Hey guys,
I was thinking about the VEX motors, and I came up with an idea. What if you overvolt the motors for more power? Possibly use passive $5 heatsink squares to cool it off perhaps. And the increments would probably be 50mV or something small like that. I looked in the rulebook but couldn’t find anything prohibiting it, as it is most likely done through the software.
Discuss.
The Vex Smart Charger has an output voltage of 16V according to the product page. You’ll find that if you test the batteries after charging them with a Vex Smart Charger you will get a much higher voltage than 7.2V. (Does anyone who currently has access to a smart charger want to test this?) Charging batteries above 7.2V is not illegal, in fact, almost every robot ever placed on a competition field will have a battery that will test higher than 7.2V if you use a voltmeter, because the Vex Smart Charger charges them higher than this.
I don’t pretend to be an expert on this though, because frankly, I have no idea how battery chargers work.
I might also add that using non-Vex chargers was only made illegal at the start of the Toss Up season, and using non-Vex chargers was completely legal during Sack Attack. The Vex Charger is now compulsory of course, but this still won’t result in an even playing field because not every Smart Charger is made equal, and neither is every battery.
Yes. Just the other day I was doing some simple testing which required consistent battery voltage. I originally charged a bunch of 7.2V 3000 mAH batteries which had been used by our competition robots earlier. I charged them using the Smart Charger (V1), and almost all of them were consistently reading 8.2V soon after coming off of the charger.
I then put one battery back onto the charger, after only using it for a short period of time, when it dropped to 8.1V. After it was finished charging, I tested it, to find that it had been “super charged” to 8.5V. I had previously heard from other teams that have used this method in order to achieve higher voltages from their batteries, and I was rather surprised how much of a difference it actually made.
~Jordan
We have never used anything but the 3000mah batteries and smart chargers. We loaned a battery to another team that asked how we got it overcharged. I guess this explains it, we replace batteries after every match and put them back on the charger so they still have a relatively good charge when we put them back on the chargers.
Same one time I got 9v out of one
Seconded. 9v is actually really common for us when we’re testing. At competitions they end up being lower because there isn’t enough charging time, but in the shop we just set them going and swap whenever we make a change to the design.
The heatsink is a non-VEX part and is not on the allowed non-VEX parts list. Thus, you can’t use it. That much is illegal.
As far as “over-volting” motors goes, I don’t think you can raise the battery voltage enough to actually over-volt them–the old 3-wire motors had an acceptable voltage range of 4.4V to 9.1V; I’d expect the newer motors are similar. It isn’t easy to get much greater than 9V off of a 7.2V battery, so you should be safe from actually providing too much voltage.
This is very wrong. A VEX battery is essentially dead when it reaches 7.2V. Your robot will not be able to move, and you will be continually losing connection.
This year, you’re only allowed to use the smart charger (or another 7.2V charger from VEX). However, the Smart Charger is perfectly capable of charging well past 7.2V, and does so without modification. I have pulled batteries off at 8.2V before, using nothing but 7.2V VEX chargers.
How do you know there isn’t a voltage limiter in the circuit from the battery to the Vout on the motor ports? (from a quick test, it appears there is not, but I haven’t opened up a Cortex to check).
//Andrew
all batteries are over their rated voltage directly off of the charger. I can’t find it now, but someone (jpearmen?) posted a graph of the battery voltage over time. The voltage quickly drops to around 7.2 and stays around there for a long time and then drops off quickly. It flattens out near 7.2 for most of the time the battery is operating; that is why it is rated at 7.2 volts.
here is a link to tons of battery info:
https://vexforum.com/wiki/Quazar’s_Battery_Load_Test
[ATTACH]7496[/ATTACH]
To be clear i did not make this it is from the vex wiki. All credit should be directed to the author of the page linked above.
hope this helps!
Yay for actual battery graphs! For auton code we purposely drop the voltage to get to where voltage doesn’t drop as quickly to make sure that the routines are as consistent as possible.
How do you accomplish this consistently?
It actually says right in your link. This was actually done by Quazar. It is a very well-done test.
~Jordan
I suppose the best way to monitor the voltage is by using the LCD, we just use a volt meter to check the voltage. It’s pretty easy to hit the part of the graph where the slope levels out. Just stall motors so that the voltage drops quicker.
Doesn’t that run the risk of heating up the motor PTCs so they trip quicker in an actual tournament?
Although I suppose one could create a sort of temporary robot with a permanently stalled motor that runs autonomous code to run that motor until the battery is at a good starting state.
You would do it far enough in advance that it doesn’t effect the breakers. Or like you said, make some makeshift stalled motor assembly off your robot to drain the batteries. That is assuming you are doing it for in match. 15 seconds of auton and battery levels probably won’t make a huge difference, but for auton skills it does…
Oh gotcha I thought you meant for the autonomous period. This does make alot of sense for the skills challenge. Thanks for the tip - we may have to try this out ourselves this year!
Another idea: Create a simple circuit with a switch, resistor, and volt meter. 1103 had one of these at Worlds, and used it to decharge batteries before recharging them. A similar concept could be used to decharge the battery until it “levels off.”
This has the benefit of not overheating any motors…
//Andrew