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View Full Version : Dual Battery and 3.8?


ax0n
10-07-2002, 08:32 PM
I just picked up the second battery, and the 3.8 from tinyrc.com's online shop. Has anyone played with this combo on the ZZ yet? If it doesn't work, I'm sure the 2.6 will work really well (I have an official microsizer 2.6 that I picked up last week)

On a side note, while at a get-to-gether this weekend I let a friend who bought a microsizer borrow my ZZ NOS Motor. It hauls so much ass, and has so much torque, that it's insane. I wish I would have remembered to bring my 2.6 motor to the event but I left it at home. With NOS the little microsizer couldn't hardly turn without massive oversteer, even when we tried swapping his rear tires with various tires that I got for my zip.

on a side note, I think I'll be getting a microsizer soon enough, just to have somehing else to play with. I need to save some cash though, it's gonna start eating into grocery money. Maybe next month. My 1st priority is helping you guys figure out how to speed up the zips. I'm still working on a design for a booster board that will hopefully dump more current to the motor.

For the time being, could someone tell me if the dual battery mod works well enough to power the 3.8 with enough torque to really make it move?

bitchar-gmotors
10-07-2002, 08:45 PM
ax0m,

The dual battery Zip Zap will power the 3.8 motor. QFM has posted some very fast drag times with that setup.

Kyle

go_zz_go
10-07-2002, 08:46 PM
on a side note somewhere i saw a pic of a bit with dual motors on the same wheel what advantage would this give? how can it make it faster if the motors will only go say for exe 22000 how would two at 22000 make it faster it wouldnt double your rpms would it?

ax0n
10-07-2002, 09:19 PM
I'm not sure about battery powered cars, but in a gas powered car, you double the wattage output of the car when you put 2 identical motors in it. some guy in a Hyundai tiburon did this. He had two 300 Horsepower motors, one in front and one in back though, but the overall point was that in theory, this thing was 600 horsepower, all wheel drive.

That's assuming he could get fuel to both engines.

In our setup, we would have to sufficiently fuel 2 motors. It still divides the torque in half per motor though. in a stock ZZ i think it would help a little but not much. There aren't enough milliamps to run both motors at full tilt. it might work with a pair of turbo motors.

you have to realize that while the 38,000 rpm motor spins at 38,000 under no load, it will never get up to 38K in any car.

the diameter of the wheels and tires are exactly .55 inch from my measurement with calipers.

.55 inch.

multiply that times 3.14 and you have a circumference:

1.727 inches.

So for every time the wheel spins the car moves 1.727 inches.

So now for every 8.25 times the motor turns, the wheels turn once, using the "fastest" gear ratio. That means in one minute, the 3.8 motor turns 38,000 times, and if there was ZERO resistance, like you're assuming, in one minute the wheels turn about 3637 times, moving the car 1.727 inches each time.

3637 * 1.727 = about 4619 inches, or 385 feet per minute

385 Feet Per Minute * 60 seconds = 33792 Feet per hour.

33792 Feet Per Hour / 5280 Feet Per Mile = about 4.36 miles per hour, or approximately the speed of most joggers who exercise daily.

I'll guarantee you that even with the 3.8 motor and the rest of your car in stock form, that your zip will NEVER achieve 4.36 miles per hour. it just is not possible. There's bearing friction and gear friction to account for, and plenty of other mechanical and electrical loss including traction, drag, and the weight of the car combined with the lackluster torque of the higher RPM motors.

So even 2 22000 rpm motors wouldn't ACTUALLY spin at 22,000 RPM once they're pushing the car across the pavement. hopefully this makes some sense.

Axel
10-07-2002, 09:55 PM
3.8 flies in a 2.4v. It's crazy fast. Drag only... there's no turning here. I think CFM posted a mod with the 2.4v and the micro board that was like 2.8 seconds on the 20 footer. I'm just figuring in my head here, but that's better than 4.8 MPH!!! pretty crazy.

Anyways, I have a question for you all. My 2.4v setup ran fine to start with (even powered the 3.8 effortlessly) but now it's died. Only one battery is charging. I've rewired everything so there's a positive power from the charger going to the pos. end of the first battery, and the negative end of the charger gonig to the negative end of the second battery. But still, only the first battery is charging... it's not going through the battery!!! Any ideas how I can fix this? I've tested all connections and everything works fine, and the batteries both work fine by themselves (not battery failure). Also, my charger is currently putting out 2.5V at well over 250 mA (that's where my meter max's out.) I'm getting a little down about this because I've rewired and rewired and it's the same results every time :-P If anybody has any ideas, please let me know!

ax0n
10-07-2002, 10:10 PM
Originally posted by Axel
3.8 flies in a 2.4v. It's crazy fast. Drag only... there's no turning here. I think CFM posted a mod with the 2.4v and the micro board that was like 2.8 seconds on the 20 footer. I'm just figuring in my head here, but that's better than 4.8 MPH!!! pretty crazy.


I said "I'll guarantee you that even with the 3.8 motor and the rest of your car in stock form, that your zip will NEVER achieve 4.36 miles per hour."

"Stock Form" means no crazy double battery crap like you and me and several other people are trying.

I plan on running my second battery in parallel.


