Yet another electric conversion
 

Ok I got the power plant ordered so thought I'll start the car build thread. here are the specs of the electrics

MGM X Series 25063 at 360 amps
Lehner 3040/6 6000 watts
KOKAM 4100 65c 2 x 3S Cells

This is all going to be shoe horned into a Kyosho Evolva M3 to make a 6 cell speed car. Target speed is 135mph.

Due to the stresses on the ESC I will have mechanical braking and also for acceleration a mechanical 2 speed gearbox. This will soften the load during the initial phase.

I'll post some pics of the build when it gets underway

Cheers

people and 2 speeds:whistle:

If I am reading this right, you are going to run a 3040 off 6s lipo's with an MGM 250amp esc, This is right?

Depending on the KV of the motor (?), you'd never see second gear. The gearing needed, you don't need to worry about the motor or esc, I'd worry about the batteries. Not sure the esc will even run on 6s lipo, I'd check the minimum on the esc specs. I have a 2250/10t (1184kv) motor and its an absolute beast on 6s, Strong enough to snap a Twinforce w/center diff (51 tooth gear) buggy diffs and a 19 tooth pinion with truggy tires Like it isn't even there, I imagine the 3040 will be stronger. Good Luck getting it to fit, I believe, diameter wise, its bigger than a soda can. I will watch your progress.

1st gear gearing will be to 90 mph. I will change the internal gearing in the car so the motor will rev to 30,000 before changing to 2nd. 2nd will be geared to 165mph at 40,000 rpm.

The MGM 250 will run from 4-15 Lipo cells and will handle 360 amp burst so 6 cells no problem

The KOKAM 3S 4100 MAH cells deliver constant 150 amps each for 4 mins. These are tested prior to shipping.

Connections are 3 x 6mm 200 amp gold plated connectors with 6mm square wire each phase.

The reason for the 2 speed mechanical gearbox is that I can fry the motor if I apply too much throttle before the motor spins up. The motor is 92mm long and 60mm diameter so the same as 1/2 a can of Red Bull. The 2250 is 40mm diameter and same length so not much in it.

The Evolva drive shafts have been upgraded to sping steel and hardened and tempered myself. The belts are carbon fibre and metal pulleys all round.

The real problem I have is seeing the car when it starts it run as the run up is 1200ft and the car staying on the ground. Nic case recently ran 173mph and the next run went through the trap at 177mph 5ft off the ground. He is preparing for his 200mph run next month.

I'll post some photos when I get back to the UK and start the build

Cheers

I guess you got it covered, I was adressing a few concerns i had. I have no experience in high speed runs, so good luck. looks like you got a mean car in the future

I've never examined an RC shifting transmission, but is there any slippage? I ask because you're going to get up to 90mph @ 30k rpm, and then it shifts right?...... So then you have that huge mass of a motor spinning at 30k, and now it's way too fast for the speed it's traveling, seems to me like you're going to either break something or spin out the wheels instantly.

The 2 speed clutch is a 2 stage clutch. As the shoes fly out under spring pressure it engages the clutch bell. This rotates the shoes and engages the clutch cam locking the clutch shoes in place with no slip.

When the car changes into 2nd there will be a reduction in revs with the same throttle input resulting in a jump in amp loads. Whether this results in wheel spin or just an increase in acceleration can only be known with testing. The obvious thing to do would be to decrease throttle input but knowing when the car changes might be a problem.

The car will have a gyro so will track straight even if it spins the wheels.

Love speed build threads, will be following this one closely.

I'm not too keep on 2 speeds myself, I have a feeling with the amount or torque that motor has the second it reaches 2nd gear it will either spin the wheels or break something.

Would you not be better off going for a single speed, and making a custom motor mount so you can fit a huge pinion? You could have the pinion machined by RW..

Still, the specs look great, that ESC is a monster! I think Nick used one of those in his Slash Insanity project.

the parts have arrive. I might have overspecified the motor...LOL

http://img18.imageshack.us/img18/7350/dscf9247dh.jpg

http://img695.imageshack.us/img695/3844/dscf9248v.jpg

http://img847.imageshack.us/img847/2302/dscf9249u.jpg

Looks like I'll need to extend the chasis about 6" to a foot.

Oh well

Thats a 1/8th circuit car by the way, not a 1/12....LOL

Man, I think just skip the 1/8 and go 1/4 scale with that motor.

