Wall hits make cells go flat?
01-03-2005, 04:59 AM
#1
Wall hits make cells go flat?
I found this comment in the 1/12 forum on this site...
"ALBERTO - Adjust the current limiter on your esc so it's not as punchy and you'll gain a little runtime. Also being smooth and not hitting anything in 1/12th goes a long way, every wall tap spikes your batteries(amp draw goes way up) and takes away runtime."
Can anyone confirm this statement, i.e. give a rational, technical reason why this might be. I swear I've experienced it before but kind of blew it off as my overactive imagination - after tagging a pipe pretty hard, the car seems to go flat.
"ALBERTO - Adjust the current limiter on your esc so it's not as punchy and you'll gain a little runtime. Also being smooth and not hitting anything in 1/12th goes a long way, every wall tap spikes your batteries(amp draw goes way up) and takes away runtime."
Can anyone confirm this statement, i.e. give a rational, technical reason why this might be. I swear I've experienced it before but kind of blew it off as my overactive imagination - after tagging a pipe pretty hard, the car seems to go flat.
01-03-2005, 06:29 AM
#2
i dont have a technical reason, but it is true....the hit spikes the amp draw....also in 12th if you hit a lot of stuff then you may not be able to run the same ratio as a guy who can run 8 min without hitting anything......
i dont have a technical reason, but that is a true statement...
i dont have a technical reason, but that is a true statement...
01-03-2005, 07:28 AM
#3
A couple things I could theorize about:
1. Causes motor drag spike. If the tire hits and catches and drags the motor is going to draw more amps(If you keep the same throttle position). Imagine driving down the road with your foot on the gas AND on the brake. Plus if you try to speed up quickly again, there goes a few more amps. Occasionally I'll get on a pipe and it actually feels like somebody slammed on the brakes. Like something is really binding or dragging.
2. Unlikely but I'll throw it out just to see how much trouble I can cause. I suppose it is possible that the cells themselves short (or high resistant short) on the chassis during a high G impact.
3. Even more unlikely is that the cell could be internally shorting (again high resistance) from a high G shock. Probably about as likely me ever beating Vang with my stock Brushless.
Somebody invest in one-o-them Eagle Tree onboard data collection system, put it in Fireriders car (for the most wall impact data points per run
) and look at the data.
OH, you're not implying that you tap the wall ONCE, recover and then you car seem like it doesn't have power? I was assuming this was an accumulation or wall taps, each one draining the battery a little bit each time, for a total effect of less potential run time.
1. Causes motor drag spike. If the tire hits and catches and drags the motor is going to draw more amps(If you keep the same throttle position). Imagine driving down the road with your foot on the gas AND on the brake. Plus if you try to speed up quickly again, there goes a few more amps. Occasionally I'll get on a pipe and it actually feels like somebody slammed on the brakes. Like something is really binding or dragging.
2. Unlikely but I'll throw it out just to see how much trouble I can cause. I suppose it is possible that the cells themselves short (or high resistant short) on the chassis during a high G impact.
3. Even more unlikely is that the cell could be internally shorting (again high resistance) from a high G shock. Probably about as likely me ever beating Vang with my stock Brushless.
Somebody invest in one-o-them Eagle Tree onboard data collection system, put it in Fireriders car (for the most wall impact data points per run
) and look at the data.OH, you're not implying that you tap the wall ONCE, recover and then you car seem like it doesn't have power? I was assuming this was an accumulation or wall taps, each one draining the battery a little bit each time, for a total effect of less potential run time.
01-03-2005, 09:34 AM
#4
actually, you can see it after one wall hit, it was really noticable when ppl were racing the 4 magnet bianarys...hit the wall, and the car would be not as punchy for a lap or two.....again i dont have any theory, just what i saw.....
01-03-2005, 12:24 PM
#5
Hmmm...that sounds like I need and entirely different theory to explain that.
That sounds like the theory of tenativeness-for-a-bit-after-you-crash theory!
That sounds like the theory of tenativeness-for-a-bit-after-you-crash theory!
01-03-2005, 12:56 PM
#6
There must be something to it, I've experienced this yesterday at MARCCA and on Saturday at Trackside.
After striking an object quickly, a wall, pipe or whatever, if it's hard and fast enough, I notice a serious loss in punch/power. It's not my imagination, I was just looking for some kind of technical explanation.
Stay off dem der pipes...
After striking an object quickly, a wall, pipe or whatever, if it's hard and fast enough, I notice a serious loss in punch/power. It's not my imagination, I was just looking for some kind of technical explanation.
Stay off dem der pipes...
01-03-2005, 01:02 PM
#7
Ok, heres another shot in the dark. Brush dust comes loose inside the motor and gets between the brush and the comm for a few laps?
01-03-2005, 03:26 PM
#8
Tech Initiate
thanks
No wonder all my battery packs suck, I hit everything that isn't nailed down and some things that are.
If this is true it explains a lot
Jon
If this is true it explains a lot
Jon
01-04-2005, 11:26 PM
#9
The actual explanation is pretty easy to visualize, and I'll try to explain it. There is probably more precise explanation but this is my understanding of it.
When your car suddenly comes to a stop, there is a moment where the motor is still trying to go at whatever speed it was going previously. Even if you lift off the throttle right away, in almost every case there will still be that brief moment (and depending on the nature of the hit and the skill of the driver, it can vary in length).
Now, during that moment, you are putting an incredible amount of strain on the motor. As a tri-rotor motor turns, there is a split second during each revolution where the current is feeding back (in a sense, shorting out) as the fields reverse to keep the armature spinning (if you have no idea what I mean, track down a copy of XRC from about 5 issues ago, there was an article on how motors work). Now, suddenly your motor is trying to go somewhere (drawing current) but the armature is not spinning and the field is not reversing. That can draw a large amount of current from the battery and act as though the battery is getting shorted. The battery will heat up, lose voltage, and become less efficient for the remainder of the run.
In modified races where the drivers run the packs close to dumping, there are times where a large hit can actually cause somebody to dump later in the run.
When your car suddenly comes to a stop, there is a moment where the motor is still trying to go at whatever speed it was going previously. Even if you lift off the throttle right away, in almost every case there will still be that brief moment (and depending on the nature of the hit and the skill of the driver, it can vary in length).
Now, during that moment, you are putting an incredible amount of strain on the motor. As a tri-rotor motor turns, there is a split second during each revolution where the current is feeding back (in a sense, shorting out) as the fields reverse to keep the armature spinning (if you have no idea what I mean, track down a copy of XRC from about 5 issues ago, there was an article on how motors work). Now, suddenly your motor is trying to go somewhere (drawing current) but the armature is not spinning and the field is not reversing. That can draw a large amount of current from the battery and act as though the battery is getting shorted. The battery will heat up, lose voltage, and become less efficient for the remainder of the run.
In modified races where the drivers run the packs close to dumping, there are times where a large hit can actually cause somebody to dump later in the run.
01-05-2005, 01:58 PM
#10
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One thing I love seeing and I saw it at trackside, is when some one get spun around and is nose to a board... and instead of waiting for the marshal just keeps punching it thinking magicly the car will come undone ... and in the ass end all you see are big ass sparks and such coming out of the motor as its stalled but the dude is opening the ESC wide up to it...
The dude I saw do that at trackside was crawling after that... it happend like 2 min into the run.. but he was saying "I lost all my power!" hehe I was thinking "well you just arc'd your comm and brushes all to hell buddy"
The dude I saw do that at trackside was crawling after that... it happend like 2 min into the run.. but he was saying "I lost all my power!" hehe I was thinking "well you just arc'd your comm and brushes all to hell buddy"
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