Why am I slow?

[lincpimp]

A center diff would be a waste of time for speed runs, you want all 4 tires going the same speed at all times, trust me.

[Unsullied_Spy]

Originally Posted by lincpimp

A center diff would be a waste of time for speed runs, you want all 4 tires going the same speed at all times, trust me.

+1, a solid center will make you wheelie worse but you'll get the power to the ground rather than waste it away unloading the front wheels.

[kazuaki]

Damn, ok. So I'll go forward with the front wing and see where that gets me. I'll have some extra weight on hand to add if necessary too. Once I can get this thing to go WOT for several seconds straight, then I can go back to compaining about not having enough power

[kazuaki]

I tried out the front wing this afternoon and it was a failure. I was getting downforce, but it made the truck handle weird and it was just too easy to bend it up. I think it was too big of a wing for such a short wheelbase truck. I scrapped that and went with the adding weight idea. I strapped a 1/2" x 2-1/2" socket extension (approx 140 grams) to the front of the chassis and put in 43/45 gearing. This kept the front end down and allowed some better runs. I was able to get up to 73 MPH with this setup before I damaged a tire. One of my HPI Super Nitro belted slicks (part #4598) broke a belt, as best I can tell. Check out the picture and you will see two flat spots while the rest of the tire is good. The tire feels firm due to the belt everywhere except between the two flat spots. Needless to say, that one tire has a pretty bad baloon and wobble now. The additional weight definitely affected the acceleration, but at least I was getting into full throttle. I could tell it is still accelerating slowly after hitting WOT though, so I know there is more in it.

One interesting note...I have been using BrianG's speed calc a lot to try to understand what is happening. I have confirmed that this motor does not seem to want to turn more than about 48k RPM, even with low gearing. This tells me that my 4S setup is making no more than 14.8 volts. Even though the lipos have a nominal voltage of 3.7V/cell, I figured they would be closer to 4.2V/cell when freshly charged. They measure that high right off the charger, but then they must be dipping to 3.7V or lower under load? Maybe this is the result of only having 1800mah of capacity? IF I am going to be limited on voltage, I should have gotten the next higher KV motor. Or, I could just get a single 3S pack to run a 5S setup :)

[DwightSchrute]

it definately sounds like your batteries aren't up to snuff when it comes to the motor needing more power under such high gearing.

[kazuaki]

Aren't these Hyperion G3 VX packs about as good as I'm going to get?

[DwightSchrute]

the 80+mph 1/16 revo's i've seen were running 2 SMC 2200mah 30c in series and 75+mph 3S Thunder power 4200mah 40c.

I don't know if you're splitting hairs over 400mah, but for larger scale models, higher mah will have a definate effect on acceleration and how fast you can get to top speed.

the neu's can be amp hogs and if the battery is too low in milliamps, it's definately going to effect acceleration. so there in lies another problem.

in theory, a lower mah battery should be able to get to the same top speed as a slightly higher mah battery, but it will take a longer distance to do so. if you don't have the space to get to top speed, hold it, and let the motor completely wind out, it dosen't suprise me that low 70's is all you're getting. i think the solution is either a longer road or slightly higher mah packs.

[kazuaki]

Would it be worth going to a higher mah pack, if I have to go to a lower "C" rating? For instance, I have a pair of Flightmax 2200mah 20C packs.

[DwightSchrute]

Originally Posted by kazuaki

Would it be worth going to a higher mah pack, if I have to go to a lower "C" rating? For instance, I have a pair of Flightmax 2200mah 20C packs.

imo, yes. since there is no real standard of testing a true C rating, they're all subjective, company to company.

besides, the C rating dosen't really even become a significant factor until you get into heavier cars and trucks but milliamps have proven to be very significant in smaller scales.

eagle tree data has shown 12C packs that were rated 8000mah were up to 10mph faster than 20C 5000mah packs in a vxl rustler.

[kazuaki]

OK, then next test will be a longer run with the Hyperions and then I will also try the Flightmax 2200's and see what they can do. Thanks for the idea.

One other thing I am wondering...could the EZRUN 60A ESC be holding me back. I wonder if it would go faster with an MM in there...

[DwightSchrute]

Originally Posted by kazuaki

OK, then next test will be a longer run with the Hyperions and then I will also try the Flightmax 2200's and see what they can do. Thanks for the idea.

One other thing I am wondering...could the EZRUN 60A ESC be holding me back. I wonder if it would go faster with an MM in there...

i'm one of those people that says you can never go too high a limit on amps for an esc. with lower voltage (ie: 3-4S), there are so many voltage spikes, that i would opt for a higher rated esc.

is this limiting your top speed? many would say no, but i'm not entirely convinced especially with the capacity of these motors. typically, in escs like the mambas or tekins if it was exceeding your escs capacity it would likely reflect in esc temps or damage but not having the ez run i couldn't tell you for sure.
Here's an exapmle: one of my friends got an RX8. he saw an increase in top speed over his 150A ezrun. was that the lone factor or was it a near perfect speed run? he says it's the rx8. only a data logger could say for sure with all other variables equal.
.

[Jabe]

For downforce, try using 1/10 touring body and dont cut rearwheels open, use rear wing and make diffusor in rear.
Then you might be able to get that extra weight off and get higher top speed.

[florianz]

The power of the motor is limited by the provided energy. I think everyone has experienced "good" or "excellent" lipos. a battery that performs better under load and thus provides more voltage ("punch") would be an option (4s). there is a lot of marketing, "paper doesn't blush". just a high c rating doen't always have to mean that the lipo has a great punch. for example on this (german) page that guy is testing various lipos. the conclusion of a 20/30c flighpower is, that it performs well up to 15c and is a good 15/20 c but NOT a 20/30c lipo, but permanent 20c is too much http://www.elektromodellflug.de/akku...htpowerevo.htm

just adding a new 3s lipo to get 5s might be a problem, when you're mixing batteries they should be in the same condition/age/capacity/manufacturer.

maybe the esc is also limiting the performance. I mean, going 70+ is not quite usual for that esc.
cool project! I like!

[jayjay283]

50mph to 80mph is a whole different game. read some threads about speed here. It took me (lame example) months and $75 of pinions to get to 50 with an emaxx. jze , mr speed king didnt do 80 overnight. every mph is lipo push and a good esc that will transfer that energy

seems fio already said it..im the lame duck shoot me and cook me for dinner

[kazuaki]

Lots of good advice guys. I'm fairly certain that a full body that covers the wheels would go faster, but I am going to save that as a last option. I will try my other batteries to see if by chance they will be faster. I'll be less than thrilled if my cheapie Flightmax's are faster than the G3's I'm also considering moving up to the MM to eliminate that as a possible issue. I can always use the extra ESC in other vehicles.

As for my idea of trying 5S...what risks are there in getting a 3S 1600mah battery to run with one of my 2S 1800mah batteries? They would be the same make and C rating and within 10 cycles of each other as far as age.