Re: [beam] Re: Ummm...where is everybody?
- Don't think you need to worry about your neck. I'm a little worried it will
just rock side to side. But on the other hand if it moves very slowly (thus
hopefully spending more energy turning) then I'll have what I wanted. We'll
see what can be done by shifting the weight of the batteries. Weight forward
and it'll do a lot of rocking but the rear legs will perhaps do a stepping
motion (poorly timed). with weight on rear legs it should be like a uCrawler
with a up-down motion. I'm thinking perhaps making the angle of rotaion
between leg pairs adjustable. Should be possible with the rubberband crank.
Whatever it does I promise to show it with a movie. :)
The "Crankshaft model of phase angle translation" you describe requires a
continous rotation. I saw such a design somewhere. It was very efficient. I
don't see it happening with a reciprocating motor though, which disqualifies
it for this project. I need to familiarize myself with the bicore.
----- Original Message -----
From: "wilf" <wrigter@...>
Sent: Sunday, April 30, 2006 6:50 PM
Subject: Re: [beam] Re: Ummm...where is everybody?
Jérôme's bot has 2 pairs of legs that rotate in the same horizontal plane,
180 degrees out of phase. E.g. when one pair is turning cw, the other is
turning ccw and both change direction of rotation at the same time.
Therefore both legs contribute to the push back and move forward motion.
While moving forward, the bot can turn left or right a small increment with
each step (wide circle) but it cannot backup if it hits an obstacle head on.
With your design, in the photos you posted, the front legs and rear legs
rotate in the vertical and horizontal planes respectively. The phasing of
leg rotation is 180 degrees out of phase.
I may be sticking my neck out but I think your bug may either move forward
very slowly and inefficiently or it may just rock side to side.
My reason for thinking this is that with your linkage the legs rotate 180
degrees out of phase. E.g. when one pair is turning cw, the other is
turning ccw and both change direction of rotation at the same time. So the
rear leg finishes its push stroke at maximum lift on the front leg just
before it starts to lower down.
Walker required leg phasing
For lift to translate into forward motion, the rotation of the legs should
be 90 degree out of phase. E.g. half the time one pair of legs is turning cw
and the other is turning ccw but the other half of the time both turn in the
same direction. You can say that that their rotations overlap with each
changing direction midway through the rotation of the other.
Bottom line: When the rear leg finishes its push stroke at maximum rotation
and changes direction the front leg just is touching down, with both feet on
the ground midway through the rotation and the other leg just starts to lift
This timing of the front leg lift causes the weight to shift from the rear
leg that is just finishing the push stroke to the other rear leg which is
just starting it's push stroke.
With a two motor walker the solution is simply to delay the rotation of one
motor with respect to the other.
Crankshaft model of phase angle translation
With a one motor walker some linkage is needed to translate the rotation of
the front legs to the rear legs with a 90 degree phase shift.
For forward and reverse motion with no turning, a single motor driven
crank shaft with 4 connecting rods would do it. The motor shaft would
rotates continuously cw or ccw (forward or reverse) . The motor shaft , the
front leg shaft and the rear leg shaft would all be at right angles to each
other in each of the 3D planes.
To visualize this crankshaft arrangement think bicycle pedals with two rods
connected to each pedal and connected horizontally to the two sides of the
rear legs. As the pedals rotate, the rods push back to front and move the
rear legs back and forth. The other two rods are also connected one to each
of the pedals and connect vertically to the each side of the front legs.
With each rotation, the front legs alternately lift up on the left or right
With the 4 rods pusing and pulling, both feet of the front legs will be on
the ground just as the rear legs start to change direction of rotation.
This is the 90 degree phase relationship between the front and rear leg
rotation I am trying to describe.
Short of a mechanical drawing or some animation I hope this will help.
- Even if it has been done I'm always ready to do a new and improved version. There have been many opamp and comparator beam projects but only few SE type.One point is that cmos opamps are not ultra low (<10ua) power. Another point is that the voltage reference and timing or hysteresis components must beadded externally. All of those are present in a 1381 and other voltage supervisorry chips. With simplicity and efficiency, it is no wonder that the most popular and refined SE circuits use a 1381.However with a quad opamp or comparator, the remaining sections can be put to good use making opamps more atractive for some 1 chip projects. Much of the circuit development can use a standard LM324 quad opamp for proof of principle and for solar or other low power applications a low power cmos device can generally be directly substituted. CMOS opamps have a nice feature that the quiescent supply current is relatively constant even when near the threshold. The 1381 and CMOS logic chips often have a steep current rise that can hang the circuit.As for misbehaving during power up, the 1381 is not guaranteed either but the minimum base or gate turn on voltage for the output transistor generally keeps the SE disabled during powerup.
From: email@example.com [mailto:firstname.lastname@example.org]On Behalf Of Dave Lag
Sent: Monday, May 01, 2006 4:26 PM
Subject: Re: [beam] First project
So my first thought upon reading this -- is that a fet opamp as a quasi
comparator + schmitt +? would be ideal to play with trigger points etc.
Would still need the transistors for current, perhaps this has been tried?
...poking around...there are some 1 volt stable opamps...
Maybe they misbehave during powerup?
I think I hijacked Doug's thread- apologies
>Thanks for that Myc and as always everyone is welcome to ask
>questions and/or contribute. These transfusions of ideas and
>information are the lifeblood of our group.
>Minor comment on your comment:
>>For some purposes almost complete discharge
>>of the capacitor is desired with the corresponding
>>long recharge cycle, while for others, small frequent
>>"pops' are desired.
>In many cases frequent short pops are desirable for visual
>An SE can be a constant voltage type (CVSE) that generates
>short current pulses without fully discharging the caps.
>Short rectangular current pulses using large caps at nearly
>full voltage provide a lot more energy than exponentially
>decaying voltage and current pulses of discharging small
>The only penalty of a CV SE is the initial wait for the
>large cap to reach its operating voltage after which the SE
>trigger in frequent short pulses.
>Since the cycle time of a CV SE can be the same for the
>large cap to charge and discharging a few 100mV compared to
>FLED or FRED to completely charge and discharge a small cap,
>the CV SE with a small difference voltage between trigger
>and reset threshold is generally much more efficient.
>In fact, converting electrical energy to work is the most
>During every exponential current pulse, the motor generally
>stops rotating before the cap is fully discharged and there
>is no merit in further discharging the cap when the motor
>has already stopped. For every CV SE current pop, the motor
>continues to provide full torque until the end of the pulse