Servos and 7.5 volts
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Posts: 46,084
I was sure this had been asked before,
but I've looked, and can't find it,
therefore:
Is there any problem running the
BOE-Bot Servo (Futaba S148) at
7.5 volts? Or even 7.2 volts?
The Futaba website gives values for
4.8 volts and 6.0 volts, but does not
give any 'max' recommended voltage.
I ask this because I've recently become
a proud owner of a BOE-Bot, and I don't
really want to kill all those batteries.
The issue is that the BOE needs 6 volts
minimum for its regulator to work. I
have a 7.5 volt adapter, which I've read
CAN be used with the BOE-Bot, but I
wanted to make sure.
Thanks.
but I've looked, and can't find it,
therefore:
Is there any problem running the
BOE-Bot Servo (Futaba S148) at
7.5 volts? Or even 7.2 volts?
The Futaba website gives values for
4.8 volts and 6.0 volts, but does not
give any 'max' recommended voltage.
I ask this because I've recently become
a proud owner of a BOE-Bot, and I don't
really want to kill all those batteries.
The issue is that the BOE needs 6 volts
minimum for its regulator to work. I
have a 7.5 volt adapter, which I've read
CAN be used with the BOE-Bot, but I
wanted to make sure.
Thanks.
Comments
Allan Lane <allan.lane@h...> wrote:I was sure this had been asked
before,
but I've looked, and can't find it,
therefore:
Is there any problem running the
BOE-Bot Servo (Futaba S148) at
7.5 volts? Or even 7.2 volts?
The Futaba website gives values for
4.8 volts and 6.0 volts, but does not
give any 'max' recommended voltage.
I ask this because I've recently become
a proud owner of a BOE-Bot, and I don't
really want to kill all those batteries.
The issue is that the BOE needs 6 volts
minimum for its regulator to work. I
have a 7.5 volt adapter, which I've read
CAN be used with the BOE-Bot, but I
wanted to make sure.
Thanks.
To UNSUBSCRIBE, just send mail to:
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[noparse][[/noparse]Non-text portions of this message have been removed]
> Is there any problem running the
> BOE-Bot Servo (Futaba S148) at
> 7.5 volts? Or even 7.2 volts?
>
Allan, I think this is one of those "are you willing to spend twenty dollars
to find out" questions.
I'm using a mix of Futabas and Parallax servos from a Taiwan mfr I'm too
tired to remember. Jon and Eric helped me work it out one day when I was
trying to match spline patterns, but the name escapes me just now. Grand
Wing? Possibly. In any case, with these specific units I've had no problems
using up to 7.0 volts in some design experiments, but I don't have any hours
of on-robot use to determine whether that shortens the lifetime. I chose
that value after finding a note posted on the San Diego Robotics group.
The writer says the 6.0V arose from intended operation on four AA cells, and
designs were modified to operate on 4.8V as well when the use of four NiCd
cells became popular. These are standard levels, not limits in other words.
But that also means different designers will provide different levels of
headroom as their whim and the parts available suggest. Above that level
works fine (he says) until you fry the control circuit, whose weak point was
an NE544 in his youth. Modern servos like the better Futabas have newer
circuit designs that will tolerate up to 9.0V. He says. Again, just quoting,
or at least paraphrasing pretty closely.
The trouble is that he also reports opening a recent servo and finding an
NE544 generic equivalent, and he speculates that clone chip would fail at a
fairly low voltage just like the original. So we take our chances anywhere
above the higher specified standard level.
This guy sounds credible enough that it was worth risking $20 or so on each
type of servo to see if I could get the higher torque and more efficient
battery usage at the higher servo voltage level. My power supply is
home-rolled and software adjustable, so I can always change the programmed
voltage level for the servo line if I start frying servos, but I don't have
any operational experience either way to report yet. Just a few casual
tests. Very casual: "Ah, no smoke and it still moves. I'll try that
level..."
