Pit Crew

BEST TIP.


REPLACE IT

Dan

iTrader: (75)

We race up here in the south bay in San Jose. About an hour below San Francisco.

Sorry, TB Evo's aren't allowed.

minicooper

iTrader: (5)

Ooops. Good thing there is always next time

psycho

Lonestar

Don't be fooled! Putting a motor in water is EXTREMELY dangerous. It only takes 500ma (1/2 an amp) to stop your heart, which equals death. You lose control of your muscles at 300ma which means that even if you want to move your hand off the source of electricity, you will not be able to. The 540 mabuchi motor will be pulling around 2A and when you mix that with water it is a dangerous combination. I suggest following good electronics tech practices of keeping one hand behind your back at all times so your two hands don't create a circuit across your chest. Keep in mind that your skin's resistance of around 30K ohms will reduce to several hundred ohms when wet, combine that with the salt in your blood and your body becomes an excellent conductor of electricity. If you guys use this technique, be very careful not to get too much water around and disconnect the battery source before removing the motor from the water. I'm only making this point because people a very often fooled by the fact that we are using relatively low voltages with our electric motors and there is a common misconception that the voltage is what is dangerous. It's not. It's the current that is dangerous. 10000V at 5ma will produce a tickle, but 2V at 1 amp will put you in the grave.

Dan

iTrader: (75)

How about wearing some rubber gloves?

Hmm...thinking about it. I'd rather not die from my own stock motor.

KINGZJ

iTrader: (4)

In a recent article I read the voltage that causes the most deaths is 110vac. I have done the water dipping method on many ocasions and have never been shocked or anything but yes be carefull. Hine sight is 20 - 20 would hate to loose any racing buddies especially trying to make a turd of a motor go faster.......

Sydewynder

pyscho is right about amps being the one that kills and not voltage. As a matter of fact as little as 2A can punch holes in your heart.

Sydewynder

Hmmm how'd I miss this?

Anywho psycho I couldn't make it as I was getting ready for a trip.

Pirvan

Hi Guys, I was just wondering whats the absolute highest you can gear for the Johnson 540? Somewhere in the 4.8-5.2 ratio alright?


THanks
Jeff

psycho

Pirvan

I don't think there is really an answer, that is meaningful, to that question. You need to gear the motor to the track for the car that you are racing. You can run 1:1 if you want, but the car will have no acceleration and you'll probably have to make your own pinion gears. You may end up burning out the motor as well. If you are racing pan-cars, you can probably get into the low 3:1 range under normal racing conditions. In a sedan, I think the low to mid 4:1 range is probably not out of the question. Again, this is dependant on the track. I usually race on either really tight tracks or really wide open tracks. You go in opposite directions for those two types of tracks.

Pirvan

HI there,

Thanks for the reply.

Yeah, i know it depends on the track, but when i am at a fairly long and wide track, i would like to know how low i can go before i kill the motor. When i geared it to 4.8-.4.9, it had pretty good speed, but the motor was hot as after a 5min heat. I was just worried that i might have killed the motor.

THats why i am curious whether 4.8 is too low and would the temperature be bad for the motor?

Thanks !

Jeff

Besercoe

iTrader: (9)

Temperature is always bad, but some motors just need to get hot to go well, both 540, and another class we run sometimes the sealed 23 turn stock motors both do not go until they are cooking. Of course their usefull life will be reduced because of the heat, but it all depends on what your intentions are, if it is a big meeting and you want ot be at the pointy end then the cost of a 540 will not break the bank.

psycho

If you look at the Johnson silver can 540 motor on a dyno, the torque curve is a straight line down and to the right. There is very little curvature to it at all. For this reason, you want to gear at a much lower ratio than you would on most "racing motors." Plus, it tops out at around 12K RPM@5V where a good 27T 24 degree stock motor will be in the low to mid 18K rpm range for the same voltage. As long as you gear for the track, you should be fine. This will be far more accurate since no two motors gear exactly alike.

Pit Crew

If you are worried about being shocked while water dipping you motors...consider this.

Do you have a 4 cell pack with alligator clips running off of it? if so, have you ever touched both leads at the same time? I do it all the time and NOTHING happens.

Electricity takes the path of least resistance. Therefore, the more amps the motor draws, the safer you are because that means there is WAY less resistance through the motor than through water. And even so, it would only short the battery through the water.

I have water dipped motors a bunch of times, and never once have I ever ever had the slightest bit of a shock.

Try dipping both alligator clips into a glass of water... Nothing will happen because fresh water has high resistance. Maybe you will see a little bit of bubbles rising from the clips because they are breaking water into hydrogen and oxygen.

Dont forget that the current would also have to pass through your heart. Like from one hand to another or you left hand to right foot. Overall, the resistance in that distance of your body will keep you safe.

You know those paddles they use to start your heart at the hospital. Well, if you put one on you thigh, and on one you foot of the same leg, do you think it would jump start your heart? NO. It would make you leg cramp really bad though.

imataquito

......... try this then ..... touch the + and - sides of the aligator clips
on one finger with the clips connected to a fully charged 6 cell pack .......


good luck