murky123

going from 15/54 to 12/54 .. wow.. i guess it will get the temps down, but I dont want to lose much topspeed

GSMnow

I don't know the trans gears and all, but if his math was right and 15:54 is 48 mph, then 12:54 is still over 38 mph, which is still faster than I have ever been able to reach on any normal sized off road track. Maybe a huge 1/8 (or even 1/5) track might have a huge straight where that kind of speed could be used, but it is just plain crazy. My 1/8 buggy is geared for a theoretical speed of just 33 mph now using 14.8 volts x 2050 KV. Fresh off charge it will rev a bit higher than that, but I am sure he also used just 7.4 for your 2S setup. The smaller pinion will make everything run better, and one tooth is just not enough in your case. As I am sure you have already found, brushless systems can produce huge peak torque and spin all the tires no matter how silly high you try to gear it. It is not like a brush motor where going up in gear can soften the bottom end. You need to use your finger to control the wheel speed, and the lower you gear, the more trigger movement you have from a 20 mph roll to 35 mph on the long straight. This makes it far less touchy and easier to control than a tall geared setup. What kind of gears do you use? See if you can borrow an 11, 12, or 13 from another racer to see how it feels before you drop $12. I am thinking about going down another tooth on mine, the 33 MPH I am setup for is still a bit much at Hot Rod Hobbies. I really can't get to top out before I have to pound on the brakes. I popped in my 3S pack with the same gearing which gives a top speed of only 25 mph and my lap times were less than 1 second off, and I was actually quicker in the entire infield, I lost all the time when I am topped out on the long straight and basically coasting for the last 50+ feet before the braking point. I really think you will like how it drives with the smaller pinion.

murky123

how does a 12/50 will relate to lets say a 15/54 ?
cooler ?
same topspeed?
less torque?

GetMetalRC

iTrader: (35)

I recently purchased a MMP and just got my free Castle link in the mail. It has 3 prongs on it which I assume plug into the receiver cable, but it plugs in one of two ways. I know the middle red wire is the +, so my question is which of the orange and brown wires is the - and which is the signal? Thanks.

Frank L

iTrader: (148)

The brown is the neg. But if you plug it in wrong it just won't work.

GSMnow

15:54 = 3.6 = about 48 mph

12:50 = 4.17 = about 41.5 mph

Better, but still very fast for any normal track. I would try just changing the pinion to the 12.

12:54 = 4.5 = 38.4 mph

That is still very fast, likely more than you can do on your track, but if you find it too slow, go ahead and bump it back up. I honestly think you will find it much easier to drive. These motors just make so much torque, that gearing up to "soften the hit" is totally false. Gearing up just makes the motor suck more current and spinn the tires faster when they break loose anyways.

ta_man

iTrader: (168)

Are those calcs based on the nominal unloaded rated kV of 5000 or the actual loaded kV which people have found to be about 4300 (for the Novak HV4.5)?

I had a HV6.5 in a 1/8th scale buggy and the loaded kV came out to about 3000 compared to the rated kV of 3400. I haven't measured the HV4.5 but some guys on RC-Monster have. I ran my HV4.5 in Slash 4X4 geared 13:54 and I didn't think it was too fast for my small, tight track.

Drift Demon

iTrader: (1)

Novak rate their BL motors unloaded, actually most companies rate them unloaded. The only brushless mob i know of that rates loaded is Lehner....

marksp

iTrader: (28)

HV4.5 calcs are based on rated 5,000Kv which might be a bit optimistic. On the other hand, they are based on nominal lipo voltage of 3.7v/cell. Most chargers peak at 4.1-4.2 which would offset Novak's rating.

Net is 15/54 is way over geared for any race track. My Slash 4x4 with exact same setup is geared 12/54 (indoor clay track) and I'm never lacking for speed. Perhaps on larger outdoor track I might gear up 1 tooth max.

Prolly should move this discussion to the Slash 4x4 thread.

Cheers

GSMnow

By the engineering definition, the KV rating must be a true totally unloaded number. It is not really the rpm it will turn for a given voltage, it is actually the rpm needed to spin the shaft to generate 1 volt of back EMF on the windings. If the motor was totallt frictionless with zero resistance, then it would also turn this rpm with one volt applied with the timing set for lowest possible current draw. Adding some timing advance can make a lightly loaded motor turn a little faster than this, and due to drag and resistance the true effective voltage in the winding is always a bit less than the battery voltage.

Some motors are more "compliant" than others. There is electrical resistance in the windings and loss in the magnetic circuit as well. The most efficient motor will hold very close to KV x Volts rpm up to a very high load, like very low turn Neu's and their brothers from Castle and Tekin. Unfortunately, this stiff motor is also what makes them hair triggers o drive, any flick of your finger spinning the tires like made. As the internal resistance of a motor goes up with more turns of thinner wire, or a bigger air gap in the magnetic circuit will soften the response of the motor making it a little less "touchy" to drive. It feels smoother and seems to have better control. The trade offs being more heat, consuming more battery mah to complete the same race, and a lower rpm than the KV x volts would suggest. This is just one of many trade offs when you choose a motor.

annonymous

iTrader: (21)

ok, so i get to the track today ready to run my MMPro in my 1/10 4wd buggy, and shortly after starting the run, it dies, loosing all power. when i went to recover the car, it started up again . . . . . . this happened every time i used the car, no more than three corners in to any run. . . . . as the day went on replaced every connection and wire i could without taking the ESC apart, and replaced the other electronics . . . . . .should i just send it in, or am i doing something wrong? Thanks!

marksp

iTrader: (28)

Based on it happening to me on 2 new MMPro's, I suspect it's the on/off switch. Either cut it out and solder the wires together, or send it in.

annonymous

iTrader: (21)

not the switch, it got cut off when i replaced EVERY wire . . . . . . . oh well, i will just send it in

jnyrcr

iTrader: (5)

Could be your low voltage cutoff is to high? that will make it cut in and out or if your batteries are old.

SalmonShark

iTrader: (8)

I have a MMP with a Novak SS13.5t. Both of which are used. Got everything soldered up yesterday and took it for a test spin. This was installed into a Strike with 90/22 gearing.

The sensor wire didn't like to hold into the sensor port too well, so I used some servo tape to help keep it in place. Default settings on the MMP. 6.5v cut off is abou the only change at first (which I run on 2 other MMP's w/o problems w/the same batteries).

First test run, seems ok, but then I notice some on/off type response from it after a little bit. Motor temps are still cool to the touch. Is this what people call cogging perhaps? I am fairly new to electrics, though was big into nitro's.

I went to the pits, changed up some things on the MMP settings; 0 punch control, Low Timing for sensorless. Same issues. Then I went and took the on/off switch out of the puzzle, soldered, and shrink wrapped wires. Same issue.

Does this sound like a motor/sensor cable issue, or more of a ESC issue? I have a 6900kv sitting in my pit box, but I know it's way too much motor for the Strike, Blitz, or SCRT10 which I have in my fleet...

Ideas/comments/suggestions/etc all welcomed.

Thanks,
SS