Author Topic: REALLY CHEAP timer? (Read 4908 times)

Larry Renger · « **on:** February 19, 2014, 09:57:56 AM »

Does anyone make a super cheap timer for brushed motors? I only need about 1 minute of flight time. This is for a trainer my club wants to make available to interested beginners. I have a motor/prop/battery/charger setup for about $25 lined up. The plane would be foam. If I could get a timer for maybe $5, we could easily hit a $50 price point complete.

Tim Wescott · « **Reply #1 on:** February 19, 2014, 10:20:42 AM »

If you keep your old copies of Flying Models magazine, go through their free-flight columns. There's a style of timer for brushed motors that works by holding the gate of a FET up with a capacitor -- when the cap poops out, the thing shuts off.

Competition ones go for much shorter times than a minute -- but the sport flyers like a minute of time or so.

Tim Wescott · « **Reply #2 on:** February 19, 2014, 11:00:56 AM »

How are your soldering skills?

The schematic below should make a fairly reliable timer for a brushed motor. With careful part selection you'll spend more on the circuit board than on the parts, and the total will be less that $5 -- but you'll have to assemble it yourself.

If you're seriously interested in this let me know and I'll get you a schematic and bill of materials, and I may even test it out. You can either get something that can be built with through-hole parts on a prototyping board from Radio Shack, or I can work up a PC board with either through-hole parts or surface-mount.

This is a screen-shot of the thing in my simulator program, which seems to think that it'll work just fine. Floyd Carter or any other EE in the group can double-check this to make sure I didn't make some dumb mistake.

Blagh! Never mind! It won't work with a real motor, unless you just want a tool for blowing up transistors.

Tim Wescott · « **Reply #3 on:** February 19, 2014, 05:38:42 PM »

Larry:

This one will work. It's more parts, but it'll work.

I can probably get this done with a parts cost under $5.00 in small quantities, but it'll be a challenge -- oddly enough, it's buttons and knobs and circuit boards that are the price drivers here: transistors and resistors are dead cheap.

It'll be easier if I can go to surface-mount components, because then the board cost (which is a big price driver) will fall.

If you look at the PCB layout, you'll see that while I could scrunch things up a bit, most of the space is taken up with transistors and resistors.

If I go to surface mount S1, C1, R7, Q2 and D1 all stay pretty much the same size, but all the other components get way smaller. The board stands at about 2.5 square inches right now; I could probably bring that under 1.5 squares with surface-mount components. Possibly less than 1 square inch if you want an off-board switch and go with a fixed flight time (R7 adjusts the flight time).

So -- how are you at soldering?

John Rist · « **Reply #4 on:** February 19, 2014, 07:10:42 PM »

Just out of curiosity how do you get cheep small quantity PCBs?

William DeMauro · « **Reply #5 on:** February 20, 2014, 03:29:17 PM »

Larry,
I may be dead wrong as, I am not an engineer and the budget misses by a few bucks, but I am pretty sure the e-flight timer would work just fine for what you need brushed or not. All you are looking for is a percentage of throttle for a given amount of time and how would the timer even know whether its hooked up to a brushless speed controller or a brushed one? I don't think they are that smart. I know they are over budget but in the time it takes you to order the parts and assemble your own it's probably just cheaper to buy the e-flight one. What size brushed motors are you using? I am pretty sure I have a bunch of brushed motors left over from my park flying days(they would be at my Dad's if he didn't get rid of them)(Maybe a few speed controller's too)If it helps your budget and I have them I'll be happy to send them your way. Send me a PM.
William

Igor Burger · « **Reply #6 on:** February 20, 2014, 03:39:07 PM »

Quote from: William DeMauro on February 20, 2014, 03:29:17 PM

how would the timer even know whether its hooked up to a brushless speed controller or a brushed one? I don't think they are that smart.

I cannot speak for Larry, but I would say the point is NOT to use any ESC, so the cheapest way is solution posted by Tim, even replacing the RC time base by processor is not so trivial, because processor will need 5V source while motor will profit from 7.4V so may be processor solution will still have similar number of components

However Larry, I think if you think simple can motors are enough, you can also use cheap BLDC motors with ESC, the $ difference will not be so large and it will be usefull not only for totally first model, bt also may be second or third ... at least some guys here fly EPP models wich such power train and they do basic maneuvers like loops and wingovers

FLOYD CARTER · « **Reply #7 on:** February 20, 2014, 06:19:20 PM »

The previous comments are correct. A brushed motor does not require a controller. You just want to run a brushed motor for 1 min, an on/off timer is in order, and not one that generates 1.5 msec pulses. Basic requirement is a motor, a battery, and a switch to handle the motor current that will also stray ON for a minute.

