Li-Po or NiMH? I'm confused.

[liborlad]

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.

[RC-Monster Mike]

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.

[lipomax]

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.

[liborlad]

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.

[lipomax]

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.

[lipomax]

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.

[liborlad]

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.

[RC-Monster Mike]

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.

[lipomax]

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.

[supermaxx4190]

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

[RC-Monster Mike]

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.

[liborlad]

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:

[RC-Monster Mike]

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.

[liborlad]

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?

[liborlad]

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