***__ The 1/8 Onroad Think-tank __***
 

I have had a look at the 1/8 conversions on this site (very impressive). I race electric 1/10 on-road in Australia in a fairly competitive manor. I have a 1/8 Serpent Vector laying around and would like to "electrify" it. I don't want to just go fast, I want to go "head to head" in a race situation against the nitro powered 1/8's. Drivability is going to be critical in this project. Like "BrianG" I would like to try and incorporate the original 2 speed and clutch assembly, my way of thinking is the clutch should slightly smooth out the delivery of power to the wheels whilst also allowing the car to free wheel when backing off. I will use the original disc braking system to slow the car. I realize this has been done before but I don't want to build something that will scare the nitro 1/8 drivers I will face, I want the cars to been relatively even for speed and power.
These are some of my first thoughts, let the ideas flow.

Cheers Andrew

What kind of speeds do the nitro cars reach? You also might want to consult Serum. I believe he did a Serpent car.

Here is a link to the car.
http://www.serpent.com/product/909010/specifications/

In the specs is says 120 Kph+

Just did some rough measuring and it looks as though I'm limited to the 1512 size Neu motors or other brand of equivalent size. I will gather all the relevant gearing information for the car and post them later today.

OK here are the gearing options. Looking for a top speed in second gear of around 120Kph (75mph)

OPTIONAL PINION SIZES
1st gear 15,16,17 I have the 16 installed
2nd gear 18,19,20 I have the 19 installed

OPTIONAL SPUR SIZES
1st gear 47,48,49 I have the 48 installed
2nd gear 44,45,46 I have the 45 installed

The ratio of the drivetrain is 2.27272727 (50 teeth on rear axle and 22 teeth on the transmission shaft)

Tyre diameter
I will be using foam tyres. I expect the average tyre diameter to be around
73mm (2.874 in)


Please feel free to offer advice on anything you may think is of importance.
I am particularly interested in hearing about motor,battery and speed controller options.
After running the particulars through http://www.scriptasylum.com/rc_speed/_top_speed.html
I may need correcting but I see 2 options using the 1512 size motors.

4s LiPo & Neu 1512 1.5 or
5s LiPo & Neu 1512 2d

Again please correct me if I'm not taking certain things into account.
Cheers Andrew

Not sure on how long a runtime you need, but for a efficient, cool running setup that can be geared higher, I would run 6S.

As I have no idea on what is possible, in an ideal situation I would like to be able to run for 15 mins.

I have worked out how much room I have available for the LiPo's it is as follows.
Could I please have peoples input on what brand/size etc. for the LiPo?

H 27 mm
W 50 mm
L 160 mm

squeeforever If run 6s what are my choices as far as speed controls go?

Hi Andrew;

Perhaps you can use the two speed on the track, on the normal road it's useless with the foam tires lacking of grip.

Your sizes might give you some troubles with the right lipo's in 6S;

A speedcontroller that is capable of doing 6S at this moment is the MGM

You could set with 4/5S though, since you don't need the 6S on a ~2.5 kg heavy vehicle

Serum, did you use traction compound on the tires?

Personally, I would go for something like a 6S1P Flightpower pack (no idea if it will fit though) with one of the 6S capable MGM ESCs and a Neu 1512 1.5y/F.


Differential Ratio: 1
Transmission Ratio: 2.2727
Other Ratio: 1
Spur Tooth Count: 45
Pinion Tooth Count: 19
Total Voltage: 23.4
Motor KV: 1900
Tire Diameter (inches): 2.874
Tire Ballooning (inches): 0
Motor Current Draw: 0
Motor coil Ω: 0.009
Spur/Pinion Ratio: 2.37 : 1
Total Ratio: 5.38271 : 1
Tire Circumference (inches): 9.03 inches (229.34mm)
Total Motor Speed: 44460 RPM
Vehicle Speed: 70.62 MPH (113.44km/h)
Effective Speed Rate: 3.02mph/V (4.85kmh/V)
Effective KV Value: 1900
Motor Torque: Amperage not specified...
Final Torque: Amperage not specified...

Are there any ill effects if I was to wire in series a 3s pack on one side of the car and a 2s pack on the other-side (to try and offset the weight of the motor and to keep my L to R balance even)

What sort of runtime can I roughly expect from a 5000 mAh pack in the combinations suggested. Is there a formula for working this out?

That should work just fine as long as both packs are built from the same lipo cells. People do that all of the time in the emaxx and revo gmaxx setups.

What parts of the car did you use to determine to boundaries of your available space for the battery? When I did my Serpent 835, I made a custom top plate using the original one as a pattern, and placed a cutout in the center area where the gas tank was to let the battery come through. I then stacked A123 cells in a 3s2p configuration (three on bottom and three glued on top like a brick). When you break down the Dewalt packs to get the cells, the paper cylinder outers on them are very good for gluing using basic wood glue. I would guess that with the extra length of the 8th, you could probably go 4s2p.

since the room is tight; can anyone explain me the reason why using 6S on a ~2.4kg heavy vehicle?

Only reason I would use a 6S setup would be shear power in combination with high efficiency. With the high speeds needed, your gonna need alot of power. 6S setup will yeild more power as far as the batteries go.

I was using the available space under the top plate, extending out toward the body. Do you have a photo of your 835 with the cells in it?

I just want to reiterate that I need to be able to RACE continuously for 15 mins (10 mins. minimum) I'm not interested in just doing speed runs.

I have also found out that a high performance nitro engine out of a 1/8 can produce nearly 3HP. Is 2237.0996 Watts out of the question? Of course this would not be continuous.

I had considered that when making my suggestion of the A123s. The first thing you need to address would be the power output match of a typical 8th in the small space that you are afforded for your conversion. I was looking around at the various batteries currently out, with your dimensions in mind, and nothing to meet your needs exists. The only hope you have would seem to be something you can quick change, akin to a fuel stop for a typical 8th. I don't really have accurate figures to go from, but it would seem that battery sizes (physically), are about 1 to 1 in runtime with the size of a gas tank when power output is that high. A typical 8th doesn't run that long without needing to be refilled, but I'd bet that if the tank was as large as a 6s high capacity battery, it could run that long.