| T O P I C R E V I E W |
| Kale |
Posted - May 14 2005 : 2:53:09 PM
A friend of mine was interested in some sort of electric vehicle for medium-short distance trips to and from work. I showed him Aaron's scooter and he was quite impressed. One of his big concerns was range; worrying about getting stuck somewhere when the batteries ran out. We tossed some ideas around, and came up with the idea of making a hybrid scooter. My friend spent some time in NY a while back and saw this guy had modified a pair of rollerblades with a very tiny gas/meth engine with handheld throttle. Kinda crazy, but cute. We were thinking that if you could get a small gas engine that tiny, and a good generator, it shouldn't be hard to have an electric-drive scooter (larger than Aaron's, like a Vespa say) with a gas engine generating electricity and a medium sized lead-acid battery for storage with an electric motor driving the back wheel. Then, if his gas tank runs out he can run on the battery to a gas station and fuel up.
I am looking for general advice on how to go about this. Can any one recommend where to get a good electric motor to provide movement? For that matter, can anyone suggest a good (cheap and lightweight) frame we could strip down? Can you think of any general project 'gotchas' that could stump us? Gearing and control recommendations?
|
| 12 L A T E S T R E P L I E S (Newest First) |
| BEatonNo1 |
Posted - May 19 2005 : 01:58:02 AM
The Texas A&M solar car uses Lithium Polymer cells....They have the best energy density as far as i know, but they are really expensive. the ones we have were manufacured by kokham but bought through someone else and cost us $20 a cell and there are 10 of those in a battery (paralell) and 26 batteries in series....for a grand total of 96v and 60 KAh (i think that number is correct...) The whole system is connected like a T with the battery pack, motor, and array connected to each other. We monitor each batteries voltage and temp, and the entire pack's current. in the case of an over voltage the array and regen are cut off.
I would suggest having an underpowered motor constatnly run and have the batteries connected into the system so that they can absorb any extra power. When the batteries get full then you can disconnect them fromt he circuit untill the motor draws more than you are getting from your generator.
as far as I know Li Poly batteries are alot safer that the Li ions they look like a pack of baseball cards and dont spontainiously combust when punctured. they also will swell up and outgas long before they will explode from overvoltage (although gas is very toxic)
|
| Kale |
Posted - May 18 2005 : 10:54:46 PM
quote:
potentially explosive in overcharging and overdischarging situations. They also respond poorly to mechanical damage
Thanks for the tips. I knew they exploded if overcharged, but I didn't know about the mechanical damage part. That's definitely something to consider for a vehicle power source.
quote:
The electric R/C airplane guys have some pretty good sized LiPo Batteries.
Can you recommend any specific dealers or manufacturers?
|
| Chamkeeper |
Posted - May 18 2005 : 9:39:35 PM
Kale,
The electric R/C airplane guys have some pretty good sized LiPo Batteries. They also have some decent low budget chargers. LiPo batteries are very poorly behaved (read that potentially explosive) in overcharging and overdischarging situations. They also respond poorly to mechanical damage. Lots of info reguarding this on the 'net. Just considerations for a passenger vehicle, I wanted to make sure you were aware.
Cham
|
| Aaron Cake |
Posted - May 18 2005 : 09:55:56 AM
quote:
Ahh... so I can almost treat the batteries as big capacitors in parallel with the generator. If the 'capacitor' voltage is higher then the gen voltage they'll source current. Inverse, they build up charge until the voltage equalizes. Increase the generator output and the batteries will build up to a higher voltage. I understand now. Thanks for clearing that up!
On a basic level, yes. Voltage pushes current, so whatever power source has a higher voltage will be the primary supplier. On a "real" setup, ideally you would provide a DC-DC conveter for both the generator and battery pack, so you could control those voltages and make any combination of gas and electric power you want. But this gets complicated.
quote:
Hmm... you almost have me sold on the idea of an all-electric Lithium battery system. The big question is where do I get high amp-hour Li batteries? Also, would they be horribly expensive?
How would the costs stack up to a hybrid system?
