1350kv...Why did I buy this?

[Havoc]

sabongi: I will take a look at Brian's calculator. Not rdy for 6s yet, the only Lipo I have even used was in a Micro Desert Truck, those little Losi 1/36 scales. Need to get some use out of these 2s's first.

I know the chances of having problems with Lipo's are slim, but you are talking to a person who has the worst consumer luck. I could go on forever with stories about dead/stuck LCD pixels, bad motherboards, beaten-to-death guitar amps courtesy of UPS, etc. Even then, I make very few mistakes when charging, but stupidity can strike anytime.

My main concern is just storing them in a good place when I am not at home. I am paranoid enough about coming home to a kicked in door to have to worry about a pile of ashes where my home use to stand. I have an old gas BBQ pit that I may sand down, repaint, and remove all the gas fixture crap from. It would be perfect for storing and charging, could be a fun project too.

Regardless, I will become a Lipo user this weekend as long as it doesn't rain again. Stupid South Texas, we get a drought in the spring and rain in the fall.

For batteries I have 2 of these:

http://www3.towerhobbies.com/cgi-bin...&I=LXYCB5&P=ML

2 of these:

http://www3.towerhobbies.com/cgi-bin...?&I=LXVHA3&P=7

And 1 of these:

http://www.teamepiconline.com/shop/i...p?item=TEP2000

I am using this charger:

http://www3.towerhobbies.com/cgi-bin...&I=LXPYT8&P=ML

With this balancer, which I haven't opened yet:

http://www3.towerhobbies.com/cgi-bin...&I=LXTSA5&P=ML

I have been using the charger on my nimh's for the last 2 weeks. Its pretty awesome, much better than the Integy and MRC Superbrains I am use to. Wish I would have gotten it a long time ago.

I think I need some adapters for the balancer though, the one included with the balancer is for Checkpoint batteries with mini-banana plugs. All my batteries have the wired balancing plug already. I will research this more tomorrow while I am bored at work.

And redshift, OMG, that poor old Emaxx!! You already win, my old Emaxx will never be that modded, that is pretty awesome. Good job. I am going for a different look, just not sure what it is yet.

[Havoc]

GO-RIDE.com: I don't think there is a problem with the rotor, but I could be mistaken. I will see how it does this weekend on Lipo's. Thanks for the info.

[jsr]

You want to power the motor so that it spins in the 30k to 40k rpm range. The higher kV motors tend to like to spin faster (35k to 40k) while the lower kV ones work well spinning a bit slower (28k to 35k). The smaller motors (36x50mm size) will spin even faster (50-60k being ok for them as long as the bearings hold).
With a 1350kV motor, you NEED 6s. You can get it to work ok on 5s, but you NEED 6s if you really want to run that motor in it's sweet spot.
IMO the 2250kV is perfect on 4s. On 4s, it's spinning at 33k rpm...perfect! And your E-Maxx will absolutely fly! Gear it slow (30mph) if you run the 2250kV on NiMH. With 4s LiPo, depending on the discharge capability of your packs (not the C rating, but the actual discharge capability), you should be able to plenty fast.
If you still don't like the 1350kV, I'm looking for one. Let me know if you'd be interested in selling it.

[scarletboa]

your motor is showing the same symptoms that my de-bonded KB was. once the motor warms up, it slips more. it was like my slipper clutch was loosening up during runs, but i found out it was the motor as it got worse with each run and after talking the motor off the truck, i can make the rotor spin while i hold the shaft still. if that is the case, send it in to teken, but in the meantime, you can use loctite to re-bond the rotor. just be sure to clean both surfaces with rubbing alcohol to get a better bond.

[emaxxnitro]

to tell you the truth i store my lipos in the cars. they are not doing anything they sit dormant. if we have a party or something i move them to the fireplace where nothing can touch them or hurt them. or we go on vacation but, it is better to store and charge in a safe place. i charge mine right here next to my cpu. if the charger finds a problem it sends the data to the cpu via fma usb and it beeps like a m-f'er and annoys the living crap out of everybody

[redshift]

Was looking at the link for your packs, seems Tower has put out some bad info.

