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Unread 27-01-2017, 09:28
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Re: Climb Stopping Mechanism

Step 1: If your climber is a winch, get rid of all of your sensors and use the PDB's built-in current sensors. When Current / Applied Voltage > a ratio (we're using 60A & 12V, so ratio of 5) then disable the motor from going in that direction for N milliseconds.
Step 2: Test
Step 3: Test Some More.

Current through the motor is responsive and reliable to read and react upon. Getting it from the PDB is one of the best things added to the control system in recent years.
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Unread 27-01-2017, 09:36
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Re: Climb Stopping Mechanism

Depending on what T=0 means, you don't NEED to hold your robot on the button after power is cut, just as power is cut, provided you have already held the button for >1 second. If your mechanism can't do that, it's not like prior years where you can't get the points at all, it just requires more commitment in advance and eliminates last-second scoring.
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Unread 02-02-2017, 09:47
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Re: Climb Stopping Mechanism

Our team is using a hex shaft, so we will include a 1/2" ratcheting wrench to help us climb. This was seen to be effective from Ri3D 1.0 and our team is worried that our bot might fall after the buzzer (or at least glide down, which still isn't safe).

I've changed my opinion since the reveal. I thought that it would be stronger to use a single grabbing motion (like the 2013 pyramid climbers), but I've noticed that you would need to dedicate a huge portion of your bot to that.

Our team is using a type of winch. It's not an original idea, but our testing shows its effectiveness. We are quite excited to be climbing this year.

Good luck all!
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Unread 03-02-2017, 14:53
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Re: Climb Stopping Mechanism

According to the 2015 FRC motor information sheet, a CIM motor pulls 133 amps at stall. Well above the allowed 40 amp breaker allowed per motor under rule R56 Table 8-3.
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Unread 03-02-2017, 14:55
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Re: Climb Stopping Mechanism

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Originally Posted by mentorDon View Post
According to the 2015 FRC motor information sheet, a CIM motor pulls 133 amps at stall. Well above the allowed 40 amp breaker allowed per motor under rule R56 Table 8-3.
133 amps at stall at full voltage. If you stall the motor at much less than full voltage, it will draw significantly less current as well. This can allow you to hold position while the robot has power (but not after power has been cut).
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Unread 03-02-2017, 15:14
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Re: Climb Stopping Mechanism

We have an encoder integrated into the climber. We plan on monitoring the current to detect when the climb starts, and set a stop distance based on that start point. The operator will have the ability to jog higher if we stop too soon, but hoping this approach leads to automatic climbing.

Still untested theory at this point. Fingers crossed. Would like to have working repeatable solution by week 1, we are going to need it.
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Unread 03-02-2017, 15:11
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Re: Climb Stopping Mechanism

Quote:
Originally Posted by JesseK View Post
Step 1: If your climber is a winch, get rid of all of your sensors and use the PDB's built-in current sensors. When Current / Applied Voltage > a ratio (we're using 60A & 12V, so ratio of 5) then disable the motor from going in that direction for N milliseconds.
I'll get our programmers on this....

thanks!

We were going to just slow down at the top, and stop after we visibly moved the touch pad up as much as it takes to get the light to go on (practice day, you know). But the current thing looks like a fun way to keep a few students busy for a few more days
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Unread 03-02-2017, 15:20
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Re: Climb Stopping Mechanism

I think the easiest solution is to simply use the motor controllers to sense when the motor is stall. This is what 6101 is doing. The Davit has a C-channel piece to protect it in brief high-stress situation and the 40A breakers wouldn't pop immediately. I don't see any reason why this wouldn't work.

To prevent gliding, we are using a ratchet head on the winch similar to Ri3D 1.0.
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Unread 03-02-2017, 15:33
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Re: Climb Stopping Mechanism

This shouldnt be too hard.
Once you see the light go on, dont drive the lift anymore.
We plan to use a simple ratchet to prevent it from backdriving.
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Unread 03-02-2017, 15:37
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Re: Climb Stopping Mechanism

Quote:
Originally Posted by waialua359 View Post
This shouldnt be too hard.
Once you see the light go on, dont drive the lift anymore.
We plan to use a simple ratchet to prevent it from backdriving.
Will you have the ability to disengage the ratchet under load?

If not, what keeps you from effectively clamping onto the field when waiting the 1 second?
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Unread 03-02-2017, 15:58
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Re: Climb Stopping Mechanism

Quote:
Originally Posted by AdamHeard View Post
Will you have the ability to disengage the ratchet under load?

If not, what keeps you from effectively clamping onto the field when waiting the 1 second?
Sorry, I'm slow. I dont quite follow?
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Unread 03-02-2017, 16:05
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Re: Climb Stopping Mechanism

Quote:
Originally Posted by waialua359 View Post
Sorry, I'm slow. I dont quite follow?
When you hit the wall on top, your motor will go to stall (unless you're current limiting) and push very hard on the top.

Now imagine everything in the system is a spring, you're going to compress/stretch parts of the robot/field and load everything up.

Now there is a ratchet on there preventing you from backdriving (and you can't go forward any more as you're already loaded pretty firm into the field).

Now that's how you lock yourself onto the field.
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Unread 03-02-2017, 16:12
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Re: Climb Stopping Mechanism

Quote:
Originally Posted by AdamHeard View Post
When you hit the wall on top, your motor will go to stall (unless you're current limiting) and push very hard on the top.

Now imagine everything in the system is a spring, you're going to compress/stretch parts of the robot/field and load everything up.

Now there is a ratchet on there preventing you from backdriving (and you can't go forward any more as you're already loaded pretty firm into the field).

Now that's how you lock yourself onto the field.
In 2010, we created a simple ratchet pawl system that worked for our climber. It should release if we at least carry the robot, releasing weight tension.
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Unread 03-02-2017, 16:15
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Re: Climb Stopping Mechanism

Quote:
Originally Posted by waialua359 View Post
In 2010, we created a simple ratchet pawl system that worked for our climber. It should release if we at least carry the robot, releasing weight tension.
You won't be able to release weight tension as you're literally clamping the field. Can't go the other way because of the ratchet as well.
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Unread 03-02-2017, 16:18
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Re: Climb Stopping Mechanism

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Originally Posted by AdamHeard View Post
You won't be able to release weight tension as you're literally clamping the field. Can't go the other way because of the ratchet as well.
Well, I guess we shall see.
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