regulated power for potentiometer
 

Apologies if this question has already been discussed in detail in another thread. A quick search returned no helpful results.

What is(are) the recommended way(s) to power a potentiometer so that the signal is less affected by battery voltage change?

Would it be helpful (and legal) to tap into the power going to the radio?

Or perhaps do A/D on both the signal and the power to the pot, and use the ratio?

Re: regulated power for potentiometer
 

I believe the converter on the Analog Breakout is pretty good at handling low battery voltages. My experience with it is limited, so YMMV.

It's definitely not legal to connect anything to the radio power slot but the radio/radio converter.

Re: regulated power for potentiometer
 

That's a good question. I know our code last year used "getAverageValue()" and seemed to be very consistent - our arm (controlled with 3 pots - shoulder and elbow using 270 degree pots, and winch using a 10-turn pot) didn't seem to be affected by power, at least not until the power got so low the motor on the winch couldn't get the robot all the way up. In our build space testing, we saw no visible difference in how the arm operated when going from a dead battery like that to a fresh, fully charged one.

Re: regulated power for potentiometer
 

It's very easy to add a jumper to the analog board and read in the supply voltage. Since it's a 0.1" pin header, you can just use a standard 0.1" jumper between the center (5v) and signal pins.

That's probably the easiest way to do it.

Re: regulated power for potentiometer
 

The Analog Breakout has an LDO 5v linear regulator, good to about 5.6 volts. Do you know a team who is getting that low consistently?

Re: regulated power for potentiometer
 

Us. At least this appears to be the problem.

-Aaron

Re: regulated power for potentiometer
 

Do your driver station logs show you getting that low in a match?

Re: regulated power for potentiometer
 

I wasn't suggesting connecting anything other than the 12-to-5 converter to the PDB regulated 12v.

Re: regulated power for potentiometer
 

You also aren't allowed to power anything but the wireless bridge from the regulated 12v slot. [R43]

Re: regulated power for potentiometer
 

Toward the end of some matches, yes.

Re: regulated power for potentiometer
 

If you're having trouble with the Analog Breakout, the Digital Sidecar isn't far behind, with much worse symptoms. It might be helpful to make a new thread about how you're killing batteries over the course of a match, and describe your robot and power systems so that people can provide suggestions on how to reduce power draw.

The dropout of Analog Breakout regulator decreases as the load decreases. You may be able to reduce the number or size of loads to gain a little more margin. See attached chart from the MIC5209 datasheet.

I agree with Max that you can't tap into the radio power supply in any way.

One option, without adding an external boost converter, is to use power a Solenoid breakout with cRIO 24v (allowed per R42). Turn on a Solenoid Output (allowed per R51), and then use a voltage divider to bring it down to 10v (The NI analog module is +/-10v). This has the disadvantage that you can't read the pot during disabled mode. You're also switching from a linear regulator to a switching regulator.

Re: regulated power for potentiometer
 

Could you wire the positive terminal of the potentiometer to the 5v port on the PDB? I'm not sure how low of a battery voltage it takes to brown that port out, but I don't see anything against it in the rules.

Re: regulated power for potentiometer
 

Can't you use the voltage regulator for the camera? I think that is legal

Re: regulated power for potentiometer
 

I'm shocked that you're having this problem and we have not run into this. My team has a penchant for using a TON of motors (13-15) and at least 3-5 pots each year and we haven’t run into this. Plus our driver drives like a bandit and we have our 6 CIM drive geared to the moon this year so I know we're sucking some serious juice out of the battery. We do buy ten brand new batteries every year and use a freshly charged battery every match which helps us.

Any major mechanical inefficiencies in the system?

Are all your crimps and terminals good? Anything getting super warm?

Have you tried swapping the analog breakout?

Re: regulated power for potentiometer
 

It may just be old batteries.

Aaron, when's the last time you guys capacity-tested your batteries?

Re: regulated power for potentiometer
 

So they're calling a 10K pot an "electrical load"?

It's more like a reference voltage.

Oh, well.

Re: regulated power for potentiometer
 

I don't make the rules. :D

Re: regulated power for potentiometer
 

All brand new batteries. I'm not the programmer, so I'm just told that we are having this issue with the potentiometer.

-Aaron

Re: regulated power for potentiometer
 

Can I see a driver station log where you drop below 6 volts?

Re: regulated power for potentiometer
 

I'll email our programmer and ask him to post it or send it to you. Due to work schedules, it likely won't be available right away. Thanks for following up with this.

