pic: FRC 1771 East (West) Coast 8wd drivetrain

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#1

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This is an eastern adaptation of the great westcoast drivetrain that I have been working on the past day or 2. It is 8wd to increase ramp climbing ability while keeping the coG low. It also is designed to take advantage of our sheet metal sponsor and to minimize parts that need to be milled. Specs are:

Custom 4.875" diameter wheels
Andymark shifter guts with custom plates for a low speed of 5.5fps and a high speed of 13.5fps
Outer wheels are tensioned by sliding the bearing block
45 degree ramp climbing ability
Total weight for 8wd 2 speed drivetrain ~35lbs

Let me know what you think

#2

what’s the side rails made out of?

now if i can only come up with a south coast drive…

#3

The frame is made up of 2"x1"x.125"thickness aluminum and 1"x1" aluminum all welded together. The entire frame right now without any work done to lighten it is 9lbs, and should be very stiff. I also have bumper mounts planned but I haven"t modeled them yet.

#4

Looks good but one question, how are you planning to run the chain? It looks like it will be a costly change during competition if you are planning on having the chain go through your support beams, I know it would be a lot easier to take the chain off as a whole instead of finding the master link and taking a chain off that way.

#5

If you look closely at the model, the round silver discs one the inside of the frame are actually sprockets bolted to the axles. The chain will run from the transmission to the 2 center wheels and then from the center wheels to the outer wheels. It will be incredibly easy to replace a chain although I doubt we will have to as I have never broken a chain. We will also be using 25 series chain. everything about this drivetrain is incredibly easy to work on. We can switch a wheel in a matter of seconds to keep the tread fresh. Also tensioning is super easy.

#6

Why not direct drive a wheel?

Also, you should simplify the wheels to make them more efficient and easier to make.

#7

I chose not to direct drive a wheel so that we don’t have to use custom gears or use an extra stage of gears. Also with this layout, the gear ratio can be switched very quickly by changing a sprocket size. This transmission uses almost no custom parts so it could be put together very quickly. I don’t see enough benefit in directly driving a wheel to make it worth the machining effort. Also the way the motors are oriented at the bottom of the transmission helps lower the center of gravity more than if the motors were at the top of the transmission.

The wheels are actually incredibly simple. They will be made from a length of aluminum tube, and 2 separate plates of aluminum that will be laser cut to form the spokes. The entire thing will then be welded. The reason I did it this way is that we are sponsored by a sheet metal shop that does not have any cnc milling equipment, but has plenty of laser cncs, and the material to make these wheels is much cheaper than buying the billet necessary to machine a single piece wheel from.

#8

I’m sure all 8 wheels are not touching the carpet, so which ones have been raised/lowered?

#9

the middle 4 wheels have been dropped by .175"

#10

That’s a neat way to do it…it’s how most automotive wheels have been made since the 1930s, although they use steel.

How does the center of the wheel work, where the spokes attach to the axle?

#11

Yeah it is very simple and a lot cheaper. The spokes have a 7/16" hex cut in them that interfaces with a hex on the end of the axle. The wheels will be held on either with a bolt tapped into the end of the axle or with a ring clip. The axles are machined out of 7075 aluminum and have a hub on the opposite side to bolt plate sprockets so that we don’t have to use hubbed sprockets, and we can have custom sprockets cut very cheaply (free :smiley: )

#12