1 Encoder, 2 Jaguars

[Deetman]

Originally Posted by techhelpbb

That's about right. You shouldn't need the transistors at all.
I wanted to make sure to lower the coupling ratio...so I used the minimum.

I have the surface mount and the through hole version of the PS2501-4 and basically all the surface mount version is, is just the leads bent parallel to the surface, so no real weight savings.

The schematic I was working on had an extra trick, in that it was designed so you could test the circuit end to end without any tools. Figured we had enough people nervous about going this route that making it 'self test' was a the best solution to calm the nerves.

Thanks for the taking the time to review the schematic. Second sets of eyes never hurt.

I'll take a look again at the diode current. I didn't consider the coupling ratio since I haven't really used opto-isolators before.

I noticed that too about the surface mount version of the PS2501-4 which surprised me. Other than automated manufacturing the benefits of going with the surface mount version are pretty small.

Also a great concept on the self test circuitry... I didn't really think of doing that since theoretically this has already been "proven" to work. I'll probably take the board into work once I get it and run a pulse generator on it to test the board.

[techhelpbb]

Originally Posted by Deetman

Thanks for the taking the time to review the schematic. Second sets of eyes never hurt.

I'll take a look again at the diode current. I didn't consider the coupling ratio since I haven't really used opto-isolators before.

I noticed that too about the surface mount version of the PS2501-4 which surprised me. Other than automated manufacturing the benefits of going with the surface mount version are pretty small.

Also a great concept on the self test circuitry... I didn't really think of doing that since theoretically this has already been "proven" to work. I'll probably take the board into work once I get it and run a pulse generator on it to test the board.

The hand soldered prototype that was slammed together made me nervous.
When I put this stuff up for people to look at, you'll see why.

However, what really made me nervous was that it is is *really* hard to get a basic piece of test equipment into the circuit, it's got wires going in multiple directions and some of the junctions are too small. Never mind the fact that on our CIMiple gear box implementations the connectors are *very* hard to get to. I wanted people to be comfortable that from end to end, the wires and the logic work as planned. This way even those that don't fully understand have the hope of testing it. After all, because of the wires...something could break even if the circuit works.

Besides I sort of hoped that people would sit down with those they are mentoring and show them what it actually does on an oscilloscope. So it's both a learning tool...and a working piece of gear.

The optocoupler probably wasn't made smaller because they'd have to change the dimension between the LED and the phototransistor. Otherwise the specifications would change.

[Ether]

Originally Posted by otherguy

Tomorrow we'll move onto speed control

Is it tomorrow yet?

I'm interested in what you've found.

[juchong]

So, any word on whether the circuit performed as intended? I assume it did, though!

[techhelpbb]

Originally Posted by juchong

So, any word on whether the circuit performed as intended? I assume it did, though!

Can I presume you are inquiring from the other teams?

What we had originally worked within the expectations we had of it. We didn't run it in competition not because of the splitter, but because CAN in general kept producing timeout errors and having other problems that eventually caused us to abandon CAN for PWM and later, after a few other troubles, to abandon the Jaguars in favor of the Victors.

To be additionally clear:

1. There were other issues in that particular drive train that caused it to be ill suited to the Jaguars. This is not an attempt to bash the Jaguars. That drive train was just not a good fit as it turned out.

2. Since the circuit in question was never actually fielded (to my knowledge) I can't be sure it's legal, but so far my research on the matter indicates it would have been legal last year and this year.

3. We did not use Jaguars this year at all.

4. I have 'too many eggs in my basket' currently the soonest I could slap all that on my test robot would be late May or June. When things finished off last year it got so quiet I didn't bother to continue with this work (by this work I mean this splitter, I built an entire robot and test equipment for that robot myself) because there didn't seam to be sufficient interest. Is there interest in me putting that on my schedule?

[juchong]

tech, I completely understand. CAN this year is particularly buggy for some reason. We managed to get it working well enough to be used on our main drivetrain. I found that loop times are very crucial and can't be easily modified, but with a little tweaking, you can get some very good performance out of it!

