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Duncan's Dubious Device

195229 Views 416 Replies 58 Participants Last post by  Duncan
I thought I should start a build thread now I have started brazing
The plan
Two seater lotus 7 Locost type vehicle
Appropriate performance for the style – not too slow
And I would like to enter some speed events – sprints, hill-climbs, 1/8th mile drags

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)
Rear Sub-frame and diff----------44.5
Rear corners (2)------------------44
Front Sub-frame -----------------20
Front corners (2) ----------------50
Wheels (4)----------------------64

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


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

Bit disappointing I was hoping for 650Kg!

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)


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Google the panisonic number on the relay.

The spec said they would guaranteed open 1 time at 400 amps then fail. THE data charts looked like it would still open at 600 amps, I thought they would fail open like a fuse.
As I recall, the typical failure mode is to weld themselves closed like Duncan's.
Too late now, but I try to give these older, used at higher voltage motors, a good dose of spray-on, good quality insulating paint. Apply at different positions so it runs down the slots, lower windings, and, if possible, apply multiple coats while the arm. is slowly rotating on something like a BBQ rotisserie.

Motor shops can also do a commercial dip, rotate, bake, and re-balance. Sometimes they use a varnish, sometimes an epoxy for the severest duty. One trade-off is that the extra insulation may trap more heat in the windings - something to watch out for.
Coat those windings! Or get the arm. and stator dipped and baked at a motor shop.

Megaohming the parts before and during the clean-up and re-coating process(es) would also be a good idea, since you're using it at such a high voltage.
Dip or laqueur the armature? - I'm inclined to leave it the way that Hitachi left it
Yes, but Hitachi probably dipped it many decades ago. The varnish may have dried out, cracked, or been worn away by now. As well as a insulator, the varnish glues the windings in place to keep them from shifting around and chafing the insulation. That's probably what doomed your old motor.

Check what the motor shops suggest for a high voltage, current, and RPM severe duty usage. Also, check the condition of the fiberglass (usually) tension bands around the exposed windings. The glue holding them on may have dried out and weakened.
Duncan! You're running the motor at 8-10 times the stock voltage. The motor is going to need all the help it can get to survive. At least apply the good part of a rattle can(spray paint can) of a good insulating varnish(paint) designed for motor windings from an industrial supplier. It's cheap insurance for the kind of thrashing you're going to put this motor through.

Since the paint is solvent based, the heavy coatings needed will take some time to dry-several days or more. Also, it can be baked. I've used it a lot. If the armature is rotated slowly mechanically or by hand incrementally every 10 to 20 minutes, initially, I've gotten good coverage and never had an imbalance problem. And, it makes the windings look good, easier to clean, shed dirt, and impress your fellow motor heads!!
Here's a giant rotor out of a hydroelectric dam:

Obviously, it is too big to dip to renew the winding insulation! Witness the paper taped to the floor below the rotor to catch the over-spray from painting the windings. It looks like Schenectady Red winding paint-the traditional paint used.

This is probably the same paint used on a giant stator:

In NZ, no less!
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Good points about the cleaning before painting. I remember one hydro dam generator was cleaned with a walnut shell blast medium before painting. I have successfully used Stoddard (close to mineral spirits, paint thinner) solvent to clean the windings on dozens of motors from small universal motors in power tools to motors larger than yours. I've never seen these mild solvents harm the insulation coatings on motor windings. If you not sure, test the solvent on a sample area. Make sure the solvent is completely dried out before painting.

One large wound-rotor induction motor from a large printing press was so heavily caked with paper dust and grease, it needed to be scrubbed with soap and a water blast. After it was cleaned, it was rinsed with a lot of distilled water and baked dry. After it was dried, and before painting, it megaohmed out as good.

Did you have a chance to talk to a motor shop about their recommendations?
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As far as the paint adhering to the surfaces, the cloth sleeves(if used) around the wires, the insulating paper, and the wood wedges(if used) that lock the windings in the slots all soak up the paint somewhat to increase the insulation around the wires. And, as you say, "glue" the parts together to keep them from shifting around and chafing.

I've also damaged windings . Sometimes, not always, you can carefully pry back the wires(if they're not burned-up) in the damaged area, insert pieces of the insulating paper to re-insulate the wires, and repaint. Motor shops will give or sell you the small amounts of paper as well as the insulating sleeve material, if needed. They also would be a good source for the insulating paint.

You're right. It is a chore to do this. And, it sounds like you can't wait to get back on the road!
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If it was just the left side glowing like a pool of molten lava, it's probably a jammed-up caliper or caliper piston(s).
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