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Padu posted on February 21, 2006, 3:40 pm
Hi, for those of you who don't know the projects I'm involved, I'm working
on two robots: Koli and Yaboo. Koli is based on a RC car platform and is
well advanced (halfway on developing the electronics). Now, the newest
project, Yaboo, is a gas powered ATV and obviously demands better control
equipment. Right now I'm researching alternatives for automating its systems
(steering, brakes, throttle, etc), and I'll use this thread to expose some
of my concerns and try to get some expert advise from you.
Shall we start with the steering column?
http://www.merlotti.com/EngHome/rover/steering_close.jpg
The above picture shows the vertical steering column connected to the two
steering rods that go to the wheels. I don't want to mess with the mechanics
of it, since the rotation of that plate is what implements ackermann. In
order to steer the ATV, it requires an average 17Nm for small corrections
and 45Nm peak torque. Whatever actuation mechanism I choose, I'm targeting
60RPM on the steering column. Power comes from one deep cycle 55A/H optima
battery.
Based on these draft specs, I was able to find the following components:
- Motor controller: Roboteq 3500
http://www.roboteq.com/ax3500closeup.shtml
- DC motor: Ampflow (Magmotor really) S28-150
http://www.ampflow.com/ampflow_motors.htm
- Gear head: Bison planetary around 45:1, still not set
- Power transfer: 1.5:1 pulleys and timing belt
- Potentiometer for position feedback
- Assorted brackets, couplings and general hardware
A few comments:
I liked the roboteq 3500, because it is very simple to use and very
flexible. It has 2x60A channels for DC motors and 8 RC servo controllers,
which will simplify my work later on.
The S28-150 was the only one that came closer to my specs: runs at 12V
(although it is more efficient @ 24V), provides lots of torque at relatively
low RPM, and not too expensive (around $300).
Planetary gearheads were a pain... too expensive (around $700). The only one
I could find a bit cheaper (around $250) was the bison one, but I may have
problems to connect the motor.
Potentiometer: although a google search return millions of pots, I wanted
one that was specific for this use, I still don't know where to find one.
So, what do you think? Is this selection appropriate of you think there may
be a better solution?
** Scenes of the next episodes: Actuating the brakes and gear shifting
lever...
Cheers
Padu
on two robots: Koli and Yaboo. Koli is based on a RC car platform and is
well advanced (halfway on developing the electronics). Now, the newest
project, Yaboo, is a gas powered ATV and obviously demands better control
equipment. Right now I'm researching alternatives for automating its systems
(steering, brakes, throttle, etc), and I'll use this thread to expose some
of my concerns and try to get some expert advise from you.
Shall we start with the steering column?
http://www.merlotti.com/EngHome/rover/steering_close.jpg
The above picture shows the vertical steering column connected to the two
steering rods that go to the wheels. I don't want to mess with the mechanics
of it, since the rotation of that plate is what implements ackermann. In
order to steer the ATV, it requires an average 17Nm for small corrections
and 45Nm peak torque. Whatever actuation mechanism I choose, I'm targeting
60RPM on the steering column. Power comes from one deep cycle 55A/H optima
battery.
Based on these draft specs, I was able to find the following components:
- Motor controller: Roboteq 3500
http://www.roboteq.com/ax3500closeup.shtml
- DC motor: Ampflow (Magmotor really) S28-150
http://www.ampflow.com/ampflow_motors.htm
- Gear head: Bison planetary around 45:1, still not set
- Power transfer: 1.5:1 pulleys and timing belt
- Potentiometer for position feedback
- Assorted brackets, couplings and general hardware
A few comments:
I liked the roboteq 3500, because it is very simple to use and very
flexible. It has 2x60A channels for DC motors and 8 RC servo controllers,
which will simplify my work later on.
The S28-150 was the only one that came closer to my specs: runs at 12V
(although it is more efficient @ 24V), provides lots of torque at relatively
low RPM, and not too expensive (around $300).
Planetary gearheads were a pain... too expensive (around $700). The only one
I could find a bit cheaper (around $250) was the bison one, but I may have
problems to connect the motor.
Potentiometer: although a google search return millions of pots, I wanted
one that was specific for this use, I still don't know where to find one.
So, what do you think? Is this selection appropriate of you think there may
be a better solution?
** Scenes of the next episodes: Actuating the brakes and gear shifting
lever...
Cheers
Padu
John Nagle posted on
Re: Autonomous ATV
For Team Overbot, we used a Maxon servomotor with a planetary gearhead,
coupled directly to the steering shaft via a shock-absorbing coupling.
The steering wheel was removed. The motor had an HP encoder.
On the steering shaft, we mounted a circular through-shaft
pot/encoder of the type used on GM cars. This produced encoder
signals at 1 degree intervals, plus a signal from a pot for
absolute positioning.
Control was provided by a Galil DMC-1416 motor controller,
which also read the encoders and pots, and the auto/man switch.
At power-up, the controller read the pots and centered the
steering.
The steering wheel became a purely electrical input device,
with an identical pot/encoder. This allowed manual driving
with electrical power steering.
Power came from a 3KW Generac generator driving Vicor
24VDC power supplies.
Today, the Roboteq controller is a good choice. That
wasn't available when we started. Get
the one with the encoder input, and connect that to the
motor's encoder. You'll need a second sensor of some
kind to home the steering. A limit or home switch is
sufficient. A useful trick is to have a home switch
or sensor that will detect if the wheels are pointed
straight ahead, plus a second switch to tell you whether
the wheels are pointed right or left. Then you can
home to center under program control. We used the
through-shaft pot for that.
Incidentally, we steered the Overbot with less than
8A peak at 24VDC, and could turn the wheels without
difficulty even stopped on asphalt. This was a
Polaris Ranger, which is a big, manual-steering ATV.
John Nagle
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