Power/weight ratios

Have you made or bought a converted vehicle if so this is for you
User avatar
nino500
Posts: 63
Joined: Tue Jul 08, 2008 11:24 pm
Location: Isleworth, Middlesex

Postby nino500 » Thu Aug 28, 2008 9:10 pm

If there were a neat, light 2 speed converterless auto ( needing no seperate clutch )


I'm not sure how you'd operate it (I think they use electric valve/hydraulic servo normally) but have you thought about an overdrive unit?.

Nino.

User avatar
EVguru
Posts: 305
Joined: Fri May 25, 2007 5:17 pm
Location: Luton
Contact:

Postby EVguru » Thu Aug 28, 2008 9:39 pm

Working around parts which are far from suitable is to be avoided, in my experience.


You've just summed up just about every conversion, many of the parts are unsuitable for the job. They do however exist and can be bought for sums of money within the realms of possibility.

I'm struggling to see exactly what it is you want to achieve. Is this a thought excercise, or are you actually proposing to build a vehicle? If you are, then;

How far.

How fast.

How much.

What skills and facilities do you have.

How much time do you have.
Paul

http://www.compton.vispa.com/scirocco/
http://www.morini-mania.co.uk
http://www.compton.vispa.com/the_named

NickJ
Posts: 46
Joined: Thu Jun 26, 2008 12:34 pm
Location: N Wales

Postby NickJ » Thu Aug 28, 2008 9:58 pm

I agree with paul decide on how far, fast etc and most importantly budget! Various solutions for a gearboxless design either use a chain drive diff (as used in bike engined cars) or a vehicle with rear wheel drive (eg BMW316 compact, Mazda MX5) Motor wise if budget allows go for AC because of the wide speed torque range.

If you decide what you want you will find kit to do it there is no "Ideal" solution, look on evalbum http://www.evalbum.com/ to see what others have done.

It is all to easy to get bogged down in "thoughts". For what its worth I haver now (for better or worse) decided on an MX5 conversion (i may or may not keep the box, both have been done) with a 22kw nominal AC motor and Lithium batteries. This gives me a nominal top speed over 70mph standing start on a 1 in 3 ish hill with the stock 4.1:1 diff and a fairly light car. Design based on others ideas, back of envelope sketches and empirical evidence from our berlingo!

It may not be "perfect" or "right" but it will be fun finding out!

MalcolmB
Posts: 423
Joined: Sat Jun 23, 2007 8:07 pm

Postby MalcolmB » Thu Aug 28, 2008 10:12 pm

NickJ wrote:It may not be "perfect" or "right" but it will be fun finding out!

Seconded!

User avatar
Jeremy
Posts: 472
Joined: Thu Jul 31, 2008 6:35 pm
Location: Salisbury

Postby Jeremy » Fri Aug 29, 2008 6:13 am

NickJ wrote:It may not be "perfect" or "right" but it will be fun finding out!


Exactly my thoughts. I f we all just hang around waiting for the perfect vehicle and perfect motor/controller/battery to arrive at a reasonable cost then we'll never move anything forward.

I guess there are two basic groups of people on here, those who want to copy stuff that's been proven to work well, accepting that the resulting compromise may have a performance that is below that which could be obtained, and those that wish to find novel ways to use newer technologies to give increased range, speed etc.

I'm a bit of both, in that the EVs I've built/am building are entirely conventional - I'm still gaining practical experience. The one I'm planning is entirely novel, even down to things like the completely different front suspension design.

I like the idea of the MX5 conversion. The Mazda handles well, has an entirely conventional set of running gear, has a low'ish frontal area and yet is reasonably well endowed with internal space. I think the only downside is weight - it's a heavy car for what it is, even though it's got lightening touches like an alloy bonnet.

Jeremy

hyve
Posts: 60
Joined: Sat Oct 06, 2007 1:35 pm
Location: Chesterfield, Derbys.

Postby hyve » Fri Aug 29, 2008 7:53 am

To answer your query Paul, I'm actually still struggling to get a clear picture of the components we're working with. Setting some sort of target, ie: clutchless-single-speed, at least gives something to measure against. Understanding motors, controllers and even batteries in all their permutations is not something which happens in five minutes for a person who has spent his life with mechanical rather than electrical stuff.

As I've pointed out several times, I'm not a beginner at specials or conversions, so am not prepared to just dive in and see what comes out. I got past that stage over 30 years ago. Nowadays I have to try to do better than my last design.
So at this stage, yes this is just a "thought exercise", as you put it. So far. You may feel this relegates me to the category of another armchair dreamer. I yield to nobody though on the sweat and effort I've put into the 80- odd specials which are the results of my life's output.
Peter Ph

User avatar
EVguru
Posts: 305
Joined: Fri May 25, 2007 5:17 pm
Location: Luton
Contact:

Postby EVguru » Fri Aug 29, 2008 9:49 am

Setting some sort of target, ie: clutchless-single-speed, at least gives something to measure against.


