Video Summary - Full Course: How to CAD a Mecanum Drivetrain From Scratch (3.5 Hours)

Main ideas / lessons conveyed

Drivetrain design is the most important early decision when building a mobile robot:
- Motor selection
- Gear ratio selection (based on desired ground speed/torque needs)
- Wheel type and size
- Belt/chain drive choice and mechanical constraints (cross bracing, modularity, compatibility with other robot components)
The speaker teaches a CAD-driven methodology to design a mechanum drivetrain from scratch, emphasizing:
- Creating a drivetrain that is modular, rigid, and E.S.D. protected
- Designing for parametric change (edit one variable, propagate through the model)
- Building efficiently in CAD by designing one quarter/one pod and then mirroring
- Using pre-made vendor STEP files for motors/wheels/pods/channels instead of modeling everything from scratch

Video structure (what’s covered)

Part 1: Choices and design setup
- Define what a parallel plate mecanum drivetrain is and why you’d use it
- Create key design constraints
- Make critical component/architecture choices:
  - belts vs chains
  - motor + gear ratio
  - side plate material
  - wheel size compatibility
- Compute gear ratio targeting via wheel RPM and ground speed
- Choose materials (plywood/multiplex, aluminum, polycarbonate, acetal) with notes on tradeoffs
Part 2: CAD flow in computer design
- Hand-ideate first, then build a CAD model
- Import vendor STEP files (motors, wheels, pods, etc.)
- Use parameters, master skeletons, and mirroring
- Design pod internals: axles, bearings, pulleys, motor mounts, timing belt path, tensioning slot
- Add modular mounting channels
- Add odometry pod mounting features
- Add structural cross bracing
- Add “lightning/pocketing” (weight reduction with hexagonal pockets)
- Validate clearances and adjust as needed

Detailed methodology / instruction list (condensed from the tutorial)

A) Define key design constraints (before CAD)

The speaker recommends writing “key design constraints” as absolute requirements and emphasizes not skipping this step.

Key constraints listed include:

Drivetrain must have:
- 4 wheels and be suitable for a mecanum chassis
- Smooth/frictionless movement (avoid clamping/grinding)
Must be:
- Modular (easy to add/remove parts; avoid designs that are impossible to modify)
- Rigid (no wobble; drivetrain must transfer power effectively)
- E.S.D. protected (examples given):
  - aluminum plates with polycarbonate/vinyl insulation, or
  - polycarbonate/cetal plates for the conductive/insulating approach
Mechanical/layout requirements:
- Two parallel plates with wide wheelbase (wheels placed close to outer edges of plates)
- Live axles (axle spins with the wheel, not a dead axle where the wheel spins around a stationary axle)
- Changeable gear ratio (example target: ability to adjust wheel RPM ~300–500 RPM range)
- Maximize internal space between pods for mechanisms/sensors (including optional control hub locations)
- Optional integrated number plates/access holes (FTC context)
- Low center of gravity (reduce tipping risk; keep motor/wheel low)
- Square wheelbase (better strafing for mecanum)
- Compatible with common build systems (explicitly names Rev/GoBilda/etc.)
- Ability to mount “dead wheels” (e.g., 3D printed or alternative odometry setups)
Wheel/power flexibility requirements:
- Support mechanum wheel sizes (speaker mentions moving toward 74–105 mm mecanum wheels to avoid vendor lock-in)
- Prefer HD5 belt-driven architecture (optionally belt swap/update tensioner instead of redesigning everything)
- Include belt tensioner design (slot/tensioner so belt stretch can be compensated)
- Include practical design practices for routing and clearance

B) Choose power transfer method: belts vs chains

Instruction/guidance given:

Avoid direct drive (motor directly attached to wheels) due to shock loading and difficulty adding ratios later.
Avoid simple gear trains if spacing makes ratio changes difficult.

Evaluate belts vs chains:

Both can perform well
Speaker’s preference: belts for slightly better efficiency
Note: chains are easier to swap and more forgiving in distance

Practical recommendations:

Prefer metal chains or timing belts
Avoid plastic chain (less durable; more friction)
Timing belt widths suggestion: around ~9 mm width
HD5 timing belt noted:
- HD5 has 5 mm teeth, considered suitable for drivetrains
For chains:
- 8 mm chain (and optionally 6 mm pitch) mentioned

C) Select wheel and motor based on target ground speed + weight class

Method described:

Identify wheel diameter (examples: GoBilda 104 mm, AndyMark 3”, Rev wheel, etc.)
Use historical/typical robot performance as guide:
- “Slow/middle/fast” bounds are described in terms of wheel RPM and resulting ground speed
Target ground speed suggested (for the general case):
- ~2 to 2.5 m/s ground speed as a “good place to shoot for”
Consider robot mass:
- Faster targets require lighter robots
- Speaker mentions heavy vs light threshold examples (e.g., >~17 kg heavy; ~13–12 kg light in their observations)
Gear ratio should match desired output wheel RPM during operation

Motor selection guidance:

Don’t necessarily choose the exact motor RPM needed by spec sheet alone.
Reason: planetary gear efficiency loss—speaker suggests:
- Use a single planetary reduction (ultra planetary motor)
- Then do the remainder ratio via belt/sprocket for better overall performance

Examples of ultra planetary motor gear reductions mentioned:

Rev HD Ultra planetary: ~5.23:1
GoBilda Yellow Jacket: ~5.2:1
Studica Maverick: ~5.2:1
Speaker favors Rev Ultra planetary for compactness and CAD convenience

D) Calculate gear ratio and pulley tooth counts

Process used:

