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  #46   Spotlight this post!  
Unread 02-23-2011, 09:35 AM
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Re: 1 Encoder, 2 Jaguars

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Originally Posted by Ether View Post
650 what? volts/sec ?
Whatever units the BDC-COMM utility expects

The documentation says it is in volts/s. However, the Jag docs indicate the calculations are performed at a 1Khz rate, so I'm guessing this is translated to 0.65 volts/ms internally.

--Jason
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Unread 02-24-2011, 12:04 AM
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Re: 1 Encoder, 2 Jaguars

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Originally Posted by otherguy View Post
We tried it today. W/ our quadrature encoders (don't know the part number off the top of my head). All pins of the encoder were wired to one JAG then GND, A & B were jumppered over to the 2nd JAG. Implementing position control (implemented on only one jag - 2nd jag was not commanded) resulted in wild responses (motors continued spinning when they showed they had reached their destination). Removing the jumper to the 2nd JAG instantly resolved the problem. We didn't spend time trying to diagnose the problem, just moved on to the below. My uneducated guess is that these inputs need to be isolated. If anyone else is successful in wiring these, please share your solution.

EDIT: maybe this is our problem? http://www.chiefdelphi.com/forums/sh...9&postcount=16

We did however have good luck setting one jag up w/ PID position control (MASTER - wired to the encoder). The other JAG (SLAVE) was commanded using the %V bus mode. Inputs to the slave were the voltage output from the master controller. Sync groups were used to coordinate outputs. This seemed to work well in our tests. Our voltage output curves looked quite clean compared to some of the graphs which I had seen reported in other posts. We're going to continue this route as long as we don't start seeing any problems.

Tomorrow we'll move onto speed control.
We never attempted this for position control, but I can confirm that you'll probably need the optoisolator as Hugh states...load on the CIMs certainly causes issues we did not see under much less load.

We made several PCBs to provide this isolation and I'm frankly not sure of any rules that prevent them, as long as they take power from the sidecar or the Jaguars.

If I read your post correctly, you didn't actually enable one Jaguar? Why?

Last edited by techhelpbb : 02-24-2011 at 12:23 AM.
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Unread 02-24-2011, 03:28 PM
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Re: 1 Encoder, 2 Jaguars

Can anyone provide guidance on how to do the isolation? Any recommended part numbers? Would limit switches have the same issue?

Thanks.
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Unread 02-25-2011, 12:37 AM
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Re: 1 Encoder, 2 Jaguars

No limit switches will not suffer this issue.

As to the parts if you implement the whole thing...TTL and all...and strip off all the extras from the prototype we made.

The input from the encoders (both of them...one on either side):
74HC14

The optocoupler:
PS2501-4

The final outputs to the Jaguars:
74HC04 (one for each Jaguar so that's 4).

We used 680 Ohm pull up resistors for the diode side of the coupler.
We used 4.7k Ohm pull up resistors for the NPN transistor side of the coupler.

Depending on how crazed you want to get you might also need the Pan Pacific (Cinch Jones) headers (like the the ones on the Jaguar).

If you want to get really nuts get the PicoBlade connectors for the U.S. Digital encoders. Be warned those crimp pins are *very* tiny and you'll need the right crimper for it. Molex wants about $200 for that tool. Dig around on eBay and you'll find a cheaper solution for less than $100.

However, in the end, you could just butcher the tails for the encoders from U.S. Digital and use some female receptacle header for the Jaguar side then hand solder the PCB end of the wires to the PCB.

I sent you an e-mail in private, I don't have all the documentation ready to present yet, but I'll send you a schematic from the original idea.
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Unread 02-25-2011, 10:16 AM
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Re: 1 Encoder, 2 Jaguars

Quote:
Originally Posted by techhelpbb View Post
No limit switches will not suffer this issue.

As to the parts if you implement the whole thing...TTL and all...and strip off all the extras from the prototype we made.

The input from the encoders (both of them...one on either side):
74HC14

The optocoupler:
PS2501-4

The final outputs to the Jaguars:
74HC04 (one for each Jaguar so that's 4).

We used 680 Ohm pull up resistors for the diode side of the coupler.
We used 4.7k Ohm pull up resistors for the NPN transistor side of the coupler.

Depending on how crazed you want to get you might also need the Pan Pacific (Cinch Jones) headers (like the the ones on the Jaguar).

If you want to get really nuts get the PicoBlade connectors for the U.S. Digital encoders. Be warned those crimp pins are *very* tiny and you'll need the right crimper for it. Molex wants about $200 for that tool. Dig around on eBay and you'll find a cheaper solution for less than $100.

