Electric dragster help ! (2 Viewers)

[Okbang]

Yo,

lol okay so for year 10 engineering we are making a battery powered dragster, and everyone uses the same kit except for batteries. I'm using Energizer Ultimate Lithiums at the moment and my dragster's the fastest and all, but recently the front axle detached and i had to reattach it. Since then it doesn't go in a straight line anymore, always turns to the left

so does anybody know how i can fix the steering on this thing?

also if any of you have made a dragster in school can you please give some pointers on how to make the dragster go faster over 20m? people are starting to copy my choice of battery so i need to find a new edge over the competition :/

 

[Havox]

Add more batteries, lower weight - power to weight ratio counts everything, you can even find a higher output motor. Just make sure your front axles are pointed straight and that your chassis isn't bent.

 

[SnowFox]

How have you got it geared?
Direct mount from the engine, or via a drive shaft?
You can improve speed via two ways:
Up the motor output: this is usually a higher output battery or a better motor in general or you can change the gearing, big gear on the engine, small gear on the rear axle.
As for battery i dont know how much space youve got to play with but hitting up hobbyco or a RC specialist might be an idea. Also paint over the label so the others dont know.
And for direction, it could be a balance issue.

 

[Parvee]

Wish I could of made a dragster in Yr10
Sounds so fun!

 

[iampeterr]

power to weight ratio ! make sure there is no wheel spin .. even through its only an RC. Get a better motor? how is the engine mounted? show us a pic !

 

[eshay lad 69]

bro ill help you it sounds like a fun assingment

-if you can, get bigger wheels for the ones that are powered by the motor, by the sounds of it its your rear wheels. for every 360 degrees the wheels rotate the car will go further, you might lose some acceleration though so think about that

-the easiest way for speed is upgrading batteries.i dunno what voltage and shit your playing with but if your handy with a soldering iron you can wire your batteries in series for extra voltage. if you do this your car will take a massive shit on all the competition it would be fucking funny though
for eg. you get two 1 volts batteries, wire them together and then you get 2 volts of power
that might burn out your motor though dont run it for too long like that. if your serious about doing this i can give you in depth advice and battery recomendations if u want

-cut out all the unnecessary shit from the chassis. lower weight= more speed
- get thinner non-drive wheels (i assume there ur front wheels) less friction equals less wasted power and more speed
-try to design the car with a low profile as possible so its like a f1 car less air resistance= less wasted power=more speed

fark to get it to go straight you gotta have your wheels aligned. im guessing your front axel isnt installed straight
-you could have also bent the axel in a crash giving your wheels funny camber

 

[iampeterr]

get bigger wheels for the ones that are powered by the motor, by the sounds of it its your rear wheels. for every 360 degrees the wheels rotate the car will go further, you might lose some acceleration though so think about that

Correct me if i'm wrong, doesn't that depend on the gear, not the size of the wheels? :S

 

[Okbang]

Thanks for your replies, guys

I'll clarify a few things or two. The kit we are using is a very simple one, it has

2 large rear wheels
2 smaller front wheels
2 axles
2 axle "covers"
4 different gears (only two can be used in one dragster)
battery pack
2 ordinary AA batteries
a piece of sheet acrylic
1 electric motor @ 6500rpm

the only things that can be changed, so far are

the piece of acrylic, which serves as the platform for all the crap
the 2 AA batteries
the body (prolly made out of plastic)

 

[Okbang]

@ SnowFox: there are 4 gears: 8, 12, 50, 60 teeth and you can use any of them as driver or driven gear. I used the 12 + 50 teeth gears cause they're kinda in the middle of top speed-acceleration balance. dunno if I can change them seeing as I've stuck them on but any -specific- suggestions? Thanks though, will try to put a cover of some sort over the battery pack.

@ iampeterr: Don't have a pic at the moment seeing as its the weekend, but the motor is mounted 7/10ths of the length towards the back. I'd like to put on a better motor but that'd disqualify me. lol

@ eshay lad 69: Nah I can't use different wheels to the ones that have been supplied, but since its a 20m drag strip for dragsters a bit bigger than a hand I think acceleration might be the way to go :S My school's got a soldering iron, not sure about wiring batteries together cause I'm using lithiums and they might explode haha. What you said is probably true, i crashed it a few times and glued the front axle back on quickly...must've done a bad job cause the steering screwed up right after that. Thanks for your advice, do you happen to know any batteries that are more powerful than Energizer Ultimate Lithium (that you can get in Sydney)?

 

[eshay lad 69]

whats the voltage on each battery and how many are you using?

