The 2 the Max Project

[hodakamax]

A couple of answers for the questions. When we did run the battery ignition for a while in the old days the standard Hodaka 6V battery was used and it seemed to last a day of racing. Harry Taylor's Bulletins on Flat track and Road Racing both showed the standard 6V battery and a 6V coil with a Hodaka number of 913009R. Harry's road races were probably quite a bit longer than the flat track agenda.

Max

[Bullfrog]

Thanks for that info Maxie. And it prompts the question, did Harry's Road Racer run total loss ignition?
Ed

[Bullfrog]

DOH. Of course Harry's road racer ran total loss ignition. His road racers (there were several) were the models/development machines which provided the specs for the road race tuning sheet!

I've looked up some part numbers and peered at some illustrated parts lists . . . and we may be on to something. First - the 913009R coil and the total loss system points cam 913007R were listed as ACE 90 racing parts. The parts illustration shows the coil to appear to be longer over all than the coils shown for the ACE 100 and the ACE 100-B, then the Model 93 Super Rat drawing shows what appears to be the same type of longer coil with a part number of 913008R (ditto for the Model 93A Rat). I wonder if anyone can provide the resistance specs for either of those coils? The specs might be in a suplement to the original Workshop Manual - but I don't have a full set of those supplements.

It sure appears that the stock chrome tank Super Rat coil may be very close in specifications to the earlier ACE 90 racing coil.

Ed

[taber hodaka]

The Ace 90 race items were used on the Super Rat including the crankshaft. All parts numbers starting with 91 were ace 90 parts including a head. -----------Clarence

[Hydraulic Jack]

. . . and what would the weight be for a lead/acid battery pack for your RC Helicopter with equivalent Watt-Hour capacity? Just curious.

Ed

Don't really know. I can't recall seeing an automotive class lead acid battery rated in watt hours, and RC models don't use lead acid batteries. I have seen RC battery packs that could easily provide the current needed, but the higher the current capacity of lithium cells, the more they cost and the hotter they get under load. I would also point out that lithium cells don't charge all that quickly, so it might become necessary to have more than one power pack at the track so you don't have to wait an hour to charge cells that run for ten minutes. A lead acid battery also charges slowly, but if it lasts all race day on one charge, recharge rates aren't really an issue.

As I said, I don't have a problem with using lithium cells. Once electrical capacity needs are worked out, it might be worth the cost to buy lithium cells and build a power pack or two. It just isn't where I would start due to cost. At about this point is where some actual research would come in handy.

[taber hodaka]

Only as I remember the small hodaka 6 volt battery did not run my total loss ignition very long, I was not impressed. I call Max's efforts research, he crawls out of the jello mold. ------------------------Clarence

[Bill2001]

He'll need to measure the current draw of his system. Best to use an old dial ammeter instead of a new digital ammeter. Since the points are opening and closing rapidly it might affect the fast digital readings. The dial meter would tend to average things out analogly.

I don't know how this "as working" value would compare with straight 12vdc going into the coil, but there is a lot of electrical stuff going on in that ignition circuit.

[Hydraulic Jack]

Looking at the tech specs for the 93 Super Rat as a starting point, I notice that the coil is specified at 5.35 ohms. That suggests to me that it is essentially a 12volt coil. Also, the 93 produced between 8 volts and 15 volts between 2,500 and 8,000 rpm. I think what you have there would pass for a 12volt system, which might explain why a 6volt battery didn't last as long as it should.

Since you intend to run high speeds anyway, start with the 15 volt output and the 5.35 ohm coil. Ohms law produces an amperage demand of 2.8 amps continuously. Round that to three amps at 15 volts, minimum.

Total loss systems used in drag cars commonly use 16 volt batteries instead of 12, probably for this reason, that demand is on the high end of he scale. Better to have 15 or 16 volts to stabilize a high rpm spark than to have a 12 volt spark that might blow out at high speeds.

So target a 12 volt battery system as a start point, with the capacity to give you not less than 3 amps for as long as you think is necessary for a target run session, with a reserve of anywhere from 50% to 100%. So if you want a half hour run time, you need to be able to produce no less than 3 amps continuously for one hour. You need a 3amp hour system, minimum. That is pretty close to what the old 12volt Hodaka battery was rated at, and a bit of surplus wouldn't hurt.

You can do that with lithium cells, but you are going to need more that a small handful of batteries to do it.

[taber hodaka]

Jack I did not know hodaka had a 12 volt,but then I was not around the newer bikes, good work detective!

[Hydraulic Jack]

I am not sure the secondary coil on the 93 series Super Rat is or was rated as 12 volts versus something else. rather, I assume that it technically is a 12 volt coil for two reasons. 1 is the operating voltage of the magneto, and 2 is the ohms rating of the coil. Coil resistance between 6 volt versus 12 volt applications isn't great, but usually, 6 volt coils have resistance in the 4 ohm range, and 12's have a rating in the 5+ range because of the difference in the number and gauge of windings.

