Question: Off Delay Timer

Hello everyone,

I know nothing when it comes to electronics, please be patient with me.

I'm looking for an adjustable off delay timer that can delay multiple (2 or 3) small dc motors (cordless drill motors).

Here is what I want to do....

Motor A & B - both motors turn on (run) when a button is pressed.

Motor A runs for 5 seconds then shuts off

Motor B runs for 5 seconds at 60 rpm's then powers up to 100 rpm's after 5 seconds and runs for a total of 10 seconds then shuts off.

I'm looking for something simple and inexpensive.

Idea....

I've seen some traffic light off delay timers on Youtube that may work, for example....

Green light turns on = Motor A & B turn on (run for 5 seconds)

Green light turns off = Motor A & B turn off

Yellow light turns on = Motor B turns on (runs at a higher speed), runs for 5 seconds then shuts off



Can you point me in the right direction on where I can purchase the above or maybe build it myself?.... again, I know nothing about electronics but I am willing to learn. The motors are 2 - 14.4 dc Dewalt drill motors.

Thanks

Do some reading about the NE555 timer chip. Two or three cascaded 555s set up so one triggers the next will produce a sequence where the timing of each step can be adjusted independently.

To switch the motor, use an NFET power transistor, controlled from the output pin of a 555. To start a motor at low speed, wire a power resistor in-series with the motor and an NFET. To speed it up, short the resistor with another NFet controlled with its own timer..

Will you be happy with the drill motors running wide open on 14.4V, or will you have to regulate the voltage to get the speeds you want?

Thanks Mike.... I'll have to study your reply, I know very little about this stuff but I am interested in learning.

Are you using the speed controls built into the drills to set the motor speed, or are you running the motors directly from a power supply?
Any idea how much current the motors draw when running?
Do you have a power supply? If so, what voltage?

Mike:
Are you using the speed controls built into the drills to set the motor speed?

Joe:
Ya, that's what I was thinking about using. Taking the switch out of the drill and somehow hooking it up to the delay timer circuit.

Mike:
Any idea how much current the motors draw when running?

Joe:
No clue.

Mike:
Do you have a power supply?

Joe:
I was think about using the batteries from the 14.4 dewalt drill. So I guess the power supply would be 14.4 volts max.

Ok, now how precise does the full speed and slow speed control have to be? I.E. how many rpm?

Have you tried to slow the motor by putting some resistance between it and the 14V battery?

Mike:
.... how precise does the full speed and slow speed control have to be?

Joe:
Not very precise. The slow speed has to be slow, I'm guessing around 60 rpm's and full speed can be whatever full throttle of the drill is.

Mike:
Have you tried to slow the motor by putting some resistance between it and the 14v battery?

Joe:
Good idea. No I haven't tried that.... how would I build that? What would I need?

Here's an idea I had....

View attachment 67798

My idea of controlling the speeds of the motor is by using different battery packs. I'm thinking if the motor turns at 500 rpm's using a full pack of 12 batteries (14.4v), I can slow down the motor to 250 rpm's by using 6 batteries. To switch between the 7.2v and the 14.4v I can insert some kind of relay. If 7.2v is too much (rpm too high) I can split that in half and use 3 batteries..... what do you think?

I think I might have to modify my design by use only one motor instead of 2 to make things easier.

Thanks Mike

It is usually not a good idea to tap off half of a battery pack. This causes some of the cells to be discharged more than the others, and since the pack is charged with all of the cells in series, then there will be an imbalance between the cells in the pack. Better to split the pack into two, and charge each sub-pack independently, but that requires a different charger...

Likely better in your case to use the full pack, and then devise a means for running the motor at a reduced speed off the full pack voltage. How about retaining the drill motor speed controller (Pulse Width Modulator, PWM), replacing the trigger rehostat with a pot, and then using that to make the motor run at the reduced speed. Bypassing the speed controller, and hooking the motor directly to the battery pack would define the full speed mode?

Mike:
.... replacing the trigger rheostat with a pot, and then using that to make the motor run at the reduced speed.

Joe:
What's a "pot?".... Oh, I know what you're talking about, a pot is a potentiometer. That's not going to work. After the motor runs for 5 seconds at 60 rpm's and shuts off, it immediately turns on again at a higher rpm. This has to be accomplished automatically. I won't be able to stand next to the motor and turn the "pot" to a higher setting. If the higher setting on the pot can be accomplished automatically that would work.

I was also thinking of building some type of mechanical device (lever or cam) that is hooked up to a slow turning motor. The motor would turn the cam and the cam would mechanically partially push the drill trigger in. Make the cam circumference long enough so a 360 deg. turn would equal 5 seconds. Then use another cam for the additional 5 seconds.

Another idea was making some type of lever that would control the trigger switch on the drill.

Any idea's?

Thanks Mike

I was proposing setting the pot only to get the slow speed. To get the fast speed, bypass the drill's speed controller, and connect full battery voltage to the motor, so it runs wide open...

Another idea is to have two pots, one for slow speed, the other for fast speed. Devise a means of switching in one pot or the other as a function of the timers...

Mike, those are two good idea's. Pots are like dimmer switches for lights. I could run an off delay timer through a pot to get the slow speed for 5 seconds. Then install a "on delay timer" that turns on after a 5 second delay, runs wide open for 5 seconds then turns off. That would work.

Now all I have to do is figure out where to get the parts and build the thing.

Thanks Mike for all your input!

sowjoe said:

Mike, those are two good idea's. Pots are like dimmer switches for lights. I could run an off delay timer through a pot to get the slow speed for 5 seconds. Then install a "on delay timer" that turns on after a 5 second delay, runs wide open for 5 seconds then turns off. That would work.

Now all I have to do is figure out where to get the parts and build the thing.

Thanks Mike for all your input!

Click to expand...

Ok, does the attached State Transition Diagram describe what you want to do?

There are just three states: Idle, State1 and State2. In the Idle state, the machine will wait for a button to be pushed with both motors off. The button will cause a transition to State 1, where both motors are running, B at slow speed . After a 5 sec delay, a transition to State 2, where A turns off and B speeds up. After another 5 sec delay, a transition back to the Idle state, where both motors are off.

That's it Mike, you're correct.

I found this website for on/ off delay timers.... https://www.curioustech.net/timers.html

Not too complicated is it?

Thanks

Those timers are cool.

Check out KIT # 141: https://www.kitsrus.com/kits3.html Timer

and this: https://www.kitsrus.com/kits3.html PWM Modulator

I have used the latter. The PWM kit ruses a voltage to change the speed or I believe a potentiometer.

Let's hope the speeds are not critical or have to be a critical ratio, I'll let you much on this for a while.