Li-Po or NiMH? I'm confused.
 

I posted this by accident in the general forum, doh!

At the moment I'm running a CF/Al Gmaxx chassis with UE and GA upgrades in most places on my Emaxx. I'm now planning on changing to a brushless system and was pretty set on a 9L/9918 combo with 7 cell GP3700 packs.

This would cost me about $360 for the motor and extras plus another $300 for 3 sets of decent batts. However I've been reading the discussions Mike has been having with lipomax and I'm thinking maybe I'm going in the wrong direction.

Would I be better with a 10L or 7xl running with a 6s Kokam 3200 setup? Are the feigao motors up to this, should I now look at the lehner motors, such as the 1600xl?
Would these batts fit OK on the Gmaxx chassis? Will the koolflight UBEC work OK with a higher input voltage? Can the 9918 work at the higher voltages these cells run at or should I look at another controller?

I haven't invested hugely in NIMH batts so far, I only have one existing set of GP3700's so if I'm going to switch to LiPo I guess now would be a good time.

Sorry for all the questions guys but I'm now very unsure as to the best way forward. I'm not using the truck for racing so top speed is not a major issue, anything around the 40mph mark would be more than enough for me. I am interested in real good punch combined with long runtimes.

I'm happy to spend around the $600 mark for this upgrade. your views would be appreciated.

Welcome to the forum! I see you have read up on a few items already so you probably know your way around somewhat already. The 9918 controller could probably handle a 6s Lipo set-up, but it would be technically over the rated voltage so any warranties would be voided. I have been working on using a 5s Lipo setup, which will be within the rated voltage of the controller. The motor I was planning on was the xl2400, but the 7xl or 10L would be about the same performance. Now that the heatsink/motor clamp is a reality, I may run the Feigo motor myself (10L for me). You could get yourself 2 sets of 3s 3200s and 2 sets of 2s 3200s (so two sets of 5s 3200s for running). These would run a little over $400. Then, a Lipo charger would run around $130 (I use the astroflight, which can charge at a high amp rate and high cell counts for Lipos). This would get you in under budget (not counting motor and controller) and I am sure you would be extremely happy with the performance. The batteries will fit fine in the g-maxx chassis as well. Also, the UBEC is rated up to 30 cells (so almost 10s lipo), so no problems there, either.

Liborland: If you haven't gotten into brushless yet, let me give you my 2 cents. If you go with an 18 cell controller for an emaxx and want to go Lipo, you have to have some high discharge lipos such as the Kokam 3200 which are 20C. However, those packs are not as energy dense as Polyquest or Thunderpower packs. Approximately 30% LESS energy density. For long runs and excellent speed, I suggest going to a controller that can handle more cells and going 8s 3500 polyquest packs. The difference between those packs and Kokam 6s3200 is only about 1.5 ounces per pack, but you're getting 33% more voltage and 10% more capacity!

Go 8s, and go with something in the 1000-1200 KV range. With that setup, you'll cruise around in first gear around high 20's or 30 mph for almost 30 minutes and second gear will take it to 40 mph w/o even breaking a sweat. Not to mention, insane torque.

The reason why I haven't done that is because I've still got the stock chassis and need my lipos to FIT into the stock 6 cell trays. So, the most powerful batteries that fit into the stock 6 cell trays is the Kokam 3s 3200 packs. I do have the 4s 3100 polyquest so I can go 8s also - but I'm not interested in going super fast anymore. If I had the 1200 motor, I'd go 8s. Figure 8s is almost 30 volts and with 1600 KV, that's 48,000 rpm - too much for good efficiency. A 1200 KV at 30 volts is 36,000 rpm - much better!

Problem is, controllers that allow you to go many cells cost more. I'm presently using a Schulze 24.89 which is slightly beyond it's limits when I run 8s but I got the controller for "only" 259$.

Heck, I think I might just go and buy that 1200 motor... So I can do what I preach.

Thanks for the feedback.

Lipomax, just so I'm clear, you think I should go with a Lehner xl1200 combined with something like a BK 30120 to handle the voltage.

I haven't checked out the prices of the 8s setup but motor/esc alone would cost about $570. The benefit being that I probably wouldn't need 2 sets of batteries, not straightaway anyhow.

I'm wondering how this would compare with the 10L/9918 combo with the 2 sets of batts Mike suggests. I'm sure either setup would give me all the power I could ever need, it really comes down to the best speed/duration.

Hmm..... It's hard to say if going higher voltage is going to justify the huge increase in cost of controller.... For me, I happen to get high voltage controllers for a really good cost so it wasn't a big issue... I got a 32.40K that I'll use in my 10s emaxx for the future... controller only cost me 160 bucks... but it's only 40 amps continuous which should be fine cuz I'm not expecting it would even draw more than 40 amps. I have the 24.89 F controller that I got for only 260 which is a pretty good price too.

