Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - The *Ultimate* Aerodynamic Car? Dave Cloud's "Dolphin"

DaveCloud · 07-01-2010, 02:52 PM

I want to clarify the data on my Watt Hours per miles. When I say 130-140 WH/mi that is at a constant rate cruising at 65 mph on the flat. When I said 177 WH/mi over the first 171 mi of my trip, it was an average that included several stops and starts that were as high as 1000 wh/mi for the first mile of a restart. The reason for the high wh/mi on the starts is because the motor is really inefficient taking off from a stop when it is geared for 71 mph on the top end because there is not a transmission (if I had a transmission I could probably drive it in a manor to reduce that number). The original 192-wh/mi figure was an average over the whole trip, including starts and stops and a conversion from amp hours to watt hours that was not accurate, it did not account for large voltage sags towards the end of my run. I have two amp hour meters set on amp hours not watt hours because I do all my battery testing in amp hours, in order to more accurately gauge differences between battery weights. Therefore I am more familiar with amp hours, verse watt-hours.

Another thing I would like to clarify is that my goal was to build a vehicle that can go 200 miles on a single charge with a speed of 60-65 mph for 85% of the miles, for under $3,000. I accomplished this goal. Because of my $3,000 limitation I made a lot of compromises in the chassis design hoping that the aerodynamics of the vehicle would make up for those inefficiencies. Inefficiencies such as front wheel bearings that rumble, back tires that are 10 years old and misshapen, single speed dual series motors (that were $100), no re-gen and inexpensive Curtis controllers.

Other facts about the vehicle:
I had an arcing issue with the right motor a month ago on the 80-mile Lacey trip. So I retimed the motor for that particular direction. Since the motors run in opposite directions I some how over looked that and did not get it timed properly. So I retimed the motor, for some reason one motor pulls a lot more current at low rpm and the other motor pulls more current at high rpm. It could be that the controllers are not identically matched to one another, or that the motors still are not timed properly, or a variety of other things. I do have a trim pot between the two motors to balance them out and make corrections on the two amp hour meters on the fly. The first 80% of the trip I was keeping the amp hours equal from one motor to the next, the last part of the trip I was going by voltage sags in the two packs, the difference in capacity between the two wet led acid battery packs is because some of the strings were more then 10 years old and therefore had different capacities. Out of the 10-72 volt strings, I tried to match all the batteries within the string.

As far as the chassis strength and the lack of noticeable triangulation:
The chassis that was added to the car was .065 x 1.5 in mild steel square tubing. The triangulation on the rear boxes is done with a 3/8 thick Kevlar composite sheeting that makes the frame stronger and lighter then you could possibly imagine.

Regarding the charging inefficiencies, they do exist. But are not my main concerns since I am a car builder, not a charger builder. I do not want to spend my time on the charging inefficiencies when other people are more experienced in those areas. I will leave that up to somebody else.

If anybody has any questions about my car or my 201-mile trip do not hesitate to call me. I live on the west coast, call anytime between 9am- 11pm. I always answer my phone or return a message. It is much easier for me to answer questions or discuss matters over the phone then write them down.
I chose this set up for economical reasons, not because I don’t have the money, I just wanted to stay within my goal. I have 8 in advanced DC motors and better controllers in stock, I just chose not use them in order to stay within that budget.
I hope I haven’t confused you further.

Dave Cloud
425-788-9293

Don't guess when you can know the facts.

07-01-2010, 02:52 PM	#102 (permalink)
DaveCloud Call: 425-788-9293 Join Date: Jul 2010 Location: Woodinville, WA Posts: 1 Thanks: 0 Thanked 15 Times in 1 Post	Answers I want to clarify the data on my Watt Hours per miles. When I say 130-140 WH/mi that is at a constant rate cruising at 65 mph on the flat. When I said 177 WH/mi over the first 171 mi of my trip, it was an average that included several stops and starts that were as high as 1000 wh/mi for the first mile of a restart. The reason for the high wh/mi on the starts is because the motor is really inefficient taking off from a stop when it is geared for 71 mph on the top end because there is not a transmission (if I had a transmission I could probably drive it in a manor to reduce that number). The original 192-wh/mi figure was an average over the whole trip, including starts and stops and a conversion from amp hours to watt hours that was not accurate, it did not account for large voltage sags towards the end of my run. I have two amp hour meters set on amp hours not watt hours because I do all my battery testing in amp hours, in order to more accurately gauge differences between battery weights. Therefore I am more familiar with amp hours, verse watt-hours. Another thing I would like to clarify is that my goal was to build a vehicle that can go 200 miles on a single charge with a speed of 60-65 mph for 85% of the miles, for under $3,000. I accomplished this goal. Because of my $3,000 limitation I made a lot of compromises in the chassis design hoping that the aerodynamics of the vehicle would make up for those inefficiencies. Inefficiencies such as front wheel bearings that rumble, back tires that are 10 years old and misshapen, single speed dual series motors (that were $100), no re-gen and inexpensive Curtis controllers. Other facts about the vehicle: I had an arcing issue with the right motor a month ago on the 80-mile Lacey trip. So I retimed the motor for that particular direction. Since the motors run in opposite directions I some how over looked that and did not get it timed properly. So I retimed the motor, for some reason one motor pulls a lot more current at low rpm and the other motor pulls more current at high rpm. It could be that the controllers are not identically matched to one another, or that the motors still are not timed properly, or a variety of other things. I do have a trim pot between the two motors to balance them out and make corrections on the two amp hour meters on the fly. The first 80% of the trip I was keeping the amp hours equal from one motor to the next, the last part of the trip I was going by voltage sags in the two packs, the difference in capacity between the two wet led acid battery packs is because some of the strings were more then 10 years old and therefore had different capacities. Out of the 10-72 volt strings, I tried to match all the batteries within the string. As far as the chassis strength and the lack of noticeable triangulation: The chassis that was added to the car was .065 x 1.5 in mild steel square tubing. The triangulation on the rear boxes is done with a 3/8 thick Kevlar composite sheeting that makes the frame stronger and lighter then you could possibly imagine. Regarding the charging inefficiencies, they do exist. But are not my main concerns since I am a car builder, not a charger builder. I do not want to spend my time on the charging inefficiencies when other people are more experienced in those areas. I will leave that up to somebody else. If anybody has any questions about my car or my 201-mile trip do not hesitate to call me. I live on the west coast, call anytime between 9am- 11pm. I always answer my phone or return a message. It is much easier for me to answer questions or discuss matters over the phone then write them down. I chose this set up for economical reasons, not because I don’t have the money, I just wanted to stay within my goal. I have 8 in advanced DC motors and better controllers in stock, I just chose not use them in order to stay within that budget. I hope I haven’t confused you further. Dave Cloud 425-788-9293 Don't guess when you can know the facts.