RAIV (Redundant Array of Independent Victors)

[Rapt0r9]

This is an idea I've been kicking around for some time. I am basically using the idea of a RAID 5 and replacing the drives with victors. The idea here is that when a victor fails, and we have had quite a few fail during competitions, the RC will acknowledge this and a spare victor will automatically take over the role of the broken victor. I figure if I use motor voltage sensors to monitor the voltage which each victor is outputting and compare that against the voltage which the victors are supposed to outputting, I can catch a failure in a victor. The only area I am skeptical is with wiring the secondary system of victors which will be acting as the "hot swaps". I am just curious to see what you guys think of this idea.

[Stuart]

the problem would be is you would have to connect multiple vics to a single motor. . . and thats against the rules. good idea though. . . as far as the wiring. not that hard. just connect the V+ pins to the output of a relay, then switch them by controlling relays.

[Tottanka]

It sounds like a great idea, only problem is, like you mentioned, the wiring.
It basicly means that u need to have your spare victors somehow connected to all victors, and when needed replacing only one of them.
I think you'd be better with having 1 spare victor for each indangered victor, though it causes other problems (weight, cost etc..)

[EricVanWyk]

I do like the spirit of this. Perhaps you can get halfway there and implement a system that will do the victor fault detection and report it to the driver. This way you know exactly what to fix before you even get off the field. If you couple this with a well designed electrical layout, you will be sittin happy while the rest of us are panicking.

The real important bit is to tell the difference between a popped breaker and a busted vic.

Good luck!

[Greg Marra]

Originally Posted by EricVanWyk

I do like the spirit of this. Perhaps you can get halfway there and implement a system that will do the victor fault detection and report it to the driver. This way you know exactly what to fix before you even get off the field. If you couple this with a well designed electrical layout, you will be sittin happy while the rest of us are panicking.

Even better, roll it into a custom laptop-based dashboard and don't leave anything up to the driver to figure out. It'd sure help to know when you're dropped a chain vs. lost electrical output to a motor, or when all your victors are non responsive vs not going anywhere in a pushing match...

[MrForbes]

Might also be worth looking into why you are losing victors. Perhaps some minor changes to the robot design, or to maintenance procedures, will eliminate the problem.

I don't recall our team ever losing a victor.

[Rapt0r9]

Well, I was considering setting up a relay to select which motor the victor would be assigned to. By using a spike, we can cut the number of victors that we need in half, thus helping to reduce the weight of the robot. The spike can also serve as protection to prevent both victors from outputting voltage to the motor at once.

I was reading up on the dashboard packet structure earlier today and I think that we should defiantly be able to write something that will give the drivers feedback as to why the bot is responding awkwardly. We have always tried to integrate a laptop into our controller to use with dashboard, but we never got around to it.

[Kevin Sevcik]

Ditto on our team never or very rarely losing a Victor. But as noted, this isn't legal for at least one very good reason. When a Victor is in brake mode instead of coast mode, it quite literally shorts the leads of the motor together so the motor goes into regenerative braking. So if your spare victor or failed victor is in braking mode, you'll rapidly have two failed victors. And if you make a mistake on whether one is broken and start up the second and they're not perfectly in sync, you could end up with current shorting from one to the other as their duty cycles don't sync up.

EDIT: You won't be able to use spikes like this. Spikes are solid-state "relays" not actual physical relays. So they take a constant 12V and GND on the input side that they need all the time at that polarity to operate properly. Then they just send 12V or GND to M+ and M- as dictated by the digital inputs. If you send a Victor output that isn't full on foward to a spike you'll just make it work weird and jitter if at all, if you're sending voltage in the forward sense. In the backwards sense, you'll probably just fry the poor thing. And wiring in physical relays instead won't be legal either.
In summary, the FIRST wiring rules are there for a reason, and it's almost always to protect your team's significant investment in IFI products.

