Using a PE switch and Mosfet to operate a motor

Thread Starter

irozak

Joined Apr 3, 2015
24
In the ready state, the beam is unbroken and the motor is not running. Push & hold the button to start the motor, which will run until the beam is broken. Release button ready for next cycle.
A more desirable (but not essential) option is the same as above but push & release, i.e. motor will start then run without holding the button down until the beam is broken. I suspect this would need some kind of latching function.
Any advice/suggestions on the circuit before going any further is greatly appreciated.
Thank you
 

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LowQCab

Joined Nov 6, 2012
1,190
How do You propose to reverse the direction of the Motor ?

A full explanation of what You are trying to accomplish is needed.
What does this device do ?
Do You already have the hardware needed ?
How fast will the Motor run ?
Is it a Gear-Motor, or maybe a Linear-Actuator ?
Is a smooth start and stop required ?
What happens if the Motor is mechanically jammed or locked-up ?
Do You need Over-Current Stopping or Reversing ?
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Thread Starter

irozak

Joined Apr 3, 2015
24
I am using a mechanical beam balance to weigh very small quantities of powder. Firstly, the scales are hand loaded (~4 grams) to just under the target weight, then a "trickler" is used to trickle powder onto the scales to reach the target weight. This is done via a small vibrating tube connected to a powder hopper. The powder slowly drops onto the scales until the beam rises up into the PE cell and stops the trickler. The scales are then unloaded and the process repeated.
The motor is attached to the tube so it vibrates the powder out of the hopper at a very slow rate.
I figured a vibrator motor from a cell phone would be perfect. No need for soft star or stop.
It would be nice to have the device start its cycle with a single momentary push of the button rather than holding it down.
I don't have any hardware yet.
Thank you for responding.
 

LesJones

Joined Jan 8, 2017
3,523
I suggest using a small SCR in the negative feed to the motor. This SCR will be triggered by the push button. Use a PNP transistor (Or P channel mosfet) in the positive feed to the motor. The base (Or gate) of this device would be driven when the beam was not broken.
When the beam wasn't broken the transistor (Or mosfet) would be in a conducting state. When the button was pressed it would send a pulse to the gate of the SCR (Via a capacitor). This would trigger the SCR into conducting so the motor would start. When the beam was broken the transistor (Or mosfet) would stop conducting so the motor would stop and the SCR would return to the non conducting state as the current through it dropped bellow the holding current level. I suspect a small TO92 package SCR such as a 2N5060 would be suitable. The SCR type would have to be selected so it's holding current was less than the motor current.

Les.
 

Reloadron

Joined Jan 15, 2015
6,139
Normally done using a slotted optical switch. I have seen it done with plenty of home brew designs. Normally the powder feed tube is a rotating tube with a threaded inside diameter. 4.0 grams (61.7 grains) is a pretty large powder drop but easy enough. Anyway you may want to give this thread a read as it has plenty of good links to powder scale adaptions which do what you seem to be looking to do. There are also commercial digital flavor powder dispensers which do what you want to do. The RCBS Chargemaster and Chargemaster Lite come to mind as well as other manufacturers. I played around with doing this with my old Lyman M5 Balance Beam and my RCBS balance beam scales. You just want a slow speed (geared) motor to rotate your trickler. The link I provided should give you some ideas. I just modified a RCBS powder trickler when I experimented with the concept. I currently use an over the counter solution. You just program the desired charge and it does the rest. When it approaches the setpoint the motor slows and it can consistently hit +/- 0.1 grain. Most guys use a slotted switch as seen in the link from Omron but about any of them can work. An inexpensive DC gear motor will do just fine.

Off the shelf solutions like Hornady, Lyman and others come to mind but you can also roll your own. Also, using an SCR is a very good way to go as was mentioned. Momentary push button starts and when the beam breaks it stops. Dump the powder pan and start again.

Ron
 

Thread Starter

irozak

Joined Apr 3, 2015
24
Thank you both for the comments, and even better from a fellow reloader. Sure, off-the-shelf tricklers are an option but where's the fun in that. I can easily build it but my circuitry knowledge is very basic so adding SCR's and caps is beyond me. Any chance of getting some assistance with a revised drawing?
Andy
F-Class (fiddlers class)
 

Reloadron

Joined Jan 15, 2015
6,139
F Class huh? Would love to have 1,000 open yards in front of me. Then too, not as young as I once was.

