Vex Robotics Pro VersaChassis Mini User manual

217-6327-751
VersaChassis Mini User Guide
vexpro.com
Copyright 2018, VEX Robotics Inc.
2018-08-16
1
VersaChassis Mini
User Guide

217-6327-751
VersaChassis Mini User Guide
vexpro.com
Copyright 2018, VEX Robotics Inc.
2018-08-16
2
Table of Contents
VersaChassis Mini Introduction............................................................................................................................................................ 3
Power-to-Weight Ratio (PWR)............................................................................................................................................................... 4
Configurations............................................................................................................................................................................................... 5
Motor Compatibility................................................................................................................................................................................. 18
Maintenance............................................................................................................................................................................................... 19
VersaChassis Mini FAQ ......................................................................................................................................................................... 21
Support......................................................................................................................................................................................................... 22

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VersaChassis Mini Introduction
The VersaChassis Mini is a versatile and lightweight
drivetrain system specifically designed for use by
FIRST® Tech Challenge and VEX U teams. This
versatility allows teams to easily re-configure their
drivetrains, giving them the ability to quickly iterate
through different drive systems. For example, the
VersaChassis Mini can be used to create 4
different types of drive systems right out of the box.
Teams have the option of buying different add-on
kits that allow them build up to 8 different types of
drivetrains.
Weight is an important factor in the design of the VersaChassis Mini system. However, lightweight does not
mean low strength. Many of the components used in the VersaChassis Mini system have been battle tested
by FIRST® Robotics Competition, FIRST® Tech Challenge and VEX Robotics Competition teams for years.
VersaFrame
The use of 1” x 1” x 0.040” Wall VersaFrame tubing gives teams a
rigid, yet lightweight structural member for their chassis. Each piece
of aluminum VersaFrame tubing comes with a scribe line in the
middle of the 1” wide face. This gives teams an easy way to drill
holes in the center of the tube.
Every VersaFrame tube comes with pre-drilled holes. These holes
are clearanced for a 5/32” rivet or a #8-32 screw and are located on a 1” pitch. This allows them to easily
mate with VersaFrame Gussets. This gives teams a construction system that can be bolted (or riveted)
together and is easily machined for more sophisticated mechanisms.

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VersaPlanetary Lite
The use of the VersaPlanetary Lite as the drive gearbox gives teams a
lightweight modular gearbox, helping to make it easier to iterate and optimize
your robot design.
The modularity of the VersaPlanetary gives teams the ability to change and
combine gear sets instead of having to buy a new gearbox or add external
gearing. In fact, a 2 stage VersaPlanetary gearbox can create up to 72 unique
gear ratios – the most of any COTS gearbox in FTC or VEX U.
Check out “VersaChassis Mini Speed Charts” to see what speeds you can get with different gear ratios, as
well as what speeds you should avoid based on the number of motors you’re using and the weight of your
robot.
VEX EDR & VEXpro Wheels
The VersaChassis Mini works great with VEX EDR and
VEXpro wheels. VEX EDR wheels give teams a high quality,
low cost wheel option. Teams can also reconfigure their
VersaChassis Mini with VersaHex Adapters to use wheels
from the VEXpro product line. More ideas on how to use
VEXpro wheels on your VersaChassis can be found in the VersaChassis Mini Tips & Tricks Guide.
Star Drive Screws
Stripped screws are a fact of life in competition robotics. Many VEX Robotics
Competition (VRC) teams use Star Drive Screws to combat this issue. These
screws have many advantages over tradition Hex Drive Screws. The Star
Drive shape has more surface area than Hex Drive which makes these
screws harder to strip. Additionally, these Star Drive Screws are cheaper
than the Hex Drive Screws available from online retailers or your local
hardware store. Most of the VersaChassis Mini assembly screws use these
Star Drive Screws. As a bonus, the VersaChassis Mini comes with (5x) T15 Star Drive Screwdrivers so
there’s no need to go out and buy special tools to assemble your VersaChassis Mini.
Power-to-Weight Ratio (PWR)
In competitions like the FIRST® Tech Challenge and VEX U where teams are given a fixed power budget (for
example, limiting the number of motors and batteries), it is important to consider a robot’s Power-to-Weight

