Brushless Drag Bike!

[Kingfish]

One controller.

If paralleled motors you still want one Controller.

It is likely your controller will be custom – at least the Motor-Driver board part. Gosh if we can finish Building the Best Controller then this project would be a great demonstration of driving off-board components. Can you spell sinusoidal?

Catch the Wave, KF

 

[Arlo1]

One controller.

If paralleled motors you still want one Controller.

It is likely your controller will be custom – at least the Motor-Driver board part. Gosh if we can finish Building the Best Controller then this project would be a great demonstration of driving off-board components. Can you spell sinusoidal?

Catch the Wave, KF

As luke and methods and others have pointed out to me you cant just stack fets in the same controler! So this is why i say multiple controlers! Although you can have a master controler and multiple slave controlers just turning fets on and off with a whole bunch of cap in each one!

 

[Arlo1]

Right now $3200 gives me enough nano tech for 720 000 watts! (based on lukes findings) $6400 acording to their actual rating!

 

[John in CR]

Right now $3200 gives me enough nano tech for 720 000 watts! (based on lukes findings) $6400 acording to their actual rating!

In that case don't you feel compelled to make it $4444 and get a megawatt? It has such a nice ring to it, though calling it a million watts is cool too. 8)

 

[liveforphysics]

Right now $3200 gives me enough nano tech for 720 000 watts! (based on lukes findings) $6400 acording to their actual rating!

In that case don't you feel compelled to make it $4444 and get a megawatt? It has such a nice ring to it, though calling it a million watts is cool too. 8)

Agreed.

 

[John in CR]

Now I'm screwed because I'm not going to be able to get the idea of a megawatt vehicle out of my head.

 

[Arlo1]

Yeh i was thinking that all day lol being able to tell every one my motorcycle is one million watts lol! Hmmmm (!)

 

[John in CR]

Yeah, claiming to have a megawatt would be the berries. Any time I hear or read "megawatt" I'm thinking in terms of numbers for a power power station for a utility company. You gotta go for it. The first to a megawatt of power will forever have bragging rights. Megarwatt Motorworks is using the word, but they don't have anything close.

Might as well get $8888 worth, because you just know one of them is gonna blow, so once pack assembly starts make absolutely sure a video camera is on hand and ready at all times, because when one goes we all want to see the fireworks. Otherwise it's just a $4444 story. With video it becomes instant promo material for the sponsor worth far more. Also, be sure those fireworks are always called an intentional display, so our lithiums don't get more of a black eye than they already have.

 

[Arlo1]

Ok so luke wanted some info. The tire is a 31/14/15 (31 inch total dia 14 inch wide and 15 inch rim) for the nitro bike and the total weight is 950lbs with rider.
I dont know how much torque it will take before slipping and the tranny is a 2 speed with a 2 stage clutch.
The first stage of the clutch is to slip for about 1 second so the traction is good before the second stage where it locks up!
It is also mandatory to have a way of dissengauging the engine from the wheel and I figure if the motor melts and becomes a big brake we need it to free spin to try to avoid a crash.

Luke see page 2 1/2 way down for more calcs.

 

[John in CR]

Great to hear the Power Station or MegaWatt is coming along. Can't wait. The thought of 1300hp electric pushing only 950lbs is just WOW. . For those who know nothing about race type stuff, I take it that the transition to second gear is spread over that 1 second interval. No doubt the entire run will be an incredible assault on the senses, but where do you expect it will be pulling the most G's? During that transition to second, on the launch, elsewhere? I'm trying to wrap my brain around what that few seconds will feel like.

Will you get a chance to ride it too?

 

[Arlo1]

I told my boss im helping build it and i wana be the rider! I will post video of a 6.28 nitro harley later!! Power wheelies the whole 1/4!!!

 

[phyllis]

A pro pos, I suspect one of the big advantages with electric is that the engine is very massive (I guess at least 3-5 g/cm3?). So it should hopefully be possible to put this weight far forward and down.
The sweet spot is when there is no weight on the front nor the trailing wheel, but if this happens before you break traction, I suggest the center of mass is too high or too far back (compared to the ideal in theory). So I'm afraid hub motor is out, without even considering the loss of suspension performance.

LFP suggested that tires on F1 cars are able to pull 4-5g IIRC. Consider that the ground suddenly starts moving forward with an acceleration rate of 5g (5*9.81 m/s^2 - you'd spend 2.72 seconds to get to 300mph, in a vacuum). The center of mass (CM) has an equal force of 5g backwards, but it also has 1g force downwards. The pivot point (PP) is where the rear tyre touches the ground. If the tangens of the angle horizontal,PP,CM is less than 1/5 (11 deg), you can make a motor to drive such a tyre. But I guess it also has to be balanced so that you have enough traction to get the weight off of the front tyre to begin with. The farther back CM is on that 11 deg line, the more authority the rider would have over pitch angle. What is the wheelbase?