"NEVER allow to Discharge below 2.5V per cell"

NO. The absolute minimum is 2.8V, and the widely used cutoff is 3.0, for a buffer zone.

Many people (myself included) use 3.2V per cell for cutoff, usually anything below that you will notice the power drop off.

I am using Hyperion Swift Classic 4000 2S 20C packs, which are very similar to the first set of Orions you linked. You'll get 15-18 minutes in a proper setup. Maybe use that for reference until you get a feel for things. The 3800 hardcase packs will be good for 12-15 probably, but will be stronger.

You can charge the 4000's and the 3800's at 4 amps for a 1C charge rate, technically you would charge the 3800's at 3.8 amps, but 4 is close enough. And just so you know I have been charging my Hyperions at 8 amps (2C) for about 9 months now, they take it just fine. Incredibly good packs, nothing but praise for 'em!

[Havoc]

Okay, so, the 1350kv can move on 14 nimh cells. It appears that only two of my Trinity batteries are good. I decided to charge both on that Checkpoint charger paying close attention to the discharge and recharge. Both stopped charging at around 2000mah, so I forced them to start again, both were very warm at the completion. With some time to cool, I prepped the Emaxx, had to resolder one of the connections on the ESC.

Anyway, slapped em in, walked outside and WTF!?!? I was riding wheelies, couldn't do a standing backflip, BUT, could get one in a few feet. It was like a different truck. The 1350kv can push this thing just fine, and the temps were great:

motor can = 115 - 125f
esc heatsink = 110 - 115f (fan kicked on once for a few seconds)
batteries = 115 - 128f

I was worried about the possibility of a bad rotor, but it looks like on each test run, one or both of the packs had bad charges due to out of sync cells.

Well, now I have a spare 2250kv I guess, there is no point is switching this out. However, I am considering a complete resolder job with better solder and using 6mm connectors instead of 4mm for the motor connection.

So, it was my crappy batteries, but the right combination of the two least crappiest yielded a good run (finally). I know, I know, ditch the nimh and get the lipos going. I will.

Need to make a few more test runs to make sure everything is solid. I got about 10-12 minutes out on that run, could have been longer except for the newly grown grass from all the stupid rain. Deep grass = power drain...

[Havoc]

One other quick question. Am I destroying these nimh batteries by using them with this RX8 1350kv combo? I would think the higher kv motors would cause more wear, but I read different stuff all over the place.

[emaxxnitro]

Originally Posted by Havoc

One other quick question. Am I destroying these nimh batteries by using them with this RX8 1350kv combo? I would think the higher kv motors would cause more wear, but I read different stuff all over the place.

the lower kv will be easier on nimh but they will fry quick. need lipos imo

[redshift]

Actually you are putting both the Nimhs and your ESC at risk, see here-
http://www.rc-monster.com/forum/showthread.php?t=17200

Do keep in mind this is straight from the president of Castle, I know you have a Tekin but this still applies.

There is also a little thing called ripple current, the simplest way I could explain would be a propeller cavitating, the ESC has very sudden gaps where it needs to bite onto the power, but it can't. This can take out your ESC in a hurry.

Not to sound like an @ss, you need to run BL with Lithium, period.

The best thing you can do with your Nimh is ziptie them together and use them for a boat anchor. Stop wasting your time, you have the lipos....

[redshift]

One other thing, compared to your 7 cell terminal voltage of about 9.6-10 volts each, the lipos may feel slow. Keep in mind any voltage advantage with your Nimhs will quickly burn off. The 2250 is worth holding onto, you may find it is a better match for the lipos. As you see the potential of the lipos you will likely want to bump up the speed.

Remember the main advantage of lipos over any other chemistry is it's voltage holding ability, which spells consistency over a full run. I am very used to my 4S Hyperion setup snapping my truck skyward until cutoff. And it's not a light truck by any means...

So the point is, get a few runs with the lipos. Keep in mind any loss in speed will be made up either by gearing the lower kv motor up, or using your 2250. You have the advantage of having 2 motors to experiment with, that is a good thing.

Hope that helped...