How to measure DC motor specs: torque, speed, current, and power

Measuring the specifications of a DC motor of unknown torque/power.
Measuring RPM, then Measuring Torque to create a torque/speed curve for the motor.
DC motors are pretty much linear , the faster they turn, the less torque they have. Max torque occurs at stall (as does maximum current)
Drawing the torque-speed curve can be done by measuring the no-load top speed and then measuring the stall torque. Now any point along the graph can give you an estimate of the motor's speed and the torque at that speed.
The torque speed "curve" can also give you an estimate on how much current draw the motor will require.
You can caculate the actual mechanical output power of the motor by using the RPM and the torque together.
Be aware that maximum EFFICIENCY, where the electrical energy is converted maximally to mechanical energy, isn't at the same point of maximum motor mechanical power. Typically max efficiency is around 75% of motor's no load speed.
This particular motor could no doubt put out up to even 140watts with higher voltages.
The best way to measure would be to use a dynamometer, or a "ponybrake", but I have not built one of those yet, so doing it this way will work to give you an estimate of what the motor can do

[@throbscottle6023]

I've been finding speed of motors pretty accurately with opto interrupter and frequency counter, but torque had me completely stumped, so big THANK YOU for this :)

[@NadimC137]

amazing idea to calculate rpm !!!

[@md.arefinrabbiemon5658]

Bhai

[@yiulambb]

yes but he just adds 3000rpm to it because of a tape? and the last part even increases it by another 2000 to 20000.

[@wchen2340]

great approach. simple, hackish and with a reasonable accuracy. plus extra love for the loudness warning from me.

[@oscar3611]

It is more easy to measure the audio frequency with an app like Spectroid. Just use your phone, watch the spike in the audio spectrum, and convert the hertz to rpm. 1 Hz is 60 rpm.

[@alirezaabbasimoshaei8726]

Great

[@vincentrobinette1507]

When using resistors, be sure to read voltage at the motor terminals, rather than the source. Otherwise, you're also measuring the wattage dissipated by the resistor, as well as the motor. Be careful, with current. The torque of a permanent magnet motor is limited by the field strength of the magnets. It's possible to saturate the motor, a condition where the armature is as strong as an electromagnet, as the permanent magnets. Applying more current will not result in more torque. If too much current is applied, not only does it heat the brushes and windings, it can actually alter the flux of the magnets, weakening the motor. If that happens, the motor won't produce as much torque as before, but, it will spin faster on less voltage, due to lower back EMF.

[@researchandbuild1751]

Good point, i did not think of saturation. However that really didnt affect my results here since i calculated mechanical power not electrical. I only ever measured current and didnt care about the voltage

[@vincentrobinette1507]

@@researchandbuild1751 When measuring torque, current is the only thing that matters. More voltage just means it will produce the same torque at a higher RPM.

[@Telectronics]

@@vincentrobinette1507 So when you control the current of the motor you limit to a precise torque value right ? I want to build an electronic screw fastener not like a cordless drill with torque that is shown on a display.

[@aguirre689]

Uauuuu !!!. Congratulations. What ingenious idea to measure rpm quickly !! Very, very good !

[@researchandbuild1751]

I actually go the idea from another youtube video and wanted to demonstrate it

[@gianlucamodenese2574]

***** was it a rulof video?

[@researchandbuild1751]

gianluca modenese i dont recall the author

[@vincentjr8013]

Which software is this?

[@researchandbuild1751]

@@vincentjr8013 this is using software called Audacity, open source, free

[@joseedwards1214]

impressed. although i may be even more if i understood any of it :)

[@muhammadmoizimran5384]

Hi there, great video! My question is can we do same for bldc motors? Kindly reply

[@ge13r]

Muchas gracias, de verdad muy ilustrativo y justamente algo asi andaba buscando para mas o menos caracterizar un destornillador electrico que estoy pensando hacer pero que tenga la opcion de torquear el tornillo, no se si sea algo muy ambiocioso pero bueno, la maxima es aprender. Saludos desde Tachira, Venezuela!!!

[@barrycarter7965]

Could you try and make the calculation procedure even more incomprehensible

[@user-pg9ms7zn8v]

amazing idea to calculate rpm!

[@kylestevens1217]

Great simple video for those who don't have access to current clamps! What AWG size wires did you use to make your measurements? Are they just 22-AWG wires?