I remembered another shooter in one of my shooting forums. He and I have had discussions about scales and powder dispensers. This is one of his videos and this is another. In the second video he is doing what you seem to be after. He throws a charge using what looks to be an RCBS Uniflow measure using VMD (Volume Metered Displacement) and lets the automated trickler finish things up. He also demonstrates how a single kernel makes a difference which is detectable. He goes by jmorris in a few shooting forums and is a real nice guy. I just assumed that like me he is a retired engineering type who loves shooting.

So what you may want to start with is an optical switch. You need to get a little creative with the mounting scheme but once it is set that part is done. You can see the tricklers used are just basic tricklers with a motor added. I would try by starting with a simple optical switch. Something like this where $10 USD gets you about 5 switches. Now if I recall correctly jmoris used pretty much just a few relays and switches along with a push button. Your beam of the scale operated the motor. Now better motors are more common in 12 Volt flavors so I would consider a 12 VDC system. What's nice is finding a motor which allows speed control only because it's a feature you may want later.

Staying basic and simple you get a low cost SCR (Silicon Controlled Rectifier) which is not at all a complicated thing. Think of it as a latching switch and once you push a start button it latches and the motor runs till your scale beam triggers a relay opening the motor circuit. Then your powder trickle is done and you repeat. I can likely cobble you out a basic motor circuit. Trick is finding a suitable speed gear motor. Too slow and it takes forever to get to charge weight and too fast they overshoot.

Now things can get complicated because if you want more features like adding a uC (Micro-Controller. But that can come later. Using a good throw as seen in the one video then trickling to top off the charge is a good and simple start approach.

So what is your cartridge in mind for F Class? While I have the guns like 300 Win Mag my days are pretty much done, hell even my 7mm Rem Mag kicks my butt or really boney shoulder. :) There are several threads on The High Road forum on this subject and also on Shooters Forum. I have seen and chatted with Jmorris on both of those. You can also find slow DC geared motors on Amazon.

Give me a few days and maybe I can cobble something together with a drawing and parts called out. I will try and keep things modular.

I figured this was about reloading. :)

Ron
 

LowQCab

Joined Nov 6, 2012
1,190
The biggest problem with this project are the Mechanical aspects.
Pushing a Button to latch-on a Motor,
and then having it turned-off by an Optical-Sensor is easy,
it's the logistics of creating that rotating/vibrating-threaded-feed-tube that's tricky.

I would recommend using a Large-ish MOSFET to directly control the Motor,
that way it would be very easy to add Adjustable-Speed-Control to the Motor.
I think this could be a very valuable feature.

The Motor could do double-duty as a Screw-Tube-Rotator, and Vibrator.
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Thread Starter

irozak

Joined Apr 3, 2015
24
Ron, I shoot 6.5 Creedmoor and I'm doing my best to upset the mainstream 308-or-nuthin culture at my club. There's nothing more exhilarating than popping X's at a 1000 with bullets that costs half as much to make, and with negligible recoil.
Anyway, in amonst the links you posted I saw this one which is EXACTLY what I want as it takes care of all the issues you mention. I found the original drawings and Fig3 shows the components but not the component value so I'm still short of a circuit diagram that I can follow.
The hardware and mounting of the PE's is not a problem as my RCBS beam balance has ample room.
I already have a bunch of small slow 6v motor/gearbox units that are perfect for the job.
The PE switches as you suggested, and I can stack them to suit the two motors.
Thank you. I appreciate it.
Andy
 

LesJones

Joined Jan 8, 2017
3,523
It looks like my suggestion is a case of re inventing the wheel. It is almost identical to the schematic in the link in post #9.
I don't think there is any advantage in using the slotted opto module in Ron's link as I think mounting just the bare slotted opto in the required location would be easier. There is also a wide range of sizes and physical designs of slotted optos to choose from.
Ron seems to be your best source of advice as he knows exactly what you are doing.

Les.
 

Reloadron

Joined Jan 15, 2015
6,139
OK since you have a motor for 6 V then 6 V it is. Now just so we are on the same channel your motor voltage is 6 V any idea what the motor current is? That is sort of important in component selection.

