Maintaining Throttle Response
 

Is there a way to even out the throttle response as a battery wears down through out the course of a race?

At the moment, there is a noticeable difference between how responsive/powerful the buggy feels on the 1st lap of the race with a fully charged battery vs. the last lap. Jumps that could be cleanly cleared with just a blip of the throttle require a more deliberate throttle application by the end of a race--effect is of course more pronounced the longer the race.

I'm running 1900kv motor with the Viper VTX8 on a Tekno EB48.2 buggy, using 6400mah 100C 4s batteries.

I'd be willing to trade off some of the initial power just to have the buggy feel the same for the full race. Any thoughts?

FULL DISCLOSURE: I Posted the same in the Viper VTX8 thread, but then later realized that this is potentially a broader question rather than specific to the Viper ESC. -- Apologies for duplicate post.

That's going to happen, but there are little things you can do about it. Running a higher voltage, lower amperage setup will give you a more efficient buggy, and running a receiver pack will let you power the servos and reciever, and transponder off of another battery. While it will be heavier, you could run a higher capacity battery. Either a larger 4s, or two high capacity 2s batteries in series.

Also, make sure you start the main with a fresh pack.

How long are the buggy mains?

That makes sense. I guess I was hoping that at the ESC level we could do some adjustments in response to decreasing voltage (e.g., increasing current/timing to compensate--or perhaps even restricting the voltage from the get-go--the goal here is consistency, not more speed per se.)

Since my current batteries are 6400mah 4S 100C, how much bigger can I go?

The mains are 10 or 12 min.

If the battery tray is not a limiting factor you could go as high capacity as you wanted. 7000,8000 etc. the only downside is that it will be heavier, so you may need to retune the car.

The main issue here is the battery run time verses the track completion time. If you have a battery that is double the track completion time then you won't see the problem.

The only other recourse is to manage the battery run time to coincide with the track run time.

Measure your lap time with your radio throttle set to 100%. The turn it down to 80%. If you can get the same lap time from the 80%setup then you have honed your driving skills and extended your battery run time for that particular track.

Trying to motor up or power up helps short term. Driving skills is the best thing to acquire. Then power or motor up.

Not aware of any way to make the power automatically consistent through the run.

How hot is your motor (and perhaps ESC) getting? Hot motors tend to fade some, may be adding to the change you are experiencing.

If it's only a matter of more trigger pull, learning to do that may be more desirable than a larger battery pack. A huge pack can make a 1/8 handle sluggish. Many guys are running smaller 4S packs or even a pair of shorties without issue.

Could be a weak pack too, may be contributing. Lipos are generally pretty good for consistent power, don't hear this type of concern much.

Motor is running fine in terms of temp, coming off around 160.

But the battery voltage drop is real: starting at ~16.8v and completing at ~15.7v; so with a 1900kv motor, the nominal max RPM goes from 31,920 (1,900 x 16.8) to 29,830 (1,900 x 15.7), which is ~6.5% decrease in speed (in terms of top-end, that's more than switching from a 17 tooth to 16 tooth pinion over the course of a race.)

I think that this effect alone could explain the difference I'm feeling...

That's not very low in my opinion. Especially running a heavy car like E Buggy. Only about a quarter of a volt dropped per cell over the entire run.

Yeah 3.925V per cell resting suggests around 60% is left in the pack, no issue with run time.

Do you have any way to test the pack's IR (Internal Resistance), as some chargers can do? Or try a different pack, perhaps a buddy will let you do a run? If the pack is getting tired it wouldn't be holding voltage under load as well, could be contributing.

If the pack is good, here's something to try. Refer to the sample discharge graph of a good cell, note a fair bit of drop off early. Don't charge the pack all the way. Some chargers have adjustable cutoff, I use a Hyperion that has a percentage cutoff feature for example. Some have a fast charge mode, etc. Or just try stopping soon after the CV portion starts where the charge amps begin dropping off.

http://www.rctech.net/forum/attachme...0-amps.cor.jpg

You could lower the punch setting in the esc to the point where you feel you have enough power initially to clear the track.

The lower punch setting will put less drain on the lipo, saving you some mah and punch for later, and the drop off in the end will feel less significant, if you start the run with less punch.

Correct....lower punch setting. That's the best option we have so far. It could be done with a regulator...but that creates a lot of heat and heat is battery juice. It would also lower efficiency and increase motor heat. So just use punch setting and deal with it...best option.