At any rate, I think it is a place to start. I wouldn't begin with anything less than a 12 volt power source, and would want to see around a 5 amp hour capacity, just so there is a margin of error. If you undersize the power source, you might end up with a 20,000 volt spark, which could easily blow out under pressure.

Given the intended purpose of the machine, I wouldn't be trying to find the minimum acceptable ignition system. I would want a strong dependable ignition, even if it cost an extra half a pound in weight. Ignition is a critical component. Losing a half pound of body weight isn't that hard to do for the pilot. You could cut a pound of weight from the machine just in building a light weight saddle. For that matter, I suppose you could adapt a CDI ignition system and lose a half pound just in the flywheel.

[hodakamax]

Just for fun I weighed the flywheel which came in at over two pounds which is about 1% the total weight of the vehicle. Not insignificant. The flywheel, whether CDI or standard ignition, still nibbles away at the F (Force) part of our equation as in F=ma. Creating electricity from spinning magnets takes power from our driving force namely the engine. Removing this system will have a two-fold effect on our equation.

Hey, thanks Jack and Gang for your comments and research. I am taking notes!

Maxie

[Hydraulic Jack]

Just to put some perspective in here, F=MA is a statement of how much force is needed to accelerate a given mass. Assuming you are more interested in top speed and not low elapsed times, once a machine approaches or achieves its top speed, acceleration drops to near zero, which means that the force needed to maintain forward motion decreases as acceleration decreases. Not that the weight of the machine isn't important. It's just that it isn't the holy grail either. At speeds approaching 100mph on a small displacement bike, you will get a lot more bang for buck from aerodynamics than from a few less ounces of mass.

[hodakamax]

In F=ma we must consider things like air resistance and friction as negative forces. They are reducing the forces available. Without any negative forces our racer would maintain the speed it had been accelerated to such as in a space environment. If engine force continues our racer would always continue to accelerate but in our earthly environment we are still limited to the F=ma equation. Acceleration is always dependent on our mass and how much force we have. We have to reduce the mass and/or get the sum of the forces increased by things like streamlining and reducing mechanical friction or more power. We can't go any faster in our environment because all our forces have been cancelled out by minus forces. When forces become net zero were going as fast as possible, acceleration is zero.

I always have to write all this down to explain it to myself. That was fun.

Maxie

Ok, a little side note. We should mention that F=ma is Newtonian physics. Relativity would come into effect as our racer approaches the speed of light after accelerating with the same engine force. More and more force would be needed as we approach the speed of light which would be the ultimate speed limit. F would have to be infinite to maintain the speed of light or our mass would have to be zero. Hey, just quoting Einstein, It's not like I understand all of this.

[Bill2001]

What is needed here is the Sagan corollary. Get out. Ride. Enjoy. Repeat.

[matt glascock]

Just to be a bit geeky and trot out what I can remember from college physics (fuzzy at best, but a required premed course), a more apt formula than the classic F=MA basis for Newtonian mechanics might be the equation used to determine terminal velocity. Of course, this equation is used to determine the terminal velocity of an object falling from height, but many of the principles contained in the equation remain consistent and applicable. The equation states that:
Terminal Velocity = the square root of ((2 x M x G)/(p x A x C)) where M = mass, p = density of the fluid being moved through, A = cross sectional area perpendicular to the direction of movement, C - drag coefficient, and G = acceleration (in this case, the 9.8 M/S x S due to gravity but in a speed run, the propulsive force of the 100 cc motor - you could replace G with F/M where F = propulsive force resulting in the numerator being (2 x M x F/M)). Any manipulation which decreases the factors within the denominator will increase the terminal velocity. Moving through lower density air, decreasing the surface area (streamlining) and drag coefficient (which applies to aerodynamics as well as the running components of the machine) will all allow a higher terminal velocity. Similarly, enhancing the ability of the motor to accelerate through higher revs and taller gears will positively effect the numerator and thus the terminal velocity. Lets just skip over the effect of mass for now. Indeed, none of this is as interesting as the Sagan Corollary provided by Bill, but I need to reconfirm my status as an over educated s#*t head.

[Hydraulic Jack]

Well, you wouldn't replace the gravity constant with F from Newton's second law of physics, because F isn't necessarily a constant, nor is it necessarily related to achievable speed, but I agree that the terminal velocity formula would be more relevant.

Given that there are a number of variables involved, let's say that a given engine can produce a specific amount of power at a certain rpm. Doesn't matter much what those numbers are, just to know that they exist. If it takes 10 horsepower, of if it takes 10 foot pounds of torque to maintain rpm at speed, what that speed can ultimately be is then a function of gear ratios and tire diameters. If you limit the motive source to, as an example, 10,000rpm, it doesn't matter if your engine make 10 horse power or 100 horsepower, you still won't go any faster than what your final drive ratios permit, assuming you can get maximum rpm in top gear. You might get there faster with a lighter bike and you might maintain it easier, but you won't go any faster.

