Sequential Timers with PWM Motor Speed Control

[audioguru2]

Hi Guys,
I've finally finished building the electric model airplane I won. ;D
It is styrofoam and had a lot of parts to be joined with special glue and epoxy.
I painted it with 4 brushed coats of shiny "red hot" latex house paint.
It has a 3A geared electric motor that swings a 10" prop and is powered by a 7 cell AAA Ni-MH rechargable battery.

There have been many thunderstorms lately so I don't know if it will fly, but I just tested the sequential timers with PWM motor speed control I designed and it works perfectly. ;D

I'm not going to make or buy an expensive radio control system for my plane.
I have a Cmos 555 timer, a CD4017 sequencer, an opamp triangle-wave PWM speed control and Mosfet driver circuit. It has 3 trimpots for timing and 3 more for speed.
I used MC33172 dual opamps for the PWM motor speed control because they are fairly fast, operate well with only a 5V supply and have equal positive and negative output saturation voltages.

The timers can be set from a few seconds to 100 seconds. The motor's speed can be set from very slow to max.
The 1st timing period is for takeoff and climbing, probably at max speed but the first flights will be reduced.
The 2nd timing period is for cruising around at about 1/2 speed.
The 3rd timing period is for a gentle descent to a slow landing, then it shuts itself off.

With the motor drawing about 3A at max speed, the Mosfet saturates with a 0.15V voltage drop. The 8.4V from the little battery drops to 7.4V due to its internal resistance and the resistance of the motor and battery's connectors and wiring.
Even though the motor gets only 7.25V at full power it produces a lot of thrust. ;D

I'll post a video and pics later of the plane flying and here's my schematics:

View attachment 37501

View attachment 37502

 

[Alun]

Nice circuit, I like a 4017/555 timer combination I would've used 3 555s but you've save an IC here and wasted a few in other places. ;D

Just a few questions,

Why didn't you use a 556 duel timer for the elevator control circuit?

Is there a reason you chose this more complex PWM circuit over a simpler design that could've been made with a one 555 timer or even a 556 dual timer or perhapps a dual op-amp?

As you've decided to do it the hard way anyway why didn't you use a quad op-amp?

You'll find you don't need a 100ohm resistor in series witht the MOSFET's gate here because the op-amp's internal ouput resistance is already high enough to remove any oscilations caused by the parasitic capacitance and inductance in the MOSFET.

 

[ante1]

Hi Audioguru,

Nice circuit, especially the ingenious timer setup! Must be quite a big plane having a 10” prop! For how long can these small AAA cells provide trust before they go below 5.6V since you only got 7.4V to begin with? Maybe you should use AA cells instead, or they would be to heavy maybe?  Your next project must be a radio-control system with onboard video to have a “birds view”.  I can see multiple uses for such a system! ;D Looking forward to see a video and some pics!

Buckle up and no smoking!

 

[audioguru2]

Nice circuit

Hi Alun, thanks. ;D

Why didn't you use a 556 dual timer for the elevator control circuit?

Because I have some TLC555 and LMC555 single timer ICs and I know their pin-out.
I didn't make the elevator control circuit after going to the hobby store to buy a servo and was told that it would strip its plastic gears if it was without power. I was going to use it only to blip the elevator up for a moment during takeoff, then use a spring to return the elevator to neutral to save power. I couldn't turn the servo by hand. A servo might eat 200mA straining to keep the elevator from flapping in the wind turbulence.

Is there a reason you chose this more complex PWM circuit over a simpler design?

I chose voltage control to make it simpler to sequence the adjustable speeds and since the motor has plastic gears I slide the speed changes with an RC filter instead of abruptly stripping the gears.

As you've decided to do it the hard way anyway why didn't you use a quad op-amp?

I have lots of dual opamps and find it easier to layout a pcb or Veroboard for them.

You'll find you don't need a 100ohm resistor in series witht the MOSFET's gate here because the op-amp's internal ouput resistance is already high enough to remove any oscillations caused by the parasitic capacitance and inductance in the MOSFET.

I know, it's just a habit. The resistor is cheap and it's leads gives me a good place to attach my 'scope (I didn't yet).

 

[audioguru2]

Nice circuit, especially the ingenious timer setup!

