drive system and feedback
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Posts: 46,084
I need some suggestions:
I am building a small robit that will need to move and rotate set ammounts.
I need to know what kind of motor i should use and what kind of feedback i
will need.
I will need to move with at least .5 cm accuracy (as of yet i have not
chosen a wheel size) and
be able to rotate the whole robot without moving forward/backward with
.001rad accuracy
I'm pretty new, both with hardware and software, but i know the basics
thanks
I am building a small robit that will need to move and rotate set ammounts.
I need to know what kind of motor i should use and what kind of feedback i
will need.
I will need to move with at least .5 cm accuracy (as of yet i have not
chosen a wheel size) and
be able to rotate the whole robot without moving forward/backward with
.001rad accuracy
I'm pretty new, both with hardware and software, but i know the basics
thanks
Comments
I'm limited to 9v or below, including driving the motors
thanks
>I need some suggestions:
>
>I am building a small robit that will need to move and rotate set
>ammounts. I need to know what kind of motor i should use and
>what kind of feedback i will need.
I think the only choice for this task is stepper motors, but your bot can't
have so much inertia (or wheel slip on whatever surface it runs on) that
the stepper motor (or wheels) slips when accelerating, decelerating, or
traveling or you will lose your frame of reference.
>I will need to move with at least .5 cm accuracy (as of yet i have not
>chosen a wheel size) and be able to rotate the whole robot without
>moving forward/backward with .001rad accuracy
For linear travel relative to an initial arbitrary position you should be
able to move a fair distance with 0.5 cm accuracy by counting pulses sent
to the stepper. The more steps the stepper has and the more it is geared
down the better. Wheel diameter matters. You'll need to do the math
before buying parts.
Rotation is another matter. Do you want to rotate a turret on the robot to
a position relative to the body/base of the robot; or do you want to rotate
the robot/turret with respect to some reference point outside the robot
such as true magnetic north? I'd say the latter is all but impossible
unless done in a room filled with benchmarks the robot can "see," and then
he better have some *VERY* sharp vision. Positioning a turret relative to
the body shouldn't be so hard. Return to a home position, then step from
there to the desired position. Use a geared down stepper motor with at
least 6283 steps (2*pi/0.001) per full rotation, preferably at least twice
that. For rotation of a turret relative to the body, if you keep track of
current position you shouldn't need to rehome before every change to a new
position.
I'm not sure what you're really trying to do in terms of the "larger
picture" so I don't know if you need extended math capability beyond what
PBasic provides to do it with the desired precision.
Jim H
If you have three reference points then the robot can compute its position.
This avoids accumulated errors. Otherwise you will definitely have to
'home' the robot from time to time at a know position.
Original Message
From: Jim Higgins [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=xqhypIME_G8uRYYs5bfjVNKsdOYpyVwdaevlOIyBCC0AcDX2e-uoPrLgRRvbrojyqyToWp5J9gnVSeyf]HigginsJ@s...[/url
Sent: Monday, July 16, 2001 1:08 PM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] drive system and feedback
At 14:09 07/16/01, Ian wrote:
>I need some suggestions:
>
>I am building a small robit that will need to move and rotate set
>ammounts. I need to know what kind of motor i should use and
>what kind of feedback i will need.
I think the only choice for this task is stepper motors, but your bot can't
have so much inertia (or wheel slip on whatever surface it runs on) that
the stepper motor (or wheels) slips when accelerating, decelerating, or
traveling or you will lose your frame of reference.
>I will need to move with at least .5 cm accuracy (as of yet i have not
>chosen a wheel size) and be able to rotate the whole robot without
>moving forward/backward with .001rad accuracy
For linear travel relative to an initial arbitrary position you should be
able to move a fair distance with 0.5 cm accuracy by counting pulses sent
to the stepper. The more steps the stepper has and the more it is geared
down the better. Wheel diameter matters. You'll need to do the math
before buying parts.
Rotation is another matter. Do you want to rotate a turret on the robot to
a position relative to the body/base of the robot; or do you want to rotate
the robot/turret with respect to some reference point outside the robot
such as true magnetic north? I'd say the latter is all but impossible
unless done in a room filled with benchmarks the robot can "see," and then
he better have some *VERY* sharp vision. Positioning a turret relative to
the body shouldn't be so hard. Return to a home position, then step from
there to the desired position. Use a geared down stepper motor with at
least 6283 steps (2*pi/0.001) per full rotation, preferably at least twice
that. For rotation of a turret relative to the body, if you keep track of
current position you shouldn't need to rehome before every change to a new
position.
I'm not sure what you're really trying to do in terms of the "larger
picture" so I don't know if you need extended math capability beyond what
PBasic provides to do it with the desired precision.
Jim H
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