However, in the end, you could just butcher the tails for the encoders from U.S. Digital and use some female receptacle header for the Jaguar side then hand solder the PCB end of the wires to the PCB.

I sent you an e-mail in private, I don't have all the documentation ready to present yet, but I'll send you a schematic from the original idea.
Any chance you could provide schematics to the group?

TIA,

Mike
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Unread 02-25-2011, 11:09 AM
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Re: 1 Encoder, 2 Jaguars

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Originally Posted by taichichuan View Post
Any chance you could provide schematics to the group?

TIA,

Mike
As stated, absolutely.

However, I need a little more time to clean them up.

We twisted this idea around quite a few ways and I want to provide just the most basic schematic...otherwise it'll be way more complicated than you really need.
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Unread 02-25-2011, 11:40 AM
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Re: 1 Encoder, 2 Jaguars

Thanks!

Mike
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Unread 02-26-2011, 05:42 PM
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Re: 1 Encoder, 2 Jaguars

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Originally Posted by techhelpbb View Post
If I read your post correctly, you didn't actually enable one Jaguar? Why?
Correct.

Our wiring was setup to split the single encoder to two jags. Our code was setup to drive only one motor at the time, to verify that the encoder counts were actually being read correctly. And to determine the correct motor polarities.

Again our tests weren't thorough, we quickly switched to a "slave" Jag being driven off the output from the "master" and this appeared to work well, so we didn't go further with the split encoder tests.
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Unread 02-28-2011, 10:56 AM
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Re: 1 Encoder, 2 Jaguars

It seems noise into the Jaguars is causing the reset issue mentioned here and in another thread. When one connects an encoder or other circuit to the encoder input it works as an antenna to pick up noise.

So far I have found a 25 uf cap across the + 5 volt pin and the gnd pin on the encoder connector fixes it.

This may not work if all ground loop issues are not resolved. The opto isolators are needed to remove the ground loops and the filter cap is needed to filter the spikes created by the back emf when the motors stop or change direction.

We are using shielded wire with the shield grounded at the Jaguar and open at the custom circuit board where the opto isolators are located.

The only connections back to the Jaguars are from the output transistor in the opto isolator. I have seen some high frequency roll off and trouble with phase shift causing direction changes. I am still working this issue. If the noise is really fixed I might try to add another pull-up on the opto board to the +5 volts from the Jaguar.

Has anyone else seen these issues?

-Hugh
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Unread 02-28-2011, 06:05 PM
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Re: 1 Encoder, 2 Jaguars

Quote:
Originally Posted by Hugh Meyer View Post
It seems noise into the Jaguars is causing the reset issue mentioned here and in another thread. When one connects an encoder or other circuit to the encoder input it works as an antenna to pick up noise.

So far I have found a 25 uf cap across the + 5 volt pin and the gnd pin on the encoder connector fixes it.

This may not work if all ground loop issues are not resolved. The opto isolators are needed to remove the ground loops and the filter cap is needed to filter the spikes created by the back emf when the motors stop or change direction.

We are using shielded wire with the shield grounded at the Jaguar and open at the custom circuit board where the opto isolators are located.

The only connections back to the Jaguars are from the output transistor in the opto isolator. I have seen some high frequency roll off and trouble with phase shift causing direction changes. I am still working this issue. If the noise is really fixed I might try to add another pull-up on the opto board to the +5 volts from the Jaguar.

Has anyone else seen these issues?

-Hugh
The board we used didn't drive the transistor into the Jaguars. It drove the inputs of the Jaguar with the outputs of the 74HC04 inverters the Jaguars themselves were basically powering (instead of the encoders). The inputs to the 74HC04 inverters were in turn connected to the NPN transistors pulled up with 4.7k - 6.8k resistors. Under other circumstances 4.7k would still leave enough margin to drive older 7400 series inputs.

To deal with the power supply issue for this circuit:

Initially we used a 7805 connected to the battery with a 4,700uF electrolytic capacitor on the input with a 10uF electrolytic and 0.022uF poly capacitor on the output. I'm almost positive we aren't allowed to do this on the robot. So we then started taking our power from the digital side car for the encoder side of the circuit.

Basically both our encoders, and the logic driving the optocoupler diodes, was powered by the digital side car with a small capacitor. As a matter of practice I'd be pretty concerned if that capacitor on the digital side car got too big as the inrush could have consequences.

I am still making efforts to provide these schematics. I'm sorry about the delay I'm extremely pressed for time lately.
I'm going to push to finish this up tonight...but no promises I haven't slept in some time.
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Unread 03-10-2011, 11:45 PM
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Re: 1 Encoder, 2 Jaguars

Here is my interpretation/design from the discussions that have taken place here.



