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Trackball Resolution
Ropi Jo:
Yeah, that's almost double the ratio of the standard Happ 2-1/4 trackball with a 0.362 inch (9.1948 mm) roller and a 24 tooth encoder wheel.
Reading what you say about backspin it would seem I need to think about the ratio a little more.
We are going to print a sleeve for the 5mm shaft to go between the bearings. This will bring the shaft to 10mm, and then we'll print a 24 tooth wheel.
This should bring us quite close to your example.
PL1:
--- Quote from: Ropi Jo on October 18, 2022, 03:29:56 pm ---Get the encoder wheel and opto spacing right then you can adjust the sensitivity in MAME.
- I'm guessing you plan to use Happ Red Boards instead of trying to design your own optical circuit, right?
I was planning to simply run optos directly to the opti pac with a current limiting resistor on each opto.
Is this not such a good idea?
--- End quote ---
Your idea should work fine at low speeds, but it probably won't work at high speeds.
The Red Board is a bit more complex than just 2 optos and 2 resistors.
Without the correct circuit design and balance of component values, you are more likely to run into problems like backspin at high speed due to high frequency roll off.
As you go faster, the high/low pulses of the quadrature waveforms become more narrow (higher frequency) but it still takes the same amount of time to transition between logic high and low.
If the transition time is too long compared to the pulse width, the optical (mouse) encoder won't have enough time to register the change in logic levels.
--- Quote from: Ropi Jo on October 18, 2022, 04:21:26 pm ---Yeah, that's almost double the ratio of the standard Happ 2-1/4 trackball with a 0.362 inch (9.1948 mm) roller and a 24 tooth encoder wheel.
Reading what you say about backspin it would seem I need to think about the ratio a little more.
We are going to print a sleeve for the 5mm shaft to go between the bearings. This will bring the shaft to 10mm, and then we'll print a 24 tooth wheel.
This should bring us quite close to your example.
--- End quote ---
The trackball riding on a printed sleeve is going to be a problem due to wear.
- There's a reason the wiki lists the trackball ratios with the caveat "(no wear)". ;)
Use a hardened 8mm or 10mm shaft instead.
Scott
Ropi Jo:
Ah... so the red board will 'square-up' the square wave from the opto, which I assume is already on the red board. That makes sense.
I wonder where do I buy those in the UK?
I have a cunning plan.... the 1200ppr encoders I used for the spinners.... I have more of those. They are very expensive industry standard encoders that I had left over from a project years ago but cost me nothing and they are not planned to be used anytime in the future. Perfect square wave at rediculously high speeds. I wonder if I can break into them and utilise the electronics. Wire my optos in place of the onboard optos? I'll need to investigate.
Thanks again for the info.
Ropi Jo:
And.. we do have 8mm shaft and bearings so we'll go with that.
My son left the 5mm parts printing before leaving for work this morning and assembled them once home (not the sleeves I mentioned) so the ball is turning directly against the 5mm shafts.
The resistance due to the high ratio is not great. The ball does not run on after a spin and just doesn't feel too great. And it's definitely slipping against the shaft.
He'll re-design for the 8mm and we'll give that a go.
PL1:
--- Quote from: Ropi Jo on October 19, 2022, 08:35:01 am ---Ah... so the red board will 'square-up' the square wave from the opto, which I assume is already on the red board. That makes sense.
--- End quote ---
Yes, faster switching between logic levels means the rounded parts on the leading and trailing edges are not as long so more of the pulse width registers as logic high/low.
The optos are easier to see in this picture.
- They will work with a standard 24-tooth encoder wheel.
--- Quote from: Ropi Jo on October 19, 2022, 08:35:01 am ---I wonder where do I buy those in the UK?
--- End quote ---
Not sure. Try search terms "A052-1011-00" or "Happ Red Board".
--- Quote from: Ropi Jo on October 19, 2022, 08:35:01 am ---I have a cunning plan.... the 1200ppr encoders I used for the spinners.... I have more of those. They are very expensive industry standard encoders that I had left over from a project years ago but cost me nothing and they are not planned to be used anytime in the future. Perfect square wave at rediculously high speeds.
--- End quote ---
Ridiculous is the operative word here. ::)
Replacing a 24 ppr encoder wheel and optos with a 1200 ppr encoder means increasing the frequency by 50x.
- Way too fast.
- Way too sensitive.
- No optical (mouse) encoder could keep up with it even if you're rolling the trackball at 1/4 speed.
--- Quote from: Ropi Jo on October 19, 2022, 08:35:01 am ---I wonder if I can break into them and utilise the electronics. Wire my optos in place of the onboard optos?
--- End quote ---
Haven't seen the encoders you're talking about, but I assume the answer is a resounding NO.
High resolution encoders might output quadrature waveforms, but they use very different components than trackballs.
Picture trying to print a 1200 tooth encoder wheel (360 degrees / 1200 teeth + 1200 gaps ==> 0.15 degrees per tooth) and perfectly align the optos so they are X + 0.5 teeth apart, but even if you could do that, the LED in the opto won't be blocked by those narrow teeth so you'll have a constant logic high.
Scott