Probably the cost would be the same. Lithium batteries require a battery management system for proper charge and discharge. It needs to look at temperature, AH in and out, and voltage. Charge or discharge them too fast and they burst into flames.  Li-Ion or Li-polymer are also fairly expensive, and it's hard to get big cells.
|
| Kale |
Posted - May 17 2005 : 11:28:46 AM
quote:
Since your generator is outputting a higher voltage then the batterie, it is now powering the traction motor and charging the batteries. By varying generator speed, you can provide just enough power to charge the batteries, or more power to charge and move the scooter.
If you really romp on the throttle, the generator will sag under load and the batteries will start to contribute current automatically.
If the SOC is low, then the generator will be the primary power source until the SOC is brought up equal to the output voltage of the gen. Once that happens, the batteries would start to contribute under high load situations.
The great part is that all this happens automatically. Ohm's law.
Ahh... so I can almost treat the batteries as big capacitors in parallel with the generator. If the 'capacitor' voltage is higher then the gen voltage they'll source current. Inverse, they build up charge until the voltage equalizes. Increase the generator output and the batteries will build up to a higher voltage. I understand now. Thanks for clearing that up!
quote:
but good Lithium batteries have about 10% the energy density of gas. Keeping in mind that 90% of the energy in gas is thrown away in heat, Lithiums and gas are about equal.
Yes, depending on the size of the scooter. With lead, this gets heavy real quickly. With NiMh, NiCad or Lithium, it's much more feasable.
Hmm... you almost have me sold on the idea of an all-electric Lithium battery system. The big question is where do I get high amp-hour Li batteries? Also, would they be horribly expensive?
How would the costs stack up to a hybrid system?
|
| Aaron Cake |
Posted - May 17 2005 : 11:03:29 AM
quote:
What is SOC? I think you mean that the battery voltage indicates the charge state? I know Lead-acid's 'droop' as they discharge. I learned that making your battery charger project.
State Of Charge. Lead acid SOC is easy to tell via voltage.
quote:
Ya lost me. OK, so say that I need extra power. The batteries are currently running the motor and I stomp on the throttle. H-bridge switches, The engine activates. H-bridge switches back. So now the generator is dumping power onto the bus, and the batteries are still connected to the bus. What happens?
Since your generator is outputting a higher voltage then the batterie, it is now powering the traction motor and charging the batteries. By varying generator speed, you can provide just enough power to charge the batteries, or more power to charge and move the scooter.
quote:
How do I get the batteries and the gen to combine their power across the motor?
If you really romp on the throttle, the generator will sag under load and the batteries will start to contribute current automatically.
quote:
If the battery voltage is too low and they are both on the same bus, won't the generator just charge the batteries, or will they both contribute their power to the traction motor?
If the SOC is low, then the generator will be the primary power source until the SOC is brought up equal to the output voltage of the gen. Once that happens, the batteries would start to contribute under high load situations.
The great part is that all this happens automatically. Ohm's law.
quote:
Yeah, 30 MPH is pretty close to my target speed. How long can you hold that speed before you drain your batteries?
Longer then I wanted to on a Razor scooter with 4" wheels and no brakes. That "quick" mode was basically just for short bursts, and would only last about a mile or so with the 48V 4.5AH pack. With a 7Ah 48V pack, I would expect several miles.
quote:
The main reason I'm considering hybrid is that it can maintain a decent speed while still having range. Gas has a much higher energy density than batteries.
That's true for lead batteries, but good Lithium batteries have about 10% the energy density of gas. Keeping in mind that 90% of the energy in gas is thrown away in heat, Lithiums and gas are about equal.
quote:
If I can maintain about 40-50 Km/h and still travel about 30 Km by piling on the batteries then that's definately an option. How feasible is this?
Yes, depending on the size of the scooter. With lean, this gets heavy real quickly. With NiMh, NiCad or Lithium, it's much more feasable.
|
| Kale |
Posted - May 16 2005 : 12:43:22 PM
quote:
All of this can be accomplished by putting the motor/gen in an "H bridge" control. 4 transistors/MOSFETs in an H configuration allow you to run the motor in either direction, and use it as a generator.