Here's the note in the SDRS archives: http://makeashorterlink.com/?O31E25457
so you can make your own judgment call. I'd love to find a list of servos
with the maximum tested voltage somewhere on the net, but I'm not holding my
breath. Even if someone spent the money frying a few dozen candidates, it
would not tell us what voltage the next production mod from the same mfr
might tolerate. Since they don't spec at anything above 6.0 V, they won't
hesitate about using parts that fry at 10% or 15% above that level. At least
hypothetically. Personally, I'm betting that any recent design will have 20%
margins at least, so I'm using 7.0 V as a working estimate until the air
gets that distinctive tangy smell around my robot<g>.
Gary
but the higher you go the more likely you are shortening the working life of
the servo.
If you just want to conserve batteries, the BOE Rev C has a great solution.
Just move the servo power selector from Vin (raw battery) to Vdd (regulated
5v). Your servos will then run at an absolutely safe 5v even though you use
a 7.2v R/C battery as input. The 1A regulator on the BOE can easily handle
the load.
I haven't done this with the BOE, but I built a similar arrangement on a
Knex robot by breadboarding an LM7805 regulator on an activity board. A
7.2v/1800ma battery runs two Knex gear motors, a servo, several IR and
ultrasonic sensors and a BS2 for quite a while. An Astroflight charger can
"refill" the battery in 15 minutes, so I can run almost non-stop by rotating
two batteries. Even after a full day of demos, no dead batteries get tossed
in the trash.
I haven't had a chance to play with them yet, but we have a new series of
Rayovac NIMH batteries coming in which promise the same kind of performance
but in a standard AA form factor -- including the 15 minute recharge time.
-- Al Margolis, founder
www.hobbyengineering.com
The technology builder's source for kits, components, supplies, tools, books
and education.
Original Message
From: Allan Lane [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=e2KlgAWVcYvaF7PvltwhXdx4-y3jU_a3HQDWi575qZWA12fHxMFIEA7fHyy--TnoeihToEjO6IoTqHsLyuJY-jklIoE]allan.lane@h...[/url
Sent: Friday, February 06, 2004 1:51 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Servos and 7.5 volts
I was sure this had been asked before,
but I've looked, and can't find it,
therefore:
Is there any problem running the
BOE-Bot Servo (Futaba S148) at
7.5 volts? Or even 7.2 volts?
The Futaba website gives values for
4.8 volts and 6.0 volts, but does not
give any 'max' recommended voltage.
I ask this because I've recently become
a proud owner of a BOE-Bot, and I don't
really want to kill all those batteries.
The issue is that the BOE needs 6 volts
minimum for its regulator to work. I
have a 7.5 volt adapter, which I've read
CAN be used with the BOE-Bot, but I
wanted to make sure.
Thanks.
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
Yahoo! Groups Links
> Running servos at higher voltages is a great way to get extra
> performance, but the higher you go the more likely you are
> shortening the working life of the servo.
>
I'm not sure that's true, Al. Could be of course, but it isn't self-evident.
The servo is doing the same amount of work in either case, and higher
voltages often improve the efficiency of a circuit so that the same amount
of work is done with less energy, and often with less wear. As long as we
don't fry the control circuit of course<g>.
> If you just want to conserve batteries, the BOE Rev C has a great
> solution. Just move the servo power selector from Vin (raw battery)
> to Vdd (regulated 5v).
>
This makes a good illustration. Let us suppose the load on the servo causes
it to draw 300 mA with a six volt supply. If we change the supply voltage to
five volts, the same load will require 360 mA. (Because doing the same
amount of work requires that VA be equal in each case. This won't read well
without subscripts, but V1A1=V2A2 if we are doing the same amount of work.)
And that assumes the efficiency is the same at both voltages. (Which it well
may be, but without experimental data we don't know either way.)
The trouble is that the first current is being drawn directly from the
battery. The second is being drawn from the regulator. Now the battery must
supply that 360 mA at 6.0 V in order for the regulator to deliver it at
5.0V. In other words, the load on the battery just increased by twenty
percent and it will discharge faster, not slower than when it was delivering
to the servo directly.
At least I think I got that right. I'm a little distracted here. It's pretty
simple arithmetic unless I've got the relations muddled -- and that's always
possible with everything we have going on right now. I welcome a correction
if I've screwed that up.
