pic: Off-Season Kicker Design

[Ether]

Originally Posted by apalrd

I would actually recommend a pot over an encoder because it's position is absolute instead of relative.

Not all encoders are relative. There's an absolute encoder in the 2010 KoP:

http://www.austriamicrosystems.com/e...5030-Downloads

Originally Posted by apalrd

The key is to isolate the pot from the shaft.

Why is that the key? Did you try it both ways and it failed when directly connected and worked when chain-driven?

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[apalrd]

The key to not damaging the pot.

We anticipated that the stresses on the shaft would break a potentiometer if it was connected directly to the shaft. We isolated it with a chain so that the rotary motion was transferred, but any other forces were not. We used a standard 270-degree pot.



Although a magnetic encoder would remove any mechanical connection between the sensor and the shaft, so that might be a better solution then a potentiometer.

[Ether]

Originally Posted by apalrd

The key to not damaging the pot.

We anticipated that the stresses on the shaft would break a potentiometer if it was connected directly to the shaft. We isolated it with a chain so that the rotary motion was transferred, but any other forces were not.

Isolating the pot from the shaft (via a chain or belt etc) is certainly a solution, but not the only way.

If you use the pot to replace one of the shaft bearings then of course that's going to put unacceptable loads on the pot. But if you mount the sensor directly to the shaft (through a simple coupling) on the outboard side of one of the end bearings it will not bear the shaft loads.

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[MCahoon]

Originally Posted by Ether

Isolating the pot from the shaft (via a chain or belt etc) is certainly a solution, but not the only way.

If you use the pot to replace one of the shaft bearings then of course that's going to put unacceptable loads on the pot. But if you mount the sensor directly to the shaft (through a simple coupling) on the outboard side of one of the end bearings it will not bear the shaft loads.

~

Essentially what we did. We had a gear on the end of the winch shaft. That gear drove an idler shaft that had the pot attached to the end of it. The pot (and the encoder that replaced it) were not bearing any loading from the kicker.

[Ether]

We had a gear on the end of the winch shaft. That gear drove an idler shaft that had the pot attached to the end of it.

Sure, that's a good solution. But the point was it's also possible to mount the pot (or encoder) directly to the shaft through a simple in-line coupler on the end of the shaft. With that approach there would be no undue loads on the pot. It's not the direct connection to the shaft per se that causes the loading problem, it's if you try to use the pot in place of a load bearing.

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[EricH]

In-line connection, 330 style: make the shaft extra-long by an inch or so, and turn that inch or so down to about the same diameter as the pot shaft. Put the ends of the shafts together in line, then put surgical tubing around the small portion and ziptie it down solidly. That way, even if something goes really wrong, the pot (or encoder) isn't going to be too banged up (it has its own mounting point off the axle).

[Jared Russell]

Our team used a US Digital MA3 absolute magnetic encoder directly coupled to a small bore in the end of our kicker shaft and it held up great. We used the sleeve bushing model, rated up to 10,000 rad/sec² acceleration and 100 RPM continuous top speed, but you can get the ball bearing model (250,000 rad/sec²; 15,000 RPM) if you want even more of a safety margin. No detents or hard stops, no gap in sensing, and no wiper wear over time - I would heartily recommend using them in this application (or wherever a pot would be appropriate).

Link: http://www.usdigital.com/products/en...ary/shaft/ma3/

[Garret]

In-line connection, 330 style: make the shaft extra-long by an inch or so, and turn that inch or so down to about the same diameter as the pot shaft. Put the ends of the shafts together in line, then put surgical tubing around the small portion and ziptie it down solidly. That way, even if something goes really wrong, the pot (or encoder) isn't going to be too banged up (it has its own mounting point off the axle).

Team 691 has done the same thing for awhile. We however create a flat on the end of the shaft so that the surgical tubing holds on better. We used this to attach encoders to a ~900 RPM shaft and had no issues.