Re: Jaguars
 

We used Victors last year, and kept cooking them, (because our motors kept shorting out, damaging their FETs. We haven't been having those problems anymore, because our shooter is disabled so we barely use it. Victors, themselves, are quite nice. They were lightweight last year, compared to jaguars, and they work nicely. I do not have too much experience with Jaguars, but it seems though the feature set is quite great. The CAN interface is nice, along with the PWM interface. These can be networked through an RS232 interface too! There are a lot more features that I won't list, but here's the manual: http://content.vexrobotics.com/docs/...e_20130215.pdf. As mentioned before, a big problem in these motor controllers is their maximum continuous current. In the product page (http://www.vexrobotics.com/217-3367.html), here is the specs table:

Never Limit Progressive Limit Immediate Limit
Pre v107 40A 50A 60A
v107 40A 50A 92A


Here are the Talon specs:
Page: http://www.andymark.com/Talon-p/am-2505.htm

Input voltage: 6-28 VDC
Continuous current: 60 A (above 40A continuous we recommend adding this fan)
Peak current: 100 A
Input PWM signal: 0.9-2 ms @ 333 Hz
Input resolution: 10-bit (1024 steps)
Output resolution: 10-bit (1024 steps)
Output switching frequency: 15 kHz
Talon SR: Synchronous sign-magnitude rectification
Smart LED, blinks proportional to throttle, now with obvious change from 99% throttle to 100%
Simple calibration
User selectable brake/coast
4% neutral dead band
Linear throttle response

I hope this helped. This is a comparison between Talons and Jaguars.

Re: Jaguars
 

The two most important features of a speed controller are reliability and cost. We don't want to worry about swapping out controllers after a match, and we really want to avoid failures during the match. Reliability is also important because we use previous years speed controllers on the practice robot. This year, our practice bot had victors from 2003 and 2004 that have already been used on at least two robots. Victors are the only controller with this type of reliability. They are also the cheapest.

As for the extra features, I think they're a waste. We end up wrapping the speed controller class to add a few utilities, so it's easy to add a pidcontroller and and the function to make the output linear. The jaguars don't really have any features that can't be done on the crio.

Re: Jaguars
 

I agree. Victors will take a lot of abuse before failing. The only failures we had were because of a shorted motor. If they added temperature sensors to the MOSFETS, they could allow it to do an emergency shutdown before damage!

Re: Jaguars
 

Please let me know where the current sensing feature is on the cRIO. My team has been unaware of this feature.

Re: Jaguars
 

With minimal hardware the feature could exist but I doubt it would be legal under the FRC rules as it would require measuring the voltage drop over a specific length of wire using the analog bumper or some other analog accessory. It can be done with a series resistor like in the Jaguar but in doing so you'd be in the path of the current with more than wire. I doubt it would be legal on the output side of an electronic motor control as it would make a connection between the bridge in the electronic motor control and the motor back to the control system. It might not be legal on the power input side of an FRC electronic motor control either. Course on the power input is both the current to the motor and the electronics in the motor control (which are small in comparison to the motor). There's also the issue that the current at the power input point will have aspects not conforming to the current at the output to the motor (the bypass diodes, various features, the resistance of the MOSFETS).

Don't think of trying this trick unless you understand the difference between a single ended and differential A/D input.

Re: Jaguars
 

That wasn't actually a serious question, but thanks for the answer! For the Talons we used on our drive train, we experimented with using a wire coiled around one of the wire leads and got some values in a custom circuit. I'm not sure of all the details, our electrical mentors worked on it.

Re: Jaguars
 

As was wondering, at the rick of sounding ignorant, what is the performance difference between Spikes, Jaguars, and Talons? I know the Jaguars have CAN but what that does is a little of a mystery to me.

Re: Jaguars
 

A Spike is simply a couple of relays, whereas Jag and Talon are speed controllers.

Performance curves for Jag, Talon, and Vic may be found here:

http://www.chiefdelphi.com/media/papers/2720


In order to help you, it would help to know if it is a mystery because you've read and don't understand the documentation, or because you can't find the documents.

Re: Jaguars
 

It sounds like your team measured the electromagnetic field around the wire with a circuit that works like a current sense transformer. It doesn't actually connect to the circuit it merely robs some of the magnetic field around the wire (which is generally there as long as current flows) and converts it to something you can measure. That might let you skate on the FRC rules about getting in the circuit path between the electronic speed control and the motor. Plus when done with a current sense transformer you bypass the grounding issues as one leg of the output can be tied to that electronics ground with little impact on the electronic motor control or the motor. Using a current sense transformer it's important to note that measuring AC and DC currents require different considerations.

There are Allegro hall effect sensors that can measure circuit current if you dig around they were recommended up on ChiefDelphi before (oddly almost precisely 3 years ago):
http://www.chiefdelphi.com/forums/ar...p/t-87568.html

I am interested if these are legal in FRC in competition. However that might be a side track for this topic.

Re: Jaguars
 

It's true that there isn't a direct way to measure current on the crio, but for the price of a jaguar, you could buy (at least in 2012) a victor and a current sensor.
Per the 2013 rules you are permitted to have a low impedance sensor to measure current.

Re: Jaguars
 

Please state the rule you are referring to. There are some caveats about what you can do this with. For example you can use a low impedance sensor to measure current but not to the D-Link radio while in competition.

Re: Jaguars
 

Well, it actually is connected to the circuit, albeit inductively via the transformer formed by the lead wire and the coil wrapped around it.

Since the current to the motor may contain a large ripple under various operating conditions due to the interaction of the speed controller PWM switching, the motor inductance, and the motor commutation, there may be some issues involved in interpreting the measurements.

Re: Jaguars
 

Entirely correct. I just wonder if it is even allowed in FRC competition external to an approved FRC electronic motor control (regardless of the issues of making it work).

Of course by extension of being connected by inductance anything that passes through the magnetic field around the wire and can have a current induced in it is connected in a similar way albeit poorly. Parts of the robot that are not designed to be electrical but can carry a current for example. So generally not recommended to wrap a nice piece of copper wire around your other wires to act like a wire guide or retainer.

Re: Jaguars
 

I am referring to
[R47]

Custom circuits shall not directly alter the power pathways between the battery, PD Board, speed controllers, relays,
motors, or other elements of the Robot control system (including the power pathways to other sensors or circuits).
Custom high impedance voltage monitoring or low impedance current monitoring circuitry connected to the Robot’s
electrical system is acceptable, if the effect on the Robot outputs is inconsequential.

I was trying to point out that it is possible to measure the current draw of a motor like a jaguar does without having to use a jaguar. You can't measure the current draw of the radio in any way.

Re: Jaguars
 

I have no doubt that this works (with the expected technical issues). I merely doubt as to whether or not it would be considered legal on a competition robot connected to a motor (at first glance R47 would not lead you to believe the radio is excluded either but it is excluded I asked in the official Q&A before this year). The closest topic I found from 2009 was this:
http://www.chiefdelphi.com/forums/ar...p/t-74138.html

It merely states that the current sense resistor needs to be a very small value. It does have mention (by Al) of using the wire as a current sense resistor. Has anyone actually fielded this on a competition robot using the cRIO to process the measurements? There seems little sense to me to go back and forth over the myriad details (as often happens) if it might not be legal on the field.

Back on the topic of the Jaguar itself: is there a poll by team number of the teams that intend to use Jaguars on competition robots this year? I was helping a student make something that was an accessory to the Jaguar and with all the admirable effort IFI is putting in to these units I wonder if the number of teams using them is actually getting smaller. I am neither for or against the Jaguar in particular myself.