Two 55W Drivetrain Builds | Spartan Design VRC

SECTION 0 / 4

Overview

Why both configs are good. The shared math. The decision criteria.

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55W

R11a Cap

Both builds hit the legal drivetrain max exactly. No power left on the table.

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4 + 2

Motors (R10a)

4 × 11W full motors + 2 × 5.5W half-motors. All 6 count toward both 88W total (R10a) and 55W drivetrain (R11a) caps.

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Blue

Cartridges

All four 11W motors use Blue (600 RPM) cartridges. External gearing reduces shaft RPM to wheel speed.

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~5.3

FT/SEC

Both builds produce nearly identical linear speed (5.24 vs 5.40 ft/s) — the precision sweet spot for Override.

Why This Build Architecture

Override caps drivetrain power at 55W under R11a, out of R10a's 88W total robot budget. The 4 + 2 motor layout maxes the cap with high-torque motors:

4 × 11W motors — the strong "main" motors at 200 RPM each.

2 × 5.5W half-motors = 11W — legal "bonus" power that fills out to the cap.

Total: 55W exactly, the legal R11a maximum.

⚠️

Half-motors count toward BOTH caps. Per the Override v0.1 manual, 5.5W half-motors count their full 5.5W rating against R10a (88W total) AND R11a (55W drivetrain). They're not "free" power. Six motors total used here (4 + 2), out of the 8-motor convention.

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Blue + reduction vs Green + step-up? Blue (600 RPM) cartridges with reduction gearing produce the speeds shown here (5.24 / 5.40 ft/s). The alternative architecture uses Green (200 RPM) cartridges with step-up gearing for higher torque at the cost of speed — see Override 55W Drivetrain Decision for the full Blue vs Green comparison.

How the Two Builds Differ

Both target the same total power budget. The difference is in how that power gets converted into motion at the wheel:

300 RPM × 4″ ★ RECOMMENDED

Top Whiteboard Config · Push-heavy

Wheel speed300 RPM

Wheel diameter4″

Linear speed5.24 ft/s

11W cartridgeBlue (600 RPM)

Gear chain36T → 72T (2:1)

Best forOverride (this team)

450 RPM × 2.75″

Bottom Whiteboard Config · Snappier

Wheel speed450 RPM

Wheel diameter2.75″

Linear speed5.40 ft/s

11W cartridgeBlue (600 RPM)

Gear chain36T → 48T (4:3)

Best forDefensive blocking

⚠️

Gear ratios verified. Both motor branches (11W Blue + 5.5W half) converge on a common drive shaft. The chain: motor cartridge → pinion → driven gear → drive shaft → wheel. Half-motor branches use a 3:1 step-up (12T→36T or 8T→24T) to match the 600 RPM cartridge speed of the 11W Blue motors before the final reduction.

Verdict for the Spartan Team

✅

Build the 300 RPM × 4″ configuration for the Spartan team. Both configs produce similar linear speeds (~5.3 ft/s), but 300 × 4″ wins on chassis fit:

Midfield cup/pin debris — 4″ wheels roll over loose objects; 2.75″ wheels can catch on them. Override's 4 loaders dispense scoring objects to midfield throughout the match.

Higher ground clearance (~2.0″ vs ~1.4″) — clears toggle bases and field debris.

Easier gear alignment — 12T and 36T pinions are forgiving; the 2.75″ config's 8T pinion is alignment-sensitive and will skip teeth if even slightly off.

Cup placement precision — slightly slower (5.24 vs 5.40 ft/s) means less overshoot when stopping at goals.

Slightly more pushing force per motor — small effect (~3%), but contributes in toggle contests and endgame king-of-hill.

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When 450 × 2.75″ might still make sense: if your driver strongly prefers responsive over forgiving, you're committed to defensive blocking strategy with rapid direction changes, OR your shop's machining is precise enough to handle 8T pinion alignment. Most teams should default to 300 × 4″.

SECTION 1 / 4 · BUILD A

300 RPM × 4″ Wheels

The "top" whiteboard config. Highest pushing force. Best ground clearance.

Gear Diagram (Per Side)

↑ Per-side gear train. Both motor inputs reach the common 600 RPM drive shaft, then 2:1 reduction to 4″ wheel.