The tricky thing about linear regulators is that we have to remember they
control their output voltage by dissipating more or less of the input as
heat. That means that anything taken from a regulator consumes more battery
power than it would if taken directly from the battery. Of course you must
first have a choice. Many things cannot tolerate the varying voltage of the
primary cell.
Gary
that their servos will run at voltages higher than 6.0v. If you kill
them, you can "gut" the electronics and run a external motor controller.
Then if the motor dies, you can always put in a new motor.
The typical RC servo is designed to run at a normal 4.8v based on nicad
or NMH battery packs. The servos are also designed to work at 6v in
order to handle dry cell battery packs as well. But AA dry cells can't
provide the currents that the rechargeable nicads and NMH batteries can
provide.
The electronics inside the servo case are not designed to handle higher
voltages, this goes out of their design specs. Now there are some servos
that are designed for higher voltages (mainly one or two cells extra),
you need to check with your servo manufacturer and see what their specs
are.
The problem is the electronics inside, the servo controller IC is rated
at 6v max. The transistors in the h-bridge may be able to go higher
though typically 20v-60v transistors are used. The higher voltage
transistors can handle the motor EMF better. But the problem for the
h-bridge is the max current capability of the transistors. The
transistors can typically handle 500ma max for cheap servos, to over 1
amp for more expensive servos. Thus as you supply a higher voltage, the
currents being shunted through the transistors goes up causing more
heat. Being inside a tiny case with no air flow doesn't help either, so
you run the risk of a transistor overheating and burning out. That's if
the servo controller IC doesn't de before then.
Now there are some servos that have a CMOS IC inside which can handle
9v-12v OK. But I don't know which ones have the CMOS controller IC's in
them anymore. It's been a while.
The next problem you run into is the motor itself. Servos are geared way
down, something like 100:1 on up to 260:1 gear ratios are common. Now
the motor at these gear ratios can really crank up some RPM's. So as you
raise the voltage you get more RPM, but this causes the motor to run
hotter, the motor brushes wear out faster, and the little bushing motor
bearings to wear out faster too. Expensive servos have ball bearing
motors and may even be coreless too. I haven't seen them put in
brushless motors yet. Some of the higher performance large servos have
metal cases that serve as heat sinks to help cool the transistors and
motor.
So basically, if the servo works at 7.5 volts, it's operational life and
reliability is reduced.
Years ago the Micromouse people tried RC servos, and tried running them
at higher voltages to get faster speeds, but the servos proved to be too
unreliable in the contests to be trustworthy. In some contests the
servos would die faster than they could put in new ones.
Now some guys have gutted (remove the electronics) the servos, and used
regular motor controllers like L293's L298's, 754410's etc. With a
gutted servo 9.6v=12v was possible. I've seen guys doing this to
mini-sumo bots to get more speed and power. Since a match is over fairly
fast, the motors don't get wore out too fast or overheat too much. Thus
they can get reasonable life out of the gutted servos in this case.
I took a look see and none of the RC servo companies will state that
their servos will run at voltages higher than 6.0v.
http://www.hitecrcd.com/product_fs.htm
Some FAQ questions off the www.futaba.com website on servos:
What can I do to ensure long life of my digital servos?
The number one concern is tight linkages which have absolutely no
binding, stiffness, or friction. Because digital servos are always
working to hold in position at full strength, if the servo has a point
it has to fight in the linkage it will literally burn itself out
'hunting' to try to hold its position. Slop at the neutral position is a
very common problem where a standard servo wouldn't notice it but a
digital servo will work very hard to try to hold the rod in position and
will drain your batteries more quickly and eventually burn up the motor.
Can I use 6v (5 cell) receiver packs with my Futaba receiver/servos?
Will I get increased performance from my equipment? Are there any
drawbacks to using 6 volts?
All Futaba systems are designed to operate on either 4.8 volts (NiCD 4
cells) or 6 volts (Alkaline 4 cells OR NiCD 5 cells), except certain
servos which are specifically labeled for use at one voltage or the
other only. Some manufacturer's systems are not designed for and do not
operate well on 6 volt, but most Futaba equipment handles the increased
power input and provides increased performance, speed and torque.
