555 timer to turn on 2nd 555 timer

[Alec_t]

Well you could try inreasing R6 further and reducing R8 further, but Ltspice is telling me your pulse width is already changing from more than 2mS to less than 1mS, i.e is exceeding the standard servo pulse width range. So perhaps the less-than-expected angular movement is due to the fact that your servo supply is only 3.7V (or less). The control IC inside the servo may not be happy with a low supply voltage if it was designed for a 5V supply (older RC systems were often supplied from four NiCd cells, 4.8V).

 

[SeniorCitizen]

Thanks. Since I don't have a 5 or 6vdc battery, I'll try two 3.7v batteries in series early next week (will be away for the weekend). To better understand your comment above.....
I googled and found this:
""It is a good beginning to say that the pulse width duration for a full drive shaft move should be within the range of 1mSec to 2mSec. If we take for example a rotary servo, a PWM with positive pulse width 1mSec would cause the shaft to revolve fully left. A 2mSec positive pulse width would cause the drive shaft to revolve fully right. 1.5mSec pulse width would cause the shaft to turn to the middle of the revolution area.""
I'm a bit confused with the above....if 2ms goes full right and 1ms goes fully left.....how do we get a servo to go from full left to full right.
Thank you again.....looking forward to trying the dual batteries.

 

[Alec_t]

I'm a bit confused with the above....if 2ms goes full right and 1ms goes fully left.....how do we get a servo to go from full left to full right.

You start with 1mS (or less) wide pulses, then change (directly or incrementally) to 2mS (or greater) wide pulses. The interval between pulses stays ~ the same (somewhere in the 20mS to 50mS range, not critical). 'Left' and 'right' may differ from one servo maker to another.

 

[Irv]

Please understand, I'm not posting this to be critical, and all this is certainly a learning exercise, but couldn't this whole thing be replaced with a $3 computer? No need for a printed circuit, or other parts; they drive servos directly, and timing adjustments would be dead simple. Something like a Chinese Arduino Nano knockoff. I've used half a dozen for various projects with no problems. I think the project could be done, start to finish, in about an hour, leaving more time with the kids.

 

[davenn]

Please understand, I'm not posting this to be critical, and all this is certainly a learning exercise, but couldn't this whole thing be replaced with a $3 computer? No need for a printed circuit, or other parts; they drive servos directly, and timing adjustments would be dead simple. Something like a Chinese Arduino Nano knockoff. I've used half a dozen for various projects with no problems. I think the project could be done, start to finish, in about an hour, leaving more time with the kids.

yeah ... if programming one wasn't a stumbling block

 

[Irv]

I have built with discrete components since around 1960, and believe me, programming is FAR easier.
With the current hardware, you don't even need any extra equipment or programmers, just your existing PC or laptop works fine.

 

[davenn]

I have built with discrete components since around 1960, and believe me, programming is FAR easier.

for you maybe

 

[SeniorCitizen]

Hi Alec,
First, the circuit works exactly as you intended.
That is. Turn ON & quickly OFF to reset, then Turn ON and 4 seconds (or whatever) later the SERVO rotates. Then turn OFF when done.

What I've recently experienced is that after RESET, when I turn ON, sometimes the servo moves immediately about 3/4 of travel, then AFTER the proper delay, it continues to full travel. This doesn't happen all the time, just every once in a while. Do you have any ideas as to what might cause this....could it be I didn't wait long enough for the capacitor to discharge ? If so, is there any estimate of time to "wait" before turn ON.
The reset works perfectly every time...The RC delay of 4 seconds works perfectly....It's just the intermittent "initial movement" that's the problem. Obviously for a parachute deployment...it's a disaster to have the chute deploy immediately at launch.

PS: this problem seemed to start after I put in a newly charged 3.7vdc battery. I'll try to go back to the orig 3.7vdc battery to see if the problem continues, but it takes a bit of time to change things out in the rocket. My next Launch Day is Sat Aug 26 (a model rocket club allowed me to join them during some of their scheduled launch days.....none of the club members use water/air rockets they use cartridge charges for lift off AND for chute deployment)

By the way, this is a photo of one of my inaugural launches July 8; the parachute payload bay is immediately below the nose cone.

Thank You, Richard.