Help sourcing the right Motor

Hi,

I am not 100% if this is the right forum so sorry if it isn't.

My application is a vehicle wiper. The existing wiper motor is 24VDC brushed motor and I need to replace this motor with a brushless motor, or a motor that does not create sparks. The existing motor is 0.4Nm 3000rpm , after gears (worm gear 1:75) it goes to about 40rpm and 5Nm.

So I have 24V supply, and need to rotate a wiper, I can use the same gears, so I need a non-sparking motor to deliver 0.4Nm, 3000rpm, or 40rpm at significantly higher torque, my complete guess would be between 1-1.5NM if I was going to hook up the motor directly to the wiper swing arm. Budget approx £90

So far I have looked into AC motors, thinking I can invert the 24V to AC and run an AC motor... however I have been unable to find a suitable AC motor.

I have been trying to find regular BLDC motors, but they don't seem to have enough torque within the price range.

Steppers are where I seem to have found appropriate motors, both to potentially drive the wiper directly, or with the gears. https://www.amazon.co.uk/gp/product/B071CN9VCW/ref=ox_sc_saved_title_1?smid=A2X0W2ER79JKG8&psc=1 The above motor boasts 1.2Nm holding torque, though I am not sure what torque I will get at 40rpm, regardless, I can hook this up to the existing gears and at 3000rpm, I think I'll be able to generate sufficient torque to move the worm gear. The problem I have with this particular motor is that I cannot find a suitable driver for it. This motor is rated at 2.8A/phase, and the A4988 for instance is rated at 2A max. I can find 15A drivers but they are very expensive, well over the budget for the drivers + motor + coupling and bracket I will need to make to attach the motor.

I am really ripping my hair out. Hoping a kind soul will be able to point me in the right direction.

P.S. It is worth noting that I do not need precise movement. I just need rotation at the desired rpm. At this point do not even care if the wiper stops in the middle of the screen when turned off, I can implement "auto park" functionality with hard wiring and limit switch.

It seems a strange requirement to need to replace a functioning brushed motor. What problem is it causing?

With a brushless motor you will also need an electronic speed control so make sure you budget for that. Poweful brushless motors are commonly used for model aircraft. Maybe have a look at the Hobby King website.

Stepper motors generally run slowly compared to DC motors. They are intended for precision rather than speed.

The A4988s stepper driver is probably good for about 1.5 amps. The DRV8825 is a little more powerful. Once you go beyond about 1.8 amps you are generally looking at expensive commercial stepper drivers. There are some drivers using TB66xx chips that can manage up to about 3 or 4 amps so might just about be capable of driving a 2.8 amp motor.

...R Stepper Motor Basics Simple Stepper Code

Robin2: It seems a strange requirement to need to replace a functioning brushed motor. What problem is it causing?

With a brushless motor you will also need an electronic speed control so make sure you budget for that. Poweful brushless motors are commonly used for model aircraft. Maybe have a look at the Hobby King website.

Stepper motors generally run slowly compared to DC motors. They are intended for precision rather than speed.

The A4988s stepper driver is probably good for about 1.5 amps. The DRV8825 is a little more powerful. Once you go beyond about 1.8 amps you are generally looking at expensive commercial stepper drivers. There are some drivers using TB66xx chips that can manage up to about 3 or 4 amps so might just about be capable of driving a 2.8 amp motor.

...R

Thanks Robin. The motor needs to be replaced because it is for a hazardous area. To protect a sparking motor, rough cost price is £800, which we sell at £1400. This is what we do currently. But if I can source a brushless motor, protecting it would cost under £100. So my cost price of the motor + interface + bracket + driver + attiny could potentially be under £300, especially since I can 3D print the interface. I am going to order the motor and driver today and start testing but need a place to start without spending too much money on R&D.

destructoboy: Hi,

I am not 100% if this is the right forum so sorry if it isn't.

