8 Wheel Chassis Design
 

Finished My 10th Chassis Today! :D

Named: Silver Stream

Specs
- SuperShifter Transmissions
- 39.96 lbs
- 8 Wheel Drive
- 6" AndyMark Performance Wheels
- #35 Chain
- 1/8" Sheet Metal
- 1/8" Center wheels Drop

And Comments or Suggestions for Improvements are Welcome :D

Thanks!

Re: 8 Wheel Chassis Design
 

Very nice there.

I'd recommend reading through this running thread. Especially the parts about perhaps spacing out the middle wheels a little more.

- Sunny G.

Re: 8 Wheel Chassis Design
 

Are you suggesting that I move the transmissions to the back? And then move the middle wheels further outward?

I can understand why I should move the wheels out. But I wold rather have a better turning radius. The Rock wont effect too much.

The transmissions in the back would make it back heavy. thus making the back and rear-middle wheels touching the ground. then it wouldn't turn on the middle wheels.

This is how I had the chassis before, but i was told I should put the Transmissions in the middle to keep the COG in the center. I literally spent 1.5 Hours changing it to the middle of the chassis.

Re: 8 Wheel Chassis Design
 

I was referring to changing the distance between the center wheels, but if you prefer the quick turns, then so it shall be.

- Sunny G.

Re: 8 Wheel Chassis Design
 

The turn speed should not change that much, unless there is significant scrub. That being said, there might be slight differences, but nothing really noticeable. It is not worth it though.

Re: 8 Wheel Chassis Design
 

Keep the transmissions centered but space the center wheels. Do a comparison between effective wheelbase between a 6wd and 8wd and you will realize the with the wheels evenly space on an 8wd your effective wheel base will already be shorter leading to quicker turns than a drop center 6wd. Try to split the difference somewhat.

Re: 8 Wheel Chassis Design
 

Everyone is assuming that a 6WD center-drop drivebase necessarily rocks and has only 4 wheels on the ground at a time. This is not always the case. With just the right amount of center wheel drop, all six wheels are in contact with the field carpet at all times and there is no noticeable rock. With the appropriate center of gravity, the robot spins around its center wheels.

Besides, some 6WD systems have no drop and still work well.

Re: 8 Wheel Chassis Design
 

This.

The average Long Base 6WD has an effective wheel base of somewhere around 14"-16" depending on wheel size and chassis design. The last two drive trains I worked on (10WD and an 8WD) had effective wheel bases of 16.5" and 17.25" and neither had any major problems turning and both liked tracking straight at speed. If I were going to make an 8WD again, I think I'd space the center wheels ~14" apart from each other to have a good mixture of straight line stability and maneuverability. (Short center wheelbase 8WD's have a tendency to over rotate)

Re: 8 Wheel Chassis Design
 

I have a few other questions/comments.

What is your reason for selecting 6" wheels?
With the ground clearance, and lack of a "wedge" on the front and rear of the chassis, I don't see an advantage to a large wheel.

For a non-direct drive application, why choose the AM Supershifter over the Gen I shifters?
The AM Supershifter contains an additional reduction but is otherwise the same internally. The output of the Gen I can be modified so that the sprockets are outside of the gearbox (see out drivetrain from 2011 or 2012).

Re: 8 Wheel Chassis Design
 

Silver Stream has just been added to FRC Designs! Check it out!

FRC Designs - Drives: http://www.frc-designs.com/html/drives.html

Matt

Re: 8 Wheel Chassis Design
 

Sorry for the delayed responses.

Silver Stream 1.0 (I will have multiple version that I reiterate and they change to 2.0, 3.0...) has a center wheel base of 8in. I think in my next iteration I will change the wheel base. I have never made an 8WD Chassis before, so I wasn't exactly sure where thee center wheels would go for optimal performance. After looking at other 8WD (such as 2056's This year) I believe you are correct that the Center Wheel base should be larger. Though for the part about them over turning, could you not technically change that in the program? Although I think the better solution would be to fix it in CAD.

@jwfoss
My choice of the six inch wheels was mainly just cause I like them. They arent too small, or Giant like 8in. My team has no experience with smaller wheels, which I know isnt much of a change, but we are just comfortable using 6in or 8in. I personally don't like 8in though.

Regarding the supershifters...
We have used the gen I/II's for every year since 2007 except 2011. And we are simply sick of them. We though we would try something new, and we were looking at 234's Robot and liked the SuperShifter's they had.

You can find a lot of my Designs on FRC-Design.com
I love the idea of the site and I encourage anyone to visit the site to look for ideas from other teams, and to submit their own designs :)

Re: 8 Wheel Chassis Design
 

In my opinion, there is no such thing as too small wheels, only wrong gearing.

Re: 8 Wheel Chassis Design
 

Why are you sick of them? Performance? Maintenance?

Re: 8 Wheel Chassis Design
 

Suggestion: Beef up the axle mounts... they look a bit skimpy and given a hard enough ramming could warp. with an integrated design like that, such a failure could be catastrophic.

Re: 8 Wheel Chassis Design
 

I have't had a problem with axle mounts like this in our 2012 chassis. What should I do to make them better? cross braces meeting in the middle? or make it wider? (currently 1")

@SuperNerd256
We've used them so much they have just been over used. We like the idea of having the gears closed in too. We wont have to worry about getting chips in the gears anymore.