[LargoEV7]

Yes, a mechanically slower mechanism is a way to reduce steering effort, but at the expense of having to spin the steering wheel even more.

The point was to get closer to 2:1, not the other way.

Duncan, you could have 2 splines, one for legal road, and one for events.

Anyway, was just a cheap fix.

 

[Duncan]

Another Autocross

Great fun!
https://www.youtube.com/channel/UC_5FQI_8-DZMjpslskj1oeA

Paul has sent me the updated software - but I haven't updated my controller yet - I intend doing that in the next few weeks before our annual 1/8th mile drag races

 

[Duncan]

Hi Guys
I now have the new software in my controller - I don't know when the next event that hammers it enough for me to check that it's working but it seems to work fine so far

Annual Cobra 1/8th mile Drags on Sunday the 4th March - see if I can beat some more of the supercharged V8's

I have gone slightly backwards in one way - the laptop power supply that I have been using as a DC-DC to keep my 12v battery topped up has died
So I have gone back to simply charging the 12v battery at the same time as the main pack
It's made of eight "16Ah" Headway cells - so that should be plenty of capacity

 

[Duncan]

First update from the Drags

Not good!
The new tyres still spun on take off - so I should have done a warm-up spin

More of a problem at the end of my FIRST run there was a bang - and while I had power if I used more than a tiny bit of throttle there was a horrible noise
One of the guys said that sparks flew out from under my car

It did 8.69 seconds at 83 mph - not a bad time!

I limped home (not very far) and it died completely on my drive

I did win an award - the broken piston "Bad Luck" trophy

So it's take the motor out and see what I have done to the com and brushes!

 

[Yabert]

Oh shit! sorry to know that.
Well this is probably not abnormal. How much Amps and Volt did you push during this race?
Can't wait to see the picture of the torn armature... and the solution you will find if you need to replace this motor.

 

[galderdi]

Dang, Really sorry to hear that. I would also be interested to know the approximate revs when it went bang?

 

[Duncan]

Hi Guys

Motor is out - brushes look chipped but not too bad

I have started adding some pictures - Armature first - it's only letting me do 10 pictures so the next post will be of the brushes

Sequence of events
Took off - spun rear tyres - backed off and they gripped - back to full throttle

Just before the end of the 1/8th there was a "Bang" and power went away
I lifted and then gently pressed the accelerator
I could get a small amount of throttle - then a rattling sort of noise - seemed to be from the front (brush end) of the motor

Rolled to the end of the parking area and turned around

I was second to last car of that group so when Owen in his electric pickup joined use we drove back to the start

I found that I could drive slowly so I drove past the start and waited to be let back onto the main road

There is a steep bank just there - managed to get up it but lots of rattling noise

Then it was about 500 meters to my house - two Stop signs which I treated as Give Way and it managed to roll almost to my drive

Then I got out and pushed it the last little bit

 

[Duncan]

These are the four pairs of brushes - each is photo'd twice - good side and bad side

 

[Duncan]

The Brush holders

One of the springs is obviously bad - and the other spring on that brush pair is also a little weak

None of this looks like enough damage to be causing the "Bang" and the rattle

I could see the bit that is broken off causing the bang - but not the rattle and lack of power

Unless the brushes were simply sticking up and not contacting at all

I'm hoping that Major or one of the other experts comments

As far as revs when it happened are concerned my top speed was 2 mph slower than last year but my time was 0.6 seconds faster - more grip from the tyres which were fractionally larger

225/45/17 rather than 215/45/70

I calculate 4580 rpm - I don't think that was relevant

I believe that my controller is on 100% before than so it would see 340v (full charge) minus the sag - maybe 300v ??

 

[Duncan]

The spring that was "Bad" - it looks as if the post that it attaches to was bent

I measured the com runout - I get a total of 0.05 mm of runout

The more I look at the damage the less persuaded I become that this was the problem but while it's all apart I should make sure that it goes together BETTER than it was

 

[Duncan]

Still looking for advice

Is that damage likely to have cause the symptoms? - possible?

Where can I get "better" brushes?
Where can I get new springs? - or new springs and brush holders

 

[major]

Hi Dunc,

Been hoping to view your photos on larger screen. But this tablet will do. Guess you're lucky not to have big damage in the motor from the sounds of it. I don't see anything obvious which would cause symptoms of shutting down or losing power as you described.

Comm looks a bit raw like high current/arcing has stripped the film. I'd definitely check out the comm for t.i.r. Needs to be 30 microns.

When you lost traction it may have oversped the motor causing a bar to lift. A high bar, or segment could damage/chip those brushes. I think you need the bar-to-bar deviation at 5 microns.

Replacement brushes/springs. Maybe forklift repair shops. Motor rebuilder.

If comm checks out or is serviced, I'd be tempted to install current brushes and do a lengthy break-in.

I found an excellent read on Mersen website.
https://www.mersen.com/publications?s=Commutator&p=63

Regards,

major

 

[Duncan]

Hi Major

Thanks for that - interesting read

I have checked runout and I get 0.05mm - 50 microns - so a bit more than you suggest

I have "fixed" the worst spring - the bar it mounts on was bent

My "plan"

Put it back together out of the car and run it on a 12v battery - just to see if it goes

Assuming that it spins OK - I will try and get it to a forklift motor shop - either that or I will try and "machine" the edges of the com blocks
Just using a stone??
To get shot of the burnt looking area and the to get the chamfer looking like the chamfer in the Mersen doc you referenced

Then re-measure the runout and go around carefully segment by segment looking for steps

See what I find

I have had a good look at the rest of the car - can't see anything else wrong but I can't test the controller until the motor is back in

 

[galderdi]

Hey Duncan,

I am no expert but I wonder if one of the Comm bars may have raised at higher revs, chipped the brushes but then were pushed back down as the revs reduced. In other words I would be gently checking if any of the comm bars move at all.

But I am no expert

Also I wonder if you have overloaded a winding/conductor. Maybe check for resistance across your terminals.

But I am no expert

You can try "Find it parts" for brush springs

Did I mention I am no expert?

 

[Duncan]

Something that I should have done FIRST

I just measured the resistance from the Com segments to the armature shaft - should be infinity or at least very high
Instead I get 0.7 Ohms - NOT GOOD!

I think the armature is stuffed

 

[Duncan]

This armature wire has blown completely through - and it has sprayed copper all across the inside

I should have taken it all apart on Monday - but I was sure that the problem was to do with the com and brushes

Time to look for another motor!
But I will ask about getting this armature re-built

 

[Duncan]

Hi Guys

Motor failure
It looks as if that wire simply cracked or otherwise nearly failed then arced

I wonder if something got into the motor - damaged the insulation on one wire then did some more damage on the one that failed

Looking for another motor!

As far as I can see a 9 inch motor will have about 25% less torque at a given current but will enable me to rev much higher

I can still spin my lovely sticky "Nitto" tyres so giving away 25% of torque may not be too disasterous

I will just have to see what I can find in the way of second hand forklift motors

 

[electro wrks]

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.

 

[Moltenmetal]

Sorry for your loss, Duncan...that's going to be a lot of work for you that I'm sure you weren't expecting.

 

[Duncan]

Hi Molten

I got five years of abuse out of a $100 motor - so I don't think I'm entitled to complain!
although I wish it had held on for another couple of runs - 8.6 seconds is good for an 1/8th miles but I think that when the track stickied up a bit I could have got into the 7's

I have found a forklift breakers in Dunedin with a "pile of motors" - so I'm going there soon to see what I can find

I'm thinking about going down to a 9 inch motor - give away some torque for higher speeds - or maybe not