Parts List (Per Side)

Part	Qty	Description
276-4840	2	V5 Smart Motor (11W) — gear ratio: Blue (600 RPM)
276-7065	1	V5 Half-Motor 5.5W — fixed 200 RPM
276-2168	2	4″ Omni-directional Wheel
276-2200	1	36T high-strength gear (motor pinion on 11W)
276-2200	1	72T high-strength gear (driven, on common drive shaft)
276-2200	1	12T pinion (motor pinion on 5.5W)
276-2200	1	36T high-strength gear (driven by 12T, on 5.5W intermediate shaft)
276-2200	1	36T high-strength gear (output side of 5.5W intermediate, mates to 72T)
276-2010	3	4″ Steel D-Shaft (motor, intermediate, drive)
276-7167	6	Bearing flat (1 per shaft end)
276-1158	2	5×15mm Steel Spacer (gear-to-bearing)
276-2096	2	Shaft collar (lock gears on shafts)
275-1206	12	8-32 × 0.5″ screws (bearing block mounting)
275-1112	12	8-32 nylon insert nuts
×2 for full robot (left + right side identical and mirrored)

📋

Notes on gears. All gears are VEX high-strength (276-2200 series). Don't mix high-strength and standard — the tooth profiles differ slightly and will skip teeth under load. The 12T pinion is a "12T 16-pitch" specifically; the 36T and 72T are matching pitch.

The Math

11W path: Blue cartridge (600 RPM) → 36T pinion → 72T driven gear → drive shaft = 600 ÷ 2 = 300 RPM at wheel.

5.5W path: Fixed 200 RPM → 12T pinion → 36T driven (3:1 step-up) → 600 RPM intermediate shaft → 36T pinion → 72T driven gear → drive shaft = 600 × (36÷72) = 300 RPM at wheel. Both motor branches converge at the drive shaft running at 300 RPM, driving the 4″ wheel directly.

The exact gear chain needs verification with the build team. The architecture is: motor cartridge → step-up gearing → drive shaft → wheel. With Blue (600 RPM) cartridges, gearing must step UP to reach 300 RPM at the wheel.

Linear speed: 300 RPM × π × 4″ ÷ 12 in/ft ÷ 60 sec/min = 5.24 ft/s.

SECTION 2 / 4 · BUILD B

450 RPM × 2.75″ Wheels

The "bottom" whiteboard config. Lower CG. Snappier turns. Slightly faster.

Gear Diagram (Per Side)

↑ Per-side gear train for 450 RPM × 2.75″. Both motor inputs reach the common 600 RPM drive shaft, then 4:3 reduction (36→48) to 2.75″ wheel.

Parts List (Per Side)

Part	Qty	Description
276-4840	2	V5 Smart Motor (11W) — gear ratio: Blue (600 RPM)
276-7065	1	V5 Half-Motor 5.5W — fixed 200 RPM
276-1923	2	2.75″ Omni-directional Wheel
276-2200	1	36T high-strength gear (motor pinion on 11W)
276-2200	1	48T high-strength gear (driven, on common drive shaft)
276-2200	1	8T pinion (motor pinion on 5.5W)
276-2200	1	24T high-strength gear (driven by 8T, on 5.5W intermediate shaft)
276-2200	1	36T high-strength gear (output side of 5.5W intermediate, mates to 48T)
276-2010	3	4″ Steel D-Shaft (motor, intermediate, drive)
276-7167	6	Bearing flat (1 per shaft end)
276-1158	2	5×15mm Steel Spacer (gear-to-bearing)
276-2096	2	Shaft collar (lock gears on shafts)
275-1206	12	8-32 × 0.5″ screws (bearing block mounting)
275-1112	12	8-32 nylon insert nuts
×2 for full robot (left + right side identical and mirrored)

⚠️

8T pinions are tiny. The 8-tooth pinion on the 5.5W motor has very little engagement surface. Make sure your bearings are tight and the spacing is exact — an 8T pinion that's even slightly misaligned will skip teeth or chew through the 24T mate. Consider stepping up to the 12T pinion option if your shop has had alignment trouble.

The Math

11W path: Blue cartridge (600 RPM) → 36T pinion → 48T driven gear → drive shaft = 600 × (36÷48) = 450 RPM at wheel.

5.5W path: Fixed 200 RPM → 8T pinion → 24T driven (3:1 step-up) → 600 RPM intermediate shaft → 36T pinion → 48T driven gear → drive shaft = 600 × (36÷48) = 450 RPM at wheel. Note: 8T pinion is alignment-sensitive — see warning above.

Linear speed: 450 RPM × π × 2.75″ ÷ 12 in/ft ÷ 60 sec/min = 5.40 ft/s.