Please note that while 6 volts provides you more torque and speed from
your servos, it also provides you a significantly shorter run time for
the same milliamp hours of capacity and may shorten the life of your
servos proportionally. This sounds confusing, so it may help to compare
the current in the battery to water in a bucket. If you have four small
holes in the bucket, the water will come out at a certain rate. Add a
fifth hole the same size, and you're supplying more water (increasing
the current and therefore making the servos stronger AND faster);
however, the bucket empties 25% sooner than when it only had four holes.
Original Message
From: Allan Lane [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=X7I46HaaWY_gmJVb8LwhdVe3-rCx1GD0KeUgB2BhnHqrIw9Csy_ioJ7Rv1n4kX3A4KVzkdZ1E2AoNBZdDcGOUC2-_DA]allan.lane@h...[/url
Sent: Friday, February 06, 2004 3:51 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Servos and 7.5 volts
I was sure this had been asked before,
but I've looked, and can't find it,
therefore:
Is there any problem running the
BOE-Bot Servo (Futaba S148) at
7.5 volts? Or even 7.2 volts?
The Futaba website gives values for
4.8 volts and 6.0 volts, but does not
give any 'max' recommended voltage.
I ask this because I've recently become
a proud owner of a BOE-Bot, and I don't
really want to kill all those batteries.
The issue is that the BOE needs 6 volts
minimum for its regulator to work. I
have a 7.5 volt adapter, which I've read
CAN be used with the BOE-Bot, but I
wanted to make sure.
Thanks.
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
from the same email address that you subscribed. Text in the Subject
and Body of the message will be ignored.
Yahoo! Groups Links
used up to 9v to power them and they are still alive. If you won't use them
for continuous operation but a couple of hours, they might work. I followed
the recommendations in the link below.
http://www.lynxmotion.com/ViewPage.aspx?ContentCode=techtips&CategoryID=22
>From: "Earl Bollinger" <earlwbollinger@c...>
>Reply-To: basicstamps@yahoogroups.com
>To: <basicstamps@yahoogroups.com>
>Subject: RE: [noparse][[/noparse]basicstamps] Servos and 7.5 volts
>Date: Sat, 7 Feb 2004 16:10:56 -0600
>
>Basically, you do so at your own risk. None of the servo companies state
>that their servos will run at voltages higher than 6.0v. If you kill
>them, you can "gut" the electronics and run a external motor controller.
>Then if the motor dies, you can always put in a new motor.
>
>The typical RC servo is designed to run at a normal 4.8v based on nicad
>or NMH battery packs. The servos are also designed to work at 6v in
>order to handle dry cell battery packs as well. But AA dry cells can't
>provide the currents that the rechargeable nicads and NMH batteries can
>provide.
>The electronics inside the servo case are not designed to handle higher
>voltages, this goes out of their design specs. Now there are some servos
>that are designed for higher voltages (mainly one or two cells extra),
>you need to check with your servo manufacturer and see what their specs
>are.
>
>The problem is the electronics inside, the servo controller IC is rated
>at 6v max. The transistors in the h-bridge may be able to go higher
>though typically 20v-60v transistors are used. The higher voltage
>transistors can handle the motor EMF better. But the problem for the
>h-bridge is the max current capability of the transistors. The
>transistors can typically handle 500ma max for cheap servos, to over 1
>amp for more expensive servos. Thus as you supply a higher voltage, the
>currents being shunted through the transistors goes up causing more
>heat. Being inside a tiny case with no air flow doesn't help either, so
>you run the risk of a transistor overheating and burning out. That's if
>the servo controller IC doesn't de before then.
>Now there are some servos that have a CMOS IC inside which can handle
>9v-12v OK. But I don't know which ones have the CMOS controller IC's in
>them anymore. It's been a while.