[EricH]

Having an onboard diagnostic tool to detect when a Victor goes out would be a good idea. The problem would be getting the feedback. I'll leave that to the programmers to figure out.

The problem with swapping in Victors automatically if one goes out (other than the rules--both wiring and cost) is the cost of Victors. It's around $100. For a four-motor drivebase alone, that's $400. And then you need spares to replace the ones that die.

Best solution: find out why you are breaking Victors. An onboard detection system can help with that, but it would be better not to have to use it.

[MrForbes]

They are not that expensive...

http://www.ifirobotics.com/victor-88...r-robots.shtml

[Al Skierkiewicz]

Originally Posted by Rapt0r9

Well, I was considering setting up a relay to select which motor the victor would be assigned to. By using a spike, we can cut the number of victors that we need in half, thus helping to reduce the weight of the robot. The spike can also serve as protection to prevent both victors from outputting voltage to the motor at once.

A few things will get in your way on this implementation. The first and foremost, the Spike is only rated for 20 amps. This rating is determined not only by the fuse but by the ratings of the contacts used on the internal relays. If allowed under the rules (and I do not believe under the current rulebook this would be allowed) a stalled FP, or Chalupa motor would turn a Spike into ash in a matter of a few minutes. Certain failure modes of the Victors would produce a dead short on the output, so just wiring in parallel would also cause more harm than good. Finally, custom circuits (i.e. a high current relay) are not allowed, under the rules, to be placed between the Victor and motor nor is a custom circuit allowed to directly control a motor.
Some teams have problems with Victors yet most do not. I could spend a few hours talking about Victor failures but essentially all failures can be reduced to just two causes. 1. Foreign material in the Victor causes internal shorts. Keep metal shavings, gear debris and drill dust out of electronics. 2. Excessive and repeated currents at 100 amps or above caused by drive train design, loose or intermittant elctrical connections, lack of calibration in multimotor systems and improper driving technique. This abuse causes extreme internal heat in the active devices resulting in electrical failure.
I would spend more time trying to deduce which failure mode is causing your Victors to die and correct the problem at the beginning of robot construction. If you have a correctable problem and ignore it, you will reach a point where your backup to the backup will also fail leaving you with a non-functional robot. Murphy says this will occur in the last match on Einstein on Saturday afternoon. I would rather have a functional robot and a medal than three dead Victors.

[Rapt0r9]

In the past we have had problems with cables coming loose from the Victors and Spikes. This has cost us a couple matches and this idea would primarily be in place to prevent this from occurring. It looks like using a spike wouldn't work as Kevin mentioned, but I am still considering using the motor diagnostics, even if it is just for feedback to the drivers.

I was also considering setting up a DPDT switch on the robot and using that to switch the connection of the motor to the victors. Basically the common leads would go to the motor's positive and negative lines and the victors would be connected to the throw leads. The switch can then be actuated by an electrical soleoid which would throw the switch. It is kind of a jimmy rigged relay, but it is a physical relay, so the victors would never be outputting to each other, or to the motor at the same time.

[Al Skierkiewicz]

Again, current rules do not allow custom circuits between the motors and the output of a Victor. Switches must be considered as a custom circuit in my opinion when used in this way. Electrical solenoids are also not allowed under the current rules. I am hoping that this rule will change in the future by having a few solenoids provided as part of the kit.

[MrForbes]

Originally Posted by Rapt0r9

In the past we have had problems with cables coming loose from the Victors and Spikes. This has cost us a couple matches and this idea would primarily be in place to prevent this from occurring.

It seems to me that adding MORE wiring connections is not the best way to solve problems caused by faulty wiring connections.

[EricH]

Originally Posted by squirrel

It seems to me that adding MORE wiring connections is not the best way to solve problems caused by faulty wiring connections.

I concur. Make sure that your PWMs and power wires are secure. Check before every match if you need to. Come up with some way of securing connections before looking into other methods.