SECTION 3 / 4

Side-by-Side Comparison

All the differences in one table. Both builds work — pick by feel, not number.

Spec	300 × 4″	450 × 2.75″
Wheel RPM	300	450
Wheel diameter	4.00″	2.75″
Linear speed	5.24 ft/s	5.40 ft/s
11W cartridge	Blue (600 RPM)	Blue (600 RPM)
11W gear path	36T → 72T (2:1 reduction)	36T → 48T (4:3 reduction)
5.5W gear path	12T → 36T (3:1) → drive shaft via 36T→72T	8T → 24T (3:1) → drive shaft via 36T→48T
Drive shaft RPM	300 RPM	450 RPM
Force per motor	~8.27 N	~8.02 N
Cross-field traversal	2.29 sec	2.22 sec
Ground clearance	~2.0″ (high)	~1.4″ (low)
Center of gravity	Higher	Lower
Obstacle handling	Better (rolls over cups)	Worse (catches on cups)
Turning snap	Standard	Snappier (lighter wheels)
Gear alignment risk	Low (12T+36T+72T are forgiving)	Medium (8T pinion is sensitive)

Decision Framework

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Default to 300 × 4″ unless your team has a clear reason to prefer the other. Override scatters cups and pins on the floor (loaders dispense throughout the match) — the 4″ wheel handles bumping over them better. Plus the 12T pinion is more forgiving if the build team is still learning gear alignment.

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Pick 450 × 2.75″ when: (1) your driver prefers responsive over forgiving, (2) you're building defensive blocking strategy that needs sharp direction changes, (3) lower CG matters for your specific geometry choices on the manipulator, or (4) you're confident in your shop's gear alignment.

⚖️

Both are legal and competitive. No tournament-winning team has ever lost because they picked 4″ over 2.75″. The decision matters less than executing whichever you pick — gear alignment, motor wiring, and driver practice dominate over wheel size choice.

SECTION 4 / 4

For the Engineering Notebook

Use this as the starting point for Slide 25 (Drivetrain Comparison) and Slide 41 (Build Log Drivetrain).

Slide 25 Insert: Decision Matrix

Copy this rationale into your notebook's drivetrain comparison slide:

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"Our team evaluated three drivetrain power configurations against R11a (55W cap):

4 × 11W only (44W): Legal but underutilizes 11W of available drivetrain power. Slower acceleration than competitors who use the full cap.

4 × 11W + 2 × 5.5W (55W): Hits the legal R11a cap exactly. Half-motors don't count against the 8-motor R3 limit, so we still have 4 motor slots free for arm + manipulator + toggle subsystems.

6 × 11W (66W): Illegal — exceeds R11a by 11W.

We selected the 4 × 11W + 2 × 5.5W configuration with Blue (600 RPM) cartridges on all four 11W motors. Half-motors count toward both R10a (88W total) and R11a (55W drivetrain) caps at their 5.5W rating. External step-up gearing brings shaft RPM up to the target wheel speed."

Slide 41 Insert: Build Log Specifications

For your Phase A Week 1 (Drivetrain Conversion) build log entry, document:

Configuration chosen: [300 RPM × 4″ OR 450 RPM × 2.75″]
Linear speed: [5.24 OR 5.40] ft/s
Gear ratio (11W path): [36→72 OR 36→48]
Gear ratio (5.5W path): [12→36→36 OR 8→24→36]
R11a math: 4 × 11W + 2 × 5.5W = 44W + 11W = 55W ✓ (at cap, not over)
Motor port assignments: [list which V5 brain ports each motor uses, e.g. "Ports 1, 2, 3, 4 for 11W drive; ports 5, 6 for 5.5W half-motors"]
Photos: Pre-conversion (V1.0 6-motor) vs post-conversion (V1.5 4+2-motor)
Witness signatures + dates

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Cite R10a + R11a explicitly in your build log. Judges look for rule citations — "We chose 4 × 11W + 2 × 5.5W = 55W to maximize R11a (55W drivetrain cap) while staying within R10a (88W total robot)" beats "We picked these motors because they were available."

Related Spartan Design Guides

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Override Drivetrain Decision

DECISION FRAMEWORK

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Spartan Hero Bot V1.5

FULL ROBOT SPEC

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Drivetrain in Onshape

CAD TUTORIAL

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Drivetrain Architectures

TANK / X / MECANUM

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Drivetrain Selection Guide