Questions about first time trying 6WD.

We’ve decided on a 6WD this year, however, we dont have any experience with it before. Right now we’re deciding how to mount the gearboxes and the wheels/chains configuration.

Any suggestion/help about this is appreciated.

Also, where could I find idelers?

Wow, that’s a pretty broad question. Is there something a bit more specific you can ask?

Allen,

We are using six skyway wheels. We are using the kit transmissions and #35 chain. We are driving the front (with the chain going to the inside sprocket) and rear wheels off the transmissions. The front wheels drive the center wheels. We used the centering hole (slightly lower) of the kit base for our center wheels.

We made a tensioner using the “wheels” used with 80/20 t-slot.

Ken

I suggest lowering the center wheels and having lower friction on your outer wheels (either through different tread or design)

My experience is that with 6WD and the middle wheels lowered so the machine rocks (even a little), you can go with as grippy of wheels as your heart desires. By ensuring that the middle wheels and only one set of other wheels (front or back) are in contact with the ground at any one time, the aspect ratio is good enough that your scrubbing effect is liveable.

I love 6WD, I believe you will be happy with the performance.

Joe J.

6WD gives you a pretty unbeatable combination of traction and maneuverability.

Getting the vertical offset of the center wheels from the front and rear right is the biggest thing - your mileage may vary.

Not only that, but finding the space and weight can sometimes be challenging :smiley:

heres a link to show ya how to run the chanis, it’s fairly easy. I wish i had more pictures of my final project it would show ya how i mounted the trannies.

Allen,

First, thank you for starting this thread! I’ve been meaning to ask a similar 6WD question, and since it seems many people are concerned about your design throwing the chain, I will post it here rather than start a new thread.

Our rookie team is also using 6WD, and our team seemed to be incredibly concerned about designing our drive system to protect for the possibility of throwing a chain. The end result was a rather complex system of chains that gave us the ability to still have 6WD even if any 1 chain was thrown.

My initial gut reaction was “This is nifty, but it seems a bit overkill…” Since I am a rookie to this as well, my question to the more experienced teams is “How often does a thrown chain happen in competition?”

In my experience, 3 years as a mentor, I have seen very few thrown chains from our robots. If your wheels run true, your chains are properly tensioned, and your wheels are spaced properly you may throw a chain once all season. Most of our thrown chains have been from broken wheels. You will be more likely to be incapacitated from tipping over than losing one chain.

It is rare unless you design something that has a tendency to fail and I’m sure you will think of a way to fix that problem. We have had that problem before (1126) in the 2004 game raising the bar. When we went to go climb the stairs our wheels would get cocked in and a chain would fall off due to the thin walled framing material we had used. So in nationals during one match break after putting on little guide rails for the chain we finally beefed up the front of the frame which was causing the chains to fall off and they never came off again and we then went on to win the Newton division.

Team 975 has never has a drivetrain failure or thrown a chain on any of the previous four chain drive robots we’ve built. All used #35 chain. Only one was 4 wheel drive, though this year’s bot will also be 4WD. Alignment, tensioning and short chain runs with proper sprocket sizing and tooth contact should prevent chain loss. 6WD just makes it more complex.

If you’re using #35 chain you should never ever throw a chain even with relatively light tensioning. however if you’re using the lighter #25 chain you do stand a chance. My team’s 2002 bot would often pop its chain. It was a very poorly constucted drivetrain in that holes were slightly off center causing the chain to tighten and then loosen as it went around. However #25 chain has a tensile strength around 1000 pounds which is not way more than certain applications can cause(think very long arms) You shouldn’t ever break #25, but under slightly out of the norm conditions it does have a slight chance of being overloaded. By slight I mean its not worth worrying about, just something to keep in mind. As always I’m going to say try to calculate the forces the chain will take and see how much it is.

We’re also trying out a 6-wheel configuration this year (the first in our team’s 9 years) and so far we’re amazed by the performance. The thing you have to think about with your chains is that you don’t want one chain running off another chain. For example, you wouldn’t want your gearbox driving your back wheels, which chains to your middle wheels, which chain to your front wheels; the first chain would have twice as much stress on it. What we did is run one chain from the back to the middle, and another from the back to front, on the other side of the frame. It’s a little more complicated than putting the gearbox in the middle, but it makes a lot more room in the robot.

We really like our chain pathing, which uses two chains on each side. One goes front -> center -> tranny the other goes rear -> center -> tranny. The upshot being, we can drop a chain on both sides and still have 4 driven wheels, without being too heavy, or needing bunches of tensioners.

Question: If the center wheels are lower such that only four wheels touch at any given time, what would be the advantage of six wheels? I suppose it could be more manueverable for the short time it is teetering on the center wheels when weight transfers from front to rear for instance.

The fact that only 4 wheels are touching is what makes 6wd so advantageous. A typical 4wd setup has 4 wheels at the farthest corners of the robot, and therefore requires the largest amount of force/torque to turn the robot. If you were to shorten the front-back wheelbase with only these 4 wheels, the robot is now easier to turn. However, it can become very unstable in full forward to full reverse (and similar) maneuvers, or when using long and/or tall arms.

6wd effectively shortens the wheelbase to 1/2 the length of the robot, due to the fact that it only rides on 4 wheels at a time. However, it regains the stability of the long wheelbase robot because of the extra 2 wheels at the other end of the bot. Add to the fact that all 6 wheels are powered, and you have a drivetrain that optimizes a long and short wheelbase robot.

Pushing power between a 6wd and a 4wd should be no different, as only 4 wheels are on the ground at a time for both robots. (also assuming the same motors, gearing, wheels, etc…) We used 6wd for the 1st time last year, and it served us extremely wheel. YMMV. Best of luck.

BEN