The required rear wheel torque turns out to be 8 400 NM so you might want to look at a bigger reduction than the 2.85 you mentioned.
With the 2.08 2nd gear ratio you'd be loafing at 6700rpm at 300mph - considering that the big piston engines can go past 15k it'd surprise me if it didn't make sense with a redline beyond 20k for a brushless electric? So then, with a 6:1 we're down to only 1400NM from the motor, unless you'd like the hassle with two gears.

If you cooled it to -196C (ln2) before start, the specific heat of copper would allow you to waste a continuous 27kw for each kg of copper for five seconds, then it would be at 150C. That's not taking into account any heat transfer. As a point of reference, 27kw for five seconds is enough to evaporate about 6cl of water.
I might be mistaken on all of this, haven't checked it very thoroughly. I use to find some zeroes misplaced or * where it should be / when I go over my math for the fifth time.

That red frame in the first post looks super flexy. But it looks easy to stiffen up once you have fitted the stuff you need on it. Is it possible that it is intended for the motor to be a stiffening part of the structure?

 

[Arlo1]

I had 2 computer crashes last month.... Ok so I will try to get pictures but the red frame is out. We are looking at a full nitro harley frame with a 31 inch dia x 14 inch wide x 15 inch rim.
Yes A hub motor was never an option as far as I was concerned.
I will post more soon But we have decided to use the best equipment from the start.
Most of the current nitro bikes are going 0-100km/h in less then .7 seconds! Biff figures thats ~4gs of acceleration from 0-100!

 

[liveforphysics]

That red frame in the first post looks super flexy. But it looks easy to stiffen up once you have fitted the stuff you need on it. Is it possible that it is intended for the motor to be a stiffening part of the structure?

Amazingly, that flex in a drag vehicle frame is all part of what makes it get the traction it does. The frame flex to tire flex interface act like a pair of springs holding the mass of the bike dampened between, and work like a buffer to try to maintain roughly even pressure at the asphalt/tire interface despite all the inevitable little micro effects occurring as the tire goes through 10's (maybe hundreds?) of little micro slip/grip phases every revolution. This is because they dial the bikes in not to run with a static mu, but with a certain amount of slip percentage that gives a dynamic mu higher than the static mu from some advanced surface interaction effects.

Drag chassis design, and drag suspension design is pretty freaking tricky stuff, generally best optimized by trial and error over years of development.

It amazed me to have my own drag civic shave nearly a whole second due to having a pro fly out to setup/tweak/tune my suspension.

On paper, identical center of gravity. Identical engine/power/gearing etc. Identical tire. (so, on paper nothing significant should have changed.)

Just changed the linkage and control arm motion behavior with various little straps and rods and linkages and shock valve settings etc. The car goes and runs it's best time by a large margin on it's first run. I can hit the tires with everything I got now it it just explodes forward so hard it feels like it's going to tear the front of the car off after it snaps your neck, and it does this extremely consistently and easily. Before his work I had to feather things to control wheel spin, launches were really technically difficult and inconsistent.

All this from some little fiddly bits that on paper don't even enter the acceleration equations/diagrams.
Made me a solid believer in chassis tuning black-magic.

 

[phyllis]

super cool. so I was talking to a fella about these ducatis, he is impressed by how fast they are compared to higher hp inlines. So, they got a bit broader torque apparently, so less gearing hassle, but then they have that odd vtwin ignition timing, and then we wondered if there was some sort of traction effect from it.
Perhaps the motor controller must implement a good heap of CV's from various accelerometers and other things, including a few specially tuned LFO's just to get it singing. A theremin interface would be classy, I bet.

 

[Arlo1]

As we design this i keep going back and fourth with a low reving engine hi torque and think it will be in its peak torque longer because it wont have to change the rpm as much 0 at start and max at end. Then I keep thinking a lighter smaller higher reving motor is better :~)

 

[Arlo1]

Up date found the gearing numbers were wrong so...

The primary (belt) reduction ratio is 1.28:1
The tranny in first gear is 2.14:1
And the final drive (chain and sprockets is) 2.11:1
The estimated torque is ~1000 ft/lbs from 3600 rpm launch to the 4800 rpm redline.
Giving a rear wheel torque ~5780 ft/lbs in first gear.