Re: Intermittent connection on field only
 

Team 846 had similar problems at New York Regional, which were resolved by swapping the power distribution board. Though it will not pass inspection, you can try mounting a spare PDB as a custom circuit off of one of the 40A breaker slots, and powering the radio off of that.

We will likely have more data on this phenomena later, as we plan to scope out the failed power distribution board under load. It is perhaps notable that we have measured large ripple voltages (up to 0.6v on a WORKING board) on the 5v supply output, and that this is likely a marginal condition for the D-Link, which expects 5v +/- 5%.

Re: Intermittent connection on field only
 

Aren't you supposed to power the D-Link AP with the DC-DC converter?

I know you can power the D-Link from that 5V source on the PDB, but you're pushing your luck as you've noticed.

I am absolutely sure this was a requirement last year because we showed up to Palmetto minus that DC-DC converter and electrical tried to get me to overnight it (luckily they found a donor).

Re: Intermittent connection on field only
 

Thanks. I was basically the only living body in spare parts and I couldn't stop long enough to test that myself. Unfortunately I normally have one of my A/B/G/N 'war driving' kits with me, but I had to move quickly to absorb spare parts and get all my tools so it ended up sitting at home on the floor.

I did have my Droid-X with WiFi Analyzer App and towards the end during eliminations (while I was moving batteries) I did see 4 networks that are not normally present and they were definitely G networks (my phone does not do A/N).

Are there G networks for field controls, or do these access points continue to transmit the G networks even when you're not using them? I don't know so I'm asking.

Re: Intermittent connection on field only
 

Yep, one and only one PD. However, ripple is not normal and the five volt output is to be used for the camera only. The correct wiring is to connect the five volt convertor to the +12 volt 'radio' output on the PD. The output of the convertor then feeds the radio.
Any idea what frequency the ripple was?

Re: Intermittent connection on field only
 

We weren't able to get a good measurement on the ripple due to difficulty getting the oscilloscope to trigger, but it was approximately 2KHz by our reckoning.

The 5v I mentioned isn't the 5v output on the PDB itself, it's the output of the DC-DC converter after the +12V radio output on the PDB. We don't use an Axis camera on our robot, and so the dedicated 5v on the PDB is disconnected (Sorry for the confusion, I'd completely forgotten that there was a 5v output on the PDB).

Re: Intermittent connection on field only
 

We had the same issue in CT. 4 out of 10 matches we were fine, 5 had intermittent, 1 had no robot control post autonomous, in now particular order. The robot ran fine on the wire and also fine on test radio's in the pit and on the practice field. After much testing (on and off the field) we discovered that our four JAG controllers on the drive were overloading. It appears there was a delay or lag in signal quality, our driver would unknowingly increase voltage through joystick position. When the signal would return the voltage position was high and the JAGS would overload. The process would repeat itself, 3 seconds off- 15 seconds on- 4 seconds off 15 seconds on, over and over. If the driver waited 20-30 seconds the robot would drive again only to suffer the same issue soon after. Very frustrating.

Re: Intermittent connection on field only
 

Mike,
What you describe is typical Jag over current trip. Once they go into fail mode, they wait about 3.5 seconds before returning to normal operation. Most teams using the Jags build in a ramp up to full throttle to help reduce current through the device when the motors are in stall.

Re: Intermittent connection on field only
 

We had a ramp up program and the jumpers on the jag moved to the appropriate position. It was definately a problem with tripping the jags, the question is what was the source of the problem. In any other drive condition the jags worked fine, on the field they failed at random intervals. If there was an overloaded bandwith issue and the controller was slow to react, would this craeate a situation where the joystick was in a full throttle position when the signal was processed ? If the bot was stationary and regained conscientiousness at full power would this overload the jag?

Re: Intermittent connection on field only
 

Mike,
Conditions for drivers on the field are rarely what they are back in the pit, back at your school or on the practice field. The drivers are pumped up for competition and adrenaline is flowing. The Jag fail state is not ported back to the Crio and therefore not through the FMS to Driver's Station. If your student is at full throttle when the Jag re-enables itself, your DS will be sending the full throttle command to your robot during a stall condition on your drives. (stall occurs anytime the motors are not moving and you apply current)

Re: Intermittent connection on field only
 

Agreed, The nagging question is root cause for the initial over current condition. Why with acceptable programming were we entering the overcurrent ? What is the protocol for recovering or re-entering normal function state?

Re: Intermittent connection on field only
 

A few possibilities I can offer that a driver might do in competition that you might not see in another environment:

1. What happens if you drive your robot forward and backwards quickly several times?

2. What happens if you push another robot with your robot (put 130lbs of bricks on something with wheels and try it)?

3. What happens if you go full throttle up the bridges?

4. What happens if you skate along a wall with the robot?

5. If your robot can turn in place, what happens if you do that then suddenly reverse rotation?

6. What happens if you run your end effector and drive train at the same time (does the battery brown out)?

Just a few instances that merely driving around might not simulate that easily crop up during matches.

Re: Intermittent connection on field only
 

Mike,
The only way to recover is to wait. The way to prevent over current fault is to limit the demand either in software or driver training under all conditions. Without watching your robot or knowing your drive train I can only speculate. Some of the more common factors are improper gear ratio choice, sticky tires, sharp turns, transmission losses, misalignment of chains and sprockets, binding drive parts, improper use of bearings or cantilevered drive shafts.

Re: Intermittent connection on field only
 

At 10,000 Lakes, our robot regularly had issues with getting connected to the FMS on-field.

The access point is mounted high in the robot, on Pleiglas at least 2" from any metal. We installed a new Ethernet cable as well. We have the DC-DC converter installed.

The solution that finally worked for us was cycling the power on the access point as we entered the field.

Has anyone had any experience using a shielded Ethernet cable? Was reading a bit about it here: http://www.l-com.com/content/FAQ.aspx?Type=FAQ&ID=4803

Re: Intermittent connection on field only
 

I am not a fan of suggesting it but I should tell you anyway.

If push comes to shove and you can't locate a reasonable resolution to your intermittent overload on the Jaguars, perhaps you could consider using Victors for at least the most likely overloaded systems.

Using the Victors won't actually stop you from overloading the system, but the Victors will just brute force until they self-destruct and if all else were to fail that might be sufficient to get you through till you can either adjust the software or the hardware to resolve this issue.

Keep in mind, what you'd be doing is not a good idea with the Victors either, but if it's rare and intermittent they'll probably survive it. If it's not a rare overload then you might literally be playing with fire (or at least smoke).

Obviously this would mean possibly adding PWM for the Victors to a robot that might not be using PWM to control the Jaguars and this might mean retuning the controls for the differences. This could also involve tinkering with some wiring. However, you could prepare for such a change in advance of competition.

Re: Intermittent connection on field only
 

I think the Victors will survive.
I actually tested this hypothesis a couple of weeks ago and the 40amp breaker on the circuit will trip before the Victor suffers harm.

The order seems to be:

• Jaguars trip first (most sensitive)
• 40 amp breakers trip second

What this means is that swapping the Jag out for Victor will help in marginal cases, but won't do any good if the problem is more than borderline.
Some gear ratios just need to be recalculated.