RB-Phi-48 versus RB-Dsp-30 - Acquisition problem?

Help & Support Robot Parts
1

Hello,
I bought, to check brushless motor speed, these materials:

  • RB-Spa-1042
  • RB-Phi-48
  • App FlowBotics pour Encodeur USB 1 Entrée Phidgets - RB-Dsp-30

When I use log mean of App FlowBotics to acquire and save Encoder positions, I find few problems with 50ms sampling.
An example below (date / time / encoder position):

[table][tr][td][table][tr] [td][size=2]12-Apr-2017[/size][/td][/tr][/table] [/td][td][table][tr][td][size=2]19:10:38.086[/size][/td] [td]
[/td][/tr][/table] [/td][td][table][tr][td][size=2]2670.0[/size][/td][/tr][/table] [/td][/tr][tr][td][size=2]12-Apr-2017[/size][/td][td][table][tr] [td][size=2]19:10:38.195[/size][/td][/tr][/table][/td][td][table][tr][td][size=2]2677.0[/size][/td][/tr][/table][/td][/tr][tr][td][size=2]12-Apr-2017 [/size][/td][td][table][tr] [td][size=2]19:10:38.197[/size][/td][/tr][/table] [/td][td][table][tr][td][size=2]2675.0[/size][/td][/tr][/table] [/td][/tr][tr][td][size=2]12-Apr-2017 [/size][/td][td][table][tr] [td][size=2]19:10:38.223[/size][/td][/tr][/table] [/td][td][table][tr][td][size=2]2683.0[/size][/td][/tr][/table] [/td][/tr][/table]
My motor, controled in open loop, turn always in the same sens.
We remark in the log file that motor change sens. It is impossible.
I think that there is a problem with RB-Phi-48 decoding board…
Somone has already had/observe this problem ?

Best regards
Jerome Perrot

2

Hi Jerome,

It is possible that your encoder sometimes triggers improperly and causes the RB-Phi-48 to think it went backwards for a step or two.
According to the datasheet of RB-Spa-1042 (page 4), its output resistance is 2 kΩ and the device can sink up to 35 mA (maximum).
The default 1 kOhm pull-up on the quadrature input of the RB-Phi-48 should not be causing issues, but it may still be worth investigating.

Also, it should be important to note that this is gathering raw data. You may want to use a low-pass filter on it afterwards, such as a moving average filter.

The issue may also be in the app itself and on how it reads and reports data from the encoder, though this is unlikely.

Sincerely,

3

Hello,
Thank you for your quick feedback.
I add 1nF capacitors on each encoder signals because that’s right, without this filtering, glitches are presents on signals.
It would be judicious to provide footprint, without components, on RB-Phi-48 borad, in order to configure/add filtering (or place directly capacitors).
Results are better, however, there are still few problems…
Best regards
Jerome Perrot