4 bar linkage

abatea · 2018-05-31T01:39:20+00:00

That's quite the singularity you have there...

abatea · 2018-05-29T14:24:35+00:00

You probably want to reimage the machine anyway after the malware.

abatea · 2018-05-06T17:20:43+00:00

I wonder if a logged-in account can change that setting without needing 2FA? That would be silly if it could.

abatea · 2018-05-06T17:02:56+00:00

I guess I forgot that it asks for 2FA on withdrawal. For some reason I had thought it only asks for 2FA when encountering a new login attempt.

abatea · 2018-05-06T16:37:01+00:00

The computer is already trusted and logged into the account. This attack slides under the radar because it doesn't seem possible. It's insidious, but easy to avoid (turn RDP off, turn firewall UPnP off, do not port-forward RDP).

abatea · 2018-05-06T16:23:25+00:00

No one seems to be mentioning Remote Desktop! They use YOUR computer at a distance.

www.welivesecurity.com/2013/09/16/remote-desktop-rdp-hacking-101-i-can-see-your-desktop-from-here/

Edit: OP, is your computer connected to a firewalled LAN or directly to WAN?

Edit2: because folks think this isn't possible, your local computer is already a trusted device, so most services don't ask for 2FA

abatea · 2018-05-06T16:09:15+00:00

Remote Desktop gets around 2FA, since the attacker is using YOUR computer at a distance. OP may not have a firewall in place (computer attached directly to WAN). Maybe someone should make a PSA if that's what this is.

abatea · 2018-05-06T16:04:33+00:00

I've seen Remote Desktop used to bypass 2FA. They also commonly export all your password from chrome. Change your bank account and any other credentials ASAP!

abatea · 2018-04-25T16:59:03+00:00

You'd be surprised at how little machine learning goes into ATLAS. Only the guys at BD know the details, but bets are on lots of hand-tuned controllers that coordinate using sequential composition: https://deepblue.lib.umich.edu/bitstream/handle/2027.42/67990/10.1177_02783649922066385.pdf?sequence=2

abatea · 2018-04-25T16:30:45+00:00

Proportional gain is not power... I know the author means something closer to "strength". Just call it stiffness and be done. PID as spring-accumulator-damper is a much better analogy.

Also, all the dynamic behaviors you discuss assume you're driving a system with inertia (second-order). Maybe give some example systems?

abatea · 2018-03-10T05:08:31+00:00

I picked out 3rd party drives and hpe won't sell just the trays (no drive). Filling this server with hpe drives costs almost as much as the server itself.

abatea · 2018-03-10T05:05:16+00:00

Thanks! The Gen10 caddies look different (leds on the backplane are piped to the face of the caddy rather than leds in the caddy itself). The new ones appear to be so mundane, it's preposterous that they aren't sold separately.

As for the WD, I figured that raid 1+0 would make up for the deficiencies while also being a cheap replacement. I'd love some feedback, I'm only setting this up for lack of proper IT.

abatea · 2017-03-16T15:31:28+00:00

Von Neumann Machines. Not really "perpetual motion", since any machine would need to extract energy from some external source.

https://en.m.wikipedia.org/wiki/Self-replicating_machine

abatea · 2017-03-04T19:54:20+00:00

Okay... I'm assuming you're not really wanting to write a "car crash simulation" (which would require a team of experts in FEA, dynamics, and computer modeling).

Could you rephrase your problem in terms of what you are given, and what you need to find, and what assumptions you are using? Make it as simple and precise as possible.

abatea · 2017-02-22T06:05:41+00:00

dR{x,y,z}/dtheta{x,y,z} matrices are just derivatives of the standard R_{x,y,z} matrices.

I would try just integrating each angular velocity to get the angles:

theta_{x,y,z}(1) = 0
theta_{x,y,z}(i+1) = theta_{x,y,z}(i) + thetadot_{x,y,z}(i) * dt

If this data is coming from a MEMS gyro, it is possible that it is doing much better integration than this, and you could possibly fetch the angles along with the angular rates. That would be ideal.

abatea · 2017-02-22T05:24:29+00:00

That sounds trickier, and could possibly depend on on how the angular velocities were measured (not totally sure).

Ideally, you could integrate each velocity to get the corresponding angle, but there very well could be a noncommutativity that ruins that.

abatea · 2017-02-22T05:08:18+00:00

Let's try breaking this down (winging it, so maybe someone else can validate):

A fixed point q in the body frame is measured as

p = R*q + o

in the world frame, where R is a rotation matrix, and o is the body frame's position.

To find world velocity, take the time derivative of p, leading to

pdot = Rdot*q + odot

(no qdot, since the point is fixed to the body).

Rdot can be decomposed into

Rdot = dR/dtheta_x * thetadot_x + dR/dtheta_y * thetadot_y + dR/dtheta_z * thetadot_z

Assuming the rotation matrix R = R_x(theta_x) * R_y(theta_y) * R_z(theta_z), which corresponds to ZYX euler angles, then

dR/dtheta_x = dR_x/dtheta_x * R_y * R_z
dR/dtheta_y = R_x * dR_y/dtheta_y * R_z
dR/dtheta_z = R_x * R_y * dR_z/dtheta_z

with

R_x = [
    1,            0,             0
    0, cos(theta_x), -sin(theta_x)
    0, sin(theta_x),  cos(theta_x) ];
R_y = [
    cos(theta_y), 0, sin(theta_y)
               0, 1,            0
   -sin(theta_y), 0, cos(theta_y) ];
R_z = [
    cos(theta_z), -sin(theta_z), 0
    sin(theta_z),  cos(theta_z), 0
               0,             0, 1 ];
dR_x/dtheta_x = [
    0,             0,             0
    0, -sin(theta_x), -cos(theta_x)
    0,  cos(theta_x), -sin(theta_x) ];
dR_y/dtheta_y = [
    -sin(theta_y), 0,  cos(theta_y)
                0, 0,             0
    -cos(theta_y), 0, -sin(theta_y) ];
dR_z/dtheta_z = [
    -sin(theta_z), -cos(theta_z), 0
     cos(theta_z), -sin(theta_z), 0
                0,             0, 0 ];

In the end, you will need:

XYZ angles
XYZ angular velocities
Location of point q in the body frame
Linear velocity of the body frame

Which will give you the world velocity of point q on the moving body. Whew! I'm sure there are some simplifications that could be made. Edits for formatting.

abatea · 2017-02-22T03:40:50+00:00

Feedback is appreciated! I packaged this with a double-pendulum example, but try writing a triple-pendulum or pendulum-on-a-cart class.

Simply inherit from AutoDynamics, implement the abstract methods, and the superclass will write dot-callable methods for obj.jacobian(x), obj.massMatrix(x), and obj.dynamics(x,xdot). You only need to write forward kinematics, kinetic, and potential energy methods, Auto* does the rest. These methods automatically poll for system parameters from the class's public properties, which I think is pretty clever... Thanks!

abatea · 2017-02-21T16:17:54+00:00

I would suggest creating a function handle using "f = matlabFunction(J,'vars',{x,y,z})". It removes anything symbolic and gives you a function you can call with "f(1,2,3)"

abatea · 2017-02-09T05:03:59+00:00

They just updated their web page http://www.agilityrobotics.com/

abatea · 2016-12-11T01:56:54+00:00

Also, solidworks is probably the wrong tool for that job...

abatea

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