Is a shifting transmission really necessary?

[JVN]

This is a debate we've had MANY times on these boards before.

Jay,
You're logic is absolutely infallible. I agree with your points 100%.
But, there are certainly arguments (within your own logic) that show it can be important to shift. (I'd like to go over those quickly, for our viewers at home.)

My calculations prove it is ABSOLUTELY necessary for the functions we'd like.

Design Parameters:
-130 lb robot, no weight added.
-4 motor drivetrain (2 drills + 2 chips)
-80% efficiency
-1.4 Coefficient of Friction Wheels (experimentally determined)
-Max Desired Motor Loading @ continuous push = 50 amps.

Desired:
-12+ fps speed

My calculations show with the above setup, in order to design your robot to not only slip your wheels while still maintaining the 50 amp continuous max current draw... one must gear their robot at about 8 fps.

So... if we're using the parameters listed above, I must design our transmission at about 8 fps (I ran some quick calculations).

Granted, I could either load my breaker a little more (maybe I'll risk 60 amps continuous draw), or decrease the traction of my tires... but I don't want to.

Another option is to over-gear my robot, and just trust my driver not to get into extended pushing matches, or possibly even implement a current limiting circuit to protect my breakers... but these options just don't cut it for me.

OR... I could put some more motor in my drivetrain.
Maybe 6 motor drive is the way to go. Right now, we'll say it's not.


In this case, I need to ask myself, is 8fps good enough?

Not for our team, no.
We'd like to be faster. We're also not willing to trade off our pushing power.
This means, we NEED to shift.

It's all about what you're willing to give up.
We feel (for most FIRST games) it is beneficial to go the extra mile and build a shifting transmission. However, maybe next year's game will be the exception.

What it boils down to for us is:
-There is always a time you want to push through someone else.
-There is always a time you want to outrun someone else.

Either we put enough motor power into the drivetrain to do both, we sacrifice one for the other (in some capacity), or we shift gears.


Again,
Only try it if your team can handle it.
To be argumentative... last year we never lost a match due to a transmission problem either. In fact, we had NO problems last year with our drivetrain (the arm was a different story!) There were definitely times where the transmissions proved themselves a worthy investment of time and energy.
Depending on the game, we will strongly consider shifting again.

$.02
John