I am in favor of mounting the motor(s) on the frame, and I think a simple chain drive would be least expensive. This would make the system more modular, and would allow use of various types of motors in standard NEMA frames. A specially wound 5 HP (3.7 kW) low voltage three phase induction motor should be easily obtained (in small production quantities) for about $300 each. They can be V/F overdriven at least 3x to 15 HP each at 180 Hz. Two motors would provide a total of 30 HP and independent rear wheel drive for better traction on ice and snow. Three phase motors can be controlled for constant torque so it would not be hard to compensate for unequal RPM when cornering. PWM controllers are easily designed with a PIC or motor control DSP IC, with IGBTs or MOSFETs in bridge configuration. The main limitation of induction motors is their relatively flat torque curve, so a transmission of some sort would be necessary to achieve good starting and low speed torque, without excessive RPM at high speeds. One idea for a simple transmission would be a chain drive durailleur as used in bicycles, but they are strictly one-way mechanisms which would not be suitable for regen. Some innovative mechanical engineering might be able to overcome that problem. Another idea borrowed from bicycles is the old three speed Sturmey-Archer hub, which should be close to 100% efficient in the middle gear position, which is direct drive. It is a fairly simple planetary gear system that could be scaled up for automotive use. A third possibility is two sets of chains and sprockets, with electrical or mechanical clutches or cogs to engage either high or low gear. Once engaged, efficiency would be quite good, and the mechanism is simple and easily repaired or modified for different ratios if needed. I think any inefficiency in a transmission would be compensated for by lighter weight, better efficiency and lower cost of a smaller motor. A good three phase motor is 90-95% efficient, and I believe motors are generally most efficient when running at close to their nominal rating. If you need a design for a three phase PWM V/F controller, I have some experience in this area. I am planning to build a prototype soon, to test a 3/4 HP motor I rewound. I have two surplus 2 HP motors I could have rewound (for about $500 each), to see if I can get 3x (and possibly 6x) by V/F overdrive techniques. If I can get 8 to 10 HP out of a three phase motor weighing only about 50 LB, this would be a great help with overall weight. It would probably be best to have the final product custom designed by a professional, using special steel optimized for higher frequencies. I think the engineering cost would be in the order of $10,000, but production costs would be about $300-$500 each. A controller would probably have a similar engineering cost, but materials would be no more than about $200 each. Paul E. Schoen www.pstech-inc.com 5/10/06 This technology may be practical for high-tech vehicles without cost constraints, but present day realities will probably rule it out for a low cost vehicle. Some figures to mull over: A 10 Farad, 2.5 V ultracap stores 31 Joules in a 0.68 cubic inch package and costs about $3 (Mouser, 1000 qty). So you have 45 J/ci and 0.1 $/J. A 2000 lb vehicle at 20 MPH is about 30,000 J. To obtain or store this energy using a capacitor would require about $3000 and would fit in a 700 cubic inch package. These are ballpark figures, but they seem about right. Please check my calculations. Cost constraints would indicate maybe a 3000 Joule package for about $300, which would absorb (or supply) 6000 watts for about 1/2 second for brief surges of acceleration and braking in stop and go traffic, without stressing the batteries. The low ESR of capacitors should help efficiency. If the capacitor pack is located close to the motor and controller, it will minimize high currents from the battery pack and possibly allow a smaller gauge cable at the batteries. Paul --- In SmallEfficientVehicles@yahoogroups.com, "Timmi" wrote: > > > Transmissions are 65%-75% efficient... I've heard of the best ones > are close to 80% or so... but how much are you willing to spend on > one? > My initial online research shows variable speed belt drive transmissions with 85-95% efficiency. See http://www.machinedesign.com/BDE/mechanical/bdemech3/bdemech3_3.html for an article from Machine Design. I cannot imagine a transmission with 70% efficiency, much less a simple chain and sprocket drive. How do you measure efficiency? Does an automotive transmission rated 100 HP lose 30 HP in heat? How hot does 22 kW make a gearbox get? What is getting hot when the transmission is 1:1? Please inform us about where your figures on efficiency are coming from. > > I think any inefficiency in a transmission would be compensated > > for by lighter weight, better efficiency and lower cost of a > > smaller motor. > > Wake up: with a transmission we would need a much larger motor to > compensate it Maybe 5% larger. Probably you can use a motor half the size of one without a transmission. > > > > A good three phase motor is 90-95% efficient, and I believe motors > > are generally most efficient when running at close > > to their nominal rating. > > Yes, please tell us which $300 5KW motors out