I'm now thinking of a pneumatic timer, or perhaps a clockwork timer. A high current switch capable of activation by a mechanical timer might take some more research.

Floyd

Tim Wescott · « **Reply #8 on:** February 20, 2014, 10:27:53 PM »

Quote from: Igor Burger on February 20, 2014, 03:39:07 PM

I cannot speak for Larry, but I would say the point is NOT to use any ESC, so the cheapest way is solution posted by Tim, even replacing the RC time base by processor is not so trivial, because processor will need 5V source while motor will profit from 7.4V so may be processor solution will still have similar number of components

However Larry, I think if you think simple can motors are enough, you can also use cheap BLDC motors with ESC, the $ difference will not be so large and it will be usefull not only for totally first model, bt also may be second or third ... at least some guys here fly EPP models wich such power train and they do basic maneuvers like loops and wingovers

A PIC processor and a 3.3V regulator can each be had from DigiKey, in SOT-23 packages (about 4mm x 3mm surface mount) for $0.65 or so in onsies. So you could significantly reduce the parts count, and probably increase the reliability (the circuit I designed relies on an electrolytic cap to hold it charge for a minute, reliably, which is barely within the realm of the doable). But I'd have to re-learn how to make PICs happy, you'd still need the button and the pot (two of the three big circles on that board are the switch and the time-set potentiometer), and since no one seems to make itty bitty through-hole micros any more, it'd have to be surface mount.

Come to think of it, the voltage regulator and a couple of resistors would allow for a sleazy low battery cutoff, which my ultra-simple circuit does not offer.

If someone wanted these for production, to be built in a factory and sold to moms for kids' Christmas presents, I'd probably recommend the PIC.

But while I'm willing to design it and support it, I'm not really interested in building a bunch of them. And it's a lot easier to build a through-hole board than a surface-mount one.

Tim Wescott · « **Reply #9 on:** February 20, 2014, 10:33:12 PM »

Quote from: John Rist on February 19, 2014, 07:10:42 PM

Just out of curiosity how do you get cheep small quantity PCBs?

This is my current supplier: www.oshpark.com. I have a few nits to pick with them on quality, but the boards they've sent to me so far have all been usable enough. You boards for $5/3 per square inch (that's $5.00 per square inch of board, three boards at a time). Or you can order 150 square inches worth for $1.00 per square inch.

There's other places too, but OshPark is the one I've used (and they're just down the road from me, so if I ever get mad at them I can go visit in person).

They're called circuit board aggregators. You send a design, they put it on a panel with a bunch of other people's designs, then when the panel is full they send an order off to China. Then, about a week later, they get the panel back, they whack it up into individual boards, and they send the boards to you. OshPark is but one of many.

Tim Wescott · « **Reply #10 on:** February 20, 2014, 10:50:15 PM »

Quote from: Tim Wescott on February 20, 2014, 10:27:53 PM

A PIC processor and a 3.3V regulator can each be had from DigiKey, in SOT-23 packages (about 4mm x 3mm surface mount) for $0.65 or so in onsies.

I just re-checked. You can still get 'em in through-hole packages. But I still don't want to mess around with programming a PIC right now.

Igor Burger · « **Reply #11 on:** February 21, 2014, 12:56:50 AM »

Tim, the trivial solution which I had on mind was single Pis and one FET, it does not need any PCB

my timers (for esc) also do not have any PCB .. look pic

Tim Wescott · « **Reply #12 on:** February 21, 2014, 12:29:42 PM »

Quote from: Igor Burger on February 21, 2014, 12:56:50 AM

Tim, the trivial solution which I had on mind was single Pis and one FET, it does not need any PCB

my timers (for esc) also do not have any PCB .. look pic

I laud your workmanship. The part of me that's designed circuits for mil-aero is wailing in dismay, but the rest of me thinks that's pretty cool.

Howard Rush · « **Reply #13 on:** February 21, 2014, 01:02:35 PM »

You kids have it easy nowadays. I used to build discrete-transistor circuits without boards. I wonder what it was like in Floyd's day. Do you suppose he used sockets or soldered directly to a tube's pins?