Anyways, I have a question for you all. My 2.4v setup ran fine to start with (even powered the 3.8 effortlessly) but now it's died. Only one battery is charging. I've rewired everything so there's a positive power from the charger going to the pos. end of the first battery, and the negative end of the charger gonig to the negative end of the second battery. But still, only the first battery is charging... it's not going through the battery!!! Any ideas how I can fix this? I've tested all connections and everything works fine, and the batteries both work fine by themselves (not battery failure). Also, my charger is currently putting out 2.5V at well over 250 mA (that's where my meter max's out.) I'm getting a little down about this because I've rewired and rewired and it's the same results every time :-P If anybody has any ideas, please let me know!

measure the milliams for both batteries after a full charge. That will tell you which one isn't charging. My DMM only goes to 200mA but the battery has way less than 100 mA by the time the car is slowing way down. your DMM should show you which battery is suffering.

Axel
10-07-2002, 10:26 PM
Oh, gotcha :-) I haven't actually used parallel yet. I did hook it up though, and there was only a very slight mA increase at the engine and .1 voltage increase over stock (could have been due to fact that these were just fresh batteries). While it lasts a lot longer, I doubt by the readouts there that it would make anything faster. It would probably slow stuff down (extra weight).

ya, I did that and found which battery isn't charging...but I don't know why it's not charging. The circuit is setup fine and it works by itself if I revert to stock setup (no dual battery). Weird, huh?
And not only does one battery not charge, but it pulls voltage and mA's off of the other battery, so it ends up that I only get like .5v and 50 mA at the motor.

I can still take both batteries out and recharge them separate and then hook back up and it zooms at 2.4v for a while (actually 2.2 to the motor was what I was getting) and then both batteries die, I recharge through the car, and only one battery recharges again... whichever one has the positive lead connected to it. can I run a positive from the charger to both batteries while in the car without screwing up the parallel/series thing, any way that you know of?

ax0n
10-07-2002, 10:47 PM
you would have to disconnect both batteries out of the chain and charge them in parallel or one at a time. I suppose you could do it with a few spdt switches. just running one + wire to both batteries would short EVERYTHING out.

ts185r
10-07-2002, 11:35 PM
Due to circumstances out of my control I know have a spare ZZ. For parts? I'm reading this thing about 2 batteries in the ZZ. Can I use the one from my parts car? What about charging on the controller with this setup? Please, please help.

ax0n
10-08-2002, 12:47 AM
That battery from the parts car will work fine.

I plan on running my batteries in parallel though, for more AMPS instead of what Axel's doing, running 2.4 volts.

you should be able to charge the 2 battery setup on the normal charger with no ill effects, if the batteries are wired in parallel.

lowerdfool
10-08-2002, 08:42 AM
Originally posted by ax0n
That battery from the parts car will work fine.

I plan on running my batteries in parallel though, for more AMPS instead of what Axel's doing, running 2.4 volts.

you should be able to charge the 2 battery setup on the normal charger with no ill effects, if the batteries are wired in parallel.

Doesn't work. I ran two in parallel and it makes the car lose all reception to the radio signal. If you can get past that it'll fly.

Axel
10-08-2002, 10:07 PM
Wow, that's really interesting...

Has anyone else had the same results?

The 2.4V felt as if it hurt my reception a tad, but not a bunch. My main problem is still getting both batteries to charge without taking them out of the car and charging them separately... :-( Anybody having any luck with this? There has to be someone doing this successfully.... Well, anyways, let me know if you have my solution... I'm only gettion one battery to charge in the 2.4v setup....

Hey, by the way, I just found a fun little toggle switch and shoved it in my controller. I don't know what I'm going to use it for yet though. Any ideas? :-)

ax0n
10-09-2002, 01:06 AM
http://buddha.jccc.net/~axon/photo/zz/zzcont.JPG

:)

I did that the second day I had the ZZ. It's actually a push on / push off. It just connects to the "forward" button. when I'm lazy I use it as cruise control, but it was originally installed so I could easily drain the internal battery and not have to hold the controller forward.

Bunta
10-09-2002, 10:29 AM
It sounds like the resistance in one of the cells is much higher than the other cell. I would think this cell is starting it's journey to battery heaven,, but you can try the following.

I wired in a switch in my latest 2cell bit, the switch allows me to switch between 1 or 2 cells. the switch isn't too big, and you can get something similiar for your dillema,,

or

I made a charging port for my Bit with a small headphone style jack. I charge directly from an external battery pack. I am using those black and decker round powercells that are rechargeable (3.6 volts!!). I know some others have talked about battery damage due to "memory", but for $3 bucks a battery (for car), I'll take it over $10+ dollars for AA batteries (transmitter). Perhaps the extra voltage can overcome the resistance you are building up in one of your cells. If you decide to go with this mod,, watch your charging times!! or you will need car batteries much sooner. 8-(

Bunta out-

QFM Racing
10-09-2002, 04:37 PM
I said "I'll guarantee you that even with the 3.8 motor and the rest of your car in stock form, that your zip will NEVER achieve 4.36 miles per hour. Stock Form" means no crazy double battery crap like you and me and several other people are trying."

STOCK ZipZap runs around 1.51 Miles per hour. I had asked Kyle to time a stock when we were doing our 2.4v/3.8 motor drag time runs. The stock ran about 9sec/20 ft. Hopefully I did the math right.