Either setup will give you MORE speed than you could use, but the 8s3500 will give you approx 40% more run time given the same speed. You can easily gear either setup to take you well beyond 50 mph.

I think if you were to bash, you'd get close to 30 minutes of runtime - and that's bashing around at high 20's mph with the occasional second gear run at 40 mph with 8s3500. With 6s3200, you should get around 20 minutes easily. Of course, it depends on gearing and driving style. I usually get bored after driving for 20 minutes straight.

BTW, I just ordered the 1200XL and if you hang on there, I'll test it with the 1200XL and 8s 3100 mah packs and I'll tell you speed and runtime. I do have 8s3500 also - but those dont' fit in the stock chassis.

You know what, I think you might be better just going along with what Mike has recommended and instead of using Kokam SHD 3200's, going with higher capacity Polyquest like 5s 4400 mah. And since you're not racing, that would be better suited. You still get the extra 40% run time using the other batteries that don't have as much "punch" but enough for 50+ mph and 30 minute runs in first gear. Yeah, that's my final answer.

Thanks for your input on this one lipomax.

After your 1st post I looked into the polyquest packs and I noticed that they had 4400 packs as well and I thought they might be suitable. I could buy a 2s and a 3s and stick with the 9918 controller, which would keep the cost down.

My only concern here was that the max discharge was 12c which is quite a bit less than the 20c of the Kokams. Obviously it's a bigger capacity cell so I would get 52.8A, but do you think this would be OK for the motor/controller setup?

Also going 6s with this setup only pushes the voltage 0.6v past the 9918 limit, would it still be OK at this level Mike? have you had any experience of problems here.

52.8 amps continuos rating should be fine as long you aren't geared to the moon or bound up. You most likely wouldn't have any trouble running a 6s on the warrior with the right motor, but it will technically void the warranty. I have doen it myself without problems, but if the controller failed, I was willing to accept it as a learning experience and move on. If you are willing to do this as well, I would unofficially say the warrior can handle the 6s. My personal recommendation would be to run 5s Lipo and stay within the posted limits of the controller.

I think with the 10L, 5s will actually work better and not get so hot.. besides, as Mike put it, balance will be better too. You'll be running in a better RPM range too.

hey mike,
what do you think a 8L/9918 on 12 cells draws for amps. like a 10lb. truck with like 15/70 gearing? i have been thinking of buying some lipos, but dont know what my motor draws for amps? thanks
Isaac

I would imagine your trucks peaks at 100 amps or better during hard acceleration, but likely averages 40 or 50 amps (well, average is probably 35 or so amps). The 3200 Kokams or similar 60+ continuos amp rated pack should work fine in your truck. The kokams will cut your weight in half (battery weight), so amp draw will decrease with the LiPo setup.

Mike, there's not a huge difference in price between the Kokam 3200 3 & 2s cells and the Polyquest 4400 3&2s cells. Is there any reason why you would go for the Kokams over the Polyquest packs?

Also I'm not clear on the relationship between the motor turns and current draw. It appears that the more turns the motor has the lower the current draw, which is then easier on the batts and the controller is that right?

If I understand things right the best operating range for the feigao motors is 35,000-45,000 rpm. With 18.5v that means a motor with between 1891-2432 rpm/v, which means that a suitable motor could be 10L,12L,13L or 7XL,8XL,9XL. The fewer the turns the higher the amps, but what impact does this have in a real situation.

I'm just trying to get my head round this:C:

I like the Kokams because they have the highest amp rating per ounce of battery. I race, so weight is a big concern for me (bigger than runtime).
You have the relationship between motor turn and current draw nailed, and your motor selections based on the 18.5 volts are on the money as well. And yes, around 40Krpms seems to be a nice place for the motors to be for performance and efficiency.
The impact the turns/amp draw has in a real situation is this - the hotter motor (less turns) will drain the batteries faster and produce more power on a given cell count. The higher turn motors are capable of the same power output (basically, all motors of the same family can produce the same power), but need higher voltage to to it. The higher voltage and lower amp draw will yield longer runtimes with the same capacity batteries, as well as increased efficiency and cooler temperatures in most cases.
It seems like you have a pretty solid understanding (got your head around it:)) of this stuff, actually.

Mike
I thiink I'm beginning to understand why the L cans would be better. Am I right in thinking that the power output of the S is about 800w, the L about 1200w and the XL about 1700w.

Therefore to keep the motor's revs around 40,000 with sensible current draw from the LiPo's a 10L would be better.

On a separate point would you suggest any kind of overload protection for the cells in use?

Hi Mike
I posted another response before I saw your comments, but it seems I was on the right tracks after all!

See, you do understand! There is a safety discharge device available as a safety to keep from overdischarging the LiPos. I will try to link it for you and another user. This is a good idea if you plan to exhaust your packs when you run (overdischarging LiPos is expensive!).

