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[EVDL] Design challenge: Low speed + traction control

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I am trying to design an battery-electric drive for a railroad "track
speeder" (the large Fairmont A4/A5 gang car, if you follow speeders).

I'm trying to figure out the right motor/controller package for it.

At first glance it seems like it calls for a small motor and the
simplest of Curtis controllers. Except for one thing: Traction
control would be so stupendously useful that I'd like an opinion on AC
drive.

The drivetrain layout is same as a rear-drive car.
http://picasaweb.google.com/WoodingsCBI/A5CRebuild#5321700282597265458
Reverse is integrated into the rear axle, so we don't need to design it - yay!

It was built with a 35hp engine, for 60 mph, but we only need a top
speed of 25.

The machine weighs 2000 pounds. Adhesion is very limited due to being
steel on steel. Fortunately so is rolling resistance. The machine is
intended to drag trailers loaded with tens of thousands of pounds of
material out to work sites. That means it has to pull hard at low
speeds for long periods or continuously while climbing a steep hill.
That'll require sizing the motor differently.

Wheelslip is a nightmare, so traction control is a BIG win.

In long trains of trailers, we put a speeder on each end, so we're
always pulling. That means half the time, a speeder is "dead in tow".
My crews aren't smart enough to take them the trailing car out of
gear. Therefore, resilience to back EMF is essential. I'm OK with
having a power contactor on the motor side.

Would it be worth simplifying the car by using direct drive?

What do you think? Is there an affordable AC drive that would attack
the wheelslip problem? Traction control on a speeder would be simply
amazing.

Robert

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1 - 18 of 18 Posts

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Discussion Starter · #2 ·
So it would not be a problem to carry a *heavy* pack of floodeds....
BTW, traction control is not a function of AC or DC drive,
it often is integrated with a car's ABS system as it needs the
same sensors to detect wheel slip from braking or acceleration.
Since you have a single driven axle here (and hopefully a limited
slip diff, otherwise the *first* wheel to slip will remove *all*
of the traction) you would need to compare wheel speed on the
unpower with the powered wheels and automatically throttle back
if there is a significant difference.
If it is not simple to get a limited slip diff, then you might
consider using two motors, each driving one wheel and thereby
maintaining maximum traction. The traction control can then
even be doubled up, each powered wheel should maintain approx
the same speed as the unpowered wheels (slight variation in a
curve must be allowed).
You may want to look into ripping a set of ABS sensors from a
car that has ABS and experiment with putting the assembly on
the speeder's wheels. I have seen people experiment with some
logic to detect improper tire inflation, which can be seen
from getting slightly different circumference and thus a faster
pulse from the wheel that has low pressure.
http://autos.groups.yahoo.com/group/Prius_Technical_Stuff/message/16003
This means that you could take the ABS sensors and use some
logic (or SW) to detect wheel slip like the ABS computer does.

Note that an easy way to double the traction is to convert the
speeder to have two powered axles. This does not change the
amount of batteries, but it may require double the number of
motors to allow independent traction front and rear.

I do not understand why you'd need two speeders, unless the
cars and speeder are not hooked to each other, as each speeder
should be able to push equally well as pull. Many trains have
a loc always on the same side and will push or pull, depending
on which direction it goes.

Regards,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.com
Skype: cor_van_de_water IM: [email protected]
Tel: +1 408 383 7626 VoIP: +31 20 3987567 FWD# 25925
Tel: +91 (040)23117400 x203 XoIP: +31877841130

-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Robert MacDowell
Sent: Tuesday, August 31, 2010 1:11 PM
To: Electric Vehicle Discussion List
Subject: [EVDL] Design challenge: Low speed + traction control

I am trying to design an battery-electric drive for a railroad "track
speeder" (the large Fairmont A4/A5 gang car, if you follow speeders).

I'm trying to figure out the right motor/controller package for it.

At first glance it seems like it calls for a small motor and the
simplest of Curtis controllers. Except for one thing: Traction control
would be so stupendously useful that I'd like an opinion on AC drive.

The drivetrain layout is same as a rear-drive car.
http://picasaweb.google.com/WoodingsCBI/A5CRebuild#5321700282597265458
Reverse is integrated into the rear axle, so we don't need to design it
- yay!

It was built with a 35hp engine, for 60 mph, but we only need a top
speed of 25.

The machine weighs 2000 pounds. Adhesion is very limited due to being
steel on steel. Fortunately so is rolling resistance. The machine is
intended to drag trailers loaded with tens of thousands of pounds of
material out to work sites. That means it has to pull hard at low
speeds for long periods or continuously while climbing a steep hill.
That'll require sizing the motor differently.

Wheelslip is a nightmare, so traction control is a BIG win.

In long trains of trailers, we put a speeder on each end, so we're
always pulling. That means half the time, a speeder is "dead in tow".
My crews aren't smart enough to take them the trailing car out of
gear. Therefore, resilience to back EMF is essential. I'm OK with
having a power contactor on the motor side.

Would it be worth simplifying the car by using direct drive?

What do you think? Is there an affordable AC drive that would attack
the wheelslip problem? Traction control on a speeder would be simply
amazing.

Robert

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Discussion Starter · #3 ·
Do have you have a differential? Unless I'm mistaken, trains don't have
differentials, so it's slip of BOTH wheels that you are concerned about, not
one? Right?

Z

Lee Hart <[email protected]> wrote:

> On 8/31/2010 2:41 AM, Robert MacDowell wrote:
> > I am trying to design an battery-electric drive for a railroad "track
> > speeder" (the large Fairmont A4/A5 gang car, if you follow speeders).
> > I'm trying to figure out the right motor/controller package for it.
> >
> > At first glance it seems like it calls for a small motor and the
> > simplest of Curtis controllers. Except for one thing: Traction
> > control would be so stupendously useful that I'd like an opinion on AC
> > drive.
>
> A series motor would be