Cheap replacement for the Power Distribution Board

[AustinSchuh]

Originally Posted by Al Skierkiewicz

Austin,
If you are using IFI controllers then power distro is simply the fuse blocks that you can purchase from the same vendors as 2008 if you need them. If you are combining 2009 and 2008 sensors, or cameras then you will need to come up with some other solutions.

Al,

Ah, now that I go back and reread my initial post after reading your response, I can see how my post could be interpreted two ways.

Since the 08 robot's electronics got completely removed, we were thinking of wiring it up to to use the cRIO to test out new algorithms for control and just get it working again. We could almost just use the old fuse blocks which we have plenty of lying around, except that we need the 24 volt boost converter to power the cRIO.

Our backup plan definitely still is to use the 08 control system in it's entirety, controller and all.

After classes close out for the semester, I'm going to do some research and work on finding a suitable boost converter as suggested. Eric gave me some suggestions via PM, so I think I'm covered. Thanks everyone for your help.

[Greg McKaskle]

Note that this is coming straight from a SW guy, but since you don't care about being competition legal, and since the cRIO doesn't require 24V, but instead needs a minimum of 9 or so volts, another approach is to use a second battery instead of a PD. The cRIO draws very little power, and in the past we've run it for I believe four hours on a small lawnmower battery.

Greg McKaskle

[Al Skierkiewicz]

Originally Posted by AustinSchuh

Al,

Ah, now that I go back and reread my initial post after reading your response, I can see how my post could be interpreted two ways.

Since the 08 robot's electronics got completely removed, we were thinking of wiring it up to to use the cRIO to test out new algorithms for control and just get it working again. We could almost just use the old fuse blocks which we have plenty of lying around, except that we need the 24 volt boost converter to power the cRIO.

Austin if you just tether then any of these options should work fine. Wireless, the access point becomes the biggest problem. So using Greg's option you could also add a third battery for the wireless. I am thinking this through, but my first guess is to put the batteries close together, and tie the negative leads together to prevent circulating currents from running the source voltage up and down for the cRio and the wireless.

[Russ Beavis]

Greg,
Doesn't the FRC cRIO require a higher minimum supply voltage (ie 19V) than the standard cRIO line? I thought that was one of the differences between the cRIO setups using separate controllers and the integrated chassis/controller being used by FRC.

Russ

[Joe Ross]

Originally Posted by Russ Beavis

Greg,
Doesn't the FRC cRIO require a higher minimum supply voltage (ie 19V) than the standard cRIO line? I thought that was one of the differences between the cRIO setups using separate controllers and the integrated chassis/controller being used by FRC.

According to the cRIO-FRC Operating Instructions that is the case.

[EricVanWyk]

My understanding is that it is only guaranteed to work over the 19-30V range. It might work lower, but you are on your own. The boost supply was designed to not test those bounds, but independent projects can attempt what they see fit and live with the consequences. I've definitely seen the cRIO operate well below 19V, but I wouldn't guarantee that it works 100% of the time.

However, if Greg (Mr. NI) says it will work, I'll believe him. He'd know much better than I would.

[SteveJanesch]

For the 24V supply, I assume you could also connect two 12V batteries in series. You'd need to connect the negative terminal of the stack to the negative rail of the robot somewhere (like the old ground lug) - you wouldn't want a floating 24V powering the cRIO. If all you're running from the stack is the cRIO, it should last for hours.

You'd probably want to connect the stacked batteries in some way to easily disconnect them for recharging - I haven't thought that part of it through.

- Steve

[Greg McKaskle]

As I mentioned at the beginning, I'm just a SW guy -- with a EE minor, but that was a long time ago. I know for certain that we have run cRIOs on a single 12 volt battery, but I can't be certain that the cRIO was stock. They may have modified the power supply, or they may have simply verified that it'd run to the 9 or so volts that I remember.

I certainly am not suggesting any modifications to the cRIO, and I'll take any EE input over my own when it comes to power.

Greg McKaskle

[Al Skierkiewicz]

How about we just stick with the 24 volt requirement for all discussions. That will simplify matters for the majority of the people who read these posts.
Yes, you can stack (series wire) two 12 volt batteries to produce the 24 volt requirement. However, everyone should note that the load on any given battery will change it's terminal voltage dependent on the current supplied to the load and the internal resistance of that battery. It is not uncommon for our robot batteries to be pulled below 8 volts during normal running conditions. That is why the 8 volt trip point was selected in the IFI controller and why Eric and Russ designed the 24 volt power in the new 2008 PD to maintain output below 5 volts. The internal resistance of our batteries is typically 11 mohm and can deliver over 600 amps at full charge. CIM motor stall current is 129 amps so four or more motors in stall can draw down the terminal voltage significantly.

[SteveJanesch]

Originally Posted by Al Skierkiewicz

How about we just stick with the 24 volt requirement for all discussions. That will simplify matters for the majority of the people who read these posts.
Yes, you can stack (series wire) two 12 volt batteries to produce the 24 volt requirement. However, everyone should note that the load on any given battery will change it's terminal voltage dependent on the current supplied to the load and the internal resistance of that battery. It is not uncommon for our robot batteries to be pulled below 8 volts during normal running conditions. That is why the 8 volt trip point was selected in the IFI controller and why Eric and Russ designed the 24 volt power in the new 2008 PD to maintain output below 5 volts. The internal resistance of our batteries is typically 11 mohm and can deliver over 600 amps at full charge. CIM motor stall current is 129 amps so four or more motors in stall can draw down the terminal voltage significantly.

I agree 100% - I was suggesting two batteries in series in addition to the 12V main, not a single battery connected in series with the main. Sorry for not being clearer. I figured a veteran team would have plenty of old batteries around - not competition-worthy, but enough to power a cRIO. Now, how to fit two more batteries on a robot, that'll take some creativity.

[xanarchyx]

Just listening in, you could use 2 of the standard robot batteries in series, use 1 for primary power and series in the second one with the hot only connected to the cRio. For power flux, you could use a large capacitor or a group of smaller ones in parallel (>20,000microF Should work). This would offset the instant V-drop from the start or reveres of motors. (The primary 12 might drop to 8V and the secondary battery in series won’t be affected so it should output 12. 12+8 =20) That is within minimum operating specs for the voltage. Easy, 2 batteries, a few caps that can be found lying around or in power supplies…. It’s a bit jerry rigged I know but it looks like it should work.

p.s. The "secondary" battery would not need to be a full sized FRC battery, it could be any 12V, a smaller one would be a lot easier to fit in.

[fsgond]

I would suggest that you look into a voltage doubler. This would give you double whatever the voltage is on the battery. I would also be sure to put in a voltage regulator circuit and some filtering, such as a capacitor. The motors on the robot cause a lot of EMI (electro magnetic interference) that can cause strange things to happen if you don't use a filter.

[Al Skierkiewicz]

Just so we can keep everybody calibrated, the robot battery voltage fluctuates during operation from over 13 volts to under 5 volts. Filters and regulators can not help on those issues. A voltage doubler works if the input voltage doesn't change and the load current remains fairly constant. The boost/buck regulator can handle these fluctuations and provide a fairly constant output.