>
>The next problem you run into is the motor itself. Servos are geared way
>down, something like 100:1 on up to 260:1 gear ratios are common. Now
>the motor at these gear ratios can really crank up some RPM's. So as you
>raise the voltage you get more RPM, but this causes the motor to run
>hotter, the motor brushes wear out faster, and the little bushing motor
>bearings to wear out faster too. Expensive servos have ball bearing
>motors and may even be coreless too. I haven't seen them put in
>brushless motors yet. Some of the higher performance large servos have
>metal cases that serve as heat sinks to help cool the transistors and
>motor.
>
>So basically, if the servo works at 7.5 volts, it's operational life and
>reliability is reduced.
>
>Years ago the Micromouse people tried RC servos, and tried running them
>at higher voltages to get faster speeds, but the servos proved to be too
>unreliable in the contests to be trustworthy. In some contests the
>servos would die faster than they could put in new ones.
>
>Now some guys have gutted (remove the electronics) the servos, and used
>regular motor controllers like L293's L298's, 754410's etc. With a
>gutted servo 9.6v=12v was possible. I've seen guys doing this to
>mini-sumo bots to get more speed and power. Since a match is over fairly
>fast, the motors don't get wore out too fast or overheat too much. Thus
>they can get reasonable life out of the gutted servos in this case.
>
>I took a look see and none of the RC servo companies will state that
>their servos will run at voltages higher than 6.0v.
>http://www.hitecrcd.com/product_fs.htm
>Some FAQ questions off the www.futaba.com website on servos:
>
>What can I do to ensure long life of my digital servos?
>The number one concern is tight linkages which have absolutely no
>binding, stiffness, or friction. Because digital servos are always
>working to hold in position at full strength, if the servo has a point
>it has to fight in the linkage it will literally burn itself out
>'hunting' to try to hold its position. Slop at the neutral position is a
>very common problem where a standard servo wouldn't notice it but a
>digital servo will work very hard to try to hold the rod in position and
>will drain your batteries more quickly and eventually burn up the motor.
>
>Can I use 6v (5 cell) receiver packs with my Futaba receiver/servos?
>Will I get increased performance from my equipment? Are there any
>drawbacks to using 6 volts?
>All Futaba systems are designed to operate on either 4.8 volts (NiCD 4
>cells) or 6 volts (Alkaline 4 cells OR NiCD 5 cells), except certain
>servos which are specifically labeled for use at one voltage or the
>other only. Some manufacturer's systems are not designed for and do not
>operate well on 6 volt, but most Futaba equipment handles the increased
>power input and provides increased performance, speed and torque.
>Please note that while 6 volts provides you more torque and speed from
>your servos, it also provides you a significantly shorter run time for
>the same milliamp hours of capacity and may shorten the life of your
>servos proportionally. This sounds confusing, so it may help to compare
>the current in the battery to water in a bucket. If you have four small
>holes in the bucket, the water will come out at a certain rate. Add a
>fifth hole the same size, and you're supplying more water (increasing
>the current and therefore making the servos stronger AND faster);
>however, the bucket empties 25% sooner than when it only had four holes.
>
>
>
>
>
Original Message
>From: Allan Lane [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=RunJeIZNS3IIl356KAOyJdv4SysxUTAvMd-s88XUKcS_NXKHGhEBV6OdsiZ9b8EjBKQ8D42CGFpytIcPKcEEd73wqfZ9]allan.lane@h...[/url
>Sent: Friday, February 06, 2004 3:51 PM
>To: basicstamps@yahoogroups.com
>Subject: [noparse][[/noparse]basicstamps] Servos and 7.5 volts
>
>I was sure this had been asked before,
>but I've looked, and can't find it,
>therefore:
>
>Is there any problem running the
>BOE-Bot Servo (Futaba S148) at
>7.5 volts? Or even 7.2 volts?
>
>The Futaba website gives values for
>4.8 volts and 6.0 volts, but does not
>give any 'max' recommended voltage.
>
>I ask this because I've recently become
>a proud owner of a BOE-Bot, and I don't
>really want to kill all those batteries.
>
>The issue is that the BOE needs 6 volts
>minimum for its regulator to work. I
>have a 7.5 volt adapter, which I've read
>CAN be used with the BOE-Bot, but I
>wanted to make sure.
