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41
Mechanics and Construction / Re: Robot Construction Log
« Last post by FIFO on March 29, 2016, 05:23:20 PM »
    I have been doing some debugging of the programer, and have discovered something very interesting.

    At first I thought that the manual programmer might not have been functioning properly because the supply voltage was too low. I thought this might have been a problem because the programmer is powered by the robot through some relatively long wires, and I thought that the voltage drop might have been enough to drop the supply rail below the tolerance of the ICs in the programmer. I then measured the supply rail at the programer, and while it was low, it was not below the minimum required by the components.

    Even though the supply voltage was in tolerance, because the supply was a little low, I wondered if I increasing the voltage might solve the problem. To test to see if this would work, I removed the main board, (which draws a lot of current and causes the voltage rail to dip a little), and attached the manual programmer. After some testing, it was clear that the programmer was functioning without error. I then measured the supply rail in the programmer, expecting to see a higher voltage, but to my surprise, the rail was only about 30mV higher.

    I now strongly suspect that the main board is somehow interfering with the programmer which is why it is acting erratically.
42
Electronics / Re: Powering Arduino and Dynamixel
« Last post by FIFO on March 29, 2016, 02:58:16 PM »
    If your servos are put under a load that is greater than they can handle, they can be damaged by drawing too much current. To prevent an over current situation from damaging your servo, you could put a fuse inline with it's supply or ground connection, so that if the servo draws too much current, the fuse will blow, preventing damage.

    One annoyance of this setup is that the fuse must be replaced if it is blown. To avoid this inconvenience, you could use what is called a PTC fuse, which unlike a normal fuse, resets after power is removed.
43
Electronics / Powering Arduino and Dynamixel
« Last post by BrokenDynamixels on March 28, 2016, 09:12:29 PM »
Can I use a 12v 5Ah lead-acid battery to power an Arduino and Dynamixel servos? Online I found that they both should be fine going up to 12v, but is there any chance that they will drawn to much current and burn up? Is a fuse all I need to be safe?
44
Mechanics and Construction / Re: Robot Construction Log
« Last post by FIFO on March 27, 2016, 07:02:56 PM »
   
Quote
I have tried also to use the wire wrap direction, and found that the wires acted like
antennas, with the bus speeds. This put out a lot of noise, and loaded down my CPU with a fanout rate.

    Yeah, I thought that might be a possibility, but I am not experienced enough to know if it is an issue in my case or not. Just to be sure, I set up a test jig for the 8155 on a breadboard, and tried to write to it slowly using an Arduino board. That proved to be unsuccessful, and after several other attempts, I came to the conclusion that the chips were dead.

    I ordered some new ones off of Ebay, and tried to write to those using the same test setup, however I was unsuccessful. At that point I began to doubt whether my test setup was correct, so I installed one of the new 8155s on robot.

    Previously, when I still was using the refurbished chips, I had attempted to program the robot using the manual programmer. It turns out that I had wired it incorrectly, and the address/data bus lines were mixed up. Instead of attempting to fix the programmer, I tried to use the automatic programmer which I thought was working. However as is evident from my previous posts, those attempts proved to be futile.

    Now that I had installed the new chip on the robot, I attempted to program the robot with the automatic programer, but that was ineffective. At this point I thought that the automatic programer might have a problem, so rather than try to debug its the hardware and code, I fixed the manual programmer and housed it in a tea tin. (Previously I had it in a cardboard box, but it looked really suspicious with wires hanging out, a red 7-segment display, and a bunch of red buttons, so I decided that I should make it a little less threatening.) I then used the manual programmer to program the robot to simply stand still, (if you remember, in its naturally unprogrammed state, the robot rolls backward,) and when I was finished, the robot did not move, indicating the the programming had been successful.

    So it appeared that the new chips and the manual programmer worked, but that the automatic programmer did not. The next day I attempted to program the robot again with the manual programmer, but the programmer acted erratically. Since then I have tried to repair it, but have had little success.

    Attached to this post are two pictures of the manual programmer. To operate the programmer, the programmer is first plugged into the back of the robot. Then the two toggle switches directly under the display are used to select which chip to write to. Next, the address to which the data is to be written is set up using the two red buttons on the right side of the programmer. Once the correct address is selected, the button on the top left of the programmer is pushed to latch the address. Then the two buttons on the right side are used again, except this time, to set up the data to write to the address that was previously latched. Once the data is set up, the bottom left button is pushed to write that data.
45
Hello again!

It took me a little while to get back to it, but today I swapped in my spare BigEasy driver and added a heatsink to the chip for good measure (using thermally conductive tape).




and tried things again.

