ASK Cubby – You Type Up Questions, I Mash Out The Answers

Voltage

Hey Cubby,

I have a 1/10 scale Traxxas 2wd model that weighs about 5 lbs. I wonder why 7.4 volts is so preferred/popular/available? Do racing regulations drive this? Or was it historical nickel battery voltage/capacity that was more or less mimicked? At this relatively low voltage, current required for acceleration becomes very high- we must have large gauge wire/large connectors/fans as a result. If battery voltage was increased while decreasing motor kv, we could arrange for the same performance with less current, smaller wires, smaller batteries. Using assumptions of my 5.5 lb car with constant gearing/weight/tires/top speed, I created an approximate chart:

15s 55.5v 500 kv 4-26 A 533-745 watts
12s 44.4v 600 kv 5-32.A 542-759 watts
8s 29.6v 900 kv 7-45A 519-726 watts
6s 22.2v 1200 kv 9-58 A 512-717 watts
4s 4.8v 1800 kv 14-91A 517-724 watts
3s 11.1v 2400 kv 18-117A 511-715 watts
2s 7.4v 3500 kv 28-182A 511-715 watts

Why don’t we have a 12s 5 lb car? We could be using 2 6s flight batteries and tiny electronics/thin gauge wires. Would we have longer run times? Am I correct in assuming the esc/capacitors would be smaller? Could driving a higher voltage/lower current car be made to FEEL the same as lower voltage/higher current car? Or would high voltage make the throttle an on/off switch? Hardware stores sell 40v/80v lithium battery lawn equipment!

Andrew”

Cubby- Ya know Andy, that is one of the best questions I have received in a long time. Congrats for having letter of the month, shoot us your snail mail and shirt size so we can totally hook you up.

So… why is roughly 2S/7.4 volts the “standard” in rc? You are correct in assuming that is has to do with the old NiMH days and with current race rules. You are also correct in assuming that running higher voltage would be highly advantageous. And yes, your 5lbs rc car could be made to drive perfectly “normal” when run on higher cell counts like 12S (or higher).

So… what is the advantage to higher cell counts? Most bashers might think “Hey, 12S is gonna be wayyyyy too fast in my Slash!”, but that doesn’t have to be the case. A low kV motor combined with proper gearing, and a 12S system could you give you “mild” power, with TONS of runtime and lower overall temps. Heat kills electronics. Let me repeat that, Heat Kills Electronics, and because of the reduced amp draw of a high voltage system, all the electronics would run cooler, thus helping them last longer with less wasted energy. So, there are a lot of upsides to running higher voltage.

So… what are some of the challenges to going to higher cell counts? Some people might say cost of the packs, but that isn’t necessarily true. Sure, a 2S 8000 might cost “X” amount while a 4S 8000 costs “2X”. But when running higher cell counts you don’t need the extra capacity. A 4S 4000 (or 8S 2000) can easily do the job that a 2S 8000 can, and would much more comparably priced. The challenge here would be to get the battery companies to make higher cell count packs with a suitable form factor, something that isn’t the case right now. You simply aren’t going to find a hard case 8S pack that will fit in the area of a 6 cell NiMH.

Another real challenge is an ESC’s internal BEC knocking down the extra voltage. Knocking the voltage down on a 4S pack isn’t easy, doing it on 10S+ can lead to real additional costs. Nobody likes running/charging a receiver pack, so a big internal BEC would be a necessity.

And yet another big challenge is… teaching old school rc’ers and the racing organizations that high voltage isn’t the devil, it is progress in performance. It took years to even get ROAR to acknowledge the existence of LiPo and brushless, getting them to accept the fact that higher voltage is actually a plus for the hobby may take decades.

Hop up Report

Hey Cubby,

Several major contributors to the lack of hopups include the sheer number of different vehicles to make them for, a lack of sales info to be able to determine if any profitability is even possible, and then the two elephants in the room: With the distributors acquiring hop up brands or creating their own since the overseas manufacturing explosion around 2005, the hop up market is in the state it’s in because of the massive mainstreaming of our hobby.

We’ve lamented about this before. The hobby isn’t the same as it was in the early 80’s when we got in, it’s not the same as the racing boom of the late 80’s and 90’s, and it’s not even the same as it was in the lipo/brushless revolution in the late 2000’s. This just isn’t “The era of the hop up,” and we can think that sucks all day and tell people it does, but the only people it holds any water with is the dinosaurs like us. 🙂

I look at it the other way: Could you imagine just 10 years ago that we would be racing four-rotor flying helicopter things with FPV? There are exactly five impossible parts of that sentence that are a reality now, and it continues to bring people into the hobby. Speed, ease of use, quick from box to play, durability, and affordability have grown the industry exponentially. The more users, the more $$ in play, the more cool stuff comes out, and it snowballs.

I’d rather it be that way, and I’d rather see us dinosaurs embrace it more, and do less of calling out the noobs that would never even be here if we were still peaking 1700 Panasonics and turning comms on the same car half of everyone we know has too.

Your forever friendly critic,
Shawn Palmer

Cubby- Yo Shawn, long time no squeeze. I hope life has been treating you well? For those of you who might not recognize the name, Shawn is a long time industry guy who knows his stuff about the hobby.

Yes, I received a LOT of email on last week’s Cub Report. It just seemed to spark an interest in people. Some people wrote in because they are ticked because the favorite car that they’ve owned for half a decade still doesn’t have any bling parts, others got riled up because they think there are already too many aftermarket parts on dealer shelves, while others wrote in to comment on what they think the aftermarket companies should be doing.

And ya, one of the main reasons there aren’t hop-up parts for every car is because they are simply so many new ones constantly being introduced. It would be impossible to try and keep up with them all. The problem is that too many manufacturers have gone to a push of trying to sell as many cars as possible, regardless of the long term cost, instead of trying to develop long term customers/hobbyists. The short term game is what it is, making maximum money over the course of a few years. But the long term game determines whether or not our hobby will even exist 2 decades from now. I have been in the meetings where someone was pounding on the table because last month’s sales were down 1.4%, so the push for short term numbers can be quite intense. However, if done properly, big money can be made from fewer new car releases with a big emphasis on pushing high quality hop-up parts afterwards. In fact, I feel that part of the reason we are seeing lower sales today is because of the sell-more-cars/who-cares-about-the-long-term strategy that many companies implemented 10 years ago.

Peace and love, peace and love my friend…

So there ya have it, and there ya are, another ASK Cubby is in the bank! Shoot me your questions, answers, rants, and whatever else is floating through that crooked mind of yours to thecubreportrc at gmail dot com. Questions that hit the front page get a free sticker pack, and “Letter Of The Month” winners get a free BSRC t-shirt.

YOUR Cub Reporter