Rookie Mistakes: Building

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Problem

Solution

2 motor drivetrain

  • Less power

  • Less acceleration

4 motor drivetrain

  • Ability to traverse obstacles

  • Improved power and acceleration

Pushbot

  • Poor agility/manuverability

  • Poor top speed

Mecanum, 6WD, etc.

  • More agile, higher top speed

  • Customizable gear ratio

Claw

  • Controls 1 element at a time

  • Easy to break

Intake

  • Controls multiple elements at a time

  • Much more efficient

Spur gear gearboxes

  • Not for high load use cases

  • Will break under shock load

Planetary gearboxes

  • Better for drivetrains and high load

  • Resistant to shock loads

Single/multi-axis arm

  • Often needs high gear ratio

  • More complex than linear extension

Linear extension

  • Generally faster than arms

  • Much more precise

2 Motor Drivetrain to 4 Motor Drivetrain

Important

In general, it is not recommended for teams to use 2 motors on the drivetrain, but instead use 4. This is mainly due to the added power and increased acceleration 4 motors provide.

Typically, top speed is determined by the gear ratio and the motor specifications, not the number of motors. However, acceleration is affected by the number of motors, and as FTC robots need to change direction and accelerate numerous times per match, slow acceleration has a significant adverse effect on the competitiveness of the robot. In addition, 2 motor robots may struggle to get over obstacles or climb up ramps, due to less power. One question that often comes up is “don’t I need more motors for other things on the robot?” This is a valid question, but the answer is generally no. It is possible to build a competitive robot with 4 motors allocated to drivetrain, and 4 motors for other mechanisms, so there should be no reason to skimp. Do remember that the drivetrain is the foundation of the robot. Your mechanisms will not be anywhere near optimized if the drivetrain can’t get your robot from A to B quickly and efficiently. There has not been a game in FTC history where the top robots needed >4 motors for the drivetrain, so this is a pretty safe rule to follow.

Passive Intake/Claw to Active Intake

Important

Active intakes (ones with continuous rotational motion) should always be prioritized over passive intakes and grippers.

Active intakes are much more efficient and effective in picking up common game elements such as balls, cubes, and rectangular prisms than claws. This has been a widely accepted rule; many Worlds-level robots over the years use intakes. The exception is that a claw should be used for irregularly shaped objects that would be impossible to control via intake; for example, the relic in Relic Recovery.

Intakes have two major advantages over claws.

  1. Intakes can control multiple game elements at a time.

  2. Intakes are indiscriminate at picking up objects, making them much more efficient.

Claws can only pick up one object at a time, and the driver needs to aim the claw at that specific object to grab it. With an intake, the driver does not need to focus on one game element - instead; intakes will just pick up anything in its path, if designed properly. Claws are also prone to breakage, and thus suffer to defensive robots. They are also generally more fragile than intakes. Therefore, active intakes are as a result much more efficient than claws. Nearly every competitive robot from past years have used active intakes to great effect, so there is plenty of precedent to follow.

Spur Gear Gearboxes to Planetary Gearboxes

Note

Spur gear gearboxes are fine for most applications for a rookie team. We are not advocating necessarily having to upgrade to planetary motors, but there are some advantages which may become useful in more advanced use cases such as high-load systems.

Important

Spur gear gearboxes have inherent disadvantages to planetary gearboxes. Spur gear gearboxes should not be used in high-load situations, primarily because the gears can strip and destroy the gearbox.

An example would be a drivetrain that has to change directions repeatedly and quickly. Planetary gearboxes are much better suited for drivetrain and arms, due to the configuration of the sun and planet gears. In addition, spur gear gearboxes are prone to shock loads; therefore, direct drive is not advisable on drivetrains. Refer to the gearbox anatomy section for more complete information on gearboxes. This refers to using spur gear gearboxes which are attached directly to the pinion gear of the motor. It does not mean external ratios outside of the motor gearbox, which will always be in a spur gear configuration.

Single/multi axis arm to Linear extension

Important

Teams are generally advised to stay away from arms and move in the direction of linear slides, primarily due to the issue of complexity. This is because arms typically are less effective than linear extensions and are harder to implement properly.

Arms require a high gear ratio, which usually in turn will require an expensive gearbox (e.g. VersaPlanetary) that teams on a tight budget may not want to invest in. However, there are more inexpensive options such as the REV UltraPlanetary gearbox to consider. Furthermore, arms must be supported extremely well to bear the torque that the motor provides. A poorly supported and/or constructed arm will cause the driver needless pain as it is exceedingly difficult to line up an arm that constantly shakes. In contrast, linear extensions do not need to worry about gear ratios and gearboxes. They can be optimized to be more efficient than arms, and typically are more precise, as linear motion is easier to control than angular motion. Another positive is that linear slides can have more extension than arms, with some reaching 5+ feet in length.