Use a calculator approach:
- Determine target ground speed (example default ~2.38 m/s-ish)
- Choose motor input RPM from gearbox reduction
- Choose timing belt/pulley tooth counts

Example selection in tutorial:

Driver/input pulley: 18 teeth
Driven/output pulley: 35 teeth
Uses AndyMark 3” wheel and Rev ultra planetary
Yields target ground speed close to desired value

E) Choose side plate material (side pods/plates)

Materials listed with tradeoffs:

Plywood / multiplex (prototype-friendly, competitive):
- Don’t go below ~6 mm
- Notes about softwood vs hardwood thickness guidance
- Option: laminate two 4 mm sheets to make an 8 mm equivalent
- Speaker suggests MDF is weak for impact situations (okay only if no impacts)
Aluminum:
- Rough guidance: 3–4 mm
- 6061 vs 7075 mentioned (7075 stronger but harder/more expensive)
- For FTC-size robots, 6061 likely fine
Polycarbonate:
- ~4–6 mm
- Easy to machine/CNC/waterjet
- Threadlocker caution: non-safe for polycarbonate with typical products
Acetal/Delrin/Palm/“Lexan” reference note:
- Speaker’s favorite: 4 mm acetal
- Self-lubricating, easy to fabricate, cheaper than aluminum
For aluminum:
- Add exterior insulation (vinyl/acetal/polycarbonate) to reduce ESD events

F) CAD workflow (Fusion 360 emphasized in subtitles)

Core CAD steps/instructions:

Ideate by sketch first, then translate into CAD.
Build a parametric model:
- Create parameters for:
  - wheel diameter
  - motor width
  - ground clearance
  - total plate length and thickness
  - buffer zones from edges (plate outer buffer)
  - belt center-to-center distances, etc.
Use a master skeleton:
- Create a ground plane based on plate max dimensions
- Add ground clearance offset (parameter-driven)
- Design one quarter pod (then mirror):
  - model one quarter to save time
  - mirror quarter → half → full (or pod duplication)
Use imported STEP files:
- Download STEP from supplier websites for motors/wheels/pods/channels
- Import into Fusion, make rigid groups
Create your main body from skeleton:
- extrude master skeleton plate to thickness

G) Pod/wheel internals to model in CAD (as described)

High-level sequence:

Create a master pod component
Design wheel “kebab” assemblies (axle + bearing + pulley + couplers):
- Place motor and wheel positions based on belt path + center distances
- Build pulley using timing-belt pulley tools (named tool source referenced in subtitles)
- Build wheel hub/coupler for mecanum wheel attachment
- Add set-screw clamp/hubs to avoid relying on 3D printed parts alone for load paths
Model timing belt pulleys and belt engagement spacing:
- Use Recalc site to compute belt sizes/center-to-center feasibility
Add odometry pod clearance and placement:
- Determine maximum pod width based on geometry and belt clearance
- Create mounting slots for odometry modules

H) Implement modularity and mounting channels

Add a modular mounting pattern/channel (speaker favors Swift Channel / GoBilda / Rev-compatible patterns)
Ensure channel alignment is symmetrical for mirroring.
Create “channel pattern” features projected onto both inner/outer plates.
Keep the modular section as a group so it can be deleted later if desired.

I) Structural features: tensioner, bracing, and lightning

Add belt tensioner slot:
- Include a slot feature near the motor side for maintaining belt tension over time and enabling ratio adjustments
Add cross bracing:
- Aim for at least something in the middle, back, and likely front
- Purpose: prevent racking/twisting/shear forces
- Uses off-the-shelf aluminum extrusion/channel + pillow block style components
- Speaker describes iterating to reduce racking (and notes initial support was insufficient)
Add “lightning/pocketing”:
- Pocket/lighten outer plates and inner plates
- Speaker prefers hexagon pocket patterns
- Use buffers around critical features (standoffs/holes/tensioner slots)
- Parameters for:
  - pocketing buffer around critical components
  - hexagon flat-to-flat size
  - spacing (“hex gap”) and row offsets
- Perform cut/extrude operations to create pockets

J) Final assembly actions

Mirror components carefully using construction planes/offset planes (avoid fragile references).
Insert odometry pods using joints and rigid grouping.
Add final cross braces and validate collision/clearance.
Save/iterate to fix mismatches (clearances, belt center distances, motor overlap issues, etc.).

Speakers / sources featured (as stated in subtitles)

Speaker

Course instructor / presenter (name not provided in subtitles)
- Mentioned as: “For over a decade, I’ve been teaching students…” and later: “When it comes to… I’ve been teaching…”

Referenced sources / tools / organizations / product ecosystems

Fusion 360 (CAD platform mentioned)
Rea.lc / Recalc belt and robotics calculators website
FFRC tools for Fusion (Fusion tools repo referenced; example team cited: Raiders Robotics 4698, plus tool set referenced via a GitHub release)
GoBilda, Rev Robotics, AndyMark, Studica/Studica Robotics, Swift Drive / Swift Channel, East Loop Components
FTC (competition context)
Mitsu-mi (Misumi) parts (bearings/collars/hubs referenced)
Timing belt/pulley standards and belt types:
- HD5 timing belts
- GT2 mentioned as not recommended
Loctite / threadlocker mentioned in context of polycarbonate safety guidance

Competitions / systems context

FIRST Tech Challenge (FTC)
Mentions of Rev and go build systems / compatibility requirements

(No other distinct named speakers beyond the instructor appear in the subtitles.)

Full Course: How to CAD a Mecanum Drivetrain From Scratch (3.5 Hours)

Key takeaways