Best Approach for Robots using Servos as Drive Motors
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Posts: 46,084
Was wondering if it is just me, or has anyone else been frustrated in
using a co-processor to off-load the task of keeping the wheels
turning on robots that use "hacked" servos for drive motors on their
robots (you know, the "BOE-bot" approach). I have tried several
servo controllers, but have not found one that has a simple, straight
forward command structure. The problem is that these servo
controllers where designed for managing servo's that have not been
hacked for continuous rotation (which makes sense). So where does
that leave an amateur newbie like me? I think I found a simple,
inexpensive solution!
I simply removed the entire circuit board that was inside the servo.
I also trimmed the manual "stop post" on the output gear. I then
soldered the wires directly to the motor (I left the white wire
unconnected). When I put the casing back on the servo, I had
essentially created a small motor with a set of reduction gears that
is in a nice little package that is easy to mount.
Now the big break-through! I found an inexpensive Dual Serial Motor
Controller from a company called Pololu (their website is
www.pololu.com). The command structure is very easy. You simply
send a one line "serout" command with a few parameters to indicate
the motor, direction, and speed (from 0 to 127). That is it. You
can't get much easier than that. I am not quite sure why this
approach has not become the "standard" for using modified servos as
wheels. Why would anyone still prefer to mess with determinining PWM
values to get a servo to rotate one way or the other at different
speeds?
I have amassed quite a collection of robot books and none of them
suggest this approach. They either describe mounting fixed motors or
simply modifying the servo for continuous rotation. Am I missing
something that others have learned? If so, please let me know the
lesson!
Thanks,
Steve
using a co-processor to off-load the task of keeping the wheels
turning on robots that use "hacked" servos for drive motors on their
robots (you know, the "BOE-bot" approach). I have tried several
servo controllers, but have not found one that has a simple, straight
forward command structure. The problem is that these servo
controllers where designed for managing servo's that have not been
hacked for continuous rotation (which makes sense). So where does
that leave an amateur newbie like me? I think I found a simple,
inexpensive solution!
I simply removed the entire circuit board that was inside the servo.
I also trimmed the manual "stop post" on the output gear. I then
soldered the wires directly to the motor (I left the white wire
unconnected). When I put the casing back on the servo, I had
essentially created a small motor with a set of reduction gears that
is in a nice little package that is easy to mount.
Now the big break-through! I found an inexpensive Dual Serial Motor
Controller from a company called Pololu (their website is
www.pololu.com). The command structure is very easy. You simply
send a one line "serout" command with a few parameters to indicate
the motor, direction, and speed (from 0 to 127). That is it. You
can't get much easier than that. I am not quite sure why this
approach has not become the "standard" for using modified servos as
wheels. Why would anyone still prefer to mess with determinining PWM
values to get a servo to rotate one way or the other at different
speeds?
I have amassed quite a collection of robot books and none of them
suggest this approach. They either describe mounting fixed motors or
simply modifying the servo for continuous rotation. Am I missing
something that others have learned? If so, please let me know the
lesson!
Thanks,
Steve
Comments
Original Message
From: "sjoblin001" <steven_joblin@h...>
To: <basicstamps@yahoogroups.com>
Sent: Wednesday, November 06, 2002 7:09 AM
Subject: [noparse][[/noparse]basicstamps] Best Approach for Robots using Servos as Drive Motors
> Was wondering if it is just me, or has anyone else been frustrated in
> using a co-processor to off-load the task of keeping the wheels
> turning on robots that use "hacked" servos for drive motors on their
> robots (you know, the "BOE-bot" approach). I have tried several
> servo controllers, but have not found one that has a simple, straight
> forward command structure. The problem is that these servo
> controllers where designed for managing servo's that have not been
> hacked for continuous rotation (which makes sense). So where does
> that leave an amateur newbie like me? I think I found a simple,
> inexpensive solution!
>
> I simply removed the entire circuit board that was inside the servo.
> I also trimmed the manual "stop post" on the output gear. I then
> soldered the wires directly to the motor (I left the white wire
> unconnected). When I put the casing back on the servo, I had
> essentially created a small motor with a set of reduction gears that
> is in a nice little package that is easy to mount.
>
> Now the big break-through! I found an inexpensive Dual Serial Motor
> Controller from a company called Pololu (their website is
> www.pololu.com). The command structure is very easy. You simply
> send a one line "serout" command with a few parameters to indicate
> the motor, direction, and speed (from 0 to 127). That is it. You
> can't get much easier than that. I am not quite sure why this
> approach has not become the "standard" for using modified servos as
> wheels. Why would anyone still prefer to mess with determinining PWM
> values to get a servo to rotate one way or the other at different
> speeds?
>
> I have amassed quite a collection of robot books and none of them
> suggest this approach. They either describe mounting fixed motors or
> simply modifying the servo for continuous rotation. Am I missing
> something that others have learned? If so, please let me know the
> lesson!
>
> Thanks,
>
> Steve
>
>
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>
> read your mess. and had the same feelings you have the site you mentioned
is very helpful
thanks for the info
max
>
You're not alone on this one. We have received inquiries on this topic and have
just started to
carry the Pololu Micro Dual Serial Motor Controller (try saying that five times
without stumbling!).
The part number is #30052 and it is priced at $23.00. Here's the link to check
it out-
http://www.parallaxinc.com/html_files/products/BS_Accessories/pololu_motor_contr\
oller.asp
We have quantity 50 in stock...they'll probably go fast.
Erik Wood
Parallax, Inc.
599 Menlo Dr., Suite #100
Rocklin, CA 95765
(916) 624-8333
www.parallaxinc.com
Original Message
From: sjoblin001 [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=dpYDQRO0ds7F8uDgsVG-6S6Ds1DtsTikt2tCE408CwFnXpE9nOOTIbVHvZ42775ijrHOeUIk9i_XXjCOysYc]steven_joblin@h...[/url
Sent: Wednesday, November 06, 2002 7:10 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Best Approach for Robots using Servos as Drive
Motors
Was wondering if it is just me, or has anyone else been frustrated in
using a co-processor to off-load the task of keeping the wheels
turning on robots that use "hacked" servos for drive motors on their
robots (you know, the "BOE-bot" approach). I have tried several
servo controllers, but have not found one that has a simple, straight
forward command structure. The problem is that these servo
controllers where designed for managing servo's that have not been
hacked for continuous rotation (which makes sense). So where does
that leave an amateur newbie like me? I think I found a simple,
inexpensive solution!
I simply removed the entire circuit board that was inside the servo.
I also trimmed the manual "stop post" on the output gear. I then
soldered the wires directly to the motor (I left the white wire
unconnected). When I put the casing back on the servo, I had
essentially created a small motor with a set of reduction gears that
is in a nice little package that is easy to mount.
Now the big break-through! I found an inexpensive Dual Serial Motor
Controller from a company called Pololu (their website is
www.pololu.com). The command structure is very easy. You simply
send a one line "serout" command with a few parameters to indicate
the motor, direction, and speed (from 0 to 127). That is it. You
can't get much easier than that. I am not quite sure why this
approach has not become the "standard" for using modified servos as
wheels. Why would anyone still prefer to mess with determinining PWM
values to get a servo to rotate one way or the other at different
speeds?
I have amassed quite a collection of robot books and none of them
suggest this approach. They either describe mounting fixed motors or
simply modifying the servo for continuous rotation. Am I missing
something that others have learned? If so, please let me know the
lesson!
Thanks,
Steve
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