>
>Thanks.
>
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the Subject
>and Body of the message will be ignored.
>
>Yahoo! Groups Links
>
>
>
>
>
>
>
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
>from the same email address that you subscribed. Text in the Subject and
>Body of the message will be ignored.
>
>Yahoo! Groups Links
>
>
>
>
>
_________________________________________________________________
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Thanks, this is a very clear and cogent
answer, which has saved me at least
a day of searching the web. Now I know
what my risks are, and what I can do to
test them.
If I powered the BOE-Bot with 4 Ni-Cd,
then the regulator on the BOE board would
not get enough voltage to regulate at 4.8 V.
If I power with 4 Alkaline, or a 6 V PS,
then the servos get enough, and the BS2
regulator gets enough. BUT, I'm using
up alkaline's all the time.
If I power with 5 NI-CD (Where do I put the
'extra' one?) then it's 6-volts, all good.
(5 * 1.2V == 6V).
If I power with a 7.2 volt rechargable, or
the 7.5 volt PS, then MAYBE I'll kill the
chip in the Futaba. In any case, it looks
like overheating the motor is the least of
my concerns.
--- In basicstamps@yahoogroups.com, "Gary W. Sims" <simsgw@c...>
wrote:
> From: "Allan Lane" <allan.lane@h...>
>
> > Is there any problem running the
> > BOE-Bot Servo (Futaba S148) at
> > 7.5 volts? Or even 7.2 volts?
> >
> Allan, I think this is one of those "are you willing to spend
twenty dollars
> to find out" questions.
>
> I'm using a mix of Futabas and Parallax servos from a Taiwan mfr
I'm too
> tired to remember. Jon and Eric helped me work it out one day when
I was
> trying to match spline patterns, but the name escapes me just now.
Grand
> Wing? Possibly. In any case, with these specific units I've had no
problems
> using up to 7.0 volts in some design experiments, but I don't have
any hours
> of on-robot use to determine whether that shortens the lifetime. I
chose
> that value after finding a note posted on the San Diego Robotics
group.
>
> The writer says the 6.0V arose from intended operation on four AA
cells, and
> designs were modified to operate on 4.8V as well when the use of
four NiCd
> cells became popular. These are standard levels, not limits in
other words.
> But that also means different designers will provide different
levels of
> headroom as their whim and the parts available suggest. Above that
level
> works fine (he says) until you fry the control circuit, whose weak
point was
> an NE544 in his youth. Modern servos like the better Futabas have
newer
> circuit designs that will tolerate up to 9.0V. He says. Again, just
quoting,
> or at least paraphrasing pretty closely.
>
> The trouble is that he also reports opening a recent servo and
finding an
> NE544 generic equivalent, and he speculates that clone chip would
fail at a
> fairly low voltage just like the original. So we take our chances
anywhere
> above the higher specified standard level.
>
> This guy sounds credible enough that it was worth risking $20 or so
on each
> type of servo to see if I could get the higher torque and more
efficient
> battery usage at the higher servo voltage level. My power supply is
> home-rolled and software adjustable, so I can always change the
programmed
> voltage level for the servo line if I start frying servos, but I
don't have
> any operational experience either way to report yet. Just a few
casual
> tests. Very casual: "Ah, no smoke and it still moves. I'll try that
> level..."
>
> Here's the note in the SDRS archives: http://makeashorterlink.com/?
O31E25457
> so you can make your own judgment call. I'd love to find a list of
servos
> with the maximum tested voltage somewhere on the net, but I'm not
holding my
> breath. Even if someone spent the money frying a few dozen
candidates, it
> would not tell us what voltage the next production mod from the
same mfr
> might tolerate. Since they don't spec at anything above 6.0 V, they
won't
> hesitate about using parts that fry at 10% or 15% above that level.
At least
> hypothetically. Personally, I'm betting that any recent design will
have 20%
> margins at least, so I'm using 7.0 V as a working estimate until
the air
> gets that distinctive tangy smell around my robot<g>.
>
> Gary