I'm willing to bet this is how Toyota does it. This is close to how Honda does it with the Insight, but in the case of the Insight, the motor is 3 phase AC (I have the schematics...don't ask how I got them...  ).
Ah... I see! I'm quite familiar with H-bridges, having built my own MOSFET motor drivers before for some robotics stuff. I just never occurred to me to use the technique in this application. Interesting. So the H-bridge would allow the rear wheel (traction) motor/generator to switch between accepting power from the bus to move the bike, and returning power to the bus while coasting or braking. Very simple, just switch direction of current flow using the bridge. Cool.
quote:
You need a voltage input from the battery to the controller so you know SOC, assuming lead acid batteries. If you want to use something more exotic (NiMh, Li-Ion, etc.) then you need to track AH in and AH out, since those batteries output voltages are not indications of SOC.
What is SOC? I think you mean that the battery voltage indicates the charge state? I know Lead-acid's 'droop' as they discharge. I learned that making your battery charger project.
quote:
It will take some experimenting. Both the motor/gen and the traction motor will be on H bridges, and you will have to come up with an internal "load" value in the microcontroller. You would then set thresholds for min and max battery voltage, whcih you would use to judge whether the gas engine should run or not...
So the H-bridge on the 'generator' motor would allow me to electronically start the motor and then swap the bridge around so it starts dumping power to the bus. Nifty.
quote:
Remember, regen can only recapture some of the energy needed to accellerate the vehicle. It's not a 100% efficient process. So you WILL find yourself either grid charging (yay!) or using the gas engine to recharge the batteries (boo!).
Yup! No infinite power delusions here. We've beaten that to death in other threads a while back. So as you mentioned up above, the microcontroller decides what to do at stoplights:
If speed < minspeed, check bat voltage
If bat voltage < threshold charge batteries
else turn off engine
quote:
It's all programming in the microcontroller. You would connect your motor/gen through the H bridge to the battery pack (36V or 48V is a good point). The traction motor would then connect to the batteries as well. So in a way, you aren't "switching" power at all. You are just using the gas engine to provide extra power when necessary.
Ya lost me. OK, so say that I need extra power. The batteries are currently running the motor and I stomp on the throttle. H-bridge switches, The engine activates. H-bridge switches back. So now the generator is dumping power onto the bus, and the batteries are still connected to the bus. What happens? How do I get the batteries and the gen to combine their power across the motor? If the battery voltage is too low and they are both on the same bus, won't the generator just charge the batteries, or will they both contribute their power to the traction motor?
I guess what I'm trying to say, is how do I make the batteries contribute power to the bus even when the generator is also connected?
quote:
Note that unless this is done right, the system will be LESS efficient then just running a gas engine. And it goes without saying that any hybrid system is less efficient then pure electric.
One thing about my Razor scooter though. When the battery pack is configured for 24/48V, the top speed is well above 30 MPH. Range and sanity suffer, though.
Yeah, 30 MPH is pretty close to my target speed. How long can you hold that speed before you drain your batteries? The main reason I'm considering hybrid is that it can maintain a decent speed while still having range. Gas has a much higher energy density than batteries. If I can maintain about 40-50 Km/h and still travel about 30 Km by piling on the batteries then that's definately an option. How feasible is this?
Edited by - kale on May 16 2005 12:45:04 PM |
| Aaron Cake |
Posted - May 16 2005 : 09:42:13 AM
quote:
Yeah, that's pretty much what I was thinking of actually. Unfortunately power systems are not my area of expertise. Fortunately Microcontrollers ARE. So what I would need to learn is how to get the motor/generator and batteries to work together on the grid. How do I connect them on the same bus without hurting the batteries? How do I control the amount of power that goes to the batteries vs. the wheel drive motor?
