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Team2168 / 2015_Main_Robot

Source code for the 2015 season
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Question: Hall-effect sensors for end of travel detection in the future #104

Open NotInControl opened 9 years ago

NotInControl commented 9 years ago

@jcorcoran

I know we discussed changing the way the code worked when using hall effect sensors to keep track of state, and once triggered we would only allow the motor to drive in a direction away from the hardstop.

I noticed these on sparkfun... https://www.sparkfun.com/products/9312

I think the best way to use these would be to use two DIO pins. 1 Input as a signal, the other as an Output for sensor power. Toggling the output should cause the sensor to reset its state once the logic to reset is satisfied.

This is cool because we don't need to keep polling the sensor and keep track of state, it has its own hysteresis.

Would these help your cause at all?

NotInControl commented 9 years ago

Also, I found these magnets on Amazon, I think they are exactly what we need if the ones you get have incorrect poles.

The company these are from have many different sizing options.

http://www.amazon.com/CMS-Magneitcs%C2%AE-Rectangle-Neodymium-4-Counts/dp/B000UU6W20/ref=sr_1_6?ie=UTF8&qid=1432939623&sr=8-6&keywords=neodymium+rectangle

jcorcoran commented 9 years ago

I don't see the polarity defined for the magnet you've linked. They're the right shape... Am I missing a spec. somewhere?

Sent from mobile.

jcorcoran commented 9 years ago

Regarding the latching hall effect sensor. I don't think this buys you anything. The way the sensor works is one pole causes one output state from the sensor, and the other pole causes the other. You're continuously latched into a state. So yes your state signal will persist as you travel past the sensor, but you will no longer be able to sense the position of the drive relative to the sensor. As you mentioned, you're going to need to rely on software to manage the latch to even make it work at all. So why not just create a latch in software using the existing sensor we have. You can't get away from polling the sensor in either configuration, because you still need to know (as soon as possible) when there is a state transition (the lift has reached an extent of its travel) so that you can respond appropriately (stop driving the lift in that direction). The fact that the sensor you've found has latched the value does you no good unless you're actually reading the discrete input.

I don't think these make sense to use in the way you've described at least. MAYBE if you mount two magnets in close proximity along the path of travel (one with north facing out, the other with south facing out). This would allow travel past the sensor to latch and reset as desired...

NotInControl commented 9 years ago

Polarity is shown in one of the pics. It wouldnt hurt to ask a question to the seller before we ever purchased just to confirm.

Sent on a Sprint Samsung Galaxy S® 5

-------- Original message -------- From: James notifications@github.com Date:05/29/2015 6:58 PM (GMT-05:00) To: Team2168/2015_Main_Robot 2015_Main_Robot@noreply.github.com Cc: Kevin kevinharrilal@msn.com Subject: Re: [2015_Main_Robot] Question: Hall-effect sensors for end of travel detection in the future (#104)

I don't see the polarity defined for the magnet you've linked. They're the right shape... Am I missing a spec. somewhere?

Sent from mobile.

Reply to this email directly or view it on GitHub: https://github.com/Team2168/2015_Main_Robot/issues/104#issuecomment-106954755