 221 Robotics.

But 973 Back in 08 used a shifter shifter in a WCD setup:

http://www.chiefdelphi.com/media/photos/31605
http://www.chiefdelphi.com/media/photos/31604
http://www.chiefdelphi.com/media/photos/31603

-RC

[Arefin Bari]

Originally Posted by HarveyAce

Hello All!
After following this thread, I was curious about what the advadntages of WCD are, and when is the optimal situations to employ such a system. I am curious because we are about to begin working on offseason training which might entail building various drive chassis and systems to get some offseason design experience. Thanks!

The one neat thing I loved about our chassis this past season was how easy it was to take the wheels off. Given the fact that we never broke a wheel this season; but after last season and going through three plaction wheels, this one feature definitely caught my eye.

[Travis Hoffman]

Originally Posted by R.C.

Normally if your going to all the trouble of making a custom drivetrain, you'll be making your own gearboxes as well. The only place that currently sells gearboxes integrated for a WCD is Team 221 Robotics.

But 973 Back in 08 used a [super] shifter in a WCD setup...

-RC

48/3193 competed in the 2011 season with our first-ever WCD-style drivetrain, using modified Super Shifters (milled the transmission plates down for ground clearance, drilled mounting holes for the angle brackets that attach gearboxes to the frame). The drivetrain has proven very reliable and resilient (and will therefore now explode at IRI, since I said that). See attachments, and also http://www.chiefdelphi.com/media/photos/36507.

The white delrin cam tensioners in the attached pics proved bulletproof - I don't believe they came loose once. There is also a thin strip of white delrin sheet velcroed to the belly pan underneath each chain that adds additional tension.

[waialua359]

I'm not sure chain tensioners are even necessary.
In the past several years prior to this year, we slotted our frame so that we could tighten our chains via movement of the bearing blocks. However, after doing 4 tournaments plus per season, we've never had to tighten it even once.

This season, we didnt even bother to slot it at all. Hasn't failed yet.

[ajlapp]

I'm not sure chain tensioners are even necessary.

I tend to agree that you could get away without tensioners on your comp bot.

That said, our practice bot saw 2 hours of practice 4-5 days a week throughout the season. We saw significant sprocket wear and as a result had to make slight chain tension adjustments routinely.

We also have a special purpose demonstration robot that sees parade duty and special event duty.....we'd be in serious trouble without the tensioners.

Having the tensioners adds a piece of mind. Not to mention the ability to quickly change wheel sizes, which has happened more than once over the years.

[Aren Siekmeier]

Originally Posted by waialua359

I'm not sure chain tensioners are even necessary.

It would seem that they aren't if you can space the axles an even number of chain links apart.

@ajlapp: How has wheel size affected your chain runs? Is there a sprocket reduction you've had to change?

[ajlapp]

@ajlapp: How has wheel size affected your chain runs? Is there a sprocket reduction you've had to change?

It doesn't have to affect your chain run...but a wheel diameter change often coincides with a wheelbase adjustment. Especially your outer most wheels.

This is the idea behind the tensioning system in both Universal Chassis and Super Light Chassis. The slot in the chassis rail supports 4, 6 or 8" wheels. You just need to adjust the length of the tensioning bolt.

[Team 3266]

If we were to use sliding bearing blocks to tension the chain what kind of bearings would we use. And where would we get the blocks if we purchased them?

[ajlapp]

If we were to use sliding bearing blocks to tension the chain what kind of bearings would we use. And where would we get the blocks if we purchased them?

We use standard 1/2" ID open ball bearings in all of our chassis products.

You can see the blocks used in our Universal Chassis here.. They support two 1/2" bearings and fit inside a 1.25" wide rail.

You can see the rest of our chassis systems at www.221robotics.com

[Team 3266]

In a live axle setup like team 254's they use a cam tensioner to slide their bearing blocks to tighten the chain.

cam tensioner-


http://team254.com/media/photos/imag...e=orig&id=3124

Can such a tensioner be purchased somewhere? or do we have to machine them ourselves?

[ajlapp]

No off-the-shelf cam tensioners of this type exist to my knowledge....

We use bolt style tensioners on our systems.

Both designs have their individual merits.