Tim Wescott · « **Reply #14 on:** February 21, 2014, 01:32:11 PM »

Quote from: Howard Rush on February 21, 2014, 01:02:35 PM

You kids have it easy nowadays. I used to build discrete-transistor circuits without boards. I wonder what it was like in Floyd's day. Do you suppose he used sockets or soldered directly to a tube's pins?

I inherited my uncle's junk box when he passed away. There's Raytheon ultra-miniature tubes in there with bits of circuit still soldered onto the leads (those tubes didn't really have "pins", per se).

You can certainly build circuits in the air and have them be reliable -- particularly if you dip them in epoxy the way Igor does. It's just not usual.

FLOYD CARTER · « **Reply #15 on:** February 21, 2014, 02:13:03 PM »

Howard is correct. When I was in college (pre-history days) I studied vacuum tube circuits! Got pretty good at it, too!

I make my own printed circuit boards using the photo resist process, but this requires a photo negative, and these are hard to make using a 4X or larger master tape-up.

I still don't understand why all the fuss with electronic timers, when a mechanical one would work.

Floyd

Igor Burger · « **Reply #16 on:** February 21, 2014, 02:16:37 PM »

I think it is not so unusual :- )))

http://en.wikipedia.org/wiki/File:Hybridcircuit.jpg

John Rist · « **Reply #17 on:** February 21, 2014, 10:59:03 PM »

Have you thought of using a 2.4 ghz radio with a small servo flipping a switch. A bit of a hassle to set up but would give instructor control over the motor. Also would work well with a brushless setup. Of course not cheep.

Igor Burger · « **Reply #18 on:** February 22, 2014, 01:36:27 AM »

little more about K7:

http://www.ctrl-c.liu.se/misc/RAM/k7giant.html

Larry Renger · « **Reply #19 on:** February 22, 2014, 09:37:18 AM »

Regarding the use of a radio, that is what we do for our kid training at shows. However the current project is to come up with a simple, cheap trainer the parent can then buy at the site. I think the whole package, fully built should come in under $50. It needs to be competitive with the low end RC stuff that runs in that price range.

We have the powwer package identified, and it is on target for cost, but a shut-off timer is the missing link. No need for power control, just on and off.

John Cralley · « **Reply #20 on:** February 22, 2014, 09:45:48 AM »

Contact Will Hubin. He might come up with just what you need.

Igor Burger · « **Reply #21 on:** February 22, 2014, 09:53:17 AM »

Larry, if that Tim's timer is too complicated, I can send you programmed PIC processors, you will need to solder it somehow together, the processor has usual connection to standard ESC and it has 1 digital input and one digital output, so you can use that output line to controll that FET transistor from Tim's timer, and you can later use it also for normal ESC if kids decite to upgrade, That input line will also allow to connect a swith for starting. They are programmable with Jetibox, you will need one programming for all timers. It costs 35Euro and available in any shop having Jeti stuff. So depends how many timers you want to make.

YOu will need to add some blocking capacitor, 5V stabilizer, 3 pin connector, diode and Fet transistor.

I mean the chip used in this timer:

http://www.netax.sk/hexoft/docu/itimer_en.pdf

Tim Wescott · « **Reply #22 on:** February 22, 2014, 12:54:13 PM »

Igor, that's a generous offer.

Larry, I'd be happy to lay out a circuit board for all that if you don't want to solder it in a ball like Igor does. It'll probably be smaller than the one I've got now.

Using a processor is actually a better way to go than my suggested circuit, but I'm lazy -- I just don't have time right now to get set up to work with PIC again.

Igor Burger · « **Reply #23 on:** February 22, 2014, 01:09:43 PM »

Yes, it WILL need a board, it is too many componenets to make it in-air.

Howard Rush · « **Reply #24 on:** February 22, 2014, 03:10:20 PM »

Igor could just send the program, and somebody could put it on hardware here. I can do it this fall if you want to wait.

Igor Burger · « **Reply #25 on:** February 22, 2014, 03:13:53 PM »

Burning s not problem, I can even prepare program I think ... I must check, but I think possible.

Larry Renger · « **Reply #26 on:** February 24, 2014, 09:00:41 AM »

Gentlemen, thanks for your interest and design efforts.

My electronic skills are nil, but I don't believe that I need a link to an ESC. All I need is an on/off switch between a battery and brushed motor. Two wires, a make or break switch on one of them. The timing accuracy isn't even all that important. Varying from 45 seconds to a minute and a half would be close enough.