[@researchandbuild1751]

Hi, ya I think two of them may have been 18 GA but the rest are simple 22GA, so they do have some resistance of their own that can lead to some inaccuracies at high currents. I used the 18GA clips on the motor to have less side effects

[@QuentinQuark]

What a great little video! Could I trouble you for some help understanding the shunt resistor pair, how/why do they work and how/why do they not affect the readings you are trying to measure? Thanks!

[@researchandbuild1751]

Hi. The "shunt resistor" is the big black thing with two screws on each side. What this is, is a very very small resistance, like 0.001 ohms or so. This allows me to measure very large currents (up to 50 amps) without affecting the circuit itself by limiting the current. The digital display connects across the shunt resistor and coverts the voltage drop across that resistor into a current reading The pair of power resistors (the gray things) I was using to *purposefully* limit the amount of current in the circuit since without them the motor would draw up to 24 amps or so and it would get hot and start to burn , in fact started to pour out smoke. The wires in the motor couldn't handle 24 amps. So I put the pair of power resistors, they are 1ohm resistors, two of them in parallel, to create 0.5 ohms. This would limit the maximum amount of current in the circuit to not get above 13 amps or so and keep the motor from burning out.

[@Yorumcu63]

I must watch again

[@finophile]

Excellent tutorial, thanks. I note you're also a left hander. No wonder :-)

[@ArmRehabHands]

I want to know how to you decide for the weight in the stall torque calculation. Was it maximum?

[@RixtronixLAB]

Nice info, thanks

[@vinayakbhatjire8537]

Thanks,bt What happen with vtg,at starting of motor,when current is maximum..vtg is min or also max???

[@nicholasrobinson5072]

Hello. Are you able to help me understand the performance of a small geared DC motor / generator and talk about the necessary things in my conclusion of I were to show the results please?

[@Friendroid]

Refreshingly clear while concise, thank you! Question: is it true that some of these motors draw a higher current while they're starting? Why is it so? Or is it common to all dc motors?

[@researchandbuild1751]

All electric motors draw a high current when starting. This is because once the motor starts to turn, it generates what is called "back EMF". The motor windings are still turning through a magnetic field which as you may know, causes an electric current. This current actually opposes the current you are putting into the motor. Because of this, the higher the RPM, the less current the motor draws. A stalled motor that is not turning will draw maximum current (voltage/ the resistance of its windings) that is why a stalled motor can get very hot and become damaged.

[@Friendroid]

@@researchandbuild1751 very well, thank you. I have two 540 motors taken from handheld vacuum cleaners that behave differently. The one that is harder to rotate with my fingers pulls so much current when starting that my 12V power supply cant make it turn when I simply connect the leads to it. It does gradually start when I use a motor controller (555 timer+LM358 to create the square wave that turns on the N-channel Mosfet).

[@talen7111]

What was the small motor in the thumbnail? Called?

[@pinakiojha8524]

wah mushadi kamaal kar diya tune.

[@yosef-yosef9414]

hi hello, how to make a dc motor stronger? because i rewind my dc motor from thin wind coil to Thicker winding coil, when no load, it's working, when i place remote card on the ground, it's not moving it can't carry load. thank you so much for those who will answer 😟

[@numbernine888]

I can use this for a physics lab class.

[@testingbeta7169]

loved the noise headsup.

[@niazmuhammad3654]

What is the formula of winding calculation and find out the wire size calculation in dc machine

[@manuel56354]

Nice video!

[@ayushmanjain4008]

When I recoiled my brushed motor with a thicker enameled wire,t hen it's RPM rose but torque reduced.How can I change the coil to increase both torque and RPM?please tell me

[@vincentrobinette1507]

More turns of wire mean it produces more torque at lower RPM at a given voltage. It's called impedance. No matter how the motor is wound, the torque is limited by the field strength of the magnets. Fewer turns of heavier wire, lowers the impedance of the motor, so it will need more current to produce the maximum torque, but you don't need as high a voltage to get the speed. You effectively reduced the voltage rating of the motor. It's still just as efficient, it just wants less voltage, more current.

[@researchandbuild1751]

@@vincentrobinette1507 thanks for the great explanations

[@user-lm6rp8cv2g]

How did you calculate the 10.000 rpm in the end kai the 75watt ?

