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

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

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

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

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