Mike
What gearing would be "safe" with a 10L on 5s 4400MaH packs? I'm concerned that peaks during acceleration could overload these packs.

Assuming stock diffs, I would start with around 15/66 or 16/66. This will put you in the mid 30s with some pretty insane torque. You could probably go higher, but unless you are doing speed runs, it isn't necessary.

With 10L geared 18/66, I was getting peaks of 50-80 amps in first gear. First gear was taking me to 35 mph though. That's with 6s. With 5s, you'll be getting 30 mph in first gear geared 18/66 and peaks should be proportionally lower. Probably peaks of 40-65 amps. That's PEAK current. In second gear, you'll probably get peaks of 70-100 or so amps and top speeds of around 42 mph or so. With those peak amps, I don't think it would harm the 5s 4400 packs. Those 4400 packs can handle over 50 amps CONTINUOUS. I don't think you'll do much damage in first gear, but you might want to take care if you plan on running in tall grass in second gear for long periods of time.

Mike is absolutely correct with regards to batteries. The Kokams are the highest power/weight lipos I know of too. Definitely a difference in the "punch" (less internal resistance and voltage). But they weigh more for the same capacity. I guess they do this by having more metal in their lipos. The metal will have lower resistance, but weigh more as a result. For racing, I think the Kokams are the way to go. For bashing, I think the 4400's giving you that extra run time is the way to go.

Thanks for the info lipomax.
BTW do you use a cell protection device on your truck? Also what has been your experience with using these packs on a day by day basis, the disclaimers make them sound like you've got an incendiary bomb in your house!

I realise this is probably a mixture of good advice and overkill in case of potential lawsuit, whats the reality?

I notice that most of the sites that sell these batts also sell overload protectors for charging, I guess these would be an essential purchase to minimise any dangers. I've got young kids in my house so I don't want to be starting any fires, but I don't know if it's realistic to say that I would always be present when the batts are being charged.

Liborlad, they are very dangerous if they are charged at the incorrect setting. At the very least, charge them in a fireproof box or can with holes on the top to allow venting (so the box doesn't explode). My whole house had burned down as a result of poor charging. Yes, you read that correctly - I had a total loss due to fire from battery chargers.

Gee that really is serious stuff, sorry to hear about your house, I hope nobody was hurt.

You know if it really is that dangerous I don't know if I should bother, you've certainly made them seem a whole load less attractive!

Maybe I should go with 16cell GP3700 instead. A lot heavier but a damn sight safer!

you got it, saftey comes first :)

Mike
Lipomax's comments have really put an end to my thoughts on LiPo batts for my truck. However, I now think I have a better understanding of how things work. I was originally wanting to order a 9918/9L setup, to run with a 14 cell pack. I now believe I would rather go with a 9918/10L on 16 cells for the following reasons:

On 16 cells the 10L will be in a nice range with a max revs of 47,200. The lower current draw from the motor will mean that both the motor and the controller will run cooler, which should help improve longevity. Finally, the lower current draw from the packs should mean a better run time than on a 9L/9918 combo.

Is this right?

If so I would like to order the 10L/9918 with the new heatsink/clamp you've designed, together with a koolflight UBEC. Do you have all this in stock?

this will work very well. Young's tragedy has made many folks think twice about LiPo since it happened (over a year ago, as I recall). Definately a hard lesson to learn.
Your thoughts are also correct regarding runtime, running temps and current draw. I actually am out of stock on the warriors. They are due in any day, though, along with the motor clamp/heat sinks.

Mike
I'm currently using the standard spur gear on my Emaxx. With a 10L/9918 combo do you advise a strobe slipper, Robinson racing stuff or someting else?

The strobe is the best one available, but you need to find mod1 5mm bore pinion gears, which is a challenge.

Mike
Starluck sells a 15 & 16T mod1 with the 51T slipper, but with gearing this high would the truck still be controllable. Any idea what sort of speeds this would produce in 1st and 2nd gears?

This gearing would bring you to the mid/upper 20s in first gear and the mid to upper 30s or low 40s in second gear. Sounds like a decent ratio , actually.

Great, incidentally, how do you figure those numbers?

I created an excel file that calculates the info. I enter tire size and motor/voltage info and it gives me speed in each gear. I have all the calculations from the tranny reduction to the diff reduction entered into the formula. I also have allotments for 1/8 diffs, center diffs, etc. in the spreadsheet, so I can pretty accurately figure out almost any combination for the e-maxx. The formula doesn't take into account wind resistance or voltage drop or tire ballooning, but with some thought when entering in the voltage (based on experience), it is very accurate. I also can adjust tire size for big foes, 1/8 buggy tires, etc..