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Ratio (PWR). This is the amount of mechanical power over the weight of the robot. For example, the average
FTC motor can produce up to 25W of mechanical power. If a robot has 8 of these motors and weighs 35lbs
the PWR would be 5.71.
25∙8 
35  = 5.71 /
Why is this important? Building a lighter robot means you will use less power moving your robot and more
power playing the game. This has multiple benefits in competitive robotics. For example, a lighter robot has
less mass that needs to be accelerated, this way your robot will reach top speed quicker than a heavier robot
with the same wheels and gearing. This means that even though you’re geared to move the same speed as
your opponent, you’ll be moving around the field faster, which allows you to score points faster, which means
you can score more points in a match.
Another example is that a lighter robot can be geared faster, where a heavier robot that has been geared at
the same (faster) speed will pull more current and potentially stall motors or trip breakers. Proof of this can
be seen in the speed charts below. The first chart is for a 20 Lb. robot, and the second is for a 35 Lb. robot.
The 20 Lb. robot can be geared faster than the 35 Lb. robot without stalling motors or tripping breakers:
20 Lb. Robot 35 Lb. Robot
3:1
4:1
5:1
7:1
9:1
10:1
2:1
10.49
7.87
6.29
4.50
3.50
3.15
3:1
6.99
5.25
4.20
3.00
2.33
2.10
4:1
5.25 3.93
3.15
2.25 1.75 1.57
5:1
4.20
3.15
2.52
1.80
1.40
1.26
7:1
3.00 2.25 1.80 1.28 1.00 0.90
9:1
2.33
1.75
1.40
1.00
0.78
0.70
10:1
2.10 1.57 1.26 0.90 0.70 0.63
Configurations
The VersaChassis Mini can be built to create a variety of different drive systems. Below is an explanation of
some of these drive systems as well as their pros & cons. Typically, a game can be played effectively with
many different types of drivetrains. Teams should consider the pros and cons of each drivetrain and how they
factor into their robot’s strategy. These configurations are meant to give teams a starting point that allows
3:1
4:1
5:1
7:1
9:1
10:1
2:1
10.49 7.87 6.29 4.50 3.50 3.15
3:1
6.99 5.25 4.20 3.00 2.33 2.10
4:1
5.25 3.93 3.15 2.25 1.75 1.57
5:1
4.20 3.15 2.52 1.80 1.40 1.26
7:1
3.00 2.25 1.80 1.28 1.00 0.90
9:1
2.33
1.75
1.40
1.00
0.78
0.70
10:1
2.10
1.57
1.26
0.90
0.70
0.63

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them to spend less time designing and building from scratch and more time iterating and optimizing for the
game they’re playing.
4 Wheel Drive
Out of the box, the VersaChassis Mini can be used to make 4 different types of 4-wheel drivetrains:

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4 Traction Wheels
This is one of the most basic
drivetrains a team can make. The
configuration shown to the right
uses 4” VEX EDR Traction Wheels
(276-6299).
This type of drivetrain uses tank-style
steering. This means the robot turns
left and right when the left and right
wheels spin in opposite directions.
However, when the robot is turning,
the wheels must be dragged along
the floor.
Since the wheels must be dragged, turning requires more power, and your motors will draw more current
than other types of drivetrains. It should be noted that this type of drivetrain is less agile than some other
types of drivetrains.
This drivetrain is good when you want to have a lot of traction to push other robots or drive over obstacles,
and don’t need to be as agile as some of the other types of drivetrains.
Pros:
•High traction to push robots or climb over obstacles
•Cheapest option for a drivetrain
Cons:
•Less agile than other types of drivetrains
•Higher current draw when turning compared to other drivetrains

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2 + 2
This type of drivetrain is named 2+2
because there are 2x omni-
directional wheels and 2x traction
wheels. The version shown uses 2x
4” VEX EDR Omni-Directional
Wheels (276-6298) and 2x 4” VEX
EDR Traction Wheels (276-6299).
This type of drivetrain has a good
balance of traction and agility. While
the traction wheels still have to drag
while turning, the omni-directional
wheels slide side to side.
Since fewer wheels need to be dragged, this type of drivetrain requires less power to turn, which means your
battery will last longer during a match.
This type of drivetrain works well when you want to have a good balance of traction and agility.
Pros:
•Balance of traction and agility
•Harder to ‘T-Bone’ than 4 Traction Wheels
Cons:
•Less traction for pushing robots or climbing obstacles
•Easier to push at the end of the robot with omni-directional wheels

