DIY Electric Car Forums banner

Duncan's Dubious Device

194930 Views 416 Replies 58 Participants Last post by  Duncan
Hi
I thought I should start a build thread now I have started brazing
The plan
Two seater lotus 7 Locost type vehicle
Performance
Appropriate performance for the style – not too slow
And I would like to enter some speed events – sprints, hill-climbs, 1/8th mile drags

Range
I live in the wrong part of the country for electric vehicles, there are only one million people in the whole of South Island and Southland has a low population density even for South Island,
This means that the limited range is more of an issue as you have to drive further to get anywhere, my commute is only 4 Km , I should use my bike!
My car will come into the “toy” category
The nearest “Big City” is Invercargill (50,000 people) so I would like enough range to get to Invercargill and back – 160Km may have to recharge in Invercargill

Budget (New Zealand Dollars)
As a Scot I intend to spend as little as possible
Motor -------------$100
Donor Car----------already owned
Chassis + Bits--------$2000?

Controller Expensive -----$2,500??
Batteries Very Expensive---- 11,000??

I will replace any parts that need to be replaced – but if it’s still good I will clean, paint and re-use

Subaru front and rear suspension – same make front/rear so the wheels fit
Subaru have four wheel drive, the front hubs can be used by removing the driveshafts
The rear has a nice diff and suspension
Common in NZ,
I had an old Subaru Legacy that died so I now have all of the bits

Hitachi 48v 10Kw motor from forklift
motor is 11 inches in diameter and weighs 102Kg

Those are the bits I HAVE,
I intend to buy:
Zilla Controler
48 off Thunder-Sky 160 (or 200) Ah cells

Pieces I have weighed (Kg)
Motor---------------------------102
Rear Sub-frame and diff----------44.5
Rear corners (2)------------------44
Front Sub-frame -----------------20
Front corners (2) ----------------50
Wheels (4)----------------------64
Total----------------------------324


Estimates of weight
Batteries ------------------270 or 290 (from spec sheet)
Zilla-------------------------15
Chassis----------------------60
Rack, -------------------------5
Driveshafts ------------------10
Interior------------------------10
Body ------------------------50

Total-----------------------420--------440

Grand Total ---------------744--------764

Bit disappointing I was hoping for 650Kg!

Suspension
I am a heretic in that I am very suspicious of “roll centres”
There is a method of logic called “Reductio Ad Absurdum”
You take an ASSUMPTION OR RULE to its extremes
If it produces an absurd or silly answer then the ASSUMPTION OR RULE is absurd or silly

The idea of a roll centre (found by extending lines from suspension components) is that the vehicle rotates around that centre and the distance between the height of the centre of mass and the “roll centre determines the roll couple which is then resisted by the roll stiffness.
It is quite easy to produce suspension with “roll centres” from under the ground to above the centre of mass.
Those will according to the “roll centre rule” produce massively different roll couples

Simple physics says that a force is required move the car around the bend (centripetal force)
This force acts at the centre of mass
For a car the force has to re-act through the tire contact patch
This causes a couple (torque)
(The centripetal force times the distance between the ground and the centre of mass)
The roll couple which is then resisted by the roll stiffness

This does not change with the suspension geometry -
If you maintain the same roll stiffness and centre of mass you roll the same

Using the roll centre you get a result that is contrary to the laws of physics -Jim
(A Silly Result)

Throw away the roll centres!

What do we have left to worry about?
The suspension's job is to cope with bumps without rattling my teeth
To keep the tires vertical
Not to move the tires sideways (scrub)

Without active suspension this is not possible so we go to
To keep the tires as vertical as possible
To move the tires sideways (scrub) as little as possible

Avoid Camber change in Roll or Acceleration/braking
Avoid Scrub in Roll or Acceleration/braking

The standard Subaru Legacy probably rolls over 5 degrees when being hooooned

The strut suspension only recovers 1 degree at the front and about 2 degrees at the back
Which means the tyres lean by 4 degrees at the front and 3 degrees at the back.
Not good for keeping the tread square to the road

It is easy to get more correction in roll – just move the strut tops inwards towards each other
(You then need to modify the base of the strut where it bolts onto the upright to achieve the correct wheel camber)
The standard setup has an effective strut angle of 76 degrees at the front and 65 degrees at the rear
If you tilt the struts inwards you get a situation where you lift the front of the car when you steer.
Many years ago I had a mini with a Lancia engine and heavily inclined struts
That handled really well and the front lifting effect was not a problem

Anyway the PLAN is to have all of the heavy things (except me) right down on the floor so I calculate the centre of mass will be between 400 and 500 mm from the ground

I intend using springs with the same rate as the Subaru,
With a lower mass this will make the vehicle sporty without rattling my teeth too much

The combination of a lower centre of mass and a lower weight along with the same roll stiffness will reduce the amount of roll
I calculate a 1g corner would result in less than 2 degrees of roll

With this amount of roll the standard suspension set-up should be fine
If I do decide to move the strut tops it will be because of aesthetics.

