Airplane machine problem

The big picture, I'm building a machine that will fold and throw a paper airplane. I'm very close but am having a problem. I have gear motors moving belts that move the paper from one process to the next. I have mosfets switching the motors on and off, and switches or infrared sensors to know when to stop the motors. My problem is that the motors keep turning several hundred milliseconds after they are told to stop by the programing. My program is working exactly like i want based on serial outputs i put into each step of the program. my questions are about the wiring that is letting the motor keep going. I have capacitors at each motor and diodes to assist in pulling down the mosfets.

I don't know much about the part numbers of the mosfets capacitors or diodes. I could try to figure it out if you guys really want to know. I'd like to know if there are specific mosfets that will switch faster than others, and anything else i can do to stop the motors faster. I don't want to use encoders because I don''t have the money to replace the motors, and I need to account for the paper slipping and not being moved perfectly by the belts. below Is a video of my machine when I had it in my BFA thesis show I have made significant changes since then I hope it will give some understanding of my project. http://www.youtube.com/watch?v=ES53pFYZUCE

wow your pretty serious…
i dont think its your mosfets not turning off fast enough, its your motors spinning after they stop receiving power. like a car rolling down a hill–doesnt stop when you put it in neutral.

you would need some way to “brake” the motors. i would use stepper motors because they can turn to an exact point in a number of “steps”.

or you could use servos(continuous) you can send a stop command from arduino that will stop the servo and not let it spin down. maybe you could do something like that for your DC motors?

i would still use a DC motor for actual launching the plane and actions like that which dont require precision.

Assuming they are permanent magnet DC motors, the way to stop then quickly is to short them. If you post the schematic of the mosfet motor drive circuitry you are using, I may be able to suggest how to do this using additional mosfets. You might find that connecting a low-value resistor in parallel with the motor is sufficient.

I don't know what I would do with it, but your project does look great !

I was wondering whether it's possible to place the sensors a tiny bit "back". That way you might be able to detect planes before... a step in the assembly process is completed and gives you the possibility to add a short delay before you turn a motor off. By experimenting with the delay needed it may be possible to have the motors stop right on time.

sirbow2: wow your pretty serious... i would use stepper motors or you could use servos maybe you could do something like that for your DC motors?

Like I said I don't have money for more motors right now, and I've tried steppers in the past and they were too steep of a learning curve for me to handle under my time constraints. I had problems getting the torque I needed. I'm out from under those forces now but have opted for the dc motors because I understand them better. Maybe this problem is the reason to learn them...

dc42: If you post the schematic of the mosfet motor drive circuitry you are using,

Never done it, what should i use to make them nice schematics I see around here?

Simpson_Jr: I don't know what I would do with it, but your project does look great !

Thanks! It's kinda my thing, you summed it up nicely. :)

Simpson_Jr: I was wondering whether it's possible to place the sensors a tiny bit "back".

good point, but my ultimate goal is to make this thing bullet proof. there is nothing worse than daily calls from the gallery curator asking you come come back in because your art isn't working again. I'm trying to keep as much control as i can over the paper, leaving a gap like you suggest worries me. there are so many variables that I cannot concieve of that can cause paperjams. In my experience this solution works for a while and then i discover that i will have to fix it again later.

I have to say that I am very impressed with the knowledge and kinship that I see here and around Arduino in general. I hope to be the one giving the help soon.

To create schematics you could download the trial version of Cadsoft Eagle at http://www.cadsoftusa.com/ for free. Besides schematics you can also use it to design PCBs. Limit of the trial version is the size of the PCBs. It takes some getting used to, but it's a great tool and well known program.

I must say personally I'm not much of an motor/robotics-man (yet). Several 100 milliseconds is like centuries for an arduino, you could time the delay in microseconds. But... if the paper moves a little slower/faster as standard visitors of the gallery may indeed see the creator often.

I hope to be the one giving the help soon.

Inspiring others = helping, you're already busy... ;-)

I don't know whether it's part of your plan yet, it could be fun to put a few printed sheets in the stack of paper. Dimensions of the planes will stay the same, but they could all look different in theory.

It doesn't have to be a neat schematic, you can draw one by hand and scan it if that's easiest for you.

dc42:
It doesn’t have to be a neat schematic, you can draw one by hand and scan it if that’s easiest for you.

Good to know, but it may be unnecessary. I was thinking about your “short it to stop” idea. I have some l298n h-bridges, left over from trying to use stepper motors, I just hooked them up so I can run the motors backwards for 50 Millisecs to stop and try to remove the spin down movement of the gear motors. Also the ability to run the motors backward will be helpful in removing paper jams.

Thanks for you help, you caused me to re-think what i was doing, which lead to a solution. I’m planning on putting up video when it’s working, I’ll link it here when Its up.

nate

That is a great project!

One suggestion I'd make is to use a positive end stop where possible, rather than relying on the transport system to give an accurate position. For example, when you move it forwards prior to folding each wing you could fit a positive stop on the side that is about to be folded, designed so that the folded wing can clear it. (Just a pin sticking up, that can be pushed aside by the taper of the wing leaded edge, would do.)

When you need to stop the motors why don't you just reverse the current momentarily so it starts to spin backwards then turn the power off befor it turn backwards.

just saw this article on hackaday. seemed pretty relevant http://hackaday.com/2011/10/28/motor-drivers-half-h-bridge-with-brake-and-more/ hope it helps

Things are gong swimmingly, I'm fixing little things all over the place, This is what I love to do. I want to put a signature of sorts on each plane. I'm thinking a dot matrix style ribbon inked print head. I want to print my name and a plane number. I think it could work as the paper is moving into the first folding station, or as a stamp it each as the paper is stationary. but i'm not sure what to use, so thoughts please...

Dot matrix print heads that rely on smacking pins into a ribbon are going to be fussy about positioning, and messy.

If you can find an old black/white ink jet you might find that's more user-friendly. Mind you, I have absolutely no idea how to drive an inkjet print head. Would it be too boring to get an old serial printer and use that as your paper stack holder and sheet feeder? It would be a charmingly simple and effective solution to deliver paper to your folding machine on demand, as well as getting you your printed planes. The serial output to trigger printing and page feeds would come, of course, from the Arduino.

Apparently Nicholas C. Lewis did get an inkjet print-head working with his arduino. It can control several heads with one Arduino, it’s open source and may… be quite interesting to use in the air plane factory.

http://nicholasclewis.com/inkshield/

It does lack the noise of an inked-ribbon solution though, hearing the sound of an ancient round typewriter print-head (or something similar) hitting the plane during production might be fun too.

what an excellent looking machine

if I may suggest a small enhancement... when I was a lad we used to fold the nose back about 1 cm before folding the body the extra weight improved the aerodynamics a lot!