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4 Omni-Directional Wheels
This type of drivetrain is one of the
most agile drivetrains you can make.
The version shown uses 4x VEX EDR
Omni-Directional Wheels (276-
6298).
Since this drivetrain can be pushed
side to side it is easier to push off
target, but harder to ‘T-bone’. ‘T-
boning’ is when a robot is pushing
another from the side.
When the robot being pushed has a
lot of traction, a ‘T-bone’ can
effectively slow it down or even stop it. The 4 omni-directional wheels make it nearly impossible for a robot to
be caught in a ‘T-bone’.
Pros:
•Very agile
•Hard to ‘T-bone’, pin or entrap
Cons:
•Less traction for pushing robots or climbing obstacles
•Can easily be pushed side to side

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Mecanum Drive
This type of drivetrain features 4x
mecanum wheels. The mecanum
wheels shown here are 4” VEX EDR
Mecanum Wheels (276-1447).
Mecanum wheels have rollers just
like omni-directional wheels.
However, these rollers are vectored
which allow to wheel to be driven
side to side.
In a mecanum drive, each wheel
needs to be controlled
independently to allow the robot to
be propelled forward, backward, strafe left, strafe right, turn left, and turn right.
Pros:
•Can move side to side, making it easier to laterally align to a goal
•Not as easy to push sideways as a 4 Omni-Directional Wheel drivetrain
Cons:
•Requires at least 4 motors to implement correctly
•Requires additional software to keep tract of positioning during autonomous mode

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6 Wheel Drive
A 6 Wheel Drive Upgrade Kit is available for the VersaChassis Mini. This kit allows teams to make 3
different types of 6-wheel drivetrains.

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Why No Drop Center?
There are two measurements: The
Wheel Width (the width, from the
outside, between two wheels) and the
Wheel Base (the center-to-center
distance between the two furthest
wheels contacting the ground).
When there’s a drop center, your
Wheel Base would be measured from a
front or back wheel and the center
wheel. When there is no drop center,
the Wheel Base is measured from the
front wheel and the back wheel.
In general, you want a Wheel Base that
is smaller than your Wheel Width. If
this is not the case, or the Wheel Base and Wheel Width are very close to equal, your robot will have
a harder time turning. However, if your wheel width is too small it can make your robot too difficult to
control.
Since the wheel base on the VersaChassis Mini is smaller, there’s no need to drop the center wheel
(like you would on a larger FRC robot).

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6 Traction Wheels
This drivetrain has 6 traction
wheels. The wheels shown here are
4” VEX EDR Traction Wheels (276-
6299). The back four wheels are
powered by a VersaPlanetary Lite
and the front two wheels are
connected to a VersaPlanetary Lite
by #25 chain so that all 6 wheels
are powered.
Over the course of an
event/season, your chain can
stretch and get loose. The front two
wheels of this drivetrain ride on
bearing blocks. Next to each of these bearing blocks is a cam which allows teams to adjust the tension of the
chain. This makes it easy for teams to ensure their chain is always properly tensioned.
This type of drivetrain is useful for a couple reasons. The first is that the two additional wheels will provide
extra traction over a 4 Traction Wheel setup. Secondly, having a wheel in the middle of the robot makes it
harder for your robot to get high centered when climbing over obstacles.
Pros:
•High traction to push robots or climb over obstacles
•Harder to get high centered on field obstacles
•Added stability
Cons:
•Less agile that other types of drivetrains
•Heaviest 6-wheel drivetrain
•Requires the use of roller chain to power some wheels

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4 Traction + 2 Omni-Directional Wheels
In this drivetrain the 2 omni-
directional wheels are unpowered.
The wheels shown here are 4x 4”
VEX EDR Traction Wheel (276-
6299) and 2x 4” VEX EDR Omni-
Directional Wheel (276-6298).
In this type of setup the two
unpowered wheels should be the
omni-directional wheels. This means
that when your robot is turning, the
unpowered wheels will slide side to
side instead of having to be dragged.
This type of drivetrain has some of the added benefits of the 6 Traction Wheel setup, such as being harder to
high center and added stability. However, the omni-directional wheels in the front give this robot much more
agility.
Pros:
•More agile than 6 traction wheel option
•Harder to get high centered on field obstacles
•Added stability
Cons:
•Less agile that other types of drivetrains
•Heavier than a 4-wheel drivetrain

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2 Traction + 4 Omni-Directional Wheels
This type of drivetrain has 2 powered
Omni-Directional wheels and 2
unpowered Omni-Directional Wheels.
The wheels shown here are 2x 4”
VEX EDR Traction Wheel (276-
6299) and 4x 4” VEX EDR Omni-
Directional Wheel (276-6298).
In this type of setup, the omni-
directional wheels at the front and
back give this type of drivetrain
added agility over the 6 Traction
Wheel and 4 Traction + 2 Omni-
Directional Wheel setups.
This is useful when you want the benefits of the 4 Traction + 2 Omni-Directional Wheel setup, but you want
even more agility.
Pros:
•Most agile 6-wheel drive configuration
•Harder to get high centered on field obstacles
•Added stability
Cons:
•Easier to push from the side, especially at the front and back of the robot