I made a couple of changes; first, I figured that perhaps the very powerful Trinamic stepper was drawing too much current from the board (or produced too much back EMF or something), so I went back to the SparkFun stepper



(Wantai 125 oz/in stepper, supposed to draw a max of 2.0A). I was still powering things with a 24 vdc wall-wart which is spec'd to product 1.33 amps
(I was worried about blowing the board again)



Then I built it into the overall rig and started stepping. What you see below is a frame built from 80/20 with a faceplate of 1/4" MDF which the stepper is bolted to. The stepper shaft is connected to an Actobotics hub, and that's connected to a disk of 1/4" ply with some rings of 1/4" MDF added to it to add mass. I'd say the whole thing weighs about 400g.



The behavior is that it ran actually fairly nicely, with a little stutter, up to about 210 steps/second; I had to gently juice the pot on the board to get it to keep running smoothly. It got to about 210, hung up, and just quit. It seems the board produces no more steps. At first, I thought this was due to a wire coming loose (step B- had come loose). But when I reinserted the wire, still no more steps. The board seems to just be done. I was hoping to make a video to show the shaky rotation, but the thing quit before I got the chance to (I got about 90 seconds from powerup to stopped working).

FWIW, I'm wired (from the stepper)

Black -> A+
Green -> A
Blue -> B+
Red -> B

Yellow and white -> not connected, just kinda hanging there.

Now I'm really confused! Maybe the red wire coming loose blew the chip? Or maybe having so much inertia on the motor is ... (here my grasp of E&M as applied to steppers is failing me a little, but I could imagine some explanation like "the mass keeps spinning causing an induced current in the wire which is backwards from what the driver expects". Or something.)

I have some backup backup stepper drivers coming eventually. But where am I going wrong?

Hope all is well with you!
46
Electronics / Reading absolute angle?
« Last post by UART.io on March 26, 2016, 09:09:23 PM »
Say I had an R/C car and wanted to sense the wheelie and measure the angle of the wheelie...What would I need to use?  I currently have a 3-axis gyro(L3GD20H) from Adafruit, but it only reads movement. Do i need both a gyro and an accelerometer to read the absolute angle?
47
Mechanics and Construction / Re: mistake in meachnics gear tutorial?
« Last post by bdeuell on March 17, 2016, 02:02:05 PM »

can you check it ? :)

torque_motor/radius_gear1=torque_gear2/radius_gear2
torque_gear3/radius_gear3=torque_gear4/radius_gear4
torque_gear4/radius_gear4=weight -> torque_gear4=weight*radius_gear4

torque_gear3/radius_gear3=(weight*radius_gear4)/radius_gear4 -> torque_gear3/radius_gear3=weight -> torque_gear3(or torque_gear2)=weight*radius_gear3

torque_motor/radius_gear1=(weight*radius_gear3)/radius_gear2 - > torque_motor=((weight*radius_gear3)*radius_gear1)/radius_gear2

looks correct to me


for your example

gear 2 and pulley 3 are attached with a shaft so the torques will be equal

torque_gear2=torque_gear3


hmmm.. but radiuses are different... it shall affect the Force value isn't it?
can not understand it correctly :/

when you are driving a pulley or gear at the outer diameter (technically the pitch diameter) you set the tangential forces equal to each other (Force=Torque/radius)

when a pulley or gear is connected with a shaft the torques will be equal
48
Mechanics and Construction / Re: mistake in meachnics gear tutorial?
« Last post by cervantes on March 17, 2016, 12:16:55 PM »
for your example

gear 2 and pulley 3 are attached with a shaft so the torques will be equal

torque_gear2=torque_gear3


hmmm.. but radiuses are different... it shall affect the Force value isn't it?
can not understand it correctly :/
49
Mechanics and Construction / Re: mistake in meachnics gear tutorial?
« Last post by cervantes on March 17, 2016, 11:45:03 AM »

can you check it ? :)

torque_motor/radius_gear1=torque_gear2/radius_gear2
torque_gear3/radius_gear3=torque_gear4/radius_gear4
torque_gear4/radius_gear4=weight -> torque_gear4=weight*radius_gear4

torque_gear3/radius_gear3=(weight*radius_gear4)/radius_gear4 -> torque_gear3/radius_gear3=weight -> torque_gear3(or torque_gear2)=weight*radius_gear3

torque_motor/radius_gear1=(weight*radius_gear3)/radius_gear2 - > torque_motor=((weight*radius_gear3)*radius_gear1)/radius_gear2
50
Mechanics and Construction / Re: mistake in meachnics gear tutorial?
« Last post by bdeuell on March 16, 2016, 05:09:58 PM »
for your example

gear 2 and pulley 3 are attached with a shaft so the torques will be equal

torque_gear2=torque_gear3

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