xbr 8.5 with a 5000mAh lipo?

[Needler56]

i have a 10x1 brushed motor with a novak tc2 esc on my 4wd touring car. how would that compare to a novak xbr 8.5 with a 5000mAh lipo? i don't want anything slower than my current brushed setup. i mainly bash.

[SpEEdyBL]

You probably want something faster than the 8.5 then. If you don't want to spend too much money, the castle creations sidewinder with the 5700kv will be the ticket. Or you can get it with the 4600 motor instead, which will not be faster than the 10 turn on 2s, but on 3s it will blow any brushed motor away.

[GSMnow]

If the XBR 8.5 motor has the sintered rotor, you may be able to gear it up and get close to the performance of the 10 turn, but that 10 turn probably has some very high rpm capability allowing it to make some very good acceleration and speed with a small pinion. The SS8.5Pro brushless is only 5000 KV so it will only rev to 37,000 rpm on 2S LiPo. On the flip side, it will have quite a bit more torque than the 10 turn, even at less current. As a rough guess, the 10 turn on 6 cell NiMh probably hits more like 49,000 rpm. So try a pinion with 25% more teeth. If you have a 16 tooth now, go to a 20 tooth on the 8.5 brushless. I think you will be pretty happy. The torque curve of brushless is much wider and smoother and they put out more power for the battery power drawn, so you can get quite a bit more run time at the same power level, more power for the same run time, or split the difference with a bit more power and a little more run time. It is all a choice of motor wind and gearing.

One minor myth is that a brush motor can make more power on mediocre NiXx batteries than you can with a brushless system. This is just not true, but I understand where it came from. Older brush ESC's are pretty dumb devices. They can turn their FET's full on even when the battery voltage falls to 2.0 volts. At very low rpm, like a punch from a stand still, this can make it look like you are making good power on a weak battery. Brushless ESC's can't function with reduced voltage like that, so they go limp if your battery voltage dips too much, making for sluggish acceleration on a weaker battery. That fact that you can keep racing that weak pack on a brush system does not make it better, it just means that the brush motor will continue to destroy an already weak battery, rather than shut down or go into current limit like most brushless sytems will.

[Needler56]

great info guys. i had to make some mods to my tb02 to accept gearing for a gtb 3.5r system i formerly had. i'm restoring worn out parts which includes the top deck which i really had to file down to accept smaller pinions and larger spurs for the 3.5r. right now i don't want to make any mods to the new parts and i can only go down to a 30 tooth pinion. with that and based off the novak gearing chart i can go as low as a 6.5r. i considered the xbr 8.5 for the price, but how would a 6.5r with 5000mAh lipo compare to my 10x1/3000mAh nimh brushed setup i have right now?

[got2bqik]

In my opinion there is no comparision. It's apples and oranges. Old school brushed and n*** batteries on there very best tune and gearing will equal the brushless and lipo at it's worst setup. Brushless is torque is only limited by how much amperage you can give it. The more batterry the more torque, the more gear the faster it is. A good batterry is key though.I'm done with brushed and nimh, as my nimh batteries get weak they become son's play packs, if I can't run a brushed equivalant brushless motor at a track I won't race there until i can.
Tim

[SS Pede]

The SS8.5Pro brushless is only 5000 KV
I think I'm missing something. I thought the SS5800/8.5 motor was 5800 kV. Is there a difference in test standards (loaded vs. unloaded or something) that gives you the 5000 kV, or does the sintered rotor affect this?

[schenck77]

http://www.teamnovak.com/products/brushless/motor_spec_chart.htm

[GSMnow]

KV by definition is an unloaded numberbecause it is supposed to be the rpm the motor would turn at 1 volt with no resistive losses. Then you use the current draw and internal resistance to calculate the real voltage in the magnetic circuit.

I believe when Novak updated their motors to a more efficient magnetic circuit (Sintered rotor, smaller gap etc.) the motor became a better generator so it needs more voltage to reach a given rpm, but on the flip side it is making more torque at less current and producing less heat. To reach the same KV it would need less wind, but since it is more efficient, just gear it up a little and it will clearly outperform the original 5800 KV version. This is basically the reason Novak stopped using KV numbers in their model numbers and adds. The general feeling among many less informed RC'ers is that higher KV means more power. That is not always the case, and many times the higher KV motor will not perform as well. I like having the real KV for setting up the system, but I understand Novak's approach as well. The more efficient the motor gets, the lower the KV will be for a given number of turns of wire. So if you looked at all of the 6.5's on the market, the one with the most torque and best efficiency would actually be the one with the lowest KV.

[SpEEdyBL]

Be aware that the motor that comes with the xbr does not have a sintered rotor, which is a must if you want good performance and no heat issues.