Electric 300sx build!

Quinc

Quinc

Buy a Superjet
Location
California
Built this over the winter with my 8 year old. He took every nut and bolt off the ski and did the fiberglass! So please give him a like and sub on youtube. :)


Max Speed run:


Ski ready to ride weight is 226lbs. Battery weighs 35 pounds! Once I figure out if I want to stay with sprockets or swap to coupler I will shave some weight off or maybe go to aluminum. Also thinking I can cut out the hood liner for a few lbs.

Specs:


Ski 1986 300sx

Skat 16 impeller
Motor sprocket 14T Driveshaft sprocket 10T (Did this so I could adjust rpm/torque with sprockets)

Still trying to Figuring out the rpms Vs Torque for a jetski.. I also have a Skat 15 and PJS 17 impeller to try. In the video I think the top speed was around 15mph.

Cool thing about it is you can adjust 3 separate speed settings so when my 4 year old rides it I can keep the speed around 10mph for him.

If it turns out to be awesome I will probably try the 8000w motor next.
 
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E350

E350

Location
Sacramento Delta
You my friend are asking an intelligent question. You must likely give up all of your worldly possessions and travel a far distance to a mountain on top of which a guru sits and then empty yourself of yourself to study with an empty mind for a number of years with the master to attain such knowledge. Please come back and post up your results.

Any gurus out there?

I wonder if asking about "speed" is actually a step ahead of asking how much volume of water a given pitch impeller pushes per single rotation.

Then calculating how much horsepower (force) it takes to spin an impeller with a given pitch a single rotation.
 
Quinc

Quinc

Buy a Superjet
Location
California
E350 said:
I wonder if asking about "speed" is actually a step ahead of asking how much volume of water a given pitch impeller pushes per single rotation.

Then calculating how much horsepower (force) it takes to spin an impeller with a given pitch a single rotation.
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I think you are onto something here! But that is more math then I want to attempt. I did a ton of googling and talked to Greg at impros, but haven't been able to find any info on how to figure it out. So like most things it comes down to trial and error. :) Maybe @waxhead @wmazz will have some insights. :)
 
S

Storbeck

Location
Minnesota
Seems like your electric motor probably has a power curve and at some rpm it makes the most power, and you'd want to size the impeller so that it spins that rpm just like an IC motor.

seems like... But I don't know anything about electric motors.

If the power curve is super flat I would think running the lowest rpm before power falls off would be the most efficient but running a little higher rpm might be more responsive. Again pure speculation so maybe totally wrong.
 
Quinc

Quinc

Buy a Superjet
Location
California
Storbeck said:
Seems like your electric motor probably has a power curve and at some rpm it makes the most power, and you'd want to size the impeller so that it spins that rpm just like an IC motor.

seems like... But I don't know anything about electric motors.

If the power curve is super flat I would think running the lowest rpm before power falls off would be the most efficient but running a little higher rpm might be more responsive. Again pure speculation so maybe totally wrong.
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Max torque at 0rpms and then it drops off as the rpms go up.

For example: Red is from a much more powerful electric motor and Blue line is a ninja 250 gas engine.
torque.png
 
S

Storbeck

Location
Minnesota
I think you would need to know power, or torque vs rpm (so you can calculate power) to really draw any conclusions. That looks to me suspiciously like it probably is a curve of constant power and likely is a theoretical curve not real world, but again keep in mind I don't know much about electric motors.

In the end..test results are king. Unfortunately I think impeller changes are not a lot of fun with that pump.
 
Quinc

Quinc

Buy a Superjet
Location
California
Storbeck said:
I think you would need to know power, or torque vs rpm (so you can calculate power) to really draw any conclusions. That looks to me suspiciously like it probably is a curve of constant power and likely is a theoretical curve not real world, but again keep in mind I don't know much about electric motors.

In the end..test results are king. Unfortunately I think impeller changes are not a lot of fun with that pump.
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With this unit I can change the power curves and rpms etc with a computer. So how much torque should I sacrifice for rpms or should I keep torque as high as possible and go with higher pitch impeller? Or what is the least amount of rpms and high pitch impeller can I pull and still hit a decent speed. o_O And yes the whole pump has to be removed and it sucks. :)
 
Harbor

Harbor

Location
Stockton
Quinc said:
Thanks man! Now explain to me how torque/rpms and impeller pitch correlate. Like can I spin a 17 degree impeller at 3000rpm and get the same speed as spinning a 15 degree impeller at 5000rpms? o_O
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Welcome!

Thanks for the example, but NO you cannot..
Not sure what speed your looking at getting to, but 30/45 mph is gonna take power and rpm…

Power/Rpm (A) is the major input
Prop pitch (b) is minor
Nozzle bores (c) is a fine tune adjustment..

B & C cannot substitute for A, they can only + or negatively compliment what (A) is is already doing..

If a 17 pitch prop is capable of 42 mph when input (A) is turning the prop 6500, turning it 3000 rpm would result in a large reduction in mph..

The good news is, you already have an idea what speed a given prop is capable of and what Rpm a gas engine would need to turn the drive shaft & prop @ to attain that speed…

So it might help to try and think in terms of what a gas engine would do to your driveshaft & props rpm and try mimicking that with your electric motor…

So at this point I don’t think much can be gained from changing minor (b) and fine (c)

We need an increase in power and rpm to your driveshaft.
 
Harbor

Harbor

Location
Stockton
Quinc said:
Take a listen to the motor and see why I added a chain guard.
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What was that flying off, sparks or metal or both or ?

Also that chain Guard, does it go all the way around the chain? Was thinking if theirs a failure it could slice the hull and sink it
 
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Quinc

Quinc

Buy a Superjet
Location
California
Harbor said:
What was that flying off, sparks or metal or both or ?

Also that chain Guard, does it go all the way around the chain? Was thinking if theirs a failure it could slice the hull and sink it
Click to expand...
Flying off was the lube I just sprayed on there. Probably order an o-ring chain to see if it helps quiet her down too. Guard on top is bent over to protect controller and hood/rider. And I have some alumn plate glued under the bottom sprocket so she wont go through the bottom.
 
Quinc

Quinc

Buy a Superjet
Location
California
Storbeck said:
Why not use a simple coupler?
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I will probably end up there. when I bought the motor the website said max rpm was 2800-4400. I ran sprockets so I could overdrive it to 6000+ rpms. but after playing with the motor settings I have been able to hit 7k+ on the bench. Not sure what it will do with a load yet.

14T motor sprocket and 10T drive line sprocket.

Only calculator I have been able to find that does overdrive.
 
Quinc

Quinc

Buy a Superjet
Location
California
can of graphite. Hopefully reduce friction with the chain and reduce some heat and noise.

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