Overspeeding or Unlimited speed controller for Hybrid Bike

[Kempy]

I have a project that I want to bounce a few ideas off those that may know better, essentially its not a road bike but one for fun on a track/ drag strip
I'm starting small and the bike will likely to get quicker as the budget allows.

I currently have a custom frame, 24" wheels with a old leafmotor 1000w hub and and KT 48v Sine wave controller.
The hub has recently been rebuilt by myself with new bearings , thicker phase wires etc.

The Hybrid part of this is that the bike is also assisted by a couple of small Jet Engines, this is my 2nd Jet powered build, but my first Hybrid, and this is where the questions start..

Currently the controller is set to its max limit of 72KPH and it seems capable of reaching that on a slight hill, but it seems to be held to 72KPH that by what seems to be feedback by the controller.

The Turbines will easily power the bike past the electronic limit, but they're also slow off the mark until they start being fed with more air and this is where the Electric hub has it's advantages. (as well as a lot less noise).

At this point, I think I either need to:

A: Go for a higher voltage battery/controller for higher top speed but current limit to the hub, as speed increases past 40/50K's the turbine thrust means the motor will effectively be coasting and drawing very little current
or
B: Have some type of disconnect so the phase wires are isolated at a certain speed, however I'm concerned that he motor then becomes a generator with no load and may arc across relay contacts or produce high voltages that may damage windings with no load
or
C: another option I haven't considered? open to thoughts...

 

[ak136]

If you reach 72km/h and the controller cuts the speed past that you can trick the controller into thinking its running slower by changing your wheel size to a smaller size

So you can trick the controller feedback of the speed

The controller will think its going 72km/h at lets say 20" wheel while in reality you are going 86ish km/h on 24" wheels

 

[ak136]

Also a comment for the B) option

Whats your no load maximum speed using only the controller right now?

As this is a 48v controller you have to be aware of the mosfets absolute maximum voltage limit.
When you are reaching higher and higher speeds (higher then capable with controller only) the back emf will create a higher and higher voltage on the mosfets and at some point if you go over the voltage limit the mosfets will blow

So having a phase disconnect would be a viable option if the type of disconnect would still have a adequate voltage rating in regard to back emf

 

[Kempy]

If you reach 72km/h and the controller cuts the speed past that you can trick the controller into thinking its running slower by changing your wheel size to a smaller size

So you can trick the controller feedback of the speed

The controller will think its going 72km/h at lets say 20" wheel while in reality you are going 86ish km/h on 24" wheels

I just tried that on your recommendation by setting the wheel size to 16" and the wheel was spinning much faster, it didn't get to top speed as it seems it doesn't have enough voltage to get it past 55Kph on the controller without load, but drawing way more current than when it was set for 24" and easlily reaching 72KPH which is a positive sign.

It really does seem like I need to grab a 72v battery/controller and fool it into thinking its running a smaller wheel

 

[E-HP]

C: another option I haven't considered? open to thoughts...

Switch to a geared hub motor.

 

[marty]

couple of small Jet Engines

Pictures?

 

[Kempy]

Pictures?

It's all a pile of bits at the moment, but as the bits come together I'll post some shots.
Heres the new project in front of the original one in a fairly stripped down state.

 

[offGridDownUnder]

by what seems to be feedback by the controller.

Perhaps this is what's called "Back EMF".

You may be able to overcome it with what's termed "Field Weakening" which I think would be better termed "Field Advancing". But read about those and see if you can make that modification with your current set up.

It's still possible that the effect you can achieve is not adequate for your desired top speed. You'll be the first to know.

Is the motor you are using listed in Grin's Motor Simulator, or can you gather the specifications to put it in as a Custom motor? That might tell you some about your situation.

 

[glennb]

You want a faster wind motor, surely.

Cranks as a kick stand, I like that.

Any bends in the track though? Because it's a flexi frame, could get hairy going around corners.

 

[SlowCo]

Nice project. I hope you'll add more photos to this thread when building as I love following this kind of projects. Good luck and enjoy the build.