It just seems to me that you're putting the cart before the horse, or rather the transmission before the vehicle.

The targets that would make sense to most potential EV builders are all performance oriented, range, speed etc. These would then be subject to a reality check in terms of cost, facilities, etc.

If you are determined that it's going to be a single ratio design, fine, but you still need to set all the other targets. Then you can work out if the targets are achievable within budget and what components are appropriate.
Paul

http://www.compton.vispa.com/scirocco/
http://www.morini-mania.co.uk
http://www.compton.vispa.com/the_named

hyve
Posts: 60
Joined: Sat Oct 06, 2007 1:35 pm
Location: Chesterfield, Derbys.

targets

Postby hyve » Wed Nov 18, 2009 11:09 am

in the interests of maybe making this discussion useful to others perhaps it's time to try to take it forward again remembering that my original query was as to some sort of rule of thumb for motor power (meaning torque of course) to vehicle all up weight which will allow single speed transmission. To clarify this further for those who may also see this approach as putting the cart before the horse,part of the attraction of using electric motors is to get a vehicle with simpler operating characteristics,ie:two pedal control;as in an electric Go-Kart or Milk-Float.
With motor torque rarely being quoted in specifications but knowing that total output in kw is in fact a function of torque and rpm it did not seem unreasonable to me to ask for a rough ratio of kw to kgs to permit the use of a nice simple single speed conversion,avoiding the retention of a multi- speed transmission and, probably,a clutch as recommended by so many. Having such a ratio to work with then permits the other calculations such as how fast a particular vehicle may go and what sort of battery power will be needed to do that plus what sort of range may be achieved with these batteries. all this stems from the fact that there is not a multitude of motors to choose from in the first place and few of the cars which one might choose to convert offer very attractive drag co-efficients for their all-up weight. It is vital to know whether there may be extra weight carrying capacity for adding to the battery pack to extend the range. I am in fact seeking information which will permit me to make viability estimations before plunging in with any particular combination rather than ask whether such and such a plan will work,which seems to be what the experts would prefer.Sorry if removing the opportunity for you to demonstrate your superior knowledge by dismissing any particular combination hurts the ego,but I prefer to gather the information to allow me to arrive at such conclusions by myself. My apologies if I've been very long-winded in pointing this out or making it clear. for most of the past twelve months health issues have interfered with communications,sorry.
Peter Ph

User avatar
EVguru
Posts: 305
Joined: Fri May 25, 2007 5:17 pm
Location: Luton
Contact:

Postby EVguru » Wed Nov 18, 2009 12:22 pm

my original query was as to some sort of rule of thumb for motor power (meaning torque of course) to vehicle all up weight which will allow single speed transmission.


I'm very sorry, you can't have one.

Cedric can give you an estimate for his motor because he knows all the performance curves, but your whole approach seems to be based around finding a surplus motor and trying to determine if it might do the job.

With motor torque rarely being quoted in specifications but knowing that total output in kw is in fact a function of torque and rpm it did not seem unreasonable to me to ask for a rough ratio of kw to kgs to permit the use of a nice simple single speed conversion


Unfortunately it IS unreasonable, there are just too many factors to take into account. Two motors with the same Kw ratings can have such wildly different characteristics that one will do the job just fine, whilst the other will burn out almost immediately. Maximum safe rpm, maximum safe voltage, the ability to handle overload currents, cooling, thermal mass, etc. are all factors that will affect the suitability of a motor for a particular application.

If you go through the archives of the Electric Vehicle Discussion email list you will find countless stories of burnt out motors, controllers and failed batteries. Many of these failures will have been becuase someone followed a 'rule of thumb' without understanding why that rule did not apply in their particular case.


Let me ask you, 'how many horsepower (Internal combustion engine) do I need for a 1000Kg vehicle?'
Paul

http://www.compton.vispa.com/scirocco/
http://www.morini-mania.co.uk
http://www.compton.vispa.com/the_named

User avatar
qdos
Posts: 2089
Joined: Fri Apr 27, 2007 10:26 pm
Location: Dorset
Contact:

Postby qdos » Thu Nov 19, 2009 8:44 am

Jeremy wrote:Exactly my thoughts. I f we all just hang around waiting for the perfect vehicle and perfect motor/controller/battery to arrive at a reasonable cost then we'll never move anything forward.

I guess there are two basic groups of people on here, those who want to copy stuff that's been proven to work well, accepting that the resulting compromise may have a performance that is below that which could be obtained, and those that wish to find novel ways to use newer technologies to give increased range, speed etc.



Been busy over the summer building some vehicles one of which we're hoping to let people have a look at this weekend at Exeter. It should facilitate a range of motors if the builder wishes to be economic they can be or if they want to do something a bit more zappy they can too. Even an old ICE could go in if they want to keep costs down.

Anyways if anyone wants to have a chat then come see me at Exeter. I'll be with the 300bhp race car but don't worry I can also talk about going slow with 1kW too ;)


Return to “Conversions”

Who is online

Users browsing this forum: No registered users and 15 guests