34mph :O( I need a faster set up.

[Tc3basher]

Today I speed tested my car with the venom speedmeter. I got 34 mph. That was kinda dissapointing since Invested around $800 in my car. I calibrated the venom to 3.2 inches. The u-force never got past 101 degrees. Is there something I'm missing. What other gearing can I try? Well here's my set up.

feigao 7s
u-force 75 (soft timing)
19t pinion/72t spur
7 gp3300 from hypercells.com

[TheSteve]

I am assuming by your nick that this setup is in a TC3.
If you calculate it out your speed is pretty much correct.

Your FDR(final drive ratio) is 72/19 * 2.5 = 9.47 (btw, when quoting gearing you're better off listing the final drive ratio since pretty much every car made has a different internal ratio)
If we assume a tire diameter of 2.5 inches and that your motor is 5070 RPM/v then the motor is spinning at roughly 40000 to 41000 rpm depending how much the battery voltage sags under load. Using the online speed calculator that puts you at around 32 MPH - right in the ballpark of the venon speed meter.
The 540 sized Feigao/Hacker motors seem a little lack-luster in the RPM department to me(compared to 400 sized motors like the C40)
You should be able to gear more aggresively though, try an FDR of 8:1 - you'll lose a little low end torque but probably not much. So try a 22 or 23 tooth pinion and see how it feels. That should get you closer to 40MPH, which is all you can really expect(in my opinion) without giving up too much torque for a technical track.
You can always go for a FDR of 6:1 but you better watch temperatures of the motor and ESC and on a technical track you'll lack punch coming out of tight corners.

[Tc3basher]

tc3 is correct. As far as listing the fdr, I still dont know the formula simply because no one has ever shown me how to calculate it. I guess now is a good time to learn. :D

I also picked up a venom temp gage and I looped it around the u-force's heatsink. That way I can view the temp without ever having to take off the body. So I'm ready to try a more aggresive gearing like you mentioned earlier. How much hotter should I expect the esc to be?

You suggested trying a fdr of 8:1. I'm assuming thats going with a 22 or 23t pinion. What does 6:1 translate to? 25? I'm still a newb if you cant tell :D

[TheSteve]

The formula to calculate your final drive ratio should be in the TC3 manual. In case it isn't though its:
spur size divided by pinion size and then multiplied by the internal ratio. In your case:
72 / 19 = 3.789, we then take 3.789 and multiply it by 2.5 which gives us 9.47
The "2.5" can be found in your TC3 manual - its the internal gear ratio used in the TC3 gears(inside the diff housings)
An FDR of 9.47 means that for every 9.47 revolutions of the motor the wheels will turn around 1 time.

A 28 tooth pinion would give you an FDR of 6.42 - again though watch for heat.
I'd try a 23 tooth pinion first.

The hottest you want to see anything is 180 degrees F or so. You can go hotter but its not very good for things and will depend on the ambient temperature.

[Tc3basher]

Thanks for your expertise Steve especially. with the formula class. If I can get close to 40mph, I guess I cant complain. I really expected more but I'd have to bump up the cell count and the motor supposedly is rated for 6-8 cells. And If i went more than 7 cells, I'd need another charger along with the price of batteries. I guess its just hitting me now how much speed really cost if your trying to be part of the 50mph club. :D

[TheSteve]

heh, we all love speed! I'd love a car that goes insane speeds all of the time. At some point though, you have to comprimise. It also depends what your needs are. I race at a track thats small to medium in size, I tend to gear my cars for about 35MPH, which is all the speed reasonable for the size of the track. If I'm gonna be drag racing on the street though then I'll gear for more speed.
If you do decide to buy another motor I recommend a Hacker C40 - 6s, its all about speed!

[Tc3basher]

How much more speed are we talking about with the C40-6s with a fdr of 8:1? On this link which Im sure your familiar with shows that the hackers rpm max is 6942 but only for 6-7 cell applications. Does 6-7 cells sound right?

http://www.leisurelectronics.com/hacker%20motor%20specs.htm


Whats a bigger speed factor? higher rpms or battery cells used?

[TheSteve]

Higher voltage is always the way to go if you're after the best efficiency.
For most people though its easier to go for a higher Kv motor and stick with 6 or 7 cells. You lose a little efficiency but you can use your existing charger and 6 or 7 cell packs fit in pretty much all touring cars without modifications.
You can only go so high in the RPM department - for most motor 65K rpm is the highest recommended. So to get more speed from higher voltage the idea is to limit yourself to 65K rpm and use a motor which provides more torque, this will allow you to gear more agressively to get the higher speeds.
The c40 6s doesn't have the same amount of torque the 540 sized 7 turn you are currently using, but its still impressive. With an FDR of 8:1 and 7 cells I'd expect you to be over 50MPH. The reason only 6 to 7 cells are recommended is because of the amp draw (current) the motor takes. I usually run my 6s with an FDR closer to 10:1, again though I'm running on a smaller track where torque is key.