Please note that this is only for 2 Jaguars. This setup aids how 1712's robot is setup instead of having everything on one central board.

I'm pretty sure R1 and R2 need to be decreased in value here since I am using one pull-up per encoder input to feed two diodes in the opto-isolator. I need to look at the datasheet again for the PS2501 to verify the If of the diodes.

I didn't want to remove the schmitt-trigger inverters on the input since they will help with some noise. Availability of non-inverting schmitt-trigger buffers is fairly limited so as a result the inverters on the output of the opto-isolator are still required. Feel free to substitute appropriate HC04 and HC14 parts from those listed as I just used what was available in my part library here.

For those of you electrically inclined please review this for me. I very easily could have made a mistake as I didn't spend as much time on this as I really should. It'd be nice to catch an error now before I get some PCBs made.

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Unread 03-14-2011, 02:11 PM
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Re: 1 Encoder, 2 Jaguars

Your schematic is unavailable, and I'm still swamped I'm very sorry about this.

It sounds like you have the right idea, however, please be aware that the source and sink of the other families of TTL are different.

I'd advise people to stick with the 74HC14 on the input side. Though the straight 7414 will work fine in this circuit, the BJT output stage can have some other issues in the capacitive realm.

In the original design we picked a pull up for the NPN transistor in the optocoupler that could accommodate the higher input requirements of the the 7400 series chips because I had considered tri-state and open collector outputs. It's not so easy to get 74HC16 or 74HC17 open drain parts.

For this application you don't need open collector, open drain or tri-state outputs from this circuit. The 74HC04 is quite efficient for the power it uses...just be sure to tie any inputs you do not use to one of the power supply rails...otherwise if you merely get near it, it might actually change state because of the 74HC series high input impedance. Now, you'd think that if the other gates in your integrated circuit were not actually driving any other circuits it wouldn't matter...but the noise from them jumping all around can walk back into the circuit's power supply locally.

I'm going to put my foot down and promise I'll have the documentation mostly done by Wednesday morning at the latest. It's entirely my issue delaying this as I have problems with my eyes.

Last edited by techhelpbb : 03-14-2011 at 02:46 PM.
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Unread 03-14-2011, 03:47 PM
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Re: 1 Encoder, 2 Jaguars

techhelpbb -

I apologize for the missing schematic... I had it taken down after I realized a serious error in it and that Chief Delphi doesn't let me edit posts. This is one case where I don't want someone to make a mistake... Jags and encoders aren't cheap. I have since corrected the error over the weekend and will probably make an updated post this evening.
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Unread 03-14-2011, 06:37 PM
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Re: 1 Encoder, 2 Jaguars


(click for full size)

Everything from my previous post still applies here. By substituting 74HC14/74HC04 parts I mean that you don't have to use the SN74HC14 or SN74HC04. For example, I will be using the CD74HC14 and CD74HC04 from Texas Instruments. Other manufacturers will probably work, just verify against the datasheets.

A few notes here...

1) I bumped down the pull-up resistors from 680 ohms to 540 ohms. This will give If = ~6mA for the diodes in the opto-isolator. 680 ohms was a bit too close to the minimum If = 5mA for the opto-isolator part for my comfort, but will still work.

2) The NPN transistors driving the opto-isolator diodes are probably a bit of an overkill here as ~12mA is well within the rated current of the 74HC14. I'm not a huge fan of driving diodes directly from an IC output, but that is probably just the conservative design practices from work rubbing off on me.

3) U1 VCC is connected to the SIDECARVCC net and GND is connected to the SIDECARGND net. U2 VCC is connected to the JAG1VCC net and GND is connected to JAG1GND net. U4 VCC is connected to the JAG2VCC net and GND is connected to the JAG2GND net.

4) All of the headers are standard 0.1" pitch (spacing) headers. You could either wire directly to these connections or use the appropriate header parts.

I finished up a PCB design last night and will be ordering some from a manufacturer either tonight or tomorrow. Due to economies of scale I will probably have a few extra that 1712 will not be using. I would be willing to part with these at cost either assembled or left to the user to assemble. Do note that the PCB utilizes surface mount components except for the opto-isolator so surface mount soldering experience is recommended for DIY assembly. The board sizes in at 2.46" x 1.4". I can't guarantee any delivery date as I would prefer to test one of them out here before I send any out to avoid issues.
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Unread 03-14-2011, 06:44 PM
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Re: 1 Encoder, 2 Jaguars

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.

Last edited by techhelpbb : 03-14-2011 at 06:49 PM.
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