6wd - chain path revisited

[JHSmentor]

I am a mentor for a rookie team - hence, I am a rookie as well.

We have been researching 6wd systems and am curious what the pro's and con's are for the chain paths that could be used. I've included some very rough drawings (please don't pick on me too much over these!) to illustrate what we have been discussing.

I have my own ideas of some pro's and con's for these designs but would like some unbiased feedback so I will keep those to myself for now.

things to consider are drag created by the tensioners (if any), chain stretch even with the tensioners, dropping a chain, sprocket changes, wheel changes, stuff like that.

we will most likely be using as much of the kit parts as possible and filling in any gaps with similar or identical equipment - unless there are other cheap alternatives presented here.


thanks for the help!!

PS. the blue circles are the tensioners (still trying to figure these out), red are the sprockets, and the light blue are wheels - probably a mix of Omni's and kit wheels.

I personally recommend the bottom one, as there are the fewest possible fail points. It's what 114 has used the last few years, and it has never failed us.

[coreyjon]

Absolutely key to keep this as simple as possible. Less things to fail, also - cheaper. Out of the options shown, I would also choose the last drawing, although there are other options as well. Let me make a quick sketch in paint.



Only one tensioner, pushing up away from the wheel. Idealy there would be more chain wrap around the middle wheels sprocket, but this was just to show one other, simpler option. regardless of your setup, chain stretch will occur, just plan on shortening your chain at some point.

Note: Disreguard - this was not thaught out.

[Madison]

Originally Posted by coreyjon

Absolutely key to keep this as simple as possible. Less things to fail, also - cheaper. Out of the options shown, I would also choose the last drawing, although there are other options as well. Let me make a quick sketch in paint.



Only one tensioner, pushing up away from the wheel. Idealy there would be more chain wrap around the middle wheels sprocket, but this was just to show one other, simpler option. regardless of your setup, chain stretch will occur, just plan on shortening your chain at some point.

This doesn't work. The middle wheel is spinning in the opposite direction of those on the ends.

[Teched3]

We drive each wheel of a six wheel drive robot with an individual chain for each wheel. Hence, if a chain (or two) breaks or comes off, you still can drive and control your robot.

[coreyjon]

Good point, I definately agree, you should look at running possibly two of the wheels off one chain, then the other wheel off a seperate chain so in an off chance the chain breaks you can still participate in some capacity.

[artdutra04]

The bottom one would be my preferred method. Simple, minimalistic, least number of chain tensioners, and they have the option to mount the transmission on any of the three axles for weight distribution purposes.


As for chain tensioners, these can be made really simple; just use round bar stock of HDPE with an off-center hole, with a bolt going through that hole. As you rotate the HDPE bar around the hole, it increases or decreases the diameter.

Team 228 has used these as chain tensioners since 2004, and we've had great success with their simplicity and performance.

Here's a good photo I found on our team website of these chain tensioners on three different applications on our 2007 robot: our elevator (25 pitch chain), arm (35 pitch chain), and drive train (35 pitch chain in the background behind the orange chassis rail).

[/img]

[Jimmy Nichols]

Originally Posted by Teched3

We drive each wheel of a six wheel drive robot with an individual chain for each wheel. Hence, if a chain (or two) breaks or comes off, you still can drive and control your robot.

That is what we did last year as well. One thown chain does not take out the entire drive on one side of your bot.

[shock190]

Team 190 used the bottom design with no failures through two regionals, championships, and a good half dozen offseasons and a few dozen demos with no failures or chains dropped. For tensioners we simply had rollers of varying sizes we could swap on and off instead of an adjusting mechanism.

[Ian Curtis]

We have used one not mentioned in your design, however similar to the bottom. In ours we we mounted our gearboxes above our center wheels and ran #35 chain from the gearbox to the wheel. We then ran #25 chain from the center wheel to both outside wheels. This means that your center wheel will have 3 sprockets. An advantage is that you should never lose complete control of one side. However, I assume in your bottom design that you have a live axle, so you wouldn't lose control of the center wheel.

We tensioned our chain by moving our wheels, but this was pretty cumbersome, so I would imagine idlers would be more convenient to change. We never threw a chain without getting something (such as a game piece) getting caught in them.

The problem I forsee with your top design is that if you throw that chain, you're done. Even if you use #25 chain correctly its quite possible that a chain will break. It shouldn't, but always plan for the worst case. If you use #35 chain, it will be heavy. Really heavy. And if you plan to play with trackballs, you will most likely have weight problems. Pretty much everyone does.

Good Luck!

[Protronie]

IMHO... the third design the best with a slight mod.
Directly connect the center wheel to the motor and run chains for each the front and rear wheels from the center (power) wheel.
Even if both chains break... you should still have control of your robot... unless the motor goes south... then you DNF.

[JHSmentor]

Okay - to summarize the inputs so far:
1. having 1 chain - you risk loosing that whole side of the drive train if you pop a chain or it breaks.

2. Love the chain tensioner design by Team 228 as a static chain tensioner.

3. Most seem to like the live axle for the center wheel (or one of the wheels depending on weight distribution).


So, a couple specific questions:
1. how about a self adjusting tensioner (spring loaded)? Has anyone had success with these?

2. If you directly connect one wheel to the gearbox output, then your top speed is regulated by the gearbox - correct? we will be using the Kit ToughBox gearboxes - how much of a limitation is this? seems like being able to change the spockets on the wheels would allow for some fine tuning of the speed and torque of the robot. Using a 3 chain design might work best for this?

thx again.

Bryan

[coolbotz]

The first design would rotate the center wheels opposite the outer wheels.

[coreyjon]

MKRass, I noticed my mistake right after I posted it, and was somewhat embarrased. You are, correct - the middle wheel would be spinning the opposite direction. I don't function well on no coffee, and I know, poor excuse. - can't believe I slipped like that.

[JHSmentor]

Yeah - I noticed that too - meant to draw it with the chain under the sprocket rather than over the sprocket - then they all rotate in the same direction.