Question on measuring speed of DC motor in treadmill application - Page 1
Forum section: electronics / projects

author: XaviPacheco
author_rank: Regular Contributor
timestamp: October 12, 2018, 03:48:37 pm
content: The DC motor speed in treadmill applications is usually geared down like shown below:https://www.gymparts.co.uk/user_resources/images/shop/os65f/575/994.jpgThe reed switch actually measures the slowed down speed, but not the actual speed of the motor. Is there any mathematical concept I can apply to find out the real speed of the motor? I once saw a motor using two sensors, the reed switch and an optotransistor directly on the motor. But I don't see a way to plug another sensor on my motor since there's not physical structure for it.

author: ataradov
author_rank: Super Contributor
timestamp: October 12, 2018, 04:47:54 pm
content: The real speed will be faster by the ratio of diameters of two pulleys.

author: perieanuo
author_rank: Frequent Contributor
timestamp: October 12, 2018, 04:55:11 pm
content: Put an optical sensor reflexive next to motor pulley, stick some reflexive aluminium on the motor pulley,count the pulses with an microcontroller.demultiplication gets you there also if you multiply readed frequence with divizion ratio,but puts error (the motor needs to turn several turns,meaning divizion ratio) in order you to see it with the sensor on second pulley.go with the first method (you can use a hall sensor if it's dirty mechanic stuff).Envoyé de mon iPad en utilisant Tapatalk

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 12, 2018, 05:11:08 pm
content: It should be trivial to find the ratio of the gears or pulleys and then simply multiply the value by the ratio.And the same principle for the linear speed of the belt surface. They are all a simple, fixed ratio.

author: XaviPacheco
author_rank: Regular Contributor
timestamp: October 12, 2018, 05:38:45 pm
content: Quote from: Richard Crowley on October 12, 2018, 05:11:08 pmCan you provide an example, or give some references to read?

author: Richard Crowley
author_rank: Super Contributor
timestamp: October 13, 2018, 12:37:06 am
content: WITH THE TREADMILL DISCONNECTED FROM ANY POWER (FOR SAFETY)!Put a mark on the motor pulley. And another mark on the tread pulley.Turn the motor pulley how ever many turns it takes to make the tread pulley go around once.That will give you the ratio of the motor to the tread pulley (where your sensor is).For example, if it takes 12 turns of the motor to turn the tread pulley once, then your ratio is 12:1 ("12-to-1")Each time the tread pulley goes around once, (as indicated by your sensor) the motor has turned 12 times.So, take the RPM of the tread pulley and simply multiply by 12.In the same manner, you can put a mark on the tread and count how many turns of the tread pulley to get 1m of movement (etc.)By that method, you can calculate linear tread speed, etc.If you watch the tool reviews/teardowns on the YouTube channel of "AvE", you will see him do this often.He will put a mark on the motor shaft and count how many revolutions it takes to make one turn of the drill chuck, (for example).

author: XaviPacheco
author_rank: Regular Contributor
timestamp: October 13, 2018, 02:04:18 am
content: Quote from: Richard Crowley on October 13, 2018, 12:37:06 amMakes sense. Thank you!