All of this can be accomplished by putting the motor/gen in an "H bridge" control. 4 transistors/MOSFETs in an H configuration allow you to run the motor in either direction, and use it as a generator. Examples:
http://www.bobblick.com/techref/projects/hbridge/hbridge.html
http://www.robotroom.com/HBridge.html
http://www.4qdtec.com/bridge.html
http://www.dprg.org/tutorials/1998-04a/
I'm willing to bet this is how Toyota does it. This is close to how Honda does it with the Insight, but in the case of the Insight, the motor is 3 phase AC (I have the schematics...don't ask how I got them... ).
You need a voltage input from the battery to the controller so you know SOC, assuming lead acid batteries. If you want to use something more exotic (NiMh, Li-Ion, etc.) then you need to track AH in and AH out, since those batteries output voltages are not indications of SOC.
quote:
I can get the microcontroller to make voltage and current measurements on the bus, and trigger the gas motor without difficulty, but I really don't know how to set up the power grid to juggle things around.
It will take some experimenting. Both the motor/gen and the traction motor will be on H bridges, and you will have to come up with an internal "load" value in the microcontroller. You would then set thresholds for min and max battery voltage, whcih you would use to judge whether the gas engine should run or not...
quote:
The scooter would be for mostly city driving, so there would be lots of stop lights and stuff to regenerate the batteries.
Remember, regen can only recapture some of the energy needed to accellerate the vehicle. It's not a 100% efficient process. So you WILL find yourself either grid charging (yay!) or using the gas engine to recharge the batteries (boo!).
If you only need to go 20KM or so, then pure electric can easily accomplish this.
at stoplights.
quote:
Now how do I rig up the power system so that I can 'dip' into the batteries when the load is increased? Do I wire the batteries in series with the generator so their voltage adds up? How do I switch from this mode of operation to battery charging when I'm sitting at a stop light?
It's all programming in the microcontroller. You would connect your motor/gen through the H bridge to the battery pack (36V or 48V is a good point). The traction motor would then connect to the batteries as well. So in a way, you aren't "switching" power at all. You are just using the gas engine to provide extra power when necessary.
Note that unless this is done right, the system will be LESS efficient then just running a gas engine. And it goes without saying that any hybrid system is less efficient then pure electric.
One thing about my Razor scooter though. When the battery pack is configured for 24/48V, the top speed is well above 30 MPH. Range and sanity suffer, though.
|
| Kale |
Posted - May 15 2005 : 10:03:34 PM
quote:
I personally love projects like this, and wish you all best.
PS: Wasn't the Segway supposed to fill this gap????
Thanks for the encouragement!
Regarding the Segway; it's too slow, and where do you park it? It's light enough that it is easy to steal. At least a large scooter or motorcycle would be harder to just pick up and walk off with than a Segway.
One of the challenges I'll be facing is that we'll need a decent level of speed. So the drive motor will probably have to be considerably larger than the one on Aaron's electric Razor.
|
| Kale |
Posted - May 15 2005 : 9:59:13 PM
quote:
That said, a hybrid scooter is a cool idea. I have been thinking about this, and have some thoughts. First, I would do it as a series hybrid. The gas engine (chainsaw/trimmer/etc...preferably 4 stroke) would drive a motor/generator. Another electric motor would connect to the rear wheel. Between them would be a battery pack and a controller. Throttle on the gas engine would be controlled via a servo. The user's throttle control would be the input to a microcontroller, which would decide the drive system to use.
For example, at light throttle or when gas engine operation is not wanted (inside, park, etc.) the traction motor would be supplied power via the battery pack, through a controller which gets it's PWM input from the microcontroller.
Yeah, that's pretty much what I was thinking of actually. Unfortunately power systems are not my area of expertise. Fortunately Microcontrollers ARE. So what I would need to learn is how to get the motor/generator and batteries to work together on the grid. How do I connect them on the same bus without hurting the batteries? How do I control the amount of power that goes to the batteries vs. the wheel drive motor? I can get the microcontroller to make voltage and current measurements on the bus, and trigger the gas motor without difficulty, but I really don't know how to set up the power grid to juggle things around.