Due to shaky hands, I can't solder anything smaller than a drainpipe. Getting the solder, iron and parts all in the same location at the same time just doesn't happen.

Paul Smith · « **Reply #27 on:** February 24, 2014, 09:44:42 AM »

How about down line shutoff like a racer?

Tim Wescott · « **Reply #28 on:** February 24, 2014, 10:02:53 AM »

Quote from: Paul Smith on February 24, 2014, 09:44:42 AM

How about down line shutoff like a racer?

I think it'd end up being "down line crash-off". Keep in mind that this is a very basic trainer that Larry is working on here.

Tim Wescott · « **Reply #29 on:** March 06, 2014, 04:08:27 PM »

Boards came in the mail today. I got a board built up, and tested into a 100 ohm resistor (so, like, 50mA instead of 2A). It works fine.

I need to dig up a suitable 2A load, and test. Then maybe I can send you something.

Larry Renger · « **Reply #30 on:** March 07, 2014, 12:32:44 AM »

How about Isend you the actual motor and battery? Might that help?

Tim Wescott · « **Reply #31 on:** March 07, 2014, 09:26:58 AM »

That would be great. I keep meaning to demand an airframe as payment for my time, but forgetting. The motor & battery is more important.

Tim Wescott · « **Reply #32 on:** March 07, 2014, 12:20:59 PM »

I cobbled together a much bigger motor, a 12V supply, and a little prop. It pulled 4A, worked just fine.

Tim Wescott · « **Reply #33 on:** March 07, 2014, 03:36:24 PM »

Proof! PROOF!

john e. holliday · « **Reply #34 on:** March 08, 2014, 11:49:13 AM »

Can the time be increased? On your other post I stated I would be interested in a package ready to put in/on the ET-1's I have still in the box.

Tim Wescott · « **Reply #35 on:** March 08, 2014, 01:30:19 PM »

Quote from: john e. holliday on March 08, 2014, 11:49:13 AM

Can the time be increased? On your other post I stated I would be interested in a package ready to put in/on the ET-1's I have still in the box.

That was a super-short time for demonstration purposes. As designed, the thing will reliably do times up to about one minute or so (which is what Larry needs). Beyond that, you end up at the mercy of the electrolytic capacitor. You'll have a device that may or may not work off the production line, and the ones that do work may or may not work a few months later, or at elevated or cold temperatures, etc.

If I had the time to resurrect my PIC development environment I'd have done the whole timer on that, because then a timer with a different run time would just be a program change away. I just don't have the time right now. Igor put something forward, but I'm not sure that it does what we need. If he could verify yea or nay, or if someone else could step forward and do the PIC programming on this, that would be cool -- I'd be happy to design the board for it.

FLOYD CARTER · « **Reply #36 on:** March 08, 2014, 05:32:03 PM »

To answer Howard's question, here is an example of my electronic building. Vacuum tube amplifier using point-to-point wiring. The circuitry is also my own design. About 30 Watts per channel.

Floyd

Larry Renger · « **Reply #37 on:** March 13, 2014, 10:01:16 AM »

So far so good! I got Tim's Teeny Timer and it works great.

Now I have no excuse but to design and build the ET-2.

john e. holliday · « **Reply #38 on:** March 13, 2014, 10:40:16 AM »

Now for a price tag for a complete power system for my ET-1's.

Tim Wescott · « **Reply #39 on:** March 13, 2014, 11:37:47 AM »

Quote from: Larry Renger on March 13, 2014, 10:01:16 AM

Now I have no excuse but to design and build the ET-2.

Larry, I got that motor & prop you sent, and man, does it seem wimpy!

What length of lines were you thinking of using, and wingspan etc.?

I remember flying a 1/2-A plane in a cul-de-sac in front of a friends house, after shortening the lines (it was my first crash on pavement!).

Larry Renger · « **Reply #40 on:** March 14, 2014, 09:06:06 AM »

Doc, Eric Rule has complete ET-1power systems. rsmdistribution.com

The ET-2 is planned to be about 20" span, 100 sq. in. area and targeted at 5 ounces or less. The power system puts out 3 ounces of thrust, so it should fly level like a trainer just fine. Current thought is that construction will be from Dollar Tree store foam sheet.

ET has meant Electric Trainer, but how about a rename to Eagle Trainer?