Longest runtimes for a 40 minute race?

[Craps]

OK RC Brushless Veterns!

Need some advice an a big 40 minute race tomorrow with runtimes and what changes get longer runtimes?

My set up will be the Schulze U-Force 75 ESC and Plettenberg Extreme motor in a T-4 2wd stadium truck. Timing is set on Medium and the frequency is set on 16khz that I think is best for the 4 pole motor. I am using a 20 tooth pinion that I have been racing in 20 minute mains with no problem. Could go a little smaller on the pinion to get more run time?

I also have taken all drag or automatic brake (set to 0%) to increase run time!

I am using a Thunder Power TP8000-2S4P SHD battery and peaking it automatically on the Astro Flight 109 charger to 8.4 volts (4.2 volts per cell). I was wondering if I added just a little more mahs after the 8.4 volt peak if that will help? (I have seen sombody else peak one at 8.75 volts before)

I am also reducing the ESCs voltage cut off from 5.9 volts to the minimum of 5.3 volts as you know the battery always comes back up about .6 of volt after it cuts off, so I am taking a chance to win a race, that's racing.

Thanks for any advice!

[DaFF]

Max voltage fully charged: 4,235 volt par cell.

So, yes, 8,470 volt is safe, but going beyond this point is a recipie for disaster.

( BTW, I would double check the voltage using a precision voltmeter, just to make sure it did not past the 8.470 volt, I heard voltage read on charger are not that precise )

DFF

[TheSteve]

Going above 8.4 volts with the LiPo pack is asking for trouble. You can generally squeeze more capacity out of a LiPo battery by exceeding the maximum voltage but you are sacrificing charge/discharge cycles and future capacity. There is also the safety concern. LiPo cells are not something you really want to mess with. If you do decide to exceed 8.4 volts I'd ensure you're storing/charging it in a fireproof container.
The low voltage cutoff is likely ok, you can pull a LiPo cells below 3 volts under load as long as it continues to come above 3 volts per cell when the load is removed. The real issue with going below a 6 volt cutoff is that if the pack isn't balanced enough one sets of the series cells could be sitting at a higher voltage then the others. Again though if you have to win and are willing to sacrifice the battery pack this isn't going to matter to you.

Removing the drag brakes is a great option, as is lowering the size of the pinion by a tooth or two. I think the biggest difference you can make is to relax while driving and not push to hard, carry corner speed whenever possible. Smooth and steady will win the race!

[DaFF]

^^^^^^^
I agree with what Steve said, smooth driving is key !

Steve, might be an idea to play with the UF setting and set the Softstart to low value or something around those line in order that it reduce the rate of acceleration ???

Good luck

DFF

[TheSteve]

^^^^^^^
I agree with what Steve said, smooth driving is key !

Steve, might be an idea to play with the UF setting and set the Softstart to low value or something around those line in order that it reduce the rate of acceleration ???

Good luck

DFF

DaFF caught me sleeping! Absolutely! the softstart delay will also save power. The default is 280ms, you could increase it to 350ms or so. Any longer and I think performance may suffer too much, it really depends on how much traction you have and if you need "punch" power to get out of corners super fast.

[Craps]

Thanks guys for the info! Leaving to go to the racetrack to test today for tomorrows race. I am going to try the Shadow motor if time permits, but that maybe my qualifier motor and the Extreme used in the long main.

I'll check the battery with a volt meter and get it as close to 8.5 volts as I can using it.

Thanks again!

[DaFF]

I wish you the best luck for your race !

Let us know how you did.

DFF

[Rotary Rocket]

Excellant advice guys, I agree with all but the one about going below 6 V for the 2S4P. I spoke with TP before and they said you could totoally kill a pack by having it go below 6V under power.

Having the pack "come back" up to 6V at rest is besides the point (it should be 6.6V at rest).

Also charge your packs at a lower rate. Instead of going all the way to 8 Amps, charge them at 4 Amps. You will be able to put in more capacity.

[kufman]

going smaller in pinion may not help you. All of the motors that I have looked at get less efficient below currents of about 15 amps. Less efficiency equals more heat which leads to even less efficiency. Same is true for the controller. More heat, more resistance. just some stuff to keep in mind.

[Craps]

I must be a better driver now than a year ago when I got 42 minutes with the same size of battery All I got was 29 minutes. So we are preparing to change batteries at the 20 minute mark.

Thanks everybody for the advice.

Also the track I did the 42 minute run on is considerably smaller and tighter than this big 1/8th scale track with long fast straights and fast jumps.

[kufman]

you will have to let us know how things turn out. Sounds like a ton of fun.

[emaxxrdr88]

Yes tell us how you did!

[Craps]

I am up early doing last minute brainstorming (panicking) trying to fiqure out a way with all my arsenal of brushless and li-pos how to get a 40 minute run non-stop.

I have the TP8000-3S4P 11.1 volt pack I made to fit the tray that was either thinking about dropping about 4 pinion gear teeth and trying it or get the knife and soldering iron out to make a 2S6P 12,000 mah 7.4 volt pack?

I probably stick with the oringinal plan that I have tested practiced and set up for the battery change at the 20 minute mark.

I would hate to take the time to change a fried ESC because of desperation.