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H-Drive
An H-Drive Upgrade Kit is available for the VersaChassis Mini. This kit allows teams to make a 3
motor H-Drive. An H-Drive gets its name because the wheels are configured like an ‘H’. There are 4
wheels facing in one direction and a 5th wheel perpendicular to the other 4. This 5th wheel can propel
the robot left and right. In addition, the all 5 wheels be used to propel the robot diagonally.

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3 Motor H-Drive
The H-Drive Upgrade Kit comes with
everything to build a 3 motor H-Drive.
Why 3 Motors? This configuration
gives teams the ability to make a
robot capable of moving left and right
with fewer motors.
Teams who build this drivetrain will
end up with an extra motor +
VersaPlanetary Lite, which can be
used to power a separate mechanism
like an arm or intake.
Pros:
•Can strafe left and right
•Uses fewer motors than a Mecanum Drive
•Very agile
Cons:
•Less traction than a Mecanum Drive
•Less power in your drivetrain, but more power available for other systems
•Requires more complicated software than most other 4 and 6-wheel drivetrains

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Motor Compatibility
Below is a list of legal FTC motors and their compatibility with the VersaPlanetary system. Please note that all
of these motors will have to have the gearhead removed prior to being connected to a VersaPlanetary. For
more information on how to remove a gearhead from one of the compatible motors, please see the
“Preparing FTC Motors for the VersaPlanetary” guide.
Picture
Motor
Compatible
AndyMark NeveRest Yes
REV Core Hex Motor No
REV Hex Motor Yes
Tetrix 12V Motor No
Tetrix TorqueNADO Motor Yes

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Maintenance
Maintenance is an important part of every robot sub-system. Below is a list of things teams can do before
and during an event to make sure their VersaChassis Mini is always running at peak performance.
Before / Between Events
Lubricate the VersaPlanetary Lite
This usually only needs to be done once a season. However, if your team is playing an extended
number of matches (50+ matches) you should check the lubrication inside the VersaPlanetary Lite.
Be care not to over lubricate your VersaPlanetary.
Inspect VersaPlanetary gear sets and ring gears for damage
This can be done when you check the lubrication inside the VersaPlanetary Lite. Things to look for
include missing/worn teeth and verifying that the planet gears are spinning freely on the carrier plate
pins.
Check wheels for excessive wear
This can greatly affect your performance. A worn wheel can ruin autonomous routines and change
your ability to accelerate up to speed or climb over obstacles. If a wheel is showing excessive wear,
replace it.
Tighten loose screws on the Chassis (replace loose rivets)
Over the course of an event, your robot chassis sees a lot of vibration and impact. These can cause
the screws or rivets holding the chassis together to come loose. Check to make sure these are
tightened.
Check for and replace any stripped screws
Having stripped screws on your robot can make it difficult to fix your robot at an event. Check all your
screws to make sure they’re not starting to strip or already stripped. If they are, replace immediately.
A $0.10 screw isn’t worth the headache of dealing with that stripped screw at a competition.
During an Event
Check set screws on the VersaPlanetary output shafts

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These set screws come with a nylon thread locking patch. However, they could still come loose over
time. If they are loosening more frequently, use “blue” Loctite (Loctite 615) to help prevent these
screws from loosening.
Run drivetrain in various directions (forward, backwards, turning left, turning right, strafe left, strafe
right, etc.).
Noises and visual observation of your robot running in your pit are easy ways of knowing something is
(or is about to go) wrong with a mechanism. Running your VersaChassis Mini in every possible
direction while on blocks is a great way to watch and listen for these potential issues. Things to be
watching and listening for are clicks and rattles or wheels/motors not running or running slowly.
Periodically check screws and rivets
Over the course of an event robots see a lot of vibration and impact. These can cause screw and
rivets to loosen up. Check all your screws and rivets and make sure they are tight. If you’re using
rivets and have a loose rivet, you should replace it.
Inspect motor connections and other robot wiring
Loose or improper wiring can rob your robot of power. This means that motors might not be running
at their full potential and your sensors could be providing incorrect data. Check for cuts along a wire,
loose connections, and potential shorts.