For our autoaim and shooter, CAN is essential, so we're trying to work out as much as possible before our regional next week. I've got the parts in hand to build the circuit and will report back once I've done some testing. We'll primarily be using this for our shooter to distribute the motor load a bit more evenly, so even if the circuit stops working, our shooter should still remain functional.

[techhelpbb]

Originally Posted by juchong

tech, I completely understand. CAN this year is particularly buggy for some reason. We managed to get it working well enough to be used on our main drivetrain. I found that loop times are very crucial and can't be easily modified, but with a little tweaking, you can get some very good performance out of it!

For our autoaim and shooter, CAN is essential, so we're trying to work out as much as possible before our regional next week. I've got the parts in hand to build the circuit and will report back once I've done some testing. We'll primarily be using this for our shooter to distribute the motor load a bit more evenly, so even if the circuit stops working, our shooter should still remain functional.

If you end up using this circuit in actual competition please update this topic to confirm that it was actually accepted on a robot at a competition.

There are a lot of things that can be made, but the more unusual things get the higher the risk that at competition questions will be raised (I mean absolutely no disrespect to anyone...the rules are fairly numerous and sometimes a bit unclear).

Thanks

[juchong]

I'll definitely keep everyone updated!

Now, as for the rules, the way I understand it I am not able to use any motor controller other than the Jags or Victors to control a motor. All control signals must originate from the cRio. Now in the case of sensors, we are much less restricted on which sensor we are allowed to use, and more restricted on how we get the control signals to their respective inputs. As long as they get there, I don't see any reason for them to disallow it.

Since the sensors don't directly control a motor (they may provide feedback, but never direct control. You could argue that, in a way, they control the motors but then you could argue that without an initial condition, they cannot) then, as long as they are powered correctly, all add-on circuits should be legal.

I also plan on having some oscilloscope screenshots showing input and output, just to show that the circuit isn't fabricating anything false.

[nuttle]

<https://www.sparkfun.com/products/9118>

I'd need to read the rules carefully, but this looks like a good off-the-shelf solution that should be easy to work with for most teams -- provided this sort of thing is legal. It doesn't violate the safety-related reasons for being very careful with motor control and solves the "1 Encoder, 2 Jaguars" problem in a clean way.

I'd actually use one of these for each of the two Jags and power them both from the DSC, in fact you could send the encoder inputs to the DSC directly, and then to each Jag through one of the isolators (for a total of three places where the encoder data could be read, the DSC and the two Jags).

[kenfox]

Is that fast enough to be used on an encoder signal? I'm just a programmer, but the 5 microsecond switching time seems like it would screw up an encoder signal.

We're probably going to use the cRIO for dual motor gearbox encoder PID control. The master-slave solutions don't seem as reliable as using the cRIO.

[jhersh]

Originally Posted by kenfox

Is that fast enough to be used on an encoder signal? I'm just a programmer, but the 5 microsecond switching time seems like it would screw up an encoder signal.

We're probably going to use the cRIO for dual motor gearbox encoder PID control. The master-slave solutions don't seem as reliable as using the cRIO.

The cRIO measures down to 6.525 us, so that is a pretty similar range.

[nuttle]

FWIW, I don't think the propagation delay is going to be a problem either.

Anyone thinking of trying this should confirm, but my reading of 2013 R72 H makes me think this is legal to do:

R72 All outputs from sensors, custom circuits and additional electronics shall connect to only the following: H. the sensor inputs on the Jaguar motor controller.

So, this is likely a viable option (subject to confirmation of the legality), but note that I have not actually done this. One could also use this trick to connect both DCS inputs and Jag inputs to the same encoder.

[nuttle]

FWIW, here's a part that seems like an even better choice, but only for teams that can deal with not having a breakout board: http://www.fairchildsemi.com/ds/FO/FOD0710.pdf.