ESC, Motor, LiPo help.
 

Well I was waiting until February to buy the electronics to finish my BL Revo (stock chassis and single speed), but this holiday sale is too good to pass up.

I want a 7xl with a 9920 but where I live the temps are usually around mid 90’s from late spring all the way through mid fall. How much hotter is a 7xl compared to a 8xl? Should I go with a 8xl or even a 9xl to keep temps cool? With the 9920 I will need a Li-Saver right?

I don’t know a thing when it comes to LiPo. At first I was thinking 4s and running them parallel but then I figured if went 2s and hooked them up in series then I would be able to use the packs seperately in other low voltage escs. Is there any advantage in parallel vs series?

What is the difference between TP taps and Hyperion taps? I have a superbrain 997, will any balancer work with it? I know if I go 4s then Ill need a different charger.

Thanks for taking the time to help a New-B.

Also how much hotter will electronics run on 5s vs 4s?

I'll let some of the other pros here answer you lipo questions. I will chime in here becuase the 9920/7XL setup is exactly what I have powering my 12 pound MGT conversion here in lo-Cal. Take a look at it run here. After figuring out my gearing and with the 25mm fan I have yet to have any temperature issues.
http://members.cox.net/tg_19/BL2.JPG

Nice Conversion!

Are you happy with the torque of your combo?

I would run the 4s in series. More power. And with the 7xl, you would have heat issues i would think on 5s

Good to know.

Your vid credits 5s 4000. I cant completely see the voltage on the top pack. Looks like another 7.4. So are you running 4s now? What charger and what balancer are you using?

Is your fan running off of a reciever pack?

I live in Moreno Valley. What part of california are you?

Yeah - the pictures show two 2S cells but I've got a 2S and 3S in it now. I'm running a Li-Saver LVC. Torque is great. The center diff keeps the wheelies in check. I have a Duratrax Ice charger and using a Hyperion LBA 6 balancer which works with the Maxamps standard taps. I plan on getting a single 5S pack so I have an Astro Flight 109 on the way since the Ice will only do up to 4S. Yes - fan and servos are running off receiver pack.

I dont get it. 4s in series = more power than 5s? Hows that?

I understand that the Li-saver gos between the Rx and the ESC and the ESC and the battery, but where does the fan get power from? EDIT: nevermind, missed that last line

No problem - In fact I wondered where to draw the current for the fan. One of the airplane guys at my LHS recommended that I splice in prior to the esc and reciever. Use a 12 volt fan and draw directly from the batteries. His reasoning was that any fluctuation in current produced by the fan may lead to glitching if it was being drawn from the reciever. Since I already had a 5 volt fan I went ahead and plugged it into channel 3 of the receiver and haven't had any glitching yet. My LST2 conversion is put together the same way and I haven't had any issues there either.

I have a 12 volt fan, maybe Ill take your guys advice. Should tap into the Li-saver or have a seperate set of deans and wires to go between the Li-Saver and batterys?
Is there any advantage in parallel vs series when total voltage is the same? Is there more resistance when wired in series? More heat?

The 12 volt hookup to the batteries work if one of them is 3S. Otherwise will need a 5 volt fan to wire to the reciever.

look here for wiring diagram

put the lvc between the batteries and esc.

http://www.rc-monster.com/prodimages..._29_%20lvc.jpg

Hmmm. Maybe I should add an external LVC diagram to my page...

I thought about contacting you with that. that would be cool :027:

There are also a bunch of guys doing LST2 conversions. I have all the ratios already memorized so I don't need them in the calculator pull downs. I do point a few of the guys on the LST forums to your calculator. If you think it worthwhile to add I can try to get exact tooth count on each of the gearing combos. The sad part is a lot of the guys on the LST forums are doing the Fine Design conversions and have no idea what the motor rating is.

If you let me know the LST gear tooth counts, I'll add them. You can either PM them to me or post in the stickied thread. What would be really nice is a seperate tooth count for the diff and each tranny speed. Also, only two tooth counts for each ratio. Sometimes, there are more than two gears in the tranny, so just let me know what they are. I'll just have to convert that to only two "output gear" and "input gear" tooth counts.

The holiday sale is a good buy. Hard to pass it up if you plan to buy.

One last look at my shopping cart
 

Well the 7xl are out of stock currently so Im going with an 8xl for the 9920 and power them with 5s.

Does the Li-Saver work with both 5 and 6s?

I have a reciever pack but do I need it for the 9920? It has "3Amp.BEC on/off Function". I dont know what that means. Will that alone provide 6.0v for my servo?

What gearing for a single speed tranny should I start with? Is 16 or 18/66 32p a good start?

You definitely need a receiver pack or UBEC for that cell count. You should be using one for anything over ~9v.

"3Amp.BEC on/off Function" means it has a built-in BEC, but it can be disabled via a jumper (the black one).

I'm sure others will answer your other questions...

The Li-Saver is supposed to auto sense between 2-12 cells. Most everyone on this forum recommends the use of BEC or receiver pack to help keep the ESC cool. As for gearing I again recommend using Brian G.'s calculator (the same link as the wiring diagram in my previous post) to start and see what speeds you are after. Hope that helps.

Ok, Li saver in combination with rx pack it is.

I diddnt understand the "gear calc" but I tinkerd with the "motor selector" and "Random Parameter Solver". Found that an 8xl with 5s and 18/54 gearing is "good" for a for a top speed of +/- 40mph, 20/54 for 45mph and 22/54 for 50mph without any overheating warnings.

Is it OK to use the Li-Saver with a car that is using reverse?
I ran into a problem with another brand of Li-Po cutoff device. Most are made for airplanes so when they do their "pulsing" they pulse down to near 0% throttle. 0% throttle on a car controller is full brake or full reverse if reverse is engaged. After coming to a complete stop it then went to full speed reverse. I really should have known better, but I guess the excitement of a new toy got to me.

Seeing a 8 pound buggy flying backwards down your driveway and into the iceplant at near 40MPH is quite alarming :026:
Perhaps the Li-Saver doesn't pulse below mid throttle (neutral for cars)?
Just thought I would bring this up.

Matt

the one that Mike sells will work good for you.

They have more than one version of the li saver.
It has a plane and car mode.
Mike sells the car mode one.
No worries on wide open reverse.

That is good to know. Since I switched to the Mamba Max, I don't need a LVC any more (I run 4S).

I just wanted to make sure the same thing didn't happen to rustnpede in case the Li-saver did the same thing. He might not have as much iceplant as me :005:

Sounds like he is good to go.

Thanks,
Matt

Like this one http://www.rc-monster.com/proddetail...avercar&cat=22

Thanks for looking out. No ice plant here just rocks, not so r/c friendly. Unless its a crawler:025: