[Jlaye]

Hello, I am in need of some motor help. I do not know much about motors at all, but my team is building a project for school.

The project is regenerative breaking.

I am in need of a motor that I will be able to charge by the rotation of the wheels a unknown distance, storing that charge (energy), most likely in a capacitor, then stop the car, and then discharge that energy back to run the motor to push the car as far as possible.

Does anybody have any ideas on the type of motor that would work best for this type of project? A DC motor that will create a good enough charge to run itself?

The car starts on a ramp with a initial unknown angle in between 20 and 30 degrees. All the car has is the potential energy that will be converted to kinetic.

If any body has a solution, I would be glad to hear it.

Thanks.

[GSMnow]

Since noone else has chimed in, I figure I can give a little shot at this.

You obviously want the most efficient setup you can to get the most energy out under braking and then turn as much of that energy as possible back into forward motion. This is a tough call. DO the rules require you to use the same motor for the generator and motor operation? If so it makes the motor choice very critical.

A brushless motor is going to be far more efficient, but, it requires a controller which will take some energy to operate, even for the braking segment. Can a small battery be used to power the electronics? How much mass are you trying to stopp and then start moving? Without knowing this, I can't even guess on a motor size.

As a general rule, use a very low KV motor, as this will generate the highest voltage as a generator. Gear it so the motor has to turn fairly fast, again this will generate more voltage, and be more efficient. I would have to recomend a sensored system for a couple reasons. First off, you can use a much less complex electronics system so it will take less of your energy to control it all. Next, the sensors will tell you when to switch the FET's for optimum braking power to pump that current into your storage capacitor. And last, it will not waste any power trying to "find" the rotor when you go to start rolling again.

With a low enough KV motor and good diodes, you might be able to have it powered just by the initial roll. Once you have enough power stored, then go to syncronous rectifying with the FET's and store more charge until the vehicle stops. With some creative design, you could use one way clutches so it will have a better gear ratio for drive to cover more distance as the voltage falls. Think of the little wind up toys, you pull it back 6 inches and it winds the spring, but when you let it go, it is under power for 6 feet as the spring un-winds. Same idea. If I was to design something like this, I would start with a fairly small out runner brushless motor but with a very high turn count (low KV) but then you would have to add your own hall sensor system to operate the electronics. Again to save power, just use a few basic CMOS gates for the MOSFET switching. A microcontroller would take too much power and have to boot up to do anything.

Look at Great Planes RimFire motors at Tower Hobbies. They are about as cheap as you can find for a project like this. Also make the car as heavy as the rules allow. More potenial energy will generate more electrical so the fixed losses become a smaller percentage.

Have Fun.

[kufman]

Brushless motors that don't have iron in the core are good for generators since they will not produce much drag when they dont have an electrical load. But... they don't have a lot of starting torque without having a ton of current. If you could post the rules or e-mail them I would be happy to give you some ideas. you will have to put the "@" back into this address

kuf_man78 at yahoo.com

I am thinking that a brushless generator and a brushed drive motor would be the best in terms of simple design. Let us know what the contest parameters are and we can help more.

I do have some basic ideas pending the rules;

-heavy wheels to roll down the ramp. Their stored potential energy will keep the car rolling longer after is off the ramp, but it will be harder to make them roll again using motor power.

-Look into super capacitors for energy storage. They are built on battery technology. they charge quickly and discharge in a controlled fashion.