Hi Ante, thanks. ;D

Must be quite a big plane having a 10” prop!

Its wingspan is only about 80cm, but the wing is wide and thick so the plane will fly slowly.

For how long can these small AAA cells provide thrust before they go below 5.6V since you only got 7.4V to begin with? Maybe you should use AA cells instead, or they would be to heavy maybe?

The motor draws 3A for only a couple of seconds 'til the plane gains speed, when the load on the motor is reduced and its current drops. Then the sequencer will reduce the motor's speed and current. With the plane just cruisin' around I expect the motor's current to be quite low. About the only wind drag is from the little heatsink on my Mosfet.
The AAA pack I'm using is rated for 730mA/hrs minimum but is actually about 900mA/hrs and gains more with each charge.
AA cells would probably fly it for hours on each charge, but would weigh more than the whole plane so it would fly too fast.

Your next project must be a radio-control system with onboard video to have a “birds view”.

 

[Alun]

I chose voltage control

Voltage control can be achieved with only two op-amps you know. ;D

Op-amp A is a schmitt trigger oscillator, op-amp B is a comparator that compares the voltage on this oscillator's capaticor to the control voltage on the pot.

I have lots of dual opamps and find it easier to layout a pcb or Veroboard for them.

My mistake, I've just noticed you've powered one IC from 5V and the other from 8.4V - this would be pretty hard to do with one quad IC. ;D

 

[audioguru2]

Voltage control can be achieved with only two op-amps you know. ;D

Op-amp A is a schmitt trigger oscillator, op-amp B is a comparator that compares the voltage on this oscillator's capaticor to the control voltage on the pot.

That's brilliant and I didn't think of using a Schmitt trigger oscillator as the triangle-wave generator. I could have saved a dual opamp! ;D

My mistake, I've just noticed you've powered one IC from 5V and the other from 8.4V - this would be pretty hard to do with one quad IC.

Yeah, I use the regulated 5V for the voltage controlled oscillator and the full 8.4V for the Mosfet and motor.
The battery is actually about 10V when fully charged so the 1st takeoff will be like a rocket! ;D

 

[ante1]

Somehow I knew you would like the “birds view” idea! Seriously, this model plane is not constructed for radio control then?  It would be interesting to see a simple radio control circuit grow from scratch though! I hope you get some nice flying whether soon so we can have pictures! Good luck Captain! ;D

 

[audioguru2]

Hi Ante,
Sure my model airplane is designed for radio control. I installed a hinged rudder with pushrod in mine. I didn't hinge the elevator nor ailerons yet. Mine is red but here's a white one:

View attachment 37507

 

[audioguru2]

Hi Guys,
I flew my electric model airplane today! ;D
Its timers and motor speed control circuits worked TOO well.

It was very windy so after setting its rudder for a big circle when gliding, I set the 1st timer for full power, the 2nd timer for half power and the 3rd timer for 1/4 power. I set the timers to 15 seconds each.

It went up like a rocket then the 2nd timer slowed down the motor too much and it made a pretty good landing with the motor still running.
I turned-up the speeds for the 2nd and 3rd timers and it flew much better.

Then it went straight up and stalled just when the 2nd timer reduced its power and it dived into the ground. Now it has a broken propeller and the battery broke through the front of the plane behind the motor. I have epoxyed the damage and tomorrow I'll get a new prop.

I did have a phoney radio control transmitter in my hand and people watching thought I was controlling the thingy. It was really just my Cmos 555 timer and CD4017 sequencer doing the tricks. 8)

I'll fly it again with full power for only a couple of seconds then reduced power for much longer and without any wind. ;D

 

[ante1]

You better fit this plane with a black box and yourself with a helmet and a parachute Captain!

Good Luck!


[move]-----pictures------ ;D----videos----------pictures----- ;D-----videos-----[/move]

 

[audioguru2]

Hi Ante,
Yeah, I'll borrow my son's digital camera and take pics and videos of my plane doing its tricks.

I think it went straight up like a rocket because its battery was sliding toward the rear when it accellerated forward, so its balance was way off. I'll fasten it securely with chewing gum or something somehow.

