Changing gears

Posted by Splash.

Student on team #53, Team Inferno, from Eleanor Roosevelt High School and NASA GSFC.

Posted on 7/23/2000 11:13 AM MST

For next years competition, we were thinking about experimenting with more than one gear. We had a couple different ideas in mind. What kind of shifting method have teams used in the past? Anyone know how the TechnoKats did it in ‘Double Trouble?’

Posted by Andy Baker.

Engineer on team #45, TechnoKats, from Kokomo High School and Delphi Automotive Systems.

Posted on 7/24/2000 8:20 AM MST

In Reply to: Changing gears posted by Splash on 7/23/2000 11:13 AM MST:

Changing gears is tricky… but it can be done.

I saw at least 5 teams (141, 314, and others) do this last year with the same method and all seemed fairly pleased with the results.

We developed this for the '99 comp, and then perfected it (almost) for '00.

Here’s the parts we used:
…drill motor with gearbox (non-modified)
…plastic sliding block (HDPE or Delrin)
…fancy motor and servo mounting sub-assembly
…extra-fancy software for smooth gear switching

The goal is to use the servo to switch the gearbox lever in order to go between high and low gear. We focused on these points in order to do this:
…1. The motor is mounted as securely as possible.
…This motor cannot move at all for this system
…to work.
…2. The plastic sliding block slides on a set of
…rails (alum. shafts) that are mounted right next
…to the motor. We put some dowels in the plastic
…block that interfaced with the gearbox switch
…lever. Two dowels were used, with one on each
…side of the lever.
…3. The servo is mounted to the same motor mount
…assembly, and moves the plastic block back and
…forth, to switch between high and low. Note
…that this servo is still pushing the lever at
…the end of stroke. The servo rotates with about
…+/- 45 deg of travel, and we used one of those
…little plastic arms that comes with the servo
…and modified it a bit.
…4. Here is the tricky part: when the servo is
…told in the software to switch gears, the
…operator loses control of the drive system. The
…motors go through a short routine that insures
…that the gears set into place. You can easily
…chew up gears by doing this, so extra care is
…needed in order to make sure the gears mesh
…before the operator is given control of the
…drive system. This routine must be done while
…the robot is NOT MOVING. Our routine takes
…under 2 seconds.
…5. Another tricky part is to get the servo arm
…adjusted correctly in order to get it to push
…past the full travel in both directions.

This system worked almost perfectly for us this year. We did not change any motors or gearboxes out the entire year… from debug to even the summer competitions, we have the same non-modified motors and gears. Yep, the pins are still in there.

We only had one match where this servo-gear-switching system did not work. The screws that mounted the servo were slightly loose, and the arm was not pushing the lever into high gear well enough. A 30 second allen wrench adjustment fixed that problem.

Note that this system limits you to switch gears while sitting still. I was impressed by two teams (at least) who could change gears ON THE RUN last year: teams 33 and 65 both had complex drive systems that enabled them to go from high to low gear on the move. These systems were very intricate and required much effort, I’m sure.

Good luck,
Andy B.