Next I looked at the schematics and yes, the components can be identified likely. However, here is a potential problem.
I can easily build it but my circuitry knowledge is very basic so adding SCR's and caps is beyond me. Any chance of getting some assistance with a revised drawing?
When building something with a handful of components / parts they all need to be mounted somehow. They need a circuit board to be placed on and even using a basic protoboard will require some soldering skills. This also requires some soldering skills and soldering tools. Now if you are good with that then we can take that route. I had in mind a simple relay type latching circuit. Sort of keeping things as simple and and modular as possible.

In the example given they are using two motors driving two tricklers. I have no idea why? Using my own unit I can drop greater than 50 grains of any stick powder in under 30 seconds and do it accurately. Just my thinking on the 6.5 Creedmoor which I don't shoot. Your best bullet choice is maybe a 140 grain match BTHP. You need to keep that bullet super sonic out beyond 1,000 yards because if it goes sub sonic before target it will become unstable as it drops from super to sub sonic. Pretty sure the guys in your club running .308 Win have stressed out over that. You will likely want a MV in excess of 2700 FPS. Going with a 120 / 123 grain bullet you can get the MV up there but I have no clue how a lighter bullet will perform at the distance. Mid range F there is a big window of suitable cartridges but when you get into Long Range F Class Open the guys I know are just about OCD over building high power ammunition. Like any match grade stuff the importance is absolute uniformity round to round. That includes the powder type and charge. With a 6.5 Creedmoor I don't see you dropping more than 45 grains of powder and doing it slowly and meticulously. I doubt the guys walking off the line with trophies rushed their hand loads. :) Anyway, I see no need for using two tricklers especially since you will be doing a powder throw followed by a trickler to top it off.

If you haven't quite worked out the motor drive to trickler using a piece of Tygon tubing can work well for coupling with a slight mis alignment. While motor speed control is real nice since you are only topping off a powder drop you will likely only be trickling a few grains of charge. When a gear motor stops it generally stops so I do not see you going over, at least my system never has. Again, the main idea here is repeatability charge to charge. Slow and constant drive is what you want.

So what works best for you as far as building a circuit? Also, do you know what your motor current and speed are?

Ron
 

sirkit

Joined Aug 24, 2008
1
Have you considered a small low voltage transformer with an open magnetic circuit set against your trickler tube instead of a motor? the voltage input can be set to give suitable vibrations and use relay to switch on & off, the relay can be operated with a simple mosfet circuit.
 

Thread Starter

irozak

Joined Apr 3, 2015
24
Ron
At 6v, my little robot gear motors are turning around 50rpm which is probably the max I need, and slows down real nice if I ever need to. Specs are...
no-load speed no-load current voltage,
6V ≤250mA 250 ± 10% rpm,
3V ≤160mA 110 ± 10% rpm
I have the tools and soldering equipment and I know how to use it, but it's when you guys get into the deep technical stuff that pulls me up. I am keen on the circuit shown in fig3 of those old drawings. This wouldn't be a problem for me to build if the details of components were shown.
A second high-volume feeder working alongside the trickler has the added benefit of a more controlled feed of the powder to the cup and less chance of bumping the balance. It would make the whole process automatic plus will enhance the accuracy of the load which as you rightly point out, is what it's all about. The Tygon coupler is a good idea.
I am using 41.5gr pushing 140gr VLD's with a MV of 2820 so at the 1000y mark I am still at 1500+ which as you correctly say, is where I need to be. Those VLD's have an exceptional BC, and I've got my eye on a slightly longer barrel with 144gr Bergers which have a better BC again so that should be interesting.
Thanks
Andy
 

LesJones

Joined Jan 8, 2017
3,523
To some extent I can see the reasoning behind the two motor system. I assume it works on the basis the the balance beam moves a small amount when the dispensed weight gets close the final value and stops the high feed rate motor. The low rate motor continues until the beam moves further and trips the second sensor. The thing I don't understand is that I would expect the beam to swing as soon as the dispensed weight exceeded the weight on the other end of the beam so it would trip both opto sensors at almost the same time.

Les.
 