I made my PWM motor speed control only about 2kHz on purpose so I can hear it.
When I turn on the circuit there is a 1 second delay while it resets, then the 2kHz whine can be heard softly then louder and louder until the motor begins its wind-up. It sounds like a jet turbine.

I thought about putting a parachute on the plane (not on me) that would be triggered after about 10 minutes. I could easily add a 4th timing period to my sequencer to do it. Then if my plane catches a thermal of rising warm air, it won't drift away like some of my planes did when I was young.

I'm going to try a touch-and-go landing and re-takeoff by adjusting its 2nd sequenced motor speed slow then its 3rd speed at full power again. I think it will work if I'm not in its path. ;D

 

[audioguru2]

Hi Guys,
Boo-Hoo! :'( :'(
My electric model airplane crashed and got broken many times.
Luckily I'm retired and have lots of epoxy glue so I have the time and resources to fix it each time. The fuselage broke in half. I joined it with epoxy glue and painted the scars and you can't see them.
Even with its PWM motor speed control turned down, it climbs straight up like a rocket, stalls then dives into the ground. A few times with very low speed it just flew around not very high. When my sequencer reduced the motor's speed further, a few times it landed with the propeller still turning.

The designers of my airplane smartly included a little thrust offset to one side so the torque from the motor and propeller doesn't turn it too much. But they forgot to add downward thrust to hold its nose down when it is flying fast. The wings near the front have more and more lift the faster it flies. But the tail doesn't have any lift, it is a source-follower!

Now the wood post that holds the motor is broken. If I can remove it then its replacement will have some downward thrust.
Maybe I should have used radio control after all. ???

 

[ante1]

Hi Audioguru,

Sorry to hear about your problems. I’ve been there gluing the pieces back together after numerous test flights (crashes) just don’t give up glue is cheap! It sound better if you call it test flights, it boosts your self-confidence! ;D   
Anyway, have you checked the prop tilt angle, which in combination with another important factor in avionics called weight & balance could be the culprit here! The ailerons can be set individually to compensate for the torque on some constructions, what about yours?

BTW. What did the”blackbox” say, was it a pilot error or malfunction electronics? ;D ;D

 

[audioguru2]

Hi Ante,
My test flights crashed not due to pilot error nor electronic malfunction. It was due to avionics physics. It goes too fast and therefore climbs too steeply. Then stalls and dives into the ground.
I have the balance, elevator, rudder and ailerons set so it glides very well. There are lots of combinations to try, elevator down a little to lift the tail then balance rearward a little so it doesn't dive. I'll also tilt down the prop angle so it doesn't climb so steeply.
I can't just reduce the motor's speed, the plane needs nearly full power for takeoff. Then if I reduce the motor's speed to reduce the rate of climb, it turns and goes in the wind's direction but takes time to gain enough speed so the ground comes up and hits it in the nose. It needs a plane to ground distance regulator to keep the ground a safe distance away.

I must find the correct timing to reduce the motor's speed before the climb becomes too steep. Also I must find the correct 2nd motor speed for it to accellerate quickly in the wind's direction without dropping nor climbing too steeply.
I still have lots of glue and a few spare props so I'll eventually get it flying properly. ;D 

 

[audioguru2]

Hi guys,
My plane crashed and broke some more since the last time.
I ran out of glue so now I am using 5 minutes epoxy.

Check out this very long video of an amazing fast electric "boat":
http://www.putfile.com/media.php?n=HydroFoam

 

[Alun]

I'm sorry can't see your video audioguru.

Has anyone else had problems?

 

[Staigen1]

Hi there

Works here, just click on the link, but i dont think it is Audiogurus video!
Where are your video, Audioguru, didn't you promise one, or, as usual, do i remember wrong ?

//Staigen

 

[audioguru2]

No, that isn't my video. I just looked at it again at its huge "800" size. Maybe hi-speed internet is required to see it since I can't figure out how to download it.
Those electric "boats" are pretty cool, aren't they, and their pilots must be experts to control them like that.

I can't find my son's digi-camera. Maybe he sold it or lost it.
My daughter recently gave me (and one for her) a tiny cell phone for my birthday with a video camera in it. It didn't come with the expensive optional PC-connection cable so I must figure out how to transfer its files to my PC by using its IR link. Then when I make my video I must make my own web-page to post it or join that "put-file" community.