It is enough, then, to simply have enough power, expressed as you will, to maintain a given target rpm in top gear, and your speed will be the math product of those rpm and gear numbers. At that point, F is no longer relevant, nor is A, nor for that matter is M. Instead, you will need only the amount of power needed to match parasitic drag from all sources. Such as air, the fluid through which you ride.

I understand that making things lighter will make the job of going fast easier, but having spent some time on a motorcycle in excess of 100mph, I know that getting out of the airstream is more important than tuning for that last have a horse. If that same bike weighed 150 pounds instead of 320, it would still be limited to 110mph unless I changed either the ability to rev at the upper limit, or the gears or tires, because once I hit top rpm for that engine in sixth gear, 110mph is all there is.

[taber hodaka]

So? --------Clarence

[matt glascock]

Hey Jack, you've illuminated the weakness of direct application. Here's my thinking - likely wrong. Yes, the force of gravity is a well-accepted constant. Its the motive force which accelerates a falling body to the ground. In a moving motorcycle, the engine is the motive force propelling the bike forward. In a loose association with reality, I made the force generated by the engine a constant presupposing it is operating wide open at its most well-tuned state and with optimal gearing and tire diameter. Flawed yes, but a feeble attempt to make the terminal velocity equation work. Other than that, you have made an excellent and deep dig into the nitty and gritty of the effects to overcome in the quest for pushing out the point where the worlds of force and resistance collide. Nicely stated.

[Bill2001]

Might be relaxing to watch "The World's Fastest Indian" to realize how good we have it...

[hodakamax]

Wow! What a fun discussion! In my simple scenario and example of F=ma, I was trying to show that each component indeed does have an effect on our record run whatever the vehicle and/or force. F will always be forces acting for or against our goal. Gravity, fluid resistance, friction and thrust are all plus or minus vectors of force. In the quest for our goal these are the factors that can be simply stated. A lot of variables are falling into the force category.

In our simple equation, gearing, horsepower, tires, barometric pressure, fuel, time, gravity and other seemingly muddying factors are relevant in achieving the total force, but the total force is one number, the sum of all the forces, F.

Since our equation only has three components we cannot discount the importance of each one or we're getting off the path. Mass is one of the components and for a record attempt should be reduced with equal importance as it's directly proportional to the force and acceleration. Acceleration is change in velocity and is how we get to our record number by applying force to a mass.

Ah, a cup of coffee, an intellectual discussion and I'm ready for another great Day!

Maxie

By the way, The Worlds Fastest Indian story is ever-present when working on the project. What a fun movie.

[matt glascock]

Agreed Maxie. What is interesting is that while we are discussing these principles in terms of the entire bike and rider moving along on a speed run, they apply equally, with certain adjustments in the variables, to all moving parts of the motorcycle. For example, within the motor, the resistance to optimal high-performance output (MAX power ) is supplied by the friction at the interface of any moving part to anything else. The upshot being the need to address all these individual moving systems with the same attention to all the individual variables effecting ultimate speed performance as you do for the bike as a whole and to optimize the numerator factors and attenuate the denominator factors since your goal is to achieve ultimate velocity performance by the bike and pilot. This concept readies the table for discussions on enhancing internal engine, drive train, and wheel hub/axle lubrication, heat dissipation, and on and on and on. Good stuff!

[hodakamax]

Thanks Matt, a good discussion for sure. I love this stuff. I'm not overly educated but I am a science geek and I do like to stir things up. I lost a very good friend last week and my memories of him will be drinking a wine or two and discussing the origins of the universe and other mind blowers like quantum physics. Not that we were qualified but interesting questions were asked and discussed. All good for the brain and we had a good time. There's more to life than TV we concurred. All strange but fascinating. It's been fun discussing practical applications such as how fast we can go with what we are limited to and Newton figuring this all out years ago to help us stay on track. Wow.

Max

[taber hodaka]

wind resistance I think is a big factor, and wheel and tire size. I think Jack could have been a professor or maybe was at MIT. ----------------- Clarence

[matt glascock]

My condolences, Max. Hopefully the happy memories of times as you've described will replace the sorrow you currently know. Also, I agree - these are great discussions.

[hodakamax]

Ok, back to reality and hardware developed to cheat the ever increasing wind force. These posture changing footpegs hopefully will allow the rider to be partially prone and reduce the frontal area of the rider. Sounds good in theory, whether I can fold up on this thing remains to be seen. Our recruited rider will have to be light and small but first things first.

Finally, one rear footpeg bracket has been fitted and the shifter linkage has been fabricated and assembled. There's still cosmetic work to do here but I must say that the mechanism really shifts smooth. It's time to mount the other side and figure out this proposed cable rear brake idea. One step at a time.

Maxie