Belt Drive Speed Calculator¶
Run the Belt Drive Speed Calculator MicroSim Fullscreen
This sketch is built on the FanPedia MicroSim kit. To run it in the
p5.js editor, add the ../shared-libs/ files it loads
(fanpedia-sim.css, fanpedia-core.js, fanpedia-p5.js, fan-models.js, fan-drawings.js),
or their published URLs, to the editor's index.html before pasting
ch11-belt-drive-speed-calculator.js.
About This MicroSim¶
This calculator puts the three belt drive formulas from Chapter 11 side by side:
- Fan speed: fan rpm = motor rpm × motor sheave pitch diameter ÷ fan sheave pitch diameter
- Belt speed: V (ft/min) = π × motor sheave pitch diameter (in) × motor rpm ÷ 12
- Belt count: design hp = motor hp × drive service factor; belts = design hp ÷ rating per belt, rounded up to a whole belt (a whole-number quotient is not rounded up)
The motor sheave and the fan sheave are drawn to scale relative to each other and joined by a V-belt. Once a drive is checked, each sheave turns at its own computed speed, so the larger sheave visibly turns slower. The outputs panel lists the fan speed, the speed ratio (motor rpm ÷ fan rpm), the belt speed, the design horsepower and the belts required.
The sim starts with four challenge drives, in this order:
| # | Motor rpm | Motor sheave (in) | Fan sheave (in) | Motor hp | Drive SF | hp per belt | Fan rpm | Belt speed (ft/min) | Belts |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 1,760 | 5.0 | 8.0 | 15 | 1.3 | 6.0 | 1,100 | 2,304 | 4 |
| 2 | 1,760 | 6.0 | 8.4 | 10 | 1.2 | 5.0 | 1,257 | 2,765 | 3 |
| 3 | 1,170 | 9.0 | 6.0 | 20 | 1.4 | 8.5 | 1,755 | 2,757 | 4 |
| 4 | 3,500 | 4.0 | 10.0 | 7.5 | 1.2 | 4.5 | 1,400 | 3,665 | 2 |
For each drive you type a fan speed and a belt count. The two answers are judged separately: the fan speed is right within ±5 rpm of the model value, and the belt count is right only when it is exactly the model value. You get two attempts per drive. A field you got right on the first attempt stays fixed, and you correct only the other one. A wrong answer shows the worked calculation; if your fan speed is the ratio turned upside down, or your belt count was rounded down, the feedback says so. After a second wrong attempt the model values are shown and the drive counts as missed. Mastery is all four drives with both answers right on the first attempt.
After drive 4, Explore mode unlocks six sliders (motor speed 860 to 3,540 rpm, motor sheave 3.0 to 12.0 in, fan sheave 3.0 to 24.0 in, motor power 1 to 100 hp, drive service factor 1.0 to 1.8, rating per belt 1.0 to 20.0 hp) and every output updates at once. A belt speed above 6,500 ft/min shows a note to check the drive manufacturer's limits. Explore mode is never scored.
All numbers are illustrative; challenge 1 matches the chapter's worked examples. Real per-belt ratings and drive service factors come from the drive manufacturer's current tables.
How to Use¶
- Read challenge 1: the motor speed and power, both sheave sizes, the drive service factor and the rating per belt. Type the fan speed in Fan speed (rpm) and the number of belts in Belts, then press Check (or Enter).
- A correct drive reads "✓ Correct: 1,100 rpm and 4 belts." in a solid green box. A wrong one reads "✗ Not quite." with the worked calculation in a dashed red box; fix the field that was wrong and check again.
- Press Next challenge (or Enter) and repeat for drives 2 to 4. In drive 3, watch the fan sheave turn faster than the motor sheave. "Challenges fully correct: n of 4" keeps the running score.
- After drive 4, press Start exploring. The panel shows the first-attempt score and the mastery line. Make the fan sheave bigger and watch the fan slow down; raise the motor sheave and motor speed until the belt speed note appears. Reset to defaults returns to drive 1's values; Start over clears the score and returns to challenge 1.
Keyboard: Enter checks the answers, and Enter again goes to the next challenge. Tab reaches both answer boxes, every button and the six sliders; the arrow keys move a focused slider.
Data label: "Motor speeds, per-belt ratings and service factors are illustrative. Use the current drive manufacturer's tables for real selections.", at the bottom left of the drawing.
Iframe Embed Code¶
You can add this MicroSim to any web page by adding this to your HTML:
<iframe src="https://moroshek.github.io/FanTASTIC-textbook/sims/ch11-belt-drive-speed-calculator/main.html"
height="742px"
width="100%"
scrolling="no"></iframe>
Lesson Plan¶
Learning Objective¶
The learner will calculate the fan speed, belt speed and required belt count of a V-belt fan drive from the motor speed, the two sheave pitch diameters, the motor horsepower and the drive service factor, with fan speed within ±5 rpm and belt count exact (Bloom: Apply, verb: calculate).
Audience¶
Adult professional development: new application engineers, sales staff, representatives and facilities staff who have read the "Belt Drive" section of Chapter 11.
Duration¶
10-15 minutes
Prerequisites¶
- Belt drive, sheave, pitch diameter, motor sheave and fan sheave
- V-belt and belt speed
- Drive service factor and design horsepower
Activities¶
- Challenges (5-8 min): Work each drive with a calculator before pressing Check. Before calculating, say which sheave is bigger and whether the fan should turn slower or faster than the motor.
- Review (2 min): Read the worked calculation for any missed drive and redo it on paper.
- Explore (3-5 min): Starting from the defaults, raise the fan sheave from 8.0 to 10.0 in and record the fan speed. Then find a motor speed and motor sheave that push the belt speed past 6,500 ft/min. Finally, set a drive whose belt quotient is exactly a whole number and confirm it is not rounded up.
Common Misconceptions Addressed¶
- A larger fan sheave makes the fan run faster: the turning sheaves and the fan rpm readout show it slowing, and Explore mode says "Bigger fan sheave, slower fan."
- The speed ratio equals the fan/motor diameter ratio the same way up: an inverted answer gets "Your ratio is inverted: the larger sheave turns slower."
- A belt count of 3.25 rounds down to 3: a rounded-down answer gets "Round belt counts up; a partial belt cannot carry its share."
- The motor's nameplate service factor is the drive service factor: every drive lists the drive service factor separately from the motor horsepower, and the chapter contrasts it with the motor service factor example from FanPedia p. 69.
Assessment¶
- The running line "Challenges fully correct: n of 4" counts drives with both answers right on either attempt. At the end the sim shows "First-attempt score: n of 4" and the mastery line; mastery is 4 of 4 drives with both answers right on the first attempt.
- Moving the sliders in Explore mode is not evidence of mastery. Ask the learner to explain why the fan in challenge 3 turns faster than its motor.
References¶
- Belt (mechanical) - Wikipedia overview of belt drives, V-belts, speed ratio and belt power transmission.
- Pulley - how pulley (sheave) diameters set the speed ratio of a belt drive.
- FanPedia: The Fan & Blower Encyclopedia - Twin City Fan's reference on fan drives, arrangements and the motor service factor (p. 69).