OH GOD! IT'S HUGE! lol....see how small of a car you can wrap around that motor... :)

Who did the testing? Math doesn't lie. In order for any battery of any capacity to deliver constant current for 4 minutes, the maximum continuous discharge rate would be 15c - and this assumes you would actually get full capacity at 15c discharge, which isn't likely. 15c on a 4100mah battery is 61.5 amps. Maybe they can discharge at 150 amps, but they can't do it for 4 minutes straight unless somebody found perpetual energy and used this amazing discovery in these cells! If the cells deliver full capacity at 150 amps, they could only do so for 1.64 minutes before they were completely discharged. :rules:
Cool project, though and I look forward to its completion. :)

A speed run takes about 20 seconds MAX and I would think 2 runs would be good enough so I can discharge the cells in less than a minute. I have 2 x 3 cell 4100 so would have thought I would have enough amps.

The idea is to make a custom chassis a lot longer than the stock one. I just put the car down to show the size of the motor. I have no doubt it will all fit in eventually

Cheers

That's wicked... the motor does not seem to be too small btw :P

I'll be watching this! :yes:

Kokam makes great cells and I don't doubt they can get the job done - just stating the absolutes regarding disharge rate, capacity, etc. - the car is small and light enough to get real speed with these batts for sure and I look forward to the result when it is all done. :)

FWIW, I tried a 2 speed setup in an Ofna Ultra GTP and didn't like it. The tires would break loose when it shifted and control was difficult to say the least. Electric motors simply produce too much torque. You can try to minimize the difference in rpms when it shifts by narrowing the ratio between 1st and 2nd gears (motor rpms don't drop as much), but I still had a really hard time keeping the tires from spinning.

Personally, simply using a large motor and gearing up high enough to get your desired speed would be the way to go. However, when geared very high, startups can be rough with sensorless systems (not enough motor revs per inch of vehicle movement for the ESC to get a good feedback for commutation). It would be nice if there were large sensored motors available, and when coupled with a sensored ESC (like a Tekin RX8), startups are much smoother and controllable, yet can still spin at high rpms.

I'm sure there's a 1/8 platform under there somewhere!

Yeah but I'll ditch the chassis and keep the back and front. I'm making the mtor mounts now. I should have something workable in a few days

Cheers

That's quite a bit of motor, this seems like a fun project, Keeping it on the ground might be an issue. Perhaps you could shift the motor to the front to make it more stable in the front end, in order to avoid the wind to get underneath it.

There might be better batteries out there, current/voltage wise, don't make a chassis that only fit these batteries, that's my advice.

The chassis will be able to take 12 cells. The ESC is good for 63v so at 250 amps thats 21hp!! LOL

I changed the chassis and installed a right andgle drive

See!

http://img221.imageshack.us/img221/9...05154007bj.jpg

http://img32.imageshack.us/img32/987...0105154019.jpg

http://img828.imageshack.us/img828/6...0105154030.jpg

Still loads to do. The chasis needs strengthening so I'll add some angle ally along each edge. Make a motor - Gearbox coupling. Install the servos. etc.. etc...

Bloody 'ell, how long is the center belt going to be? Are you going to use multiple belts to get the power to the front? Looks insane though. Good insane, not bad insane. :lol:

Holy crap! This looks AWESOME! :party: Is that a custom gearbox?

I positioned the front so the middel belt pulleys are 597mm apart. With 18/26 gears I can then use the HPC gears HTD3 3mm Pitch belt 1263mm long.

The gearbox is also from HPC gears Its the HPC-GBK-101. It came packed with grease so I washed it out and oiled it with light oil. Its only supposed to be rated to 3600 rpm and I'll be reving it to 60,000 rpm. LOL. Lets see what happens

Cheers

Um Wow,
Not to into speed runs but i like watching them,
Ill definitely be watching this thread...

Things I found to help with a multi speed electric motor driven rc.
Make the shift points lower.
It changes gear it changes a precentage.
slower speed means less rpm difference.
you only need to get the car rolling not up to 90 mph.
Motor should have plent power after going to pull 2nd with no issues.

I connected the ESC, Motor and cells and had the car running on the bench. Just a couple of small things to do and it will be ready for a run.

Still wating for the long side belt to make it 4WD

Cheers

Testing the MGM 25063 throttle ramp. As you can see in the video I apply full throttle and the ESC ramps from 0-100 over 30 seconds. I dont let the car get to full speed


http://www.youtube.com/watch?v=IB-1D...ature=youtu.be

Cheers