servo control via lpt problems

[Mitch__]

Hi all
i am working on a small project in VB, Controlling Servos by voice.
everything is working great except for one thing.
If i use one power adapter to control more than 1 servo, then
following happens
While 1 servo moves , second servo seems to get enough of a voltage
fluctuation that it will move one way or the other.
so
currently for this to work for me, i need to have a separate power
supply for each servo, then
everything works great.
TIA
Mike

 

[martin griffith]

Hi all
i am working on a small project in VB, Controlling Servos by voice.
everything is working great except for one thing.
If i use one power adapter to control more than 1 servo, then
following happens
While 1 servo moves , second servo seems to get enough of a voltage
fluctuation that it will move one way or the other.
so
currently for this to work for me, i need to have a separate power
supply for each servo, then
everything works great.
TIA
Mike

would it be possible for you to post the LPT interface circuit
somewhere, so we could have a quick look?
Otherwise we could all be collectively be pissing into the wind


martin

 

[Mitch__]

would it be possible for you to post the LPT interface circuit
somewhere, so we could have a quick look?
Otherwise we could all be collectively be pissing into the wind

martin

ok, well there is not much to it, i do not have a diagram, but can be
easily explained.
LPT ground to Servo Grounds and to 5Volts ground
LPT Pin 2 out to Servo White wire (and pin3 out to second servo white
wire)
Both servo red wires to +5 volts

 

[martin griffith]

ok, well there is not much to it, i do not have a diagram, but can be
easily explained.
LPT ground to Servo Grounds and to 5Volts ground
LPT Pin 2 out to Servo White wire (and pin3 out to second servo white
wire)
Both servo red wires to +5 volts

what sort of current are you using for the servos?
what does it look like on a scope?
where are you getting the 5V from, and how good is the supply?
whats the current through the servo ground to PC ground?


martin

 

[DaveM]

ok, well there is not much to it, i do not have a diagram, but can be
easily explained.
LPT ground to Servo Grounds and to 5Volts ground
LPT Pin 2 out to Servo White wire (and pin3 out to second servo white
wire)
Both servo red wires to +5 volts

What kind of servos are you using?
How much drive current do these servos need? (Hint: LPT ports usually can't
source more than a few milliamps of current. Most have TTL or LSTTL
characteristics.)
Post the relevant part of your VB code.

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer to the end, the faster it goes.

 

[Mitch__]

What kind of servos are you using?
How much drive current do these servos need? (Hint: LPT ports usually can't
source more than a few milliamps of current. Most have TTL or LSTTL
characteristics.)
Post the relevant part of your VB code.

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer to the end, the faster it goes.- Hide quoted text -

- Show quoted text -

futaba rc servos
using a dc adaptor to power them

Dim icount As Integer
For icount = 1 To 75
Call PortOut(888, 1)
Threading.Thread.Sleep(0.8)
Call PortOut(888, 0)
Next icount
Return
like i had mentioned, everything works fine if i use separate power
source for each servo, if i use one power source then when 1 servo is
instructed to new position then the second servo glitches alot.

thanks

 

[Genome]

--
Dave M

Life is like a roll of toilet paper; the closer to the end, the faster it
goes.

Life is like a roll of toilet paper.

You buy your own they last for months.

You enter into a purchase share scheme. You will experience at least one
shit a month with nothing to wipe your arse on...... after you have made
your deposit.

And then they will philosophize about the origins of War!

DNA

 

[DaveM]

futaba rc servos
using a dc adaptor to power them

Dim icount As Integer
For icount = 1 To 75
Call PortOut(888, 1)
Threading.Thread.Sleep(0.8)
Call PortOut(888, 0)
Next icount
Return
like i had mentioned, everything works fine if i use separate power
source for each servo, if i use one power source then when 1 servo is
instructed to new position then the second servo glitches alot.

thanks

Ummm ... sounds like a classic case of insufficient current capacity from the
DC adapter or insufficient filtering.
Have you actually measured the voltage level from the DC adapter under load?
What is the voltage/current capacities of the adapter (should be on the label)?
What are the servo voltage/current specs?
Have you actually measured the current that the servos need?
Have you actually measured the drive voltages from the LPT port when the servos
are being commanded?

Those are very basic things that you should do, and those measurements will tell
you nearly everything you need to know about your problem.

One suggestion... connect a 100uF capacitor across the DC terminals of each of
the servos and see if the operation improves. Voltage rating of the capacitors
should be a bit above the output voltage from the DC adapter.

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer to the end, the faster it goes.

 

[Mitch__]

Ummm ... sounds like a classic case of insufficient current capacity from the
DC adapter or insufficient filtering.
Have you actually measured the voltage level from the DC adapter under load?
What is the voltage/current capacities of the adapter (should be on the label)?
What are the servo voltage/current specs?
Have you actually measured the current that the servos need?
Have you actually measured the drive voltages from the LPT port when the servos
are being commanded?

Those are very basic things that you should do, and those measurements will tell
you nearly everything you need to know about your problem.

One suggestion... connect a 100uF capacitor across the DC terminals of each of
the servos and see if the operation improves. Voltage rating of the capacitors
should be a bit above the output voltage from the DC adapter.

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer to the end, the faster it goes.- Hide quoted text -

- Show quoted text -

thanks all
problem solved with resistors between servo and +5
everything is working great now
thanks agin