Thansk again for all the advice.

[TheMartian]

Craps we are all waiting impatiently on how the race went.

[rpmmaxxed]

What he said.

[glassdoctor]

Seems like it should be possible to run 40 minutes on a 12000mah pack, with the right motor setup. And the runtime-per-mah increases a little with a big A$$ pack like that, because the current draw (c rate) is very low. You get more out of the battery at lower current levels.

BUT, I still think it's best to just plan on one battery change, for a few reasons...

1. Less battery weight/size
2. Less risk of dumping a Lipo to low.. and killing it.
3. YOU get to decide when to pit, like @25 minutues...
4. You don't have that voice in your head "am I going to make it, or dump with two laps to go?"
5. You can run the 11.1 setup if you want to

[OptimaMan]

You know what? I think you need to run a different motor. Sure, the extreme is like 89% efficient, but that's at higher currents. I believe you need a slower motor and higher voltage. Slower motor, higher voltage will have less voltage sag during acceleration and won't hurt the Lipos as much. The extreme is over 4500 rpm/volt. Drop down to a 300- rpm/volt motor (basic 3100, basic 3600, c40 12s, c40 14 s) and use that 11.1 volt pack with 8000 mah. As of now, I get close to 15 minutes of runtime with only a 2000 11.1 volt pack with this setup using the c40 12s.

I believe when you ran 40+ minutes, you were using a Hacker C40 8s? Probably more efficient than the extreme at lower amp or partial load.

In addition, I don't believe a stadium truck should be using a motor that large. All of my experience with motors and vehicles lead me to this direction: TC and 1/10 buggies shoud only use 400 size motors unless you are doing extreme speed runs. 1/10 stadium trucks should only use 400 size motors or extra short 540 size motors. Lightweight emaxxes should be using smaller 540 sizes whereas heavier ones should use larger ones.

I don't believe you are using the right motor for your vehicle. I don't believe you're in the right "powerband". Only during max acceleration will you ever see the effiency into the 80+ percent range, most of the time, you're probably not running very efficiently. In addition, larger rotors need more energy to accelerate and decelerate. For a 2wd stadium truck, I'm really thinking c40 s motor in the 3000 rpm/volt range with 11.1 volt and 8000 mah.

[OptimaMan]

I used to be one that only bought high speed motors. All my motors were 6 turn, 5 turn, etc. At least 5000 kv/volt or more. Ever since I went to slower motors and higher voltages, everything is running smoother, faster, cooler, longer, and more efficiently. I believe you said you have the shadow, extreme, 4200, c408s. All these motors are relatively hot.

[TheMartian]

OptimaMan is perfectly right... I learnt so many things from his posts. I bow in front of the master.

[Craps]

I believe when you ran 40+ minutes, you were using a Hacker C40 8s? Probably more efficient than the extreme at lower amp or partial load.

I agree with this and yes I ran a Hacker M/C ESC with a Hacker C40 8 turn motor. I was going to mention that. Who makes a 4 pole 400 can motor?

[Craps]

By the way, my driving stunk and broke parts during the main.

A Team Losi NT driver, Mike Kendall (4th), a Team Associated GT driver, Will McIver (2nd) and a Team Mugen GT driver, Seth Worbel (won). A local kid Chris Pace with Associated GT TQ'ed and finsihed 7th.

Me, I was the only electric entry that with a battery change, the local 20 minute regulars did not want to attempt it that are a better driver than me. Anyway, I qualified 9th to make the "A" main without having to run the lower mains to get in. My last qualifier was barely enough to make it which for me to make it with such stiff competition here and my little over one year's experience was a victory to me to just be in the "A" main. I was running 4th during the first 3 minutes, when I landed wrong after a jump and broke a camber block, the only plastic piece on the front of my truck. We changed it and got back in with 27 minutes to go and a fresh battery. We did not get it perfect with the ball for the camber link in the wrong hole and a bent steering arm, bringing it home to a disappointing 8th place finish with one ugly driving truck.

Live and learn to race another day! Back to just 20 minute mains for me!

I think I will put my C40 8 T with the Schulze U-Force 75 esc to see how that works.

Thank you guys for all the advice!

PS. Plastic parts become brittle when it around 40 degrees F outside. The main was ran after dark when it was alot colder.

[kufman]

Hey atleast you were out there running the electric setup. You did better than me this weekend. I ran 8min 1/12th scales on carpet. Unfortunately, the only system that I own that will run on 4 cells is my novak. I qualified in the "BQ" position so to speak and won the B-Main. Mechanical problems were present as my T-plate tried to fall off, but it was drivable enough to crawl to the line. I turned 39 laps in 8'03" and the winner of the A turned 43 in 8'somthing. If i am going to try that class againg I will need to invest in some new batteries.

[DaFF]

Good job Craps !

Eventhough it might be frustrating for you to be 9th and 8th, I applaude you to enter and finish a tough challenge like this one with a BL+Lipos setup nobody even venture in...

BTW, having raced in Canada where the cold is always there, you can boiled some plastic/nylon parts ( namely suspension arms and shocktower ). They will become more flexible and less brittle, thus more foregiving on hard landing and crash... I've done it on my 1/10 trucks running on snow and ice with good results.

DFF