DIY Electric Car Forums banner
1 - 16 of 16 Posts

·
Registered
Joined
·
38 Posts
Discussion Starter · #1 ·
I'm very new to all this, but I've been involved with engineering all my life and am now in the motor trade. So... I can do most things, but am not smart enough to do the maths. Kind of a "suck it and see" engineer! LOL

I'm looking into building a small EV and I think back to the early 1970's when my father talked about building an electric Morris Mini Van. His idea was the accelerator pedal (I'm in the UK :) ) would be nothing more than an on/off switch. The motor would run constantly, reducing the amount of amps it draws on startup. The speed would be controlled by the gear selected and "in between" speeds found by feathering the clutch.

My updated idea is very similar, but with the accelerator pedal having three or four positions. The positions would be as follows starting from the pedal in the "up" position..

1 - OFF (Obviously)
2 - Re-Gen (if possible...)
3 - Idle (limited rpm for gear changes. Maybe by switching to 12v?)
4 - ON (full power)

So basically.... You stick it in gear, press the pedal and go. To change gear... Press the clutch, release the pedal to the next position, change and reverse the process.

I could also just use my fathers off/on idea and add an extra switch for re-gen...

Has anyone ever tried anything like this? Am I missing something that would make this impossible? I know that with a controller, I would have the feel of driving with complete throttle control, but is that really needed?

Also... I am wondering if keeping the flywheel would be a good idea. Instant torque and maybe smoother gear changes being the reason......
 

·
Registered
Joined
·
511 Posts
You could do it like this. I've seen a post from someone out in the desert somewhere, forget where, that parts were hard to come by and he did something similar. He had it set up where he had three different voltages he could switch between, in addition to off.

The thing is, this is a very unnatural way to drive. Imagine that as soon as you turn on the ignition, the car starts off full throttle, and it never drops its acceleration the whole time you're driving, unless you set it to effectively coast. There's no technical reason why the setup you describe wouldn't work, but it would be very weird - and to your average driver, very hazardous - to drive.

Changing gears would not be so simple either. You'd have to switch to idle (so you don't blow the motor up with it on full throttle as it's disengaged from the drive), push in the clutch, change the gears, let out on the clutch, and then switch it back to ON. It would lurch like crazy and I think be very uncomfortable.

With today's EV tech, you're looking at saving a few hundred dollars by not getting a controller and a potentiometer. To me, it sounds worth it.
 

·
Registered
Joined
·
462 Posts
yep that is right it is very jerky to drive like that, I did that same thing when first building my car. the problem was that even at 12 volts the torque would strip the coupler, once i fixed that problem it drove ok rom 12 volts on up to 48 volts, but it was still scary to drive that way, if you plan to build one please use a controller, you will like it better.
 

·
Registered
Joined
·
1,378 Posts
My car does something similar to what you ask now. My controller is not quite done yet.

I have a shunt motor. If I just switch it to 48 Volts, it spins at 1600 rpm. I slip the clutch to get going, and the shunt motor works hard to get to 1600 rpm -- the acceleration is surprisingly good. You shift to change speeds. If you downshift it regens to try to get back down to 1600 rpm. This is really simple, the car goes about 40 mph, and can hit 35 mph in about 1 block, here's a little video: http://explodingdinosaurs.com/9electric/2009saltflats/MVI_0308burningsalt.MOV . Regen is so intense it can skid the wheels. I have found these big bursts of regen keep the batteries closely balanced.

There are disadvantages to so simple an approach!
  • You work the clutch harder
  • You shift often
  • Big current surge every upshift shift = less range
  • It would be way too jerky to just turn it on in gear -- you need to slip the clutch -- but the shunt motor doesn't overspeed, so that's OK.
I have thought a shunt motor with a continuously variable tranny, like some Hondas had, might be a doable low cost conversion.
... I'm looking into building a small EV and I think back to the early 1970's when my father talked about building an electric Morris Mini Van. His idea was the accelerator pedal (I'm in the UK :) ) would be nothing more than an on/off switch. The motor would run constantly, reducing the amount of amps it draws on startup. The speed would be controlled by the gear selected and "in between" speeds found by feathering the clutch.

My updated idea is very similar, but with the accelerator pedal having three or four positions. The positions would be as follows starting from the pedal in the "up" position..

1 - OFF (Obviously)
2 - Re-Gen (if possible...)
3 - Idle (limited rpm for gear changes. Maybe by switching to 12v?)
4 - ON (full power)

So basically.... You stick it in gear, press the pedal and go. To change gear... Press the clutch, release the pedal to the next position, change and reverse the process.

I could also just use my fathers off/on idea and add an extra switch for re-gen...

Has anyone ever tried anything like this? Am I missing something that would make this impossible? I know that with a controller, I would have the feel of driving with complete throttle control, but is that really needed?

Also... I am wondering if keeping the flywheel would be a good idea. Instant torque and maybe smoother gear changes being the reason......
 

·
Registered
Joined
·
1,760 Posts
You can always test the feeling by driving an ordinary ICE but only allowing yourself to use no or full throttle and nothing in between. It won't be exactly the same since an electric motor is even more brutal with it's excellent torque curve, but when all loose gadgets are scattered to all those hard to reach places (below the seats, between seats and doors, in that sealed space where the parking break stick is mounted and that takes half a day to dismantled etc) and your passengers tell you that you have to stop the car NOW before they throw up, I think that you'll probably rethink your strategy and realise that a smooth throttle does, indeed, has it's advantages.
 

·
Registered
Joined
·
308 Posts
Sure, EVs been around a lot longer than silicon motor controllers. Here's some inspiration for you, http://www.evdl.org/docs/hawkins_ev.pdf

I'd recommend a few more voltage steps than one though unless you like burning rubber or clutch, also add a resistor for starting. The most common method I've seen is to series parallel the batteries for more voltage levels while ensuring even discharge of all cells. As an example a 48/24V pack with a starting resistor will give you 4 steps:

1. 24V with resistor (only used for starting)
2. 24V for low speed cruising,
3. 48V with resistor (for smooth transition from 24 to 48V)
4. 48V for high speed cruising

Coupled with a transmission this setup will give you plenty of control, you can also do field weakening for higher speed, and of course you can add more series parallel steps, but the wiring gets more complicated.

For switching between the modes you can use contactors controlled by micro-switches on the accelerator pedal or build a drum controller as described in the linked PDF above. Just remember, break before make :)
 

·
Registered
Joined
·
601 Posts
Hi ; I ran my 36v hillman in three stages 24v, 36v, 60v using micro switches in the forklift pot box, with the original 36v solenoids and contactors for each stage,; minor jerking on changes which could be eliminated with another contactor. This is a DC series motor.
 

·
Registered
Joined
·
1,760 Posts
But then you're talking about using a controller, just not a silicon based. Unless you get the contactors for free or cheap it'll all add up to quite some bucks.
 

·
Admin: 'one of many'
Joined
·
4,838 Posts
For the cost saving you would be better off, and happier driving, if you bought somethign like the Open Revolt kit from Paul and Sabrina and built your own controller.
That is my plan.

The contactors that you will need are not cheap and the cost of getting even more to work your switched control system will push the cost up to the point where you might as well get a controller kit.

I agree with Qer about the comparison of driving your ICE with full/no throttle.
My tractor will pull a little wheelie if I was to put 12v straight to the motor. With a controller at 48v, I stamped hard on the throttle to try and pull a wheelie and strip a tooth off the diff gear and nearly fell off the back.
It isn't a good way to drive, especially in traffic where other vehicles stubbonly refuse to drive at your motor's set speed. You will be feathering the clutch all the time to not catch them up and the clutch won't last long and the burning smell will put you off.
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #11 ·
Thanks for the input guys! :)

I know that a controller is the way to go or nobody would use them. I was just thinking of alternatives.... But I suppose everyone has done that!

rillip3 - I have no problem driving "difficult" systems. I've already set my wifes car ( a possible donar, Vauxhall Corsa 1000cc 3 cyl) to idle at 3000 rpm and took it for a spin as a test. I found it no problem at all to drive without using the right pedal. Changing gear was all about clutch control. :)

PhaseShift - PLEASE don't worry! I'm an engineer and understand the dangers of everything I see. By "suck it and see", I simply meant that I would have an idea, build it and see if it works. Not dis-regard safety. :D

peggus - Thank you for the link! Inspiration indeed! I can see myslef now... Driving to the local supermarket in a Babcock Electric Roadster! That's a cool car! :D

Anyway... I'm not going to dive into anything silly for a while, but you guys have given me some more to think about. At the moment, I'm looking for an electric fork lift, so if I'm lucky, I'll have motors, controllers and all sorts of goodies to play with. :)
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #13 · (Edited)
On a slightly different subject, but still on topic (sort of)...

Gear changing and clutches...
Has anyone done anything with variomatic / CVT transmission yet? It's a very old (and odd) system, best known in a Daf 33 many years ago. I think Volvo did a version too, but they were not liked because of belt slipping in the wet amongst a few other things. Overall, it was quite reliable. Maybe it could be a good system for EV builds? Someone told me there are newer versions of this system using steel belts instead of glorified fan belts. I even think I remember something about Formula 1 teams developing a very advanced system usin the same principal.

I'll maybe have a look on the web later and see what's out there now.

Just found this very interesting article and was amazed at how many manufacturers have been and are using it!

http://cars.about.com/od/thingsyouneedtoknow/a/CVT.htm

Chris.
 

·
Registered
Joined
·
1,378 Posts
He has done great things for low bucks. One caution is that looks like he taps his pack at different spots for different voltages. That can work for a few seconds of drag racing, but would horribly imbalance your batteries for daily driving. That's why road going voltage switching schemes usually do something like 24V to 48V (parallel to series), so all the batteries get exercised equally.
Have you seen this. Its pretty ingenious if you ask me. Would be interesting to see a more refined version

http://www.poormansev.com/id24.html
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #16 ·
He has done great things for low bucks. One caution is that looks like he taps his pack at different spots for different voltages. That can work for a few seconds of drag racing, but would horribly imbalance your batteries for daily driving. That's why road going voltage switching schemes usually do something like 24V to 48V (parallel to series), so all the batteries get exercised equally.
Yes! Clever man indeed. I like to do things a little more tidy and refined, but it's practical and seems to work well. :)

Even with my limited knowlege on this subject, I spotted the battery thing as a possible issue for a road car, so maybe I'm not as thick as I thought??????? :cool:
 
1 - 16 of 16 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top