Hey, before you give up on Lipos: First of all, I *DON'T* know for sure if it was the lipos! I was charging my 12 cell emaxx pack too at the same time and my Triton charger had on occasion, never "peaked" and would charge till the GP3300's melted the solder joints and came apart. Melting solder joints meant that the batteries got OVER 400 degrees F. Last time I checked, paper has a flashpoint in the 400 degree mark too. Those batteries were simply sitting on top of a cheap plastic table! Talk about smart huh? Especially since just a month or two prior, they blew up in my garage. At the same time, a AA charger was on... and so was the Astro 109 charger with TP 1900 11.1 volt pack. I SUSPECT it might be the 3s 1900 mah TP pack because the pack that I charged PRIOR to that the day before was a 2s4p TP8000 mah pack... I still wonder if the charge setting was at 8.0 amps for a 1900 mah pack! I might actually purposefully charge my 2000 mah packs at 8 amps just to see what happens. If nothing happens, it could've been the NiMH!!!!!!!

SO, whatever happened, I can't blame one battery over another. I've had NiCads BLOW up when I charged them with my homemade 5 minute charger (I charged them at 20 amps!!!!)

SO, all batteries ARE DANGEROUS. All batteries should be charged with caution and with supervision and if not, charged in a container where they could blow up and not harm anybody. So, Liborland, I don't think you should quit lipos so early.

My 2cents worth.

BTW, Mike, I have an excel file that has different vehicles, different KV motors, battery voltage, RPM, tire diameter, pinion, spur blah blah blah just like you! Hahaha That's pretty interesting. I started doing it back when I was 14 or so years of age on Appleworks spreadsheet. Back then, it was done so I could measure speed, motor RPM, tire RPM, and stuff based on a speed trap and I had different ratios etc. I used it and came to the realization that sometimes a super large pinion will actually be slower than optimal gearing. After a couple hundred entries, the old Apple IIe would take a good 3-4 minutes just to recalculate and that's how I got an IBM AT. Fast forward like 17 years... and now we have Excel worksheets. LOL

I've found voltage drop pretty minimal actually in speed runs. Most of the voltage drop occurs during hard acceleration, but as it nears top speed, voltage drop is usually within 10% of "voltage". Have you noticed that too?

Guys, are these spreadsheets confidential, or are you prepared to send one over for me to play around with, it would come in handy for sure.

I hear what you are saying Lipomax about all batteries being dangerous. In normal circumstances though it seems pretty clear that LiPo's are far higher up the "death & mayhem" scale than NiMH.

I think I'll stick with regular batts for the time being and look into LiPo's further down the line when I have more experience. Thanks for all your input.

And Mike also has it on his palm computer so he can check and change combinations at the track. Its really pretty cool... But that eagletree - Now thats the sheezy.........

Lipo- Yes, I have found the spreadsheet to be very accurate for calculating top speed. I usually use 1.1 volts or 1.05 volts per cell and can get the speed within a mph or so of real life. I guess great minds think alike ;)

Liborlad - In my opinion, the LiPos are only more dangerous than the Nicad and nimh because they have more energy. The same precautions must be taken with either battery. I have seen plenty of nimh and nicad batteries blow up at the track over the years. I LiPo will just have more energy per pack, so is that much more dangerous. With respect and diligence, the packs will be very reliable and safe. The batteries won't spontaneously combust, as some posts suggest. If misused, they may be dangerous, just like all batteries.

Okay, try going here for a copy of a simplified version of my excel worksheet.

http://home.comcast.net/~youngsongdmd/rc.xls

I have a lipo setup I'd like to get your opinions on.I have an Emaxx with the 9L/9918 combo,with 14 3300 cells installed,a steel rolecage and stock tires the truck weighs 10 lbs 2 ounces.As a basher I run 15/65 gears,for top speed I run 18/65.I love the performance I get with this setup but want more runtime.I'm looking to go with 2 PolyQuest 4400 3s lipo packs in parallel,what can I expect in runtime and performance?Would 3500 4s be a better way to go?My charger can charge up to 3 lipo cells.I run 40 mph with no problem,will I be able to exceed this by much? Thanks

The 3s Lipos will reduce your top end quite a bit compared to the 14 cells you are using now. Your punch will probably be pretty close, depending on the cells you use. I would pick up a couple 3s packs and a couple 2s packs and run them in pairs (a 3s and a 2s in series to give you 5s). This would be like a little over 15 cells worth of voltage (nicad/nimh), so you could drop a tooth or so and retain your speed, but pick up some runtime from the lower weight and increased capacity.

Mike mirrored my thought here. I'd agree with Mike here. Going 5s 4400 mah lipos will give you approximately 40% more run time geared for the same speeds. With the higher voltage, you would have to drop a pinion gear or so. That would reduce amperage. In addition, the MUCH lower weight will also reduce amperage some more.