Why is it not faster?

[JOHNNYMAXXIMA]

I know guys, most of my questions always have to do with speed.
That's just the horsepower junkie in me.:D (I know you can appreciate that coolhand).

So I got my new 9L in on my Maxx today and took it out for a few hot laps up and down the street. Everything went fine, ran smooth, lots of power but it just wasn't as fast as I thought it was going to be. Not as fast as my dual 9L anyway.

You see, I thought that by going a single setup with allot less weight was going to give me similar performance.
Here's the specs for both, RTR.

Dual 9L w/28 cells = 14lbs 10.9oz. geared 66/20
Single 9L w/14cells = 8lbs. 11.3oz. geared 66/19

Yes boys, that is a 6 pound difference!

So I thought that maybe it was the tire difference. I had buggy tires on the single and revo tires on the dual, so I put regular maxx tires on the single and took it back out. Maybe a couple mph difference but still way off the mark. I didn't bring out the radar gun but I guesstimate maybe 35-40mph with the single compared to about 50mph for the dual setup.

So what's the problem? Could it be something wrong with the motor. I bought it used on ebay and the guy said he only had 2 runs on it? (yah right)
Thanks.

[Dafni]

40mph is a decent speed for 14 cells. Theoretically, the 9L on 14 cells with 19/66 and stock diffs should give you an optimistic 38mph (calculated).

[rhylsadar]

hi
to go fast is easy. low rpm high torque big motor, high voltage, adequat gearing.
drawback: high voltage = lots of money.

what you have is more a light setup that takes advantage of 2 speeds. to me your reported performance looks quite good.

depends on what you want to do with the car. its not a highspeed setup you have there.

bye
rhylsadar

[Serum]

you can gear it higher with the dual. you've got about thice the power.

If you have got good cells, you should be able to get to 60 mph with that dual setup on 28 cells.

I personally am a fan of bigger single setups.

I'm going for a 20 cells setup, with 60 mph in mind. (lehner 2250 motor)

[Promod]

If your not using a GPS or Radar gun you really don't know how fast it is. Get a base line on both systems and work from there. Play with gearing and make sure the batteries are up to power. Don't expect the world from a 9L on 14 cells but it "should" run 45mph easy with top speed gearing.
Not sure what batteries your using but the old GP3300 were very heat sensitive. When warm/hot they would run 4 to 6 mph faster than when cold.

Thank you,
Promod

[Serum]

Most GPS systems take too long to get the right speed, they need a LONG run before they tell the actuall speed. A radargun is the best way. Perhaps i have got experience with low end gps systems though.. But this is my experience with gps.

[coolhandcountry]

You should have got a big motor john. I think you would like it better than the single 9l. Promod is right on temps of batts. I had my gp s out in the cold and thought they where going dead. As the heat built up it ran faster. :D Don't forgot john you have to push the maxx threw the air.

[Gustav]

The Garmin Gekko (small and pretty cheap)i've got seems to work well,gives fairly consistant repeatable readings anyway,i don't normally keep it at max for long,a second or two maybe,but it gives the same reading if you keep it there for longer.As long as it covers a few metres at max speed it seems to be ok.But yeah,ideally radar would be better.

[JOHNNYMAXXIMA]

Thanks guys.
I do have a radar gun so I will get some baseline runs and see what does what.

My whole thinking on this setup was the lighter weight vs. the heavier dual setup. I thought that the 6 lb. difference would be more significant.

Dafni.
You said that a 9L with that gearing gave a calculated speed of 38mph. But at what weight? What is the average weight of an E-Maxx? I thought 8.5lbs. for a maxx was light? Or does weight not really make that big of a difference with electric motors?

Well with that being said, what gearing do you guys think I should run for max speed? And also, what motor would be recommended for the 9920 for top speed?

Thanks again.

[Dafni]

Originally posted by JOHNNYMAXXIMA
Dafni.
You said that a 9L with that gearing gave a calculated speed of 38mph. But at what weight? What is the average weight of an E-Maxx? I thought 8.5lbs. for a maxx was light? Or does weight not really make that big of a difference with electric motors?

The weight has a bigger impact on acceleration than top speed. However, this calculation takes voltage drop into account (assuming top notch batts) but the actual weight of the truck is not included. Making a truck lighter would mostly affect acceleration anyway.

An important thing are the quality of batteries.

I think 45mph is a bit taxing on a 9L, would give you high temps. I would gear it for 35-40 mph (just what you did)

For top speed setups, I would suggest higher votage. 18 cells and more.
However, as for Feigao/Wanderers, I would say get an XL motor. If you want to stick with 14 cells, get a 7XL. (this motor works well on up to 18 cells)

[coolhandcountry]

8.5 lbs is good for a maxx. Is that with the 14 cells on it to? You can get more out the 9L but the heat may drag you down. If you don't want a whole lot bigger motor but more performance you need a lehner 19 series. Bang for your buck john the bk has it beat. Let us know how it goes.

[JOHNNYMAXXIMA]

Thanks guys.
That makes sence Dafni, weight affecting acceleration but not top speed as much.
Yes coolhand that 8.5lbs is on 14cells. If my truck is doing say 40mph now and I went to the 7xl or lehner 19 series, how much faster am I looking at approximately?
I will stick with my 14 cells for now because I am going to be going to LiPo in the future.
Thanks.

[Dafni]

If you wanna buy Lipos in the near future, get a low rpm/V motor. Like a 9XL for 6S, which would be a killer setup, and the 9XL works well on 14cells too (nice runtime, they say)

[coolhandcountry]

You would have to step up on the gearing some. You could get a little faster but the real hold back is you batts. Promod posted a test he did on motors. He had that it takes about 2000watts to run 60 mph. I think the thread name was david vs goliath. I try to find it. That may help you out.



Here is the link iwas talking about.
http://www.rc-monster.com/forum/show...=&threadid=923
Hope this helps you out.

[JOHNNYMAXXIMA]

Forgot about that thread.

First off, would that 2240 fit without any mods? That's a pretty big motor. Promod says it will work with the 9920.
Secondly, would it work on 14cells until I go lipo?
Lastly, how much one of them bad boys cost?
Thanks.