There are many fast motors out there, some likely cheaper then a Hacker C40. I'm sure others will chime in with what they recommend. If you want to stick with 6 or 7 cells and the U-Force I think you'd be very impressed with a c40 6s - its certainly my favorite.

btw - make sure you have good solder connections and high-current connectors.

[mac0326]

The 7s motor you have will get you to the "50mph club" with the right gearing. It might heat up the controller, though.

[Tc3basher]

Now you got me dreaming more about that hacker motor. I could of got one initially but there was a lot of talk on how fast the feigao was comparing it to a hacker. I dont regret getting the feigao 7s but a whole 10mph more almost seems worth it to me. I dont race but I love ripping through a parking lot at full speed :D

About my connecters too, I use deans all the way and since I dont trust myself with soldering, the lhs does it for me.


Mac-Your gonna have to give me more info than that.Your refering to the "feigao 7s" correct. My ultimate goal is to be able to break 50mph all the time, not just one time after frying the esc. :D

[starluckrc]

If you like the Hacker Steve, you will probably love the Shadow. Both are great motors, but the Pletty is tough to beat for driveability.

[TheSteve]

Yes I know, I was on the edge of buying one before - for a good deal even. I've had Aveox RC7's for years so I know how nice a 4 pole motor "feels". As much as performance though I love how the C40's look installed in the car..

[mac0326]

25 or 26 pinion will get you in the ballpark. Like Steve said, though, you might want to go up slowly to make sure your not heating up the controller too much. My guess is you aren't real hard on the controller if all you want to do is blast across the parking lot at full speed. The "right way" to get these speeds is through voltage instead of amperage, though. For example, my tc3 runs a basic 4200 on 11.1 volts. I am sure it goes over 50mph(I haven't clocked it, but I've been there before) and I run a 58 amp speed control using the factory bec. Higher voltage and an even slower motor would most likely be even better(14.8 volts and a 3100 for example).

[TheSteve]

My xxx-s running 14.8 volt LiPo's and a 3500 rpm/v motor geared 9.88:1 is doing 46 MPH on radar so far. Again, I gear for torque out of corners, with 7:1 I could likely hit 60 MPH. Always start conservative and go from there...

I find most people think their cars are much faster then they really are(not saying your car isn't doing 50 MPH mac0326), so don't be worried by other peoples claims of speed Tc3basher. Unless they are verified by a radar gun(or a GPS in some cases) take them all with a large grain of salt...

[Tc3basher]

At 101 degrees on the esc, I know I'm not pushing it hard. At first I was a little worried about having the wrong gearing and frying something. Now I'm ready to see what this esc/motor combo can really do. I'm pretty anxoius to try these different set ups. I really wasnt for sure the range of different pinion teeth I can try.

[mac0326]

TC3 - overgearing or undergearing could mean many things to many people. Temps, acceleration, runtime, top speed are all factors to consider in selecting the proper gears. And Steve is correct-don't believe anything your hear and only half of what you see when it comes to some people's speed claims.
Steve- the rollout on my car is similar to yours(slightly lower rpm but taller gearing-about 8:1) and performance is likely similar as well.

[Tc3basher]

I had another question about the feigao 7s I have. This is off the topic a little but its concerning me since I think I may have screwed something up.

When I was calibrating the car to the speedmeter, I left the motor on and basically forced the shaft to spin by force since I was only moving a couple of inches. Im not sure if thats what caused this but now it seems as though the shaft is somewhat locked . It will go in the right direction but it wont budge a mm moving the opposite way. The effect it has on my car is that it seems to brake really hard when I let off the throttle and It wont coast to a stop. It wasnt doing this before and messing with the calibration is the only thing I can think of. Does any one know If I somehow managed to tighten my shaft where it wont spin back and forth freely or is it something else?

[e_lm_70]

Today I speed tested my car with the venom speedmeter. I got 34 mph. That was kinda dissapointing since Invested around $800 in my car. I calibrated the venom to 3.2 inches. The u-force never got past 101 degrees. Is there something I'm missing. What other gearing can I try? Well here's my set up.

feigao 7s
u-force 75 (soft timing)
19t pinion/72t spur
7 gp3300 from hypercells.com

Mumble Mumble,

Using a 8:1 final ratio on my Kyosho KX-One and a cheap 35$ Yokomo 8x3 brushed motor, I mesured via GPS 40mph, with just 6x3300GP !

Nothing less then 60mph top speed can give sense to a BL set up for high speed bushing.

e_lm_70

[Tc3basher]

disreguard my last post. I took the pinion off and reseated everything. Now it works just like before????

[mgs9]

Hey dont feel too bad. My 4-tech dose about 27mph. Thats running 15.6 volts and a realy wide ratio.