My application is a vehicle wiper. The existing wiper motor is 24VDC brushed motor and I need to replace this motor with a brushless motor, or a motor that does not create sparks. The existing motor is 0.4Nm 3000rpm , after gears (worm gear 1:75) it goes to about 40rpm and 5Nm.

So I have 24V supply, and need to rotate a wiper, I can use the same gears, so I need a non-sparking motor to deliver 0.4Nm, 3000rpm, or 40rpm at significantly higher torque, my complete guess would be between 1-1.5NM if I was going to hook up the motor directly to the wiper swing arm. Budget approx £90

So far I have looked into AC motors, thinking I can invert the 24V to AC and run an AC motor... however I have been unable to find a suitable AC motor.

No, that's not going to end well - for most of the types of mains AC motor I can think of.

I have been trying to find regular BLDC motors, but they don't seem to have enough torque within the price range.

You need a gear motor if you want the extra torque, torque is a property of the size of the motor, so isn't an independent variable until you add a gear train or equivalent. Basically both power and torque depend on size. So you can't find 0.4Nm motor on your budget? What is the budget for motor and controller? You know you'll need a controller for a brushless motor?

Steppers are where I seem to have found appropriate motors, both to potentially drive the wiper directly, or with the gears. https://www.amazon.co.uk/gp/product/B071CN9VCW/ref=ox_sc_saved_title_1?smid=A2X0W2ER79JKG8&psc=1 The above motor boasts 1.2Nm holding torque, though I am not sure what torque I will get at 40rpm, regardless, I can hook this up to the existing gears and at 3000rpm, I think I'll be able to generate sufficient torque to move the worm gear. The problem I have with this particular motor is that I cannot find a suitable driver for it. This motor is rated at 2.8A/phase, and the A4988 for instance is rated at 2A max. I can find 15A drivers but they are very expensive, well over the budget for the drivers + motor + coupling and bracket I will need to make to attach the motor.

Steppers are very much less efficient than any other kind of motor, they come into their own for position control - for a wiper you'll get annoying vibration too with a stepper, as well as greater power consumption.

I am really ripping my hair out. Hoping a kind soul will be able to point me in the right direction.

P.S. It is worth noting that I do not need precise movement. I just need rotation at the desired rpm. At this point do not even care if the wiper stops in the middle of the screen when turned off, I can implement "auto park" functionality with hard wiring and limit switch.

This might be the kind of product to look at:http://www.motioncontrolproducts.com/motors/brushless-motors-with-integrated-electronics.php?cat=4

(It annoys me how coy manufacturers are with their prices)

MarkT: No, that's not going to end well - for most of the types of mains AC motor I can think of.You need a gear motor if you want the extra torque, torque is a property of the size of the motor, so isn't an independent variable until you add a gear train or equivalent. Basically both power and torque depend on size. So you can't find 0.4Nm motor on your budget? What is the budget for motor and controller? You know you'll need a controller for a brushless motor?Steppers are very much less efficient than any other kind of motor, they come into their own for position control - for a wiper you'll get annoying vibration too with a stepper, as well as greater power consumption.

Hi Mark

Thanks for replying. Yes indeed that is why I went to BLDC motors first. I definitely agree with you, steppers is not the way to go, BLDC is what I should be looking at.

I already have a gear box, just need to find a motor and controller to run it. I will go through the website you suggested. I just wish the websites would be more helpful recommending the controllers with their motors and put up prices as well.

Hey guys. I managed to find one that should work perfectly https://uk.rs-online.com/web/p/dc-motors/5366024/

The drivers I am seeing are like £30+: https://www.amazon.co.uk/WS55-220-Brushless-Spindle-Driver-Controller/dp/B07HB1TBGT/ref=sr_1_2?ie=UTF8&qid=1543331421&sr=8-2&keywords=brushless+dc+motor+with+controller

Do you know of any cheaper ones? Especially since the motor I'm after is under 100W and this driver is rated 500W.