here’s a real close view of our transmission output shaft. An idler sprocket, chain tensioner, and a wheel are also visible.
By the looks of it you have an automatic spring tensioner on your chain, but you may want to check the effects of driving in reverse, to the right in the photo on the tensioner, as the slack will be placed in the other side of the chain/ wheel connection, I don’t know if you have thought of this yet, but you may want to try it before competition. If that is a locking type tensioner that isn’t solely spring tensioned your ok.
but looking good guys/gals
Looks pretty.
Why do you have an idler on one side and a tensioner on the other–do they have different purposes? Also, what plastic is the tensioner made of?
1270 used those for I believe 2 years and they work nicely I never had a problem with them.
I was wondering the same thing… It appears that both chains are going to wheels; so wouldn’t it make it easier to manufacture spares if only one mechanism were used?
If I am looking at the picture correctly, and correct me if I am wrong. There are two chains, each coming off of the main drive shaft and going to two different wheels. Also if you look closely, the idler and tensioner are both on the same bracket. From this, I would assume that the bracket is either slightly adjustable or secured. I would assume that is slightly adjustable so that when the chains were cut for each wheel, that the idler on the left could be put into place so that is tensions the one chain run. Then the Spring Loaded tension could tension the other chain run, without having to be moved from its spot, it uses the spring forced to tension it. But that is just what I get out of the picture and the knowledge that I have gained from my engineering classes.
Needless to say, I love it, and have been trying to engineer/manufacture a design for the team that i was a part of to use in their drive systems. Really neat, and would love to see it in action.
Mike
The green tensioner looks suspiciously like a McMaster-Carr 7332K9 or 7332K11.
I guess I should get a paper version of their catalog…this online stuff is hard to find if you don’t know what to look for!
It appears that you have 4 wheel drive with all 4 wheels being traction wheels, you may want to run that on carpet and try to turn around. In my experience we have always had problems with the robot “walking” since tank drive requires low traction to turn. Other than that your setup looks sweet! i like the color of the tread on your wheels i wish we could have found that before we put ours together.
They have a 6wd…
First off, thanks for all of your input.
Justin, no problems here since the tensioner/idler takes out all the slack so there is no slack regardless the direction the wheels spin.
worldbringer and Cody, Mike is right, the idler and the tensioner are both mounted on the same bracket, one is spring-loaded the other is not. Mike, you pretty much nailed it perfectly. Also to Cody, you don’t need spares if the engineering is done right!
Squirrel, thats because it is! Though I don’t remember how much tension force they are, I think its the weaker one.
wrong to some extent…
wrong. Arefin spreading lies, tsk, tsk.
Anywho, Caleb, you got the first part, we are using a 4 wheel drive or 4 x 6 to be exact. This is a tried and true setup for us, we used it last year. It is true this can be problematic for the reasons you described unless you know what you are doing and can account for it accordingly.
You can ask anyone who saw us at the Florida Regional or anywhere else that our bot had absolutely no problems turning, we were able to spin with the point of rotation being nearly perfectly in the middle of the robot!
Thanks for your thoughts and concerns anyways.
I was under the impression it was 4x4 drive. That has been the most problematic setup for our team because the rotation is centered between the wheels instead of on a center wheel in a 4x6 setup (we ended up switching the front wheels to Omni-wheels to resolve chattering. Glad to see you know what you are doing and best of luck to you thru the rest of the competition! 
Wait, does that mean that you don’t Keep a spare tire in your trunk?
Nice treads 
we got them also, I like them a lot. They seem like they won’t strip very fast. Other than that, nice setup!
Looks almost like you could take a link out of each chain to reduce the angles involved. When we have the gearbox centrally located between the drive wheels, we make the chains as short as possible. Then we use washers under the transmission mounting plate to raise the tranny to remove slack. It is amazing how little is required if the chains are short, perhaps one or two washers will suffice, as there is little chain wear or stretch (we use #35 chain). Any sort of shim material will work, and it only takes a couple of minutes to loosen the mounting bolts a bit and slide in more shims.
it would be great to have spares if we had the money, so were hoping that we engineered everything right to get us through the regionals.