An open-loop motor slows down when you load it, which is why almost every real drive is closed loop. This project commutates a brushless DC motor from its three Hall sensors, measures speed from the same sensor edges, and closes a proportional plus integral loop around it so the motor holds its commanded speed as the load changes. The demonstration that matters is not that the motor spins — it is the recorded step response showing speed recovering after a load is applied, next to the open-loop response where it does not.
Not just the parts. Teams budget from a component list, then run out in week six on wire, connectors and the driver board they destroyed. These are the lines that catch them.
| Line | Cost |
|---|---|
Components and materials From the bill of materials | Rs 6,100 to Rs 16,250 |
Spares and replacements 15 % — you will destroy something | Rs 915 to Rs 2,438 |
Consumables and hardware Wire, connectors, headers, screws, heatshrink | Rs 732 to Rs 1,950 |
Perfboard and assembly | Rs 150 to Rs 400 |
Report, printing and binding Two or three bound copies, plots and the plagiarism check | Rs 400 to Rs 1,200 |
| Total | Rs 8,297 to Rs 22,238 |
| Each, split 3 ways | Rs 2,766 to Rs 7,413 |
Indicative bands last checked in August 2026 — a guide, not a quotation. Prices move and vary by seller, and anything you can borrow from the lab comes straight off the total. The 4.3 week figure assumes 10 person-weeks of work shared between 3; students past 4 add coordination rather than output, so the estimate stops improving there.
The same chain in words
The three Hall sensors give six distinct states per electrical revolution, so the controller always knows which of the six commutation steps applies. Each step energises one phase positive, one negative, and leaves the third floating.
Speed comes from the same Hall edges. At high speed the controller times the interval between edges; at low speed it counts edges over a fixed window, because the interval becomes too long and too noisy to be useful.
The speed error drives a PI controller whose output is the PWM duty cycle applied to the bridge. The proportional term responds to the present error and the integral term removes the steady-state error that a proportional-only controller always leaves.
A current limit sits inside the speed loop. If the DC link current exceeds the limit, duty cycle is reduced regardless of what the speed loop wants, which is what protects the bridge during a stall.
Applying the mechanical brake drops the speed, the integral term winds up, duty rises and speed recovers. Logging that recovery is the project's result.
This is the chapter that separates an engineering project from an assembly job. Every value below carries the formula that produced it and the assumptions it rests on — check them against your own ratings before you use them, because your motor is not this motor.
f = N x pole pairs / 60
3000 x 4 / 60 = 200 Hz. Six commutation events per electrical cycle gives 1200 commutations per second, so the controller has 833 microseconds between steps at full speed.
Above the audible range, below the point where switching loss dominates
Below about 15 kHz the drive whines audibly. Far above it, switching losses in the MOSFETs rise and the gate driver has to charge the gates more often. 16 to 20 kHz is the usual compromise for a small drive.
Compare the PWM period against the motor's electrical time constant L/R
With 200 uH of phase inductance and 0.2 Ohm of resistance, L/R is 1 ms — sixteen times the PWM period, so the winding current is smooth and the motor sees an effectively DC average. If that ratio were the other way round, the current would be a triangle wave and the losses would be far higher.
I rated = P / V, then add margin for transients
250 W at 24 V is 10.4 A. The limit has to sit above rated current so normal acceleration is not clipped, and below the bridge's capability so a stall does not destroy it.
Fast enough for the mechanical time constant, slow enough for a clean speed estimate
The mechanical time constant of a small motor with a load is tens to hundreds of milliseconds. Sampling ten times faster than that is ample; sampling much faster only amplifies the quantisation noise in the speed measurement.
Stop integrating whenever the output is saturated
During a stall the error stays large and the integral term grows without bound. When the load is released, that stored term drives the motor far past the setpoint before it unwinds. Clamping is one line of code and it is the difference between a controller that works and one that overshoots wildly.
| Item | Qty | Unit cost |
|---|---|---|
BLDC motor 24 V, 250 W, with three Hall sensors | 1 | Rs 1,400 to Rs 3,500 |
Three-phase driver board Six MOSFETs with gate drivers, 30 A class | 1 | Rs 700 to Rs 2,000 |
Microcontroller board STM32 or ESP32 with hardware PWM and input capture | 1 | Rs 350 to Rs 900 |
Current sensor ACS712 30 A or a shunt with INA226 on the DC link | 1 | Rs 150 to Rs 450 |
Power supply 24 V, 15 A SMPS, or a 24 V battery pack | 1 | Rs 1,200 to Rs 3,000 |
Mechanical load Friction brake, or a small DC generator with a resistor bank | 1 | Rs 600 to Rs 1,800 |
Coupling and mounting Shaft coupling, base plate, bearing blocks | 1 | Rs 500 to Rs 1,500 |
Tachometer for verification Optical or contact tachometer Borrow from the machines lab if possible. | 1 | Rs 600 to Rs 1,600 |
Display and logging OLED display and an SD card module | 1 | Rs 250 to Rs 600 |
Fuses, wiring, enclosure Blade fuses, 4 sq mm wire, vented enclosure | 1 | Rs 350 to Rs 900 |
Specifications are written as ratings rather than brands, so any equivalent part works. Where a line says to borrow from the lab, do — it is usually the largest number on the page, and the total drops to Rs 7,697 at the low end without them.
