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Mini-generator?

I was sitting here today wondering how could an electric car with a gas generator possibly be useful, then it hit me.  I could add a gas powered generator to an RC car to give it the ability to fill up and run again without the need to charge a battery.  The idea was brilliant so I went out looking for a platform to use.  I decided on a traxxas E-Maxx.  It has a lot of space to build on, and it is a pretty awesome truck.  I decided I would leave the batteries in the equation and they would be sustained by the generator.  Now, what on EARTH DO I USE FOR A GENERATOR that doesn't cost as much as the motor itself.

Picture of Mini-generator?
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frollard5 years ago
I've wanted to build exactly this for a long time;

I feel that you should be able to hook up a nitro motor to a brushless motor -- given a 3-wire WYE configuration of the rectifier diodes you could feed a supercap of appropriate voltage...

From there you would just need a charge level detector to control the throttle of the motor through a servo. It would take some tweaking to figure out how fast the motor can charge the cap, and how fast your electric motor can pull power from said cap.
Long story short, there would always be a delay between when you hit the throttle and when the engine spooled up - likewise, after you stop the engine would stay at high rpm until the cap was charged again. As I commented below, it would be quite efficient, and getting rid of a complex drive shaft system/clutches would help - especially if you kept the motor/generator lighter than a battery.
jj.inc (author)  frollard5 years ago
You are brilliant, after posting this question I thought of using a super cap instead of a battery too.

Maybe this will help

http://www.krohpit.ru/2013/11/hybrid-car-power-station-eng.html

why not just put a gas engine in it.

mulan20155 years ago
r u sure something like this will not over heat?
i have quite a high-end rc truck and after 10minutes driving it gets realy hot so the whole theory for what u trying to do is to keep it going for longer that the battery life so u should be careful to watch the temp aswell, but other wise realy cool idea n looking forward to seing an instructable of it if u make one.
jj.inc (author)  mulan20155 years ago
Castle has some of the most efficient motors out their (coolest, less heat lost). Traxxas also brags about their engines cooling a lot. You can also buy fans to aid in cooling everything on the vehicle, but yes, thanks for that pointer.
bwrussell5 years ago
Why don't you cut out the middle man and just buy a gas powered RC car? What are you gaining by using gas to recharge the battery? It's more expensive than electricity and the processes of of charging the batteries with the gas generator means the car won't be as efficient as if you just hooked the gas engine directly to the wheels.
I'm not sure I agree...

Electric brushless motors are quite efficient, and their torque at low rpm (or even stalled) is unmatched by internal combustion engines...

Using an ICE to drive a generator to drive an electric motor has been shown to be quite efficient -- also known as a 'serial hybrid'. The trick is to balance the amount of power generated to the amount consumed, and size the battery appropriately so that the ICE can always run at peak efficiency.
Right, a like any number of full size Range Extended Electric Vehicles or some trains, but the question is, is it really going to scale this small? Is there an efficient enough ICE in a small enough form factor with a low enough price?

How long will it run on one tank of gas, are you really going to fill up the gas less than you would have to charge the batteries? Is the difference enough to offset the higher cost of fuel?

And again, what are you really gaining? The only possible thing I see is slightly extended run times but a REEV is really a step back from a full electric vehicle and only necessary in full size vehicles because of the distances people travel. In a toy RC car I think it's going to be cost and performance prohibitive (The additional weight and size of the ICE and generator being the main issues with performance). Since this tech already exists it's not a breakthrough it's only real use is "Because I could". If that's jj.inc's purpose then all the power to him, it would be cool, but if he is trying to revolutionize RC car drive trains I think it's probably a miss. Just keep it simple and buy a second battery.
jj.inc (author)  bwrussell5 years ago
My lipo battery cost me about $75, plus a $100 charger. So I found a good engine for about $80 and a good motor/generator can be found for about $90. Now I can fill the engine instantly without having to pay for the extra battery, and I don't have to worry about lipo hazards charging in my house, just a tank full of gas outside. An ICE will also outlast a battery by a long time.
Well not instantly. You still have limits on how fast you can charge the battery no matter how much power you can generate. You still need some sort of charge controller.

What you're describing is basically an RC Prius.
jj.inc (author)  Re-design5 years ago
I had a change of plans, I will be using a super capacitor (charges in seconds, and has more C's than any battery ever will) While not moving the capacitors will quickly be charge, when I punch the throttle the capacitors are drained, as the speed levels out the generator sustains.
Keep us posted.
jj.inc (author)  Re-design5 years ago
Will do, if it works, it will sure get an instructible
frollard jj.inc5 years ago
*if properly maintained :)
True, they're more than 90% efficient AFAIR
+1
Surely it is more efficient and simpler to directly drive it from the engine (in this application at least)?

In theory, almost any DC motor can be used as a generator, but you will need to find one that will put out more power than the truck is using when driven at the same RPM as the output from the engine/gearbox.

If you don't want to charge batteries, either go straight engine powered or see how much fuel cells are now.
jj.inc (author)  The Skinnerz5 years ago
Well, I am not looking for efficiency, I am looking for performance. The Brushless motor in this truck delivers insane torque and power instantly, goes into reverse instantly, brakes itself instantly. Engines are laggy, and slow. They have a limited RPM range, and that results in the choice of acceleration or top speed, not a combo of both. The only downfall to electric is batteries.
Depends how you define efficient -- gearboxes/clutches are brutally inefficient - as are combustion engines 'outside their efficient rpm range' -- the generator allows the engine to run at its peak efficiency rather than constantly changing rpm.