Thread Starter

irozak

Joined Apr 3, 2015
24
Both motors start at the same time. The beam doesn't move until the bulk motor throws (say) 95% of the powder into the cup, then the beam moves up a few millimeters and trips its sensor. The second motor carries on dropping powder for another few millimeters then it trips.
The total beam movement at the gauge end where the sensors are is about 8mm and the beam itself is used as the opto interupter.
Andy
 

LesJones

Joined Jan 8, 2017
3,523
That is what I thought the intention was but I expected the beam to move all of the available free travel as soon as the weight of dispensed powder exceeded the weight on the other end of the beam. (Assuming the beam pivot was at the center.) It will depend on the design of the balance. Possibly some weight on the balance beam to bring it's center of gravity lower than the pivot point.

Les.
 

Reloadron

Joined Jan 15, 2015
6,139
OK, just so we are all tuned to the same channel, this is similar to what the thread starter has.

Typical beam scales for measuring smokeless powder charges.
Scales 1.png

Most scales like this allow setting desired weight to a 0.1 grain resolution. The scale in the upper image actually has 0.1 grain increments on the pointer. Most scales like this have a pointer span of one grain (+/- 0.5 grain) The pointer will not move until the pan weight is very close to the set point weight.

Below is a powder trickler and most look just like this.
Trickler 1.png

Trickler 2.png

The dispenser tube has an OD of about 0.311" (US Inch) and while hard to see the ID of the tube is threaded. As a user rotates the thumb screw powder (ball, flake or stick) travels down the tube and follows the threads dropping in the powder pan on the scale.

In this case the user wants to use a volume metered density device to throw a powder charge weight just below his desired weight. Then a trickler is used to get the exact desired weight. Rather than manually rotate the trickler thumb screw a slow little DC motor rotates the shaft. When the set weight is reached the motor stops. So we push a NO (Normally Open) push button to start the motor. When an optical sensor detects the beam is at zero the motor stops. That is the objective. Actually yes, the entire charge could be dispensed rather than "top off" a pre charge.

The drawings referenced several post back look like this. No values are given for the parts and this is likely because the actual schematic (Figure 3) Image 3 of 4 was submitted for a US Patent back in the mid 80s so it is merely a proof of concept. Resistors R1 & R2 are current limiting resistors for D1 and D2. Q1 and Q2 are receivers for the light emitting diodes. Today all of that is accomplished just using a modular slotted optical sensor. Based on the thread starter's motor specs a simple SCR (Thyristor) could be used and a small relay to break the circuit. The available motor is a 6 volt motor.

So we are all now on the same channel. :)

Ron
 

LesJones

Joined Jan 8, 2017
3,523
If a relay was being used then that could provide the latching function. I seem to remember a comment in the above links that advised against using open contacts for switching to avoid any risk of igniting the gunpowder.
I would think a sealed relay would be OK. The spec on the 2N5060 SCR is a max current of 0.5 amps so that would be enough to drive the motor. (The 2N5060 is a TO-92 package device. ) I was thinking of possibly a TIP32 for the PNP motor driver transistor. (That is just a suitably rated device from memory. I have in the past used some surface mount P channel mosfet that would also be suitable. I would have to look up the part number of them.)

Les.
 

Reloadron

Joined Jan 15, 2015
6,139
If a relay was being used then that could provide the latching function. I seem to remember a comment in the above links that advised against using open contacts for switching to avoid any risk of igniting the gunpowder.
I would think a sealed relay would be OK. The spec on the 2N5060 SCR is a max current of 0.5 amps so that would be enough to drive the motor. (The 2N5060 is a TO-92 package device. ) I was thinking of possibly a TIP32 for the PNP motor driver transistor. (That is just a suitably rated device from memory. I have in the past used some surface mount P channel mosfet that would also be suitable. I would have to look up the part number of them.)

Les.
The likelihood of a relay, even open frame relay igniting powder is about nil. I would not worry about it. When people are loading and handling powder they apply good work habits. The 2N5060 would handle the thread starter's motor. Smokeless Powder itself isn't really all that dangerous. :)

6V ≤250mA 250 ± 10% rpm,
3V ≤160mA 110 ± 10% rpm

Using two motors as mentioned we would use two. That or a single 1.0 amp SCR.

Ron
 
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