[@researchandbuild1751]

I knew someone would ask that since I FORGOT to include it! Basically Power is work over time. And work is energy over distance - so you can use torque and RPM to calculate mechanical power The 18,000 RPM is full speed of the full speed of the motor, and 20oz-in is the full torque. DC motors are linear so halfway down the line (where max mechanical power will be) you will be around 10,000 rpm and 10oz-in torque. To figure out the mechanical power at that point I used these calculators online: First, convert oz-in to N-m here: www.convertunits.com/from/oz-in/to/N-m Then take the N-m and the RPM and plug them in this calculator here: planetcalc.com/1908/

[@user-lm6rp8cv2g]

Thank you very much .

[@climatechangepreppersfaceb2148]

Is it the same for ac motor?

[@gjracing5595]

I find that the .004 (from video) for determining RPM isn't accurate enough. Is there a way to increase the precision? I'm using Audacity and I can't figure out a way to get a more precise time measurement.

[@Fisicracks]

Try to increase the sample rate of the audio to increase the number of points of measure, most of the times we record audio at 48Khertz, increase it at double at least I don´t know if a I understand correctly your question

[@m0ther_bra1ned12]

In this DC series circuit, there is a 24V battery, an 8-ohm resistor, an electric motor, and 1amp going thru the circuit. What is the maximum amount of weight this motor can lift 5 feet in 30 seconds? Show work...

[@sachinattri3800]

Sir, which moter you used in this practical.. tell me the name ????. How much current it's produced ???

[@yousifalqallaf8095]

But the torque? :D

[@vmm4610]

Nice work

[@gavohsachibani2412]

Sir I use resistor and it control the current flow. Our wires and motors does not get hot but the resistors got hot. Do we need to use high ohms resistors or what is the solution sir?

[@researchandbuild1751]

You should get high wattage rated power resistors. The higher wattage ones actually have a metal case with fins on them for better cooling

[@IamOmkarD]

hey, Thanks for sharing the knowledge. Actually I wanted to know what would be the difference in torque of a 6000w hub motor with 28v/36v voltage rating and what battery I would require to run this motor. Thanks in advance for your reply.

[@researchandbuild1751]

a Watt is pretty much one newton meter per second, or about .224lbs - 3.2feet / second. So for example if you lifted a 1000lb weight at a rate of 1 foot per second that would be 224Newton - .3084meter / second, which would be 69 Watts. So you can see a 6000Watt motor is a LOT of power. It's going to have massive torque. Battery would need to be very large - Watt = Voltage * current, so at 28Volts you need 214amps, that is going to be pretty tough to deliver, you would need very thick wires for that. Better to use higher voltage for less current needs

[@IamOmkarD]

Research and Build thanks.. There's one more thing. there's a bicycle named Kraken 2.0 which has dual 6000W motor. Could you please analyse what battery they have used and inform me. Thanks in advance!

[@researchandbuild1751]

Wow, that's crazy! Although, I think that is only about 14 horsepower when it comes down to it (1HP = @750watts) In one of their screenshots it looks like the battery pack is running at 96V. So to get 600 watts at 96V volts it would only take about 6 amps - but the thing is, usually electric motors are powerful with AMPS and not Voltage. So it's a bit hard to say what current they really run at. I would guess the batteries are probably LiPo batteries, being two reasons: LiPo are very light for the energy they store, and: LiPo can output huge currents without damage. They *may* be Li-Ion but I'd bet they would be LiPo.

[@raguramangvignesh]

nice video sir

[@researchandbuild1751]

Thank you, I hope it's helpful in some way

[@jeanpierredaviau7478]

What's the use of the ounces? What do you calculate with that number? You get 20 ounces at x amps and y volts?

[@researchandbuild1751]

I was using ounces because most small motor specs are in oz-in. So its a good way to compare the unknown motor to other motors even ones you find in online catalogs

[@gavohsachibani2412]

Is it possible to connect power resistors with motor directly without shunk resistor and lcd

[@researchandbuild1751]

Yes, just remove the shunt resistor from the circuit and keep everything else the same

[@climatechangepreppersfaceb2148]

Hi, how about peak efficiency?