I will still have the option of changing all of the rubber bits for aftermarket bushes if necessary

Motor and driveline
The motor I got second hand, it had just been rebuilt when its forklift was scrapped so everything looks new. The brushes were not bedded in so I shaped them using sandpaper.
The motor had a splined output shaft and a brake on the commutator end.
Inside the brake was a female spline adapter with a spigot and four studs.

The original plan was to use a ford gearbox but I calculated
Motor torque
Assume it’s like a Warp 11 then 135 Ft-lb’s is available
Diff ratio 4.1:1
Torque at wheels 135 x 4.1 = 553 Ft-lb’s
Wheel + Tire radius (185/70/14) = 1 ft
Force at tire contact = 553 lbs-force

Using my planned wt
Vehicle wt ,650 kg = 1430 lbs ------------(750 Kg = 1650 lbs)
50% on rear = 715 lbs --------------------(825 lbs)
Tire grip (std road tires) 80%
Tire grip = 80% of 715 lbs is 572 lbs--------(825 lbs = 660 lbs)

It did not seem to be worth the extra complexity of a gearbox,
the extra weight makes it less definitive but by then I had found that the gearbox would have made the drive train too long

The plan then became
Use the Motor driving the diff through a prop-shaft,
The Subaru used a two piece shaft
I laid out the motor and diff and the rear of the Subaru shaft –
RATS too long I will have to get it shortened
The drive-train was too long as I was planning on using the “engine bay” as my main battery box

The female spline adapter from the brake will be used with a simple adapter to match it to the prop-shaft.
The spline adapter will be left free to move along the motor splined shaft
(Like the output from a gearbox)

Attachments

See less See more
2
  • Like
Reactions: 1
361 - 380 of 417 Posts
Do you think TIG welding would also be a bad idea, due to the potential of ripples? Or was that specific to brazing? I really like the idea.
The problem was the heat from the brazing - MIG or TIG should be better
There is also the rivet and glue approach - which I found tempting but chickened out as I was not sure about getting it through our certification process
  • Like
Reactions: 1
Im wondering if anyone here has sucessfully welded to car sheet metal with a arc welder? (cheaper than other types of welders) It seems possible if you turn the welder right down and tac weld back and forth with stops to cool?
Yes I have done a fair amount of that in the past - it requires much more careful preparation than gas welding but it is doable
I know you've increased your tire diameter to decrease motor RPMs, is it worth changing diff gearing? Did the increase in tire diameter noticably decrease your low speed power at all? Seems like you have plenty of it?
I know you've increased your tire diameter to decrease motor RPMs, is it worth changing diff gearing? Did the increase in tire diameter noticably decrease your low speed power at all? Seems like you have plenty of it?
Not really
I went from my 195/60/15 to 225/45/17 Nittos to get more grip - THEN I went to 235/45/17 Nexxens to drop the revs a wee bit but mostly so that I could use the Nittos on the front when on the track

195/60/15 --- 518/km - initial -- RPM at 96 mph (153 kph) - 5436 rpm
225/45/17 ---- 502/km - 3% larger RPM at 96 mph (153 kph) - 5248 rpm
235/45/17 ----- 495/km - 4.6% larger RPM at 96 mph (153 kph) - 5175 rpm

I'm having difficulty getting the Nexxens to grip - the slightly smaller Nittos appear to have more grip - so that is the limit - not the available torque

A taller diff might help - If I see one I will grab it - currently a 4.1:1 Subaru limited slip diff
  • Like
Reactions: 1
Not really
I went from my 195/60/15 to 225/45/17 Nittos to get more grip - THEN I went to 235/45/17 Nexxens to drop the revs a wee bit but mostly so that I could use the Nittos on the front when on the track

195/60/15 --- 518/km - initial -- RPM at 96 mph (153 kph) - 5436 rpm
225/45/17 ---- 502/km - 3% larger RPM at 96 mph (153 kph) - 5248 rpm
235/45/17 ----- 495/km - 4.6% larger RPM at 96 mph (153 kph) - 5175 rpm

I'm having difficulty getting the Nexxens to grip - the slightly smaller Nittos appear to have more grip - so that is the limit - not the available torque