 

[SnowFox]

Thanks for your replies, guys

I'll clarify a few things or two. The kit we are using is a very simple one, it has

2 large rear wheels
2 smaller front wheels
2 axles
2 axle "covers"
4 different gears (only two can be used in one dragster)
battery pack
2 ordinary AA batteries
a piece of sheet acrylic
1 electric motor @ 6500rpm

the only things that can be changed, so far are

the piece of acrylic, which serves as the platform for all the crap
the 2 AA batteries
the body (prolly made out of plastic)

First up fix your axles.

Next try using NiMH 2200mah batteries, ie camera specific ones.

These are high output batteries, so more juice to the motor.

Can you post pics of the kit?

 

[Okbang]

Yeah I have engineering class tomorrow so I will make sure to fix that up and I will try to take a picture for you guys

About the 2200mah NiMH batteries...the ones I am currently using are pure (i think) Lithium batteries rated at about 3000mah...can you suggest any better ones or is that it?

 

[SnowFox]

http://australia.rs-online.com/web/p/aa-batteries/7020799/
??
3.6v of Lithium Thionyl Chloride based destruction?

 

[Okbang]

Awesome. It says its 2500 maH, but whats the difference between volts and mah on a battery?

Update: Changed the gearing yesterday to increase acceleration. But turning is still a problem. to give you an idea it does donuts (i.e drifts in a circle) in an anti clockwise direction. the axles have been fixed but i don't know why it still happens?

would it help if i cut my dragster narrower so it would go straight?

 

[SnowFox]

Watts my good friend

Electrical power is measured in watts. In an electrical system power (P) is equal to the voltage multiplied by the current.



As for steering, redo all the axles maybe?

 

[eshay lad 69]

bro

mah is the capacity of the battery - the equivilent of the size of a petrol tank

the voltage is (sort of) power your giving to the engine. more volts = more power.

 

[SnowFox]

bro

mah is the capacity of the battery - the equivilent of the size of a petrol tank

the voltage is (sort of) power your giving to the engine. more volts = more power.

what.

Amps is the unit used to measure current.
Voltage is the unit used to measure the amount of electricity stored.
Easy concept: Water inside a plumbers pipe.
The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is relative to the pipe size.

 

[eshay lad 69]

Voltage is the unit used to measure the amount of electricity stored.

sorry bro thats an incorrect definition of voltage. voltage is more or less (yes its an analogy) the excitedness or enthusiasm for electricity to run through the wires. It is not the capacity of the battery.

MAH (milliamp hours IIRC) if the capacity of a battery. a battery with a higher MAH 'rating' will run for longer under the same load vs a lower MAH 'rating'.

your analogy of amps vs voltage makes sense to me as I see where your coming from and im pretty sure its in some textbooks. I understand what you mean though in in it so i made a little diagram using bike/car tires to help yo.

see how you can have the same pressure (voltage) but at different sizes of tires (capacity)? it probably doesnt make it any easier to understand but i tried my best brah.

for eg. ( was gonna get links to batteries as examples but i cbf'd if you want em ill get em)

2800mah battery at 7.4volts = 17 inch tire @ 18psi
5000mah battery at 7.4volts = 22 inch tire @ 18psi

amps (once again its another analogy so it makes sence to me but mabye not you) is the rate at which you put the air in the tire.
for eg.
putting air in a tire at low speed takes 1 minute to fill it to 30psi
putting air in a tire at high speed takes 30 seconds to fill it to 30psi

source: personal experience building electric rc devices and building battery packs.

lol at this essay i just wrote bra

 

[SnowFox]

Not sure if you are trolling.
A battery is a power storage device.
Volts is the amount of energy stored inside. Think of it like a compressed air cylinder.
Amps is current or its flow rate.
Output or watts is directly affected by both.

Two years of elec courses in Highschool.
Numerous years of personel elec engineer projects.

In any case the 3.7v battery i suggested will piss all over the 1.5v.
The only problem is the motor possibly burning out.

 

[eshay lad 69]

Not sure if you are trolling.
A battery is a power storage device.
Volts is the amount of energy stored inside. Think of it like a compressed air cylinder.
Amps is current or its flow rate.
Output or watts is directly affected by both.

Two years of elec courses in Highschool.
Numerous years of personel elec engineer projects.

In any case the 3.7v battery i suggested will piss all over the 1.5v.
The only problem is the motor possibly burning out.

everything you just stated aside from the bold supports my previous post. I understand that it is energy, but it is not the 'capacity' of the battery.

Ill make it simpler for you. Lets say your battery is the size of brick from a house, and mine is the size of a mobile phone. Both our batteries have the same voltage, but have a differing capacity. Which one would last the longest connected to a mobile phone?