there are 95% > efficient. I really want to know... because that is exactly what we > need. Please provide us with the links where we can see pricing and > a distributor... especially the pricing. > > > If you need a design for a three phase PWM V/F controller, I have > > some experience in this area. I am planning to build a prototype > > soon, to test a 3/4 HP motor I rewound. I have two surplus 2 HP > > motors I could have rewound (for about $500 each), to see if I can > > get 3x (and possibly 6x) by V/F overdrive techniques. If I can get > > 8-10 HP out of a three phase motor weighing only about 50 LB, this > > would be a great help with overall weight. would probably be best > > to have the final product custom designed by a professional, using > > special steel optimized for higher frequencies. I think the > > Special steel optimized for higher frequencies??? Please give me a > metallurgy course on this. > Motors are optimized for 50/60 Hz, so you can use thicker laminations of cheaper steel. Thinner laminations of premium grade steel would reduce eddy current losses at higher frequencies. The basic motor design and construction would be the same. > > engineering cost would be in the order of $10,000, but production > > I think there are lots of electrical companies out there that would > like to hear how you can bring down their engineering costs to a > mere $10K. > I have contacted a custom motor design company, and they said NRE costs would start at about $10,000 to produce a prototype motor. Of course, rigorous testing and optimization would add to that. > > costs would be about $300-$500 each. A controller would probably > > have a similar engineering cost, but materials would be no more > > than about $200 each. > > I think it would be best if we found something off the shelf... > especially if you already have a motor available for only $300, I > would go with that and forego the engineering costs. BTW, tooling > will be astronomical in costs to do casting on a mass scale. I'm not > sure that we want to get into that line of business. > I'm not talking about making a custom motor with non-standard frame and internal components. We could probably obtain a standard rotor and an unwound stator from a motor manufacturer, and it only costs about $500 to rewind a motor. A three phase motor is a very cheap and simple device. There are some special considerations based on number of slots in the rotor and stator, but a motor is really very easy to build. You punch out a stack of laminations and press them together to make the stator, which fits inside a standard housing. The rotor is also a stack of laminations, with a squirrel cage of heavy copper or aluminum wire welded at the ends. Then a shaft is pressed through it, bearings are pressed on the ends, and it is dynamically balanced. A machine winds loops of wire which are set into the slots in the stator, insulation strips are added, and the end bells are bolted on. A good day's work, a couple hundred dollars of materials, and you have a motor. Please don't be so negative and narrow minded about technology. I don't claim to be a professional motor designer, but I've built a working motor and I've done enough research to know what is practical. > If I sound a bit harsh on you, it's because you overstepped the > bounds of your knowledge and expertise, and you didn't even take > time to read much before posting. I don't rattle off to my dentist > on how I think teeth should be repaired - I respect his area of > expertise and don't start telling him how we had this technique with > silly-putty to fill holes in a toy but it isnt hard enough so with a > bit of re-engineering he could maybe do that and change his dental > techniques. Your idea of a bicycle derailleur is absurd, and > displays your total lack of awareness of existing types of > transmissions and mechanicals that would do the job just fine. > > Shorten up your messages by sticking to what you are good at, and > you will be a great help to us in your area of expertise. > You are being overly critical and juvenile in your final remarks. I was throwing out some ideas for consideration and seeds for thought to build upon. Blatant criticism will not get you where you want to be in your project. ===================================================== --- In SmallEfficientVehicles@yahoogroups.com, "Timmi" wrote: > > > problem I see is that you must store 96 W-H of energy in only 15 > > to 30 seconds for a full stop (even faster for an emergency stop, > > but that's where regular brakes are needed). For a 48 VDC battery > > pack, this is 240 to 480 amperes. You could store this energy in a > > capacitor, but it would require like 200 farads at 50 VDC. > > I don't really mind if we lose some energy and regeneration doesn't > recover it... it's not an efficiency gaining thing at this point > (Prototype-1) - it's to compensate for the generator that can't > supply current fast enough and in enough quantity in stop-and-go - > so we can right-size our motors for desired speed but use their peak > power to get better acceleration without increasing engine size - > that is where I'm placing my bets that the biggest efficiency gains > will come from: a smaller engine because we are doing this. > > Would you be able to help us right-size the battery pack > requirements so that we can at least get acceptable recharge > (combination of regen plus what the engine is already doing) for > normal traffic driving? Everything you say is correct, and it is a > problem - I've suspecting that for a long time and many have > confirmed it to me... so there's no argument there - what we need is > help right-sizing this. Goal: minimal battery pack to function in > traffic, a residential neighborhood with lots of stop signs, or on a > downtown street with stop lights. > What might really help is to monitor the battery current over a period of time in an existing EV (with regen) of similar size and weight, driven moderately in a variety of traffic conditions and terrain. This would provide a benchmark for realistic needs as far as maximum motor power and optimal battery requirements. Along with the battery current, we would monitor and record vehicle speed and wind speed. It may be helpful to run a videocam along with this test run to make comments and observe driving conditions. > > It may be possible to use a pneumatic pump to make compressed air, > > which could then be used to drive a generator for regeneration, or > > a direct drive pneumatic motor for propulsion. > > Yech! It makes sense... but I don't like the idea... increase the > complexity of the car (parts and systems)... and the size of the > storage tank required will not be nice-looking... can we try to > avoid doing that, and do our best with motors, regeneration and > batteries? > > Timm > Probably the most effective source of regen will be long downhill runs where minimal braking action will be necessary, and usually following an uphill run that will have depleted the batteries so they will be ready to accept a charge. It may be best to have two banks of batteries, so you can drain one set while charging the other at an optimal rate. For short bursts, you could connect both together, and then resume the optimal charge and discharge cycles. It might be worthwhile to include a fair size capacitor to absorb brief high current charges and discharges, and avoid stress on the batteries. A right-sized battery pack will depend on many factors. A plug-in hybrid that will be used for a 50 mile round trip commute could be designed so that the on-board generator would hardly need to run at all, and could be very small. If the vehicle will also be used for long trips, the generator/motor will need to be sized for continuous average power required, but the battery pack could be smaller. I think overall vehicle weight will not be a major factor if you don't accelerate very much when going uphill. If the drive train is efficient, and rolling friction is low, an uphill climb will be storing potential energy which can be reclaimed by regen on the next downhill. Larger, heavier motors tend to be more efficient, and I would think the absolute energy losses in a large motor running at half capacity may be less than a smaller motor running at maximum, so I would tend to oversize the motor somewhat. Paul --- In SmallEfficientVehicles@yahoogroups.com, "Timmi" wrote: > > You're right about the RPMs - I guess I made a miscalculation. > > For a motor rated at 3000 RPM, I'd vote for a 3:1 reduction. > (now if the motor can fo faster than 3000rpm, our maximum speed is > above our top speed target... that's OK, we can live with that). > > So I guess we can conclude that we can use less powerful motors - > maybe 2HP continuous, instead of 6... much cheaper! > > Now, why would I use a planetary gear reducers and get additional > efficiency losses times 2 (for each side), plus increased costs, > when all I have to do is select a pulley on the motor with 1/3 the > teeth of the pulley on the wheel? They're much cheaper, much > lighter, smooth, over 99% efficient, easier to design for easier > > to install... > V-belt pulleys may not be too good when exposed to critical automotive conditions, although they are used in lawn tractors and such. Timing belt pulleys in higher HP can be expensive. Chain and sprocket drives have proven reliability in motorcycles, and I would vote for that technology. Now, for the torque and horsepower requirements. I think it is necessary for the vehicle to be able to negotiate a minimum 20% grade (such as a driveway), and 10% grades on the highway. For a 2000 lb vehicle, this means a driving force of 200 lb. With no transmission, this equates to 100 ft-lb per wheel, and 19 HP per motor at 60 MPH. You might be able to get 2x to 3x torque at low speeds to get up a short 20% grade. 5 HP motors would only deliver enough torque to get moving on a 5% grade. However, an additional 4:1 reduction would make the 20% grade possible, but the maximum speed would be about 15 MPH. If you could then switch to 1:1, you could cruise on the highway up to 60 MPH, but you might have trouble on any grade more than 2.5%. 2 HP motors would be of no use whatsoever, unless you geared them down by 10:1 and would be satisfied with a 6 MPH top speed on a flat surface and no wind. I am fairly certain that a nominal 5 HP three phase induction motor could be pushed to at least 3x, or 15 HP continuous, and still have 2x to 3x breakdown torque for low speed intermittent operation. A motor like that would be about 150 lb, about 12" dia and 12" long. An off-the shelf unit from Grainger would be about $500, but you could probably get one made in China for about $200. Off-the-shelf motors of this size are 230 or 460 VAC. They could probably be pushed to about 2x by using 120 Hz and double voltage. Any more than that will exceed the insulation voltage rating. In any case, you need about 1.5 x the AC rating for your DC bus, and I don't think I want 720 VDC of batteries in my vehicle. For this reason, the motor will need to be specially wound for a nominal 8-16 VAC, so at 3x it will be 24-36 VAC, using a 36-72 VDC battery pack. This hybrid design requires a gasoline or multifuel engine to be coupled to a generator, which is in turn coupled to batteries, a controller, electric motor, and drive train to the wheels. Each of these components adds some inefficiency. I propose that the fueled engine be coupled with a variable speed mechanical drive to a standard front wheel drive transaxle, capable of powering the car on its own, but minimally sized. As a separate assembly, the rear wheels will be powered by two electric motors and the battery pack. For maximum acceleration and hill climbing, both systems will be in output power mode for maximum total power. Under normal driving, the fuel motor will supply all of the motive power, and a bit extra to charge the batteries using the wheel motors in regen. When going downhill, the fueled motor can be shut off, and the wheel motors will act as brakes to regen the batteries. If the batteries must be recharged while the vehicle is stopped, a small alternator on the engine can be used. This system would (1) eliminate the large generator on the fueled engine, (2) lower the size and weight of the battery pack, (3) provide 4 wheel drive, and (4) provide two separate systems that could be used individually if either system fails. This is probably similar to the Prius Synergy drive, but transmits mechanical power from the fueled engine directly to the road, and from the road back to the electric motors (as generators) to the batteries. Otherwise, it may be good to design the vehicle as a true EV, and have a removable motor/generator module or trailer which could be attached when longer trips are necessary. Just some more ideas to toss around as food for thought. Paul E. Schoen 5/13/06 --- In SmallEfficientVehicles@yahoogroups.com, "Timmi" wrote: > > from: > http://www.geocities.com/CapeCanaveral/lab/8679/evcalc.html > > Uve's Electric Vehicle Calculator The results I got from trying a few calculations confirm what I have been trying to say. If you want a vehicle that will perform adequately in real world situations, you need a motor of at least 20 HP continuous and at least a two speed transmission. You can make concessions on some parameters, but at some point you will have a vehicle that nobody will buy, or that will be unsafe and probably illegal to drive on an interstate highway. This calculator is optimized for vehicle EV conversions, and should be redone for a hybrid system as conceived here. I will try to make an Excel spreadsheet with inputs for real world conditions and target values for maximum low speed grade, maximum high speed grade, base vehicle weight, number of 150 lb passengers, and minimum acceptable speed on maximum high speed grade. From these figures, it should be possible to determine the continuous HP requirements. It will then show maximum intermittent capabilities at 1.4x, 2x, 3x, and 4x HP. It will also show approximate duty cycle at each overload point, based on heating factors which are proportional to the quare of the overload. Thus the duty cycles would be 50%, 25%, 10%, and 6%. Typically, this is based on a total time of about 20 minutes, so you have short time overload capacities of about 10, 5, 2, and 1 minutes. I'll post my file in a day or two when I've had time to make an initial effort. It can be fine tuned and enhanced as desired. This will be an attempt at a reality check, which is clearly needed. Paul E. Schoen 5/14/06 I have posted an Excel file which may serve as a starting point to see what sort of motor, battery pack, and transmission may be required based on various parameters such as weight, transmission ratios, grade climbing capability, acceleration, and top speed. I have not included aerodynamic drag and rolling friction. For a first shot, a 20 HP motor with a single speed transmission will allow 60 MPH up a 5% grade, or 0-60 in 39 seconds on flat ground. An additional 4:1 reduction will allow about 15 MPH up a 20% grade, or 0-15 MPH in about 2.5 seconds. I was surprised to find that a 200 lb battery pack would allow operation at this nominal power for 30 minutes. I may have made a miscalculation somewhere. I assumed a 100 A-H 12 V battery was about 30 pounds. I also made some rough guesses on Weight/HP for the gas engine, drive motors, and generator. You are welcome to fix any errors you may find, and add anything that might be helpful. Paul E. Schoen 5/15/06 It can be very risky to push motors to their peak HP for any more than very short bursts of a few seconds. Nominal ratings are based on optimal efficiency and maximum temperature. Exotic ways to extract heat from the windings might allow a bit more "push", but that will add cost and complexity. Motor efficiency drops sharply when run above nominal ratings, so you will reduce overall MPG. In general, a device like a motor heats up according to the square of the overload current, so a motor at 2x will heat up 4x faster. This means a duty cycle of 25% must be used, with perhaps 5 minutes of overload and 15 minutes of cooling (with no load). A 6x overload would need about a 3% duty cycle, with 30 seconds or less before overheating will occur. These estimates are from my experience with transformers. Motors probably heat up even more quickly. 30 seconds might easily get you out of the driveway, but will just barely make it to the top of a 1/4 mile hill at 30 MPH, or to the top of a parking garage at 5 MPH. Also remember, with no transmission, you will be pushing the motor to its torque limit (which equates to current), even if you must creep up the hill at 5 MPH. A motor turning very slowly (with its cooling fans doing very little cooling), at several times its rated current to produce the required torque, will be heating up more quickly than at its full RPM, and running at perhaps 10% efficiency, which will soon deplete the batteries. A wide range variable speed transmission would be ideal for this application, but a simple low/high dual reducer would help a lot. You need to keep in mind the required torque and speed, which determine the HP. You only need 5 HP to get a 2000 lb vehicle out of a driveway or up a 20% ramp at 5 MPH, but you need a ratio of 28:1 so your motor can turn at 3600 RPM. It's all high school physics, and my Excel spreadsheet shows the reality of the situation. Paul E. Schoen --- In SmallEfficientVehicles@yahoogroups.com, "Timmi" wrote: > > > I am not saying that we "Should" design for one of the same motors > > as a generator, I am just saying that it "Might" end up that way. > > Yeah, OK, cool. I've been referencing 12HP on the rear wheels, only > because those two 6HP-each motors will give us, together, 60HP peak > (and that's geared 1:1), for going up a driveway or hill... but > isn't that a bit much? I have trouble believing it's too little... > as the one who built a three-times-heavier-than-ours EV to drive in > the hills where he lives is saying... > http://tinyurl.com/rmmr4 > > But since we only need 1000rpm wheel speed to do speed limit, I'm > thinking maybe we can gear this other one one 3:1, and it might just > do the trick, what do you think? > http://tinyurl.com/p8etq > > I just don't know anything about the D&D and how good they are for > regenerative braking and variable speed... > 5/16/06 http://www.cloudelectric.com/generic.html?pid=66 "Electric cars are driven by large electric motors usually rated between 3.5 and 28 horsepower. For those accustomed to gas engines, this may not seem like much power, but the rating systems used for gas engines and electric motors are so different that the numbering system is almost meaningless. Gas engines are rated at their peak hp, electric motors are rated at their continuous hp. The peak hp of an electric motor is usually 8 to 10 times its continuous rating." http://home.att.net/~NCSDCA/EVAoSD/emotor.htm The Advanced DC Motor Model 203-06-4001 is a typical, series wound motor that is often used in Electric Vehicles. It can be reasonably characterized with the above two equations. Note that torque is measured in ft-lbs. The motor is about 8 inches in diameter, almost 15 inches long (not including shaft), and weighs about 107 pounds. It is designed for a maximum voltage of 120 volts. With an input of 91 volts and 178 amps, it can continuously deliver 19 horsepower at 5000 rpm. With an input of 86 volts and 322 amps, it can deliver 31.5 horsepower at 3600 rpm for about 5 minutes. Both of these ratings assume standard ambient temperature. Power generation is limited by heat. Maximum speed is about 8000 rpm, but high speed operation results in greatly increased brush wear. Series wound motors are also known as traction motors since they can generate great torque at low speed. But only for a short time. Great torque requires great current which quickly heats the motor. 5/17/06 I added kinetic energy in W-H to my spreadsheet, and found that a 1500 lb vehicle has 30 W-H of energy at 40 MPH. At 10 cents a kWH, each stop costs $0.003; if obtained from gasoline, it would probably cost three times as much. At one stop per mile, and 10,000 miles per year, regen would save about $100 in gas. You probably save a lot more on long downhill runs at low speed, where the batteries can more easily accept the recharging current. Regen would probably make the difference between a 100 MPG and 150 MPG vehicle. At $4/gallon, that would save about $1300 over a 100,000 mile vehicle life. If fluid cooling were added to the motors and the brakes, the heat could be used for winter defrosting and passenger comfort. Paul 5/19/06 My simple spreadsheet calculator came up with similar figures. My percent grades are slightly different than the established standard of vertical rise over horizontal run. I use the percentage compared to a vertical wall, so a 45 degree slope would be 50% for my figures and 100% otherwise. At grades of 20% or less it results in less than 5% error. My spreadsheet is on my website at: www.smart.net/~pstech/VehiclePower.xls. You are welcome to download it and modify it for your own purposes, or to convert to metric units. It is also interesting to note that acceleration on a flat surface will be determined by the torque at the wheels based on a particular available HP and the drivetrain ratio. On my spreadsheet, for instance, a 20% grade is 0.2 G. Elsewhere I have figured the maximum grade for a given HP and ratio, and an overload factor which may be reasonably about 2x to 3x (not 6x), and this also determines the maximum acceleration and the time to maximum speed. Of course, a multispeed transmission will allow a very low HP engine to make it up a very steep hill or out of a ditch (slowly of course), as well as allowing normal highway speeds at near optimal motor RPMs. Electric motor torques and reasonable efficiency are generally in the range of 50% to 150% of design RPM. A four speed transmission with something like 16:1, 8:1, 4:1, and 2:1 ratios would probably be a good choice for a small motor. Transmission efficiency is best at low ratios, so you will get best economy at high speeds, where it is most important. Precise speed and torque control are especially important in low traction conditions of ice and snow. AC induction motors and modern vector based V/F controls are well suited to this, and the motors are rugged and inexpensive. I have just read that 400 Hz 3 phase induction motors can be made as low as 2 lb per HP for 5 minute duty cycles. How about two 20 HP motors each of which you can lift with one hand? BLDC motors may be a bit more efficient in small sizes, but the exotic magnets and position sensors make them more expensive and delicate. Paul As I have posted before, I am a big fan of three phase AC Induction motors because they are rugged, cheap, fairly efficient, and easy to control. There are also some 400 Hz designs that are only about 2 lb per HP. I think the production version of this vehicle should have special low voltage motors that can be powered directly from a 48 to 72 VDC battery pack. However, for an initial prototype, I have an idea where we may be able to use off the shelf motors and controllers. What I propose is a moderate frequency DC to DC converter, that can apply a 400 Hz to 2 kHz modified sine wave to a 15 kVA (20 HP) transformer, rectify the output, and have a 360 VDC or 720 VDC source which can be applied directly to the DC link of modern V/F drives for 240 or 480 VAC. I think a pair of 10 HP 230/460 VAC 1760 RPM motors like Grainger / Dayton 4FN75 ($642, 175 lb, 91.7% eff) could be V/F boosted to 20 HP at 3600 RPM. The 20 HP DC/DC converter could be made from a nominal 1.5 kVA transformer (60 Hz rating), which is about 8" dia x 4" high and weighs about 30 lb. I plan to build such a DC/DC converter and use it with my GE/Fuji V/F drive to control a 2 HP motor I have, and I may install the system on an old lawn tractor to see how it operates under real world conditions. Of course, it does have a transmission, and I think there is no question that some sort of multispeed or variable reduction drive will be necessary for a viable design. Paul 5/22/06 There is often considerable time lag between posting messages and having them appear. Also, some messages have been rejected only because they have been critical and not because they are vulgar, spam, or off-topic. Moderation can hinder active discussion, and if there is a lot of participation, the moderator may become overwhelmed. I suggest that members who have made several posts be allowed to post messages without moderation. If any member grossly abuses the privilege, membership could be revoked or restricted. Paul 5/25/06 There are a number of factors that have been discussed which will affect the final choice of motors. (1) Will it have a transmission, and if so, how many ratios? This is the only way to get reasonable torque to the wheels under all conditions with a small motor. (2) What is the best motor technology, based on cost, weight, ruggedness, efficiency, overload capacity, simplicity of control, regen capability, and power source requirements. My suggestion is two 1800 RPM 10 HP nominal 3 phase AC induction motors that can be pushed to 20 HP each at 3600 RPM, with a switchable 4:1 and 1:1 planetary speed reducer and an additional 2:1 reduction in the final belt or chain drive to each wheel. The specifications for ACIMs are well defined and reasonable, and many controllers are available. I have not found detailed specifications on any of the exotic BLDC motors, especially true duty cycle and efficiency ratings at overload multiples as proposed for the 6 HP units. Series wound traction motors are harder to control and have problems with regen. If you look at the total cost for the motor and the drive, I think the choice will become easier to make. Paul 6/1/06 I tried to post the following response on 5/25/06. It has not appeared after a week. Other messages have appeared since that time. I also expressed my concern about the delays caused by moderation, and got an email response from Timm, but it was not posted. There has not been much meaningful dialog in this group lately. I think this project is going nowhere and is doomed to failure. Good luck - I feel like I'm wasting my time trying to offer my help. Paul