A taller diff might help - If I see one I will grab it - currently a 4.1:1 Subaru limited slip diff
On the 1/4 mile I got to 104 mph (no traction at the start)
195/60/15 --- 518/km - initial -- RPM at 104 mph (168 kph) - 5946 rpm
225/45/17 ---- 502/km - 3% larger RPM at 104 mph (168 kph) - 5762 rpm
235/45/17 ----- 495/km - 4.6% larger RPM at 104 mph (168 kph) - 5682 rpm

No chance of getting there with the 15 inch wheels! - no grip
I intend to try the Nittos at the next meeting

The chief forklift motor Guru (Major) has said that my motor "should" be OK at 6500 rpm !!!
At 6000 rpm with the Nittos I would be doing 175 kps - 109 mph

At 6500 rpm - 189.6 kph - 118.5 mph
See less See more
Went Drag racing on Sunday
Great day out
I joined the local club so they put me in their shoot out - randomly selected lanes and opponents
First run against a turbocharged 5 liter Mustang - I won
Second run against an M3 BMW - I won
Third run against a supercharged and nitro Falcon - I won
Fourth Run - this guy had a bloody parachute bolted to the back of his EVO - I lost!

I only have the times for the last run
1/8th mile - 7.987 - 95.1 mph
1/4 mile - 12.218 - 109.5 mph

The EVO nearly broke into the 8's - 9.01 and 157 mph

109.5 mph is 6045 rpm - I think I need slightly taller tyres
See less See more
Did you note the EVO's time/speed in the eighth?
Did you note the EVO's time/speed in the eighth?
It did 5.967 and 125.4 in the 1/8th

It was going a lot faster than me at the end but when he opened the parachute I was leaning hard on the brakes to stay behind him - then he stopped to remove it and I tootled past him and around the rest of the track
This drag race was set up as part of the Teretonga circuit so after the drag bit you are meant to drive sedately around the rest of the circuit - which of course is what I did!
On Saturday we had our first Autocross of the new year

Gardners Autocross - in a paddock owned by the Gardner family

It was superb - great fun




A couple of autocrosses - video on my Youtube page

Last Sunday we had a triple event - 1/4 mile drags - grass autokhana and tarmac autocross

Tried something new for the drags - 40 kg of sand in the boot

Made a HUGE difference - ended up with an 11.75 !!! - the next fastest guy was 12.54

The grass event was a wee bit bumpy but fun

Then in the Autocross the organizer asked if I would take a passenger - I said yes and took one of the lady firefighters
(took the sand out)
Made a surprising difference - the car felt much better with a passenger - I ended up 4th - I'm normally more like 14th

With that behind me I went to the Good Friday Drags - used the sand again but could not quite get below the 12 seconds - the Autocross club uses a timer that starts when the car breaks the beam - which means that my 0.3 seconds reaction time doe not count

Still had a great time
First run was against a supercharged V8 T bucket - his reaction time was better than mine - we were almost level at the end but he was just in front
Then a nice newish white Falcon - beat him
Then another supercharged V8 T bucket - beat him

My last run was against the BMW M3 that I beat last time - he had got a "chip" and some drag tyres
A great race! - he beat me by about the length of his bonnet!

Last event for this season - My device has been on the road for 9 years so its time for some paint and a bit of a rework

I'm thinking about moving some of the batteries into the boot and trying to lose a bit of weight (the car as well)

I'm 55/45 rear/front at the moment - should I aim for 60/40 ???

Any thoughts?
See less See more
  • Like
Reactions: 1
[\quote]
Tried something new for the drags - 40 kg of sand in the boot

Made a HUGE difference - ended up with an 11.75

I'm thinking about moving some of the batteries into the boot and trying to lose a bit of weight (the car as well)

I'm 55/45 rear/front at the moment - should I aim for 60/40 ???

Any thoughts?
[/QUOTE]
Sandbag and passenger suggests you're traction limited. Ever go rock hard on the tires and did it get worse or go softer and it got better? In my V8 pinto we ended up with 15 psi in the rear M50-15 but should have used bead locks.

Sandbag also trends towards 50/50 but moving batteries means re doing the cables which would be a can of worms. Could add a couple of ohms and reduce motor power significantly. What happens with 2 sand bags or even 3?
See less See more
A couple of autocrosses - video on my Youtube page

Last Sunday we had a triple event - 1/4 mile drags - grass autokhana and tarmac autocross

Tried something new for the drags - 40 kg of sand in the boot

Made a HUGE difference - ended up with an 11.75 !!! - the next fastest guy was 12.54

The grass event was a wee bit bumpy but fun

Then in the Autocross the organizer asked if I would take a passenger - I said yes and took one of the lady firefighters
(took the sand out)
Made a surprising difference - the car felt much better with a passenger - I ended up 4th - I'm normally more like 14th

With that behind me I went to the Good Friday Drags - used the sand again but could not quite get below the 12 seconds - the Autocross club uses a timer that starts when the car breaks the beam - which means that my 0.3 seconds reaction time doe not count

Still had a great time
First run was against a supercharged V8 T bucket - his reaction time was better than mine - we were almost level at the end but he was just in front
Then a nice newish white Falcon - beat him
Then another supercharged V8 T bucket - beat him

My last run was against the BMW M3 that I beat last time - he had got a "chip" and some drag tyres
A great race! - he beat me by about the length of his bonnet!