The scooter would be for mostly city driving, so there would be lots of stop lights and stuff to regenerate the batteries. Given that, I should be able to go with an 'average' capability motor, and dip into the batteries for acceleration, etc, while recharging the batteries while coasting or at stoplights. Now how do I rig up the power system so that I can 'dip' into the batteries when the load is increased? Do I wire the batteries in series with the generator so their voltage adds up? How do I switch from this mode of operation to battery charging when I'm sitting at a stop light?
|
| Aaron Cake |
Posted - May 15 2005 : 09:52:47 AM
The scooter page is actually VERY out of date. Since that page was written, I have switched the horrid fan motor for a proper 36V 350W motor. This motor was bought via eBay and is a very high quality and efficient part. Proper ball bearings, replacable brushes, etc. The battery pack capacity has also been increased to 14AH @ 24V, 28AH @ 12V. With this kind of capacity, I have never discharged the pack, even after 3 hours of (brutal) riding. The scooter will run for far longer then I am willing to ride it. My best guess is perhaps 20-25 KM.
That said, a hybrid scooter is a cool idea. I have been thinking about this, and have some thoughts. First, I would do it as a series hybrid. The gas engine (chainsaw/trimmer/etc...preferably 4 stroke) would drive a motor/generator. Another electric motor would connect to the rear wheel. Between them would be a battery pack and a controller. Throttle on the gas engine would be controlled via a servo. The user's throttle control would be the input to a microcontroller, which would decide the drive system to use.
For example, at light throttle or when gas engine operation is not wanted (inside, park, etc.) the traction motor would be supplied power via the battery pack, through a controller which gets it's PWM input from the microcontroller.
As the battery pack drains, the microcontroller uses the motor/generator to start the gas engine, and then controls throttle via the servo. This recharges the battery pack and powers the vehicle. Needless to say, this motor/generator must be larger then your traction motor to supply the necessary current to keep the battery charged, move the vehicle, and make up for all the inefficiencies.
A battery charger then allows grid connectivity to recharge the pack.
The advantage of this system is that it allows pure electric operation. The disadvantage is it's complexity, and inefficiency of going from gas to electrons to traction. This system is similar to Toyota's hybrids.
In another config, you undersize the gas engine and motor/generator, so that it is incapable of moving the vehicle by itself under high loads. Under normal operation, the gas engine and generator directly power the traction motor. Under high loads, the extra energy comes from the battery pack, which is then recharged when energy demands are lower and during regen.
Another way to do things is how Honda does it with their IMA (Integrated Motor Assist). The gas engine is undersized so that it can only supply enough power for average requirements. The motor then connects directly to the crank of the engine, and then to the flywheel. The engine runs all the time, but the electric motor is responsible for giving the engine the power it needs to accellerate, climb hills, etc. When braking, the motor regenerates power to the battery. At idle, the gas engien stops then is instantly restarted by the motor when you want to move. This config is VERY efficient, and probably the easiest. But you can't run electric only as the gas engine must always be turning to spin the wheels. My Insight works in this way, and works very well. Unfortunately, this system does not lend itself to grid charging.
Both hybrid systems can be set up for "charge depletion", which the batteries are gradually depleted during the trip and must be recharged through external means. In this case, the gas engine is simply a range extender on an EV.
|
| Chamkeeper |
Posted - May 15 2005 : 01:17:13 AM
I have seen those gas milage competitions in the past. Volume of fuel vs. range thing. Many of them used a model aircraft/car/boat engine. They are designed to run on a mix of Nitromethane and alcohol (racing fuel for cars). The hotter the mix the more power, and less engine life. However, they do make Diesel fuel conversions for these motors.
A tiny diesel for uphill runs and standing stops, and a good regen system to charge the batts on downhill runs. Electric to maintain velocity in the flats, charge on downhill runs, diesel for the rest.
The real issue is the RPM operating range of tiny motors. You will need a very efficient gearing system.
I personally love projects like this, and wish you all best.
Cham
PS: Wasn't the Segway supposed to fill this gap????
|
|
|