[@ravikoushik4176]

Where we get 12v dc motors

[@vincentrobinette1507]

You need an accurate way to measure torque, to get efficiency. You can get close, by determining the DC resistance of the motor, then, multiplying that resistance with the current squared. That tells how many watts of heat is dissipated by the motor. Subtract that from the total wattage drawn by the motor, then, just simply divide that loss by the total power, and that will give you your approximate efficiency. Be sure to measure voltage at the motor terminals, so you don't add the loss of resistors, or losses in the wires connecting the motor to the power source.

[@anshulagx]

Beautiful....

[@yiulambb]

Is it the same if i use a battery for power supple plus a rc speed controller

[@researchandbuild1751]

rc speed controllers are most of the time designed to run brushless DC motors. The motor I have in this video is not brushless

[@welshpete12]

No, Some speed controllers are designed to be used by brushed motors . @@researchandbuild1751

[@yiulambb]

@@researchandbuild1751mine is also brushed, a 540J dc motor and a Tamiya esc tble-02s.

[@hewelgeduwelbeh7418]

please, how do you measure torque?

[@yiulambb]

Any connection diagram?

[@Bananananamann]

You wont be able to measure RPM higher than 20k with this method, depending on the sampling frequency. Your motor will always make some noise so you may not be aware of the fact that you arent measuring the real thing. Dont get me wrong, its a good method, but you gotta know its limits.

[@researchandbuild1751]

Thats a good point i didnt think of, thanks.

[@Shubham-po2tp]

@@researchandbuild1751 Please tell me is it true Motor will eat as much we give Means if I connect 3000mah battery , Battery can draw 10 amp constant Motor will eat all 10 amp Do I need to attach power resistor Pen signal

[@breezetix]

What if the motor was at like 100,000 rpm? I tried this, measured it. 60/0.001 is 60,000 rpm. How do i measure a motor rpm that is more than 60k RPM and only 0.001?

[@sk.taohidahmed585]

Please make free generator. I want to see

[@karanpandey1602]

@@sk.taohidahmed585 There is no free energy because It will break the laws of Thermodynamics.

[@samanthawayne728]

I need a dc motor that can generate the most power at 1600rpms anyone know of a good model? I am not sure on how to even find one. Something small would be best!

[@ucronotopia1988]

www.igus.eu/e-motors/electric-motor

[@jeanpierredaviau7478]

When you measure with no load, do you use the resistors?

[@researchandbuild1751]

yes I still kept the resistors in there to have consistency

[@joew4202]

Is there a reason you aren’t talking ?

[@pacerodi]

You said the motor came from a battery drill. Somehow, you omitted, battery drills, have, from 1, to 4, planetary gears, in order to make it to have more torque. I busted my wrist with an 18 volt, Makita drill.

[@researchandbuild1751]

That's right, a drill will have higher torque with lower speed (RPM). But the "power" output is the same. So for example a 100watt motor will give you high torque/low speed or low torque/high speed. A drill is somehwere probbaly near the low end of the speed curve, so it can have more torque. The planetary converts much of the RPM to torque instead

[@ArcanePath360]

I like maths but maths doesn't like me

[@alibacanak8711]

i am not understand plase suggest a book !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1

[@blazingblazers14]

Electric machinery and power system fundamentals by Chapman is helpful for understanding electric machinery and power systems

[@venomgaming7181]

What is that on motor

[@researchandbuild1751]

I wrapped tape around the gear that is on the shaft so it would be thick enough to fit into the hole in the wood arm used to measure weight

[@jeanpierredaviau7478]

Can we say 20 ounces * 12 / 16 = 15 pounds/feet?

[@researchandbuild1751]

No, it would be much smaller than that. The way torque works is, the number will get smaller as the distance gets larger. So, 20oz-in. to ft-lb, you would first divide 20oz-in to get lbs, so 20/16, now you have 1.25lb-in. At 1 foot, that's 12 inches, so you have 1.25/12, so you would have .1046 lb-ft of torque

[@gawrbage]

nice video, but i recently started to suffer severe brain damage due to the fact you are using troglodyte units (such as fluid ounces incher shit) instead of civilized units (Newton-Meters).

[@genericpieceofbread25]

This man speaks the truth

[@researchandbuild1751]

Haha good point.

[@flashingsword]

Lol. Foot lbs! Degrees! Gallons! Are you bleeding from your ears yet?

[@oz93666]

ounces and inches !!!! give me a break ...how can you work with those stupid measurements !!! I'm a UK citizen , but imperial system is a blight on the Earth .... only the US still cling to it .