Li-Po or NiMH? I'm confused.

[RC-Monster Mike]

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!).

[liborlad]

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

[RC-Monster Mike]

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.

[lipomax]

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.

[liborlad]

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.

[lipomax]

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.

[liborlad]

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!

[Sylvester]

you got it, saftey comes first :)

[liborlad]

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?

[RC-Monster Mike]

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.

[liborlad]

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?

[RC-Monster Mike]

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

[liborlad]

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?

[RC-Monster Mike]

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.

[liborlad]

Great, incidentally, how do you figure those numbers?