Re: regulated power for potentiometer
 

This.

A serious mechanical issue can cause a severe battery drain too.

2474,

Without knowing more about your robot, assembly techniques (how did you crimp your 6awg terminals?), its mechanisms, etc. I fear that you are trying to band-aid the symptom of a much more significant problem.

Re: regulated power for potentiometer
 

I cannot answer your question about the 6awg terminals right now, but as for the Mechanisms:
Drivetrain- 2 CIMs on this Sonic shifter (am-2509_37) for a total of 4 regular CIMS

Collector- 2 banebot RS-550 motors each on P60 PGBs with 5.09 ratio

Pneumatics- We use pneumatics for shifting and lifting our collector up and down. The compressor only runs when motors (other than the drive motors) are not spinning.

Arm/Shooter- 2 am-0912 with that are reduced by 630:1 ratio. The shooter uses 2 more CIMs for spinning up our wheels.

Summary:
- 6 CIMs total
- 2 banebot RS-550
- 2 am-0912
- 1 Compressor

-Aaron

Re: regulated power for potentiometer
 

Assuming an 11 milliohm battery internal resistance and 4 total feet of 6 gauge wire on your electrical system, you only need about 400 amps to lose 5 volts. 4 CIMs alone can use over 400 amps at stall. If you run most of/all your motors at once, you could be looking at significantly more than 5 volts of loss.

Re: regulated power for potentiometer
 

I'm curious about your drivetrain. I wager a guess you're seeing this in high gear when accelerating your cims near stall from a stand still.

The sonic shifters in their default ratio, direct driven to four inch wheels with 4 cims are at the very extreme end of gear ratios - a full battery easily drops to 8 volts under acceleration from a stand still in high gear.

Re: regulated power for potentiometer
 

This can be fixed by having your shifter shift to low gear when the robot's not moving. Shouldn't take more than a few lines of code.

Re: regulated power for potentiometer
 

I forgot to mention that we are using 4" wheels. Voltage is not as much of a problem accelerating as it is turning. We are going to switch our outer wheels on our 6 wheel drive to omni wheels.

Re: regulated power for potentiometer
 

You're using a flat 6wd? (As opposed to a drop-center 6wd.)

Do you know what your drivetrain is geared for?

Re: regulated power for potentiometer
 

Correct. We have a wide base.

The ratio in high gear is 3.7 : 1.

Re: regulated power for potentiometer
 

We never run all of our motors at once. The AM-0912 motors power the arm which has very high torque and holds it's own weight un-powered. The collector wheels spin only when we pick up a ball, so it's not the often. The shooter CIMs spin only when we are shooting a ball. The 4 Drive motors are the ones that spin most often.

Re: regulated power for potentiometer
 

Wow. :eek:

I used the JVN calculator (which I think everyone should have in the Excel 'recent docs') and it seems that in high gear you're set for 20+ft/s. Which is insanely fast. It predicts a maximum drive-train draw of 680A, which will definitely cause the voltage sag issues you've been seeing.

This issue is probably compounded by the fact that you've so deeply discharged most, or all, of your batteries by now and damaged them.

Omni wheels will definitely help turning. I would strongly encourage some sort of software feature that uses low gear as much as possible.

Re: regulated power for potentiometer
 

I believe there is nothing in the electrical part of the rules this year that prevents you from putting a bypass cap across the power and ground leads of your sensor. It will be considered a custom circuit, but thats ok. You can then plug it into the analog bumper as normal.

Hope this helps,
Kevin

Re: regulated power for potentiometer
 

Guys,
The elephant in the room is that the DSC will drop out at 5.5 volts if sustained for more than a second or two. At that point all output ceases. If using Jags, the Jags will drop out and fault for under volt even if the CAN buss stays up. Please check to see if you are dropping voltage across primary wiring. i.e. all #6 wire, terminals, battery, etc. In over 90% of the cases, this is simly a loose battery terminal or a bad crimp or terminal. If you are using the KOP screw terminals for the battery and the PD I would suggest moving to a crimp or an SLA connector where the screw is not contacting the wire but is trapped by a clamp. Be sure to strip the wire correctly.
While it is not mentioned more, there is a voltage drop across the PD. If you see drops on a critical supply (analog module), you might try moving the breaker position to one closer to the PD input terminals. You are trying to put it upstream of high current 30 and 20 amp loads.