Gear Sensor Competition Usage Feedback

[de_]

I'm looking for feedback on actual competition usage of the gear sensors. How did they do ? If you used the manufacturers recommended circuit for noise reduction/filtering, did the sensors prove to be noise resistant (no missed state changes, false state changes). Could they be counted on for very accurate, repeatable measurements from dead stop to full rotation in autonomous mode ? Any issues keeping within the 2mm air gap requirement under with shock and gear wear/wobble etc ? Anyone find the 2mm max materially conservative or optimistic ? What did you trigger off (gears in the standard transmission, chain drive sprockets ?) We have tested them on the bench and they look promising but things could be quite different in "combat".

[Robby]

Originally Posted by de_

I'm looking for feedback on actual competition usage of the gear sensors. How did they do ? If you used the manufacturers recommended circuit for noise reduction/filtering, did the sensors prove to be noise resistant (no missed state changes, false state changes). Could they be counted on for very accurate, repeatable measurements from dead stop to full rotation in autonomous mode ? Any issues keeping within the 2mm air gap requirement under with shock and gear wear/wobble etc ? Anyone find the 2mm max materially conservative or optimistic ? What did you trigger off (gears in the standard transmission, chain drive sprockets ?) We have tested them on the bench and they look promising but things could be quite different in "combat".

I used them hooked directly to the digital input on the robot, as we have for a few years and found that i could position the robot to within 2 inches after driving a little over 20 feet with two turns using nothing else but a gyro. I'd say that they work pretty well. They were mounted on our gearbox and counted every revolution of the worm gear, which rotates 16 times for every rotation of the 5.5 inch diameter wheels we used. The gap did not seem to be much of a problem, i think ours were actually about 3 mm away from the gear. The only thing that threw off the autonomous was the fact that the field had numerous divots and holes which caused wheels to spin too much which required the use of encoders on all 4 wheels to have an accurate count.

[Al Skierkiewicz]

I inspected a number of robots using the gear tooth sensors and all of them reported that they worked very well. The majority used them for counting teeth on a chain sproket rather than gear teeth.

[eugenebrooks]

Originally Posted by de_

I'm looking for feedback on actual competition usage of the gear sensors. How did they do ? If you used the manufacturers recommended circuit for noise reduction/filtering, did the sensors prove to be noise resistant (no missed state changes, false state changes). Could they be counted on for very accurate, repeatable measurements from dead stop to full rotation in autonomous mode ? Any issues keeping within the 2mm air gap requirement under with shock and gear wear/wobble etc ? Anyone find the 2mm max materially conservative or optimistic ? What did you trigger off (gears in the standard transmission, chain drive sprockets ?) We have tested them on the bench and they look promising but things could be quite different in "combat".

We used the reccommended circuit "for regulated power supplies" for noise reduction and filtering, putting it all on a small PC board that mounted the sensor. Our "pull up" resistor was around 2K ohms (might have been 2.2K), the standard value for TTL circuits. We sensed the drive sprocket on the KOP gearbox from the side, positioning the sensor to get as close to a 50/50 on/off signal as we could get, optimal for busy polling. The spacing to the sprocket was 2mm.

If the pulse rate is slow enough (sensing a sprocket and relatively slow robot operation) you can busy poll the sensor without losing state transitions. If you require reliable high speed operation, or want to sense the relatively faster pulse rate of a gear, you will want to use interrupt based wheel counter code. In this case, there is the rare possibility of an interrupt hitting while reading the counter via your state machine that controls the robot, resulting in a bogus value. A bogus value is unlikely, but a bogus value read two times in a row is even more unlikely.

[Sparks333]

Hi!
We never used the sensors in competition (we wanted quadrature, so we made our own hall-effect sensors) but we did fiddle with them. What we found matches what Eugene found: follow the sample circuit. That resistor makes the waveform much cleaner.
Furthermore: Those are some good sensors. They count very accurately (we used them on a gear) and the programmers had loads of fun learning about how to use interrupts.

Sparks

[ChrisCook]

This is kinda off from your discussion, but when you started taking about feedback - that were we come in Team 670 has developed a close-loop steering mechanism that allowed our robot to have semi-real time feedback from our robot. I'll try and post a pic or it soon but here's the rundown.
We used the new window motor along with a steel plate attached to the gears on the motor. The plate has a slit down the center of it an as the motor turns from side-to-side it moves a bolt attached to a rack n' pinion. Directly over the motor output gear is a rubber stopper, which hold the end of a 0-255 Potentiometer. Our operator mechanism was a wheel and stick system, when the stick was moved in the X direction the robot would move forward or reverse.
The wheel when turned left or right would generate a negative feedback loop and move the motor in the correct direction. If you have anymore questions on the closed negative feedback loop steering system. Email me at chrisccts@yahoo.com

[Captain Rich]

We used the hall effect sensors from the kit. We actually mounted them inside of the kit transmission. They worked well, although the lack of a direction is annoying. We only had one match where they malfunctuned, which resulted in a run away auton. Next year we plan on using somthing diffrent (I don't know what they are, the programmers have HUGE plans for this summer).