2
$\begingroup$

I have been working on trying to get the angle of the Create 2. I am trying to use this angle as a heading, which I will eventually use to control the robot. I will explain my procedure to highlight my problem.

I have the Create tethered to my computer.

  1. I reset the Create by sending Op code [7] using RealTerm. The output is:

    bl-start
    STR730
    bootloader id: #x47175347 4C636FFF
    bootloader info rev: #xF000
    bootloader rev: #x0001
    2007-05-14-1715-L
    Roomba by iRobot!
    str730
    2012-03-22-1549-L
    battery-current-zero 252

(The firmware version is somewhere in here, but I have no clue what to look for--let me know if you see it!)

  1. I mark the robot so that I will know what the true angle change has been.
  2. I then send the following codes [128 131 145 0x00 0x0B 0xFF 0xF5 142 6]. This code starts the robot spinning slowly in a circle and request the sensor data from the sensors in the group with Packet ID 2. The output from the Create seen in RealTerm is 0x000000000000, which makes sense.
  3. I wait until the robot has rotated a known 360 degrees, then I send [142 2] to request the angle difference. The output is now 0x00000000005B.

The OI specs say that the angle measurement is in degrees turned since the last time the angle was sent; converting 0x5B to decimal is 91, which is certainly not 360 as expected.

What am I doing wrong here? Is the iRobot Create 2 angle measurement that atrocious, or is there some scaling factor that I am unaware of? are there any better ways to get an angle measurement?

$\endgroup$
  • $\begingroup$ Is 6 in "packet 6" a typo? "Create Open Interface_v2.pdf" shows Group Packet ID 6 returning 52 bytes instead of half a dozen. Also, why not use ID 20? Also see the question create2 angle (packet ID 20), $\endgroup$ – James Waldby - jwpat7 Apr 28 '15 at 20:26
  • $\begingroup$ Great catch; I have updated the post. Using [142 20] works, but the problem is the same. $\endgroup$ – NBCKLY Apr 28 '15 at 21:23
2
$\begingroup$

There is a known bug in the angle command. We are still working on a workaround. In the meantime, please extract the angle yourself by using the left and right encoder counts. See this question for detailed equations.

$\endgroup$
  • $\begingroup$ I have been trying to work with the encoders. I use the same procedures and experimental setup detailed above. I call [128 131 145 0x00 0x0b 0xFF 0xF5 149 2 43 44]; it reads 0x00010001. Then, after moving 360 degrees, it reads 0xF97C0693, which when plugged into the equation listed in the other post yields -117.639 (that lots of radians!). Do you have any advice on what I need to change to get a usable measurement? I searched the document linked in the other post and could not find a direct derivation of the angle equation. Will the measurement be invalid if the robot spins in place? $\endgroup$ – NBCKLY Apr 28 '15 at 21:22
  • $\begingroup$ I get the correct result. The left wheel is 0xF97C ticks which is twos complement for -1668, the right wheel is 0x0693 which is 1683. $\frac{(1683 \pi 72 / 508.8) - (-1668 \pi 72 / 508.8)}{235}$ = 6.34 radians = 363.2 degrees $\endgroup$ – Ben Apr 28 '15 at 23:38
  • $\begingroup$ Isn't the encoder count an unsigned integer? Is it possible to just treat the encoder count as signed despite what the OI spec says? $\endgroup$ – NBCKLY Apr 29 '15 at 0:57
  • $\begingroup$ Thank you for pointing this out. The encoder counts are indeed signed. The document will be updated fixed shortly. $\endgroup$ – Ben Apr 29 '15 at 15:33
  • $\begingroup$ The summary table in "Create Open Interface_v2.pdf" also shows angle units as being in mm (rather than degrees or something) so while fixing the docs you could adjust that too. $\endgroup$ – James Waldby - jwpat7 Apr 29 '15 at 18:19
1
$\begingroup$

To get the firmware version:

To get what software the robot has, connect it to a serial application (such as PuTTy) and turn the robot off then on. It should print it out then

New says: r3_robot/tags/release-3.4.1:

old says: r3_robot/tags/release-3.2.6:

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.