None of these blocks you — they are learnable inside a semester. Each one you do not have costs a couple of weeks, so count them into your plan.
Anything marked required is a blocker, not a difficulty. Arrange the access before you commit to the project, not after.
Use these when your guide says the scope is too small, or when you want something in the results chapter that nobody else in your batch will have.
The structure below is what a project report is marked against, with the mistake that costs marks in each chapter. There is no template to download and there will not be one: the writing is your work, and a site that did it for you would be helping you cheat rather than helping you pass.
A mini project report runs to about 40 to 50 pages, and the literature survey is usually brief. Guides expect one clear objective, met and measured. A final year report is normally 60 to 90 pages with a substantial literature survey, and many departments expect a paper submission alongside it.
The full report guide — front matter, conventions and page countsOne paragraph covering what the problem is, what you built, and what the result was. Written last, even though it appears first.
Loses marks: Describing the problem and the method but never stating a result. If there is no number in your abstract, it is not finished.
Why the problem matters, the context it sits in, and a clear statement of the objectives your project set out to meet.
Loses marks: Objectives written so vaguely that nobody can tell at the end whether they were met. Write objectives you can tick off in the conclusion.
What has already been done, what each approach achieved, and the specific gap your work addresses.
Loses marks: A list of paper summaries with no comparison and no gap. The survey exists to justify your design choice, so end it by saying what you chose and why.
The system as a whole: the block diagram, what each block does, and the signal or power path between them.
Loses marks: A block diagram copied from a datasheet or another report. Draw yours to match what you actually built, including the parts that are inconvenient.
Every component value and rating, with the formula, the assumptions and the arithmetic that produced it. This is the chapter that distinguishes an engineering project from an assembly job.
Loses marks: Component values with no justification. If a resistor is 10 kOhm, the report must say why it is not 1 kOhm.
The circuit as built, the PCB or wiring, the flowchart, and the parts of the code that carry the actual logic.
Loses marks: Twenty pages of pasted source listing. Include the flowchart and the few functions that matter, and put the full listing in an appendix.
What you measured, in tables and graphs, compared against what you predicted in the design chapter — including where they disagreed.
Loses marks: Photographs of the working model presented as results. A photograph is evidence that it exists, not evidence that it works. Results are measurements.
Whether each objective was met, what the measured performance was, and what the honest next step would be.
Loses marks: Future scope written as a wish list of unrelated features. It should follow from a limitation you actually hit.
Every source in a consistent style, plus datasheets, full code listings and the complete bill of materials.
Loses marks: Citing a blog or a video where a datasheet or a standard exists. Cite the primary source for anything you relied on.
The demonstration is half the assessment. These are the questions this project invites, and the answers are written the way you would give them out loud.
A brushed motor commutates mechanically — the brushes and commutator physically switch the winding current as the rotor turns, so the switching is inherently synchronised with rotor position. A BLDC motor has no brushes, so the switching has to be done electronically, and the electronics need to know where the rotor is. The Hall sensors provide that position information.
Three Hall sensors spaced 120 electrical degrees apart give three binary signals, and of the eight possible combinations, two are invalid states that indicate a sensor fault. The six valid states divide the electrical revolution into 60 degree sectors, and each sector corresponds to one energising pattern of the three phases.
It accumulates the error over time, so as long as any error remains the controller output keeps changing. That is what drives the steady-state error to zero. A proportional-only controller must have a residual error to produce any output at all, so it always settles slightly off target under load.
Because the resolution of each method goes the opposite way. Timing the interval between edges is very precise when edges come quickly but becomes slow to update and noisy when they are far apart. Counting edges in a fixed window is steady at high speed but at low speed you might count only one or two edges, so the quantisation error is enormous. Switching methods at a threshold gives good resolution across the whole range.
Because a trip stops the drive, whereas a limit lets it keep working at reduced output. During acceleration or a temporary overload, clamping the duty cycle keeps the motor running within the bridge's capability and the speed loop recovers naturally once the load falls. A trip would shut the whole drive down for a condition that is often transient.
When the output is saturated the error persists no matter how much the integral term grows, so it accumulates a large value that has no effect at the time but must be unwound before the output can come back down. The result is a large overshoot when the constraint is released. The fix is to stop accumulating whenever the output is saturated, which is a clamp on the integral term.
Normally taken as a B.E. mini project (5th/6th sem) or B.E. final year project (7th/8th sem) project. If yours is a different course, the extensions above scope it up and the simpler half of the design scopes it down — the arithmetic does not change. Back to all projects.