Last event for this season - My device has been on the road for 9 years so its time for some paint and a bit of a rework

I'm thinking about moving some of the batteries into the boot and trying to lose a bit of weight (the car as well)

I'm 55/45 rear/front at the moment - should I aim for 60/40 ???

Any thoughts?
Ask the firefighter to be your girlfriend, throw her either in the trunk or the passenger seat as race conditions warrant.
[\quote]
Tried something new for the drags - 40 kg of sand in the boot

Made a HUGE difference - ended up with an 11.75

I'm thinking about moving some of the batteries into the boot and trying to lose a bit of weight (the car as well)

I'm 55/45 rear/front at the moment - should I aim for 60/40 ???

Any thoughts?
Sandbag and passenger suggests you're traction limited. Ever go rock hard on the tires and did it get worse or go softer and it got better? In my V8 pinto we ended up with 15 psi in the rear M50-15 but should have used bead locks.

Sandbag also trends towards 50/50 but moving batteries means re doing the cables which would be a can of worms. Could add a couple of ohms and reduce motor power significantly. What happens with 2 sand bags or even 3?
[/QUOTE]
I'm thinking of increasing the voltage at the same time !
Tyre pressures
For the track events I'm using 18 psi - which seems to work
For the drag races I drop down to 9 psi - and I have paint marks of the tyre/rim to check for any movement - OK so far
Ask the firefighter to be your girlfriend, throw her either in the trunk or the passenger seat as race conditions warrant.
Don't think I would get away with that! - I would be in favor but she is (I think) about half my age
That's why most old guys buy Corvettes over here....
  • Like
Reactions: 1
That's why most old guys buy Corvettes over here....
Wife says it is embarrassed response to lack of male endowment. She also says she is sorry for them
Winter is here! - no more events for a few months - so its time for a titivate

I have stripped down to a bare chassis - when I have completed my modifications its going for a sandblast and new coat of paint

Improvements
Stainless steel cycle type mudguards - the front ones to go up and down and steer with the suspension
Stainless steel sides (replace the tatty MDF ones)
Diff - I have been telling everybody it was a 4.1:1 LSD - it wasn't ! it was a 4.44:1 LSD!! - so when I thought I was doing just over 6000 rpm I was doing over 6500rpm
So either a 4.1:1 or a 3.9:1 diff is going in there
Slight modifications to the front suspension geometry - reduced castor
Front and rear suspension optimised about a 5.5 inch ground clearance
Increase the battery from 84S to 96S - with three modules in the rear of the car - part of the drive to change from 45% front 55% rear to 40% front 60% rear
Move the controller - to enable better access to the battery
New Forwards/Reverse contactor
Charger - going back to a Garage based charger - the motorsport guys were nervous about me charging at events so I agreed not to - in which case I don't need to carry the weight
Move the 12 volt battery back to the back of the car
The front is desperate for a respray - and I'm going to modify it a little first - got to keep the Kermit the frog look
New dashboard and instruments
I have another later Hitachi motor - I think its got a longer "barrel" and would give me more torque - I will have to decide if I should change it
Replace the tired aluminium rear panel with stainless steel
Tyre sizes - I'm going to 225/45/17 all round - the 235/45/17 I did have on the back were a bit of a disappointment and that extra cm makes the rear wheel arches more difficult

So this will keep me out of mischief for a while
See less See more
  • Like
Reactions: 3
Stainless is heavy - real men use titanium...
  • Like
Reactions: 1
Stainless is heavy - real men use titanium...
Cheapskates use stainless - or possibly aluminium
Cheapskates use stainless - or possibly aluminium
I have a mentor who, whatever he suggests, I start thinking about a halfassed step down from it as sufficient.

He suggests welding? Bah, JBWeld should hold.
He suggests JBWeld? Ehn, duct tape or superglue.
He suggests steel? Aluminum.
He suggests aluminum? Chunk of wood.
He suggests wood? Cardboard.

I'm usually wrong but only after a while. Always worth a chuckle, and most of what I build is just goofing off for a laugh around the shop anyway.
361 - 380 of 417 Posts
Top