Drive Base Transmission Viability in ITZ

VEX Robotics Competition Discussion VRC > In The Zone (17/18)
1

This game requires your drive base to be fast, but there are a lot of situations where a high torque drive base might be critical. For example:

  • Pushing mobile goals
  • Getting over the starting bar
  • Pushing battle over the last few cones
  • Bumping other robots to mess up their autonomous or their stack.

So, do you think a drive base with a transmission is the way to go? Why? If so, planetary transmission or normal pneumatic shifter? Thoughts?

2

Planetary transmissions are never the way to go. The "high torque"setting actually has less torque than the “high speed” setting. A pneumatic shifter could work this year, but my experience with them turns me away from them.

3

@PSR_12 No

4

@PSR_12 No

5

@PSR_12

  1. Having a torque transmission setting/torque motors isn’t necessary, speed motors should do it fine.
  2. If you go fast enough you can get over it, and it isn’t all that high to begin with.
  3. Get your teammate to push you.
  4. It’s not that hard to mess up an autonomous, trust me.
6

I think you should start by doing some tests and math to find out exactly how much torque is necessary to do all the tasks you want to do. Then you can make judgement based on how many motors you want to use and the speed you want to attain.

7

Do explain. I thought they were pretty robust, but I’ve never built one.

8

I want to comment that using a pneumatic shifter for a transmission will make you use only 10 motors instead of 12. I don’t know until what point having 2 extra motors on the base will surpass a pneumatic transmission without losing speed or torque. The good thing of a transmission is that you can change between speed and torque depending on the situation but what if you can add two motors, adding more torque (and pushing force) while keeping the speed? Also, transmissions can be a bit heavy imo.

9

I have also never built one myself, but i have looked into several VEX Transmission designs and there are some potential issues.

  1. If the pneumatics run out mid actuation, you are dead in the water.
  2. Gears meshing at the wrong alignment can be hard on them.
  3. The internal gears on the motors are not very strong, and a sudden change in applied toque at full speed can easily shred all the teeth off, so you need to slow down or stop to shift safely, or mechanically protect the motor (clutch, torque converter, non-backdrivable ratchet)
  4. For smooth gear meshing, you can modify the gears to have a bevel, but this will lead to faster wear and tear on the gears, and possibly make them less useful for other application in the future.

Weight and Motor trade off are also both concerns, good call.

10

In my experience the last one about weight and motor/pneumatic tradeoff is the only real concern. That and complexity. For those reasons alone I wouldn’t do it.

I don’t see how one would help this year anyway because the small bar should be no big deal, and you are more or less always going to be pushing/pulling/carrying a mobile goal, so you are always going to need that torque.

IMO, having a fast lift is more important, as I think most of your time will be spent driving small distances between cones and then waiting for your lift to stack.

11

I really don’t think in vex there has ever been a real need to have a transmission on the chassi of the robot, just seems like a lot of work for pretty minimal result

12

  1. Maybe before the higher motor limit and stronger motors.

  2. Green Eggs. Maybe not necessary, but effective. Although i believe their shifted power between different subsytems rather than just a simple torque/speed shift in drive.

13

I believe that was to transfer the base motors to the lift for quick hanging in Toss Up.

14

#1&2. I’m less concerned about actually being able to do those things but not tripping motors while doing them. The more stress you put on the motors, the less consistently you’ll be able to preform.
#3. If there’s anything I’ve learned from competition, it’s that you shouldn’t rely on your partner. Also, it would be extremely difficult to coordinate this in the heat of a match. This remains my primary reason why I think a transmission would be useful.
#4. True

15

I was thinking of their drive/score/descore/throw-the-ten-pound-weighted-base-over-a-4-inch-ladder-rung mechanism in Round Up.

16

Oops, my bad.

17

No worries, i actually need to go look at their other years. Round Up was my senior year and the only year before Starstruck that i really paid attention to the competition on a global scale.

18

Way beside the main point, but i was doing some sketches and playing with some math on planetary gears and realized that they can be (at least partially) modeled as a pulley system!

19

You may run in to problems since strings only support load in tension, not compression. But for the high speed config, it works!

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20

I’m not sure about the practicality of it early in the season. However, I think at worlds it will be extremely helpful. At the worlds level people(well, most people) are going to be able to stack cones very fast rather internally or externally and with four robots on the field it’s probably going to be very important to get every last cone possible, resulting in a need to outdo your opponents in speed and torque to make sure you can get past opponents if they’re in the way.

That’s just my two cents :slight_smile:
I think it can be helpfull especially at higher level competitions when every last cone can count.