Stopping a BLDC motor

[Trey Tull]

On my conveyor, there is a sensor that when it detects a pen, it turns the BLDC (brushless dc) motor off and then it triggers the laser. Just stopping the motor is an issue b/c sometimes the belt will rotate backwards ever so slightly and when it happens, wellll the part gets scrapped. What I need to happen is for the controller to stop the motor but hold its position. Sort of like locking it in forward and reverse at the same time.

Are any of you guys good with bldc motors and schematics?

Thank you!!

[Bill George]

Cogged belt? Make up a simple ratchet out of a spring and a perhaps a clothespin? The wood clothespin rides on the belt held down by a slight spring pressure or just the weight. The belt can't turn backwards with the pin in a cog. Some adjustments may be needed.

[Trey Tull]

I was overthinking it. I’m going to incorporate a sprag bearing into the setup.

[Bill George]

I was overthinking it. I’m going to incorporate a sprag bearing into the setup.

Or a DC solonoid like a car door lock opener as I used to trip a remote cray trap thrower. Its powered up off the belt when the motor is powered, drops when power is turned off. About 6 bucks or so each on eBay.

[Gary Hair]

I'm surprised they don't use a stepper for that, it could turn just as fast and give you way more accuracy than a bldc.

[Trey Tull]

I'm surprised they don't use a stepper for that, it could turn just as fast and give you way more accuracy than a bldc.

I thought the same thing. Sprag bearings will be here Thursday, so I’ll report back once it’s back together.

[Kev Williams]

If the 'ever so slight'-ly distance it moves isn't so much the main issue, as say, the machine engraving WHILE it's moving leaving you with gobbledygook-- you can set a delay time for the laser to fire (in the F3 parameters)... It will delay every time, which does add up after awhile, but so does the frustration and cost of screwing up parts

My new fiber engraved my finger the other day, a 200ms delay would've prevented it

[Trey Tull]

If the 'ever so slight'-ly distance it moves isn't so much the main issue, as say, the machine engraving WHILE it's moving leaving you with gobbledygook-- you can set a delay time for the laser to fire (in the F3 parameters)... It will delay every time, which does add up after awhile, but so does the frustration and cost of screwing up parts

My new fiber engraved my finger the other day, a 200ms delay would've prevented it

I have thought about that. I engraved my hand when I first started messing with the conveyor. I didn't know what was going on and thought I was being shocked....it was funny after the fact.

[Trey Tull]

Update - the sprag bearings did the trick. It was tricky getting them in b/c the housings needed to be keyed and it was an odd size key. As you would imagine, I didn’t have key stock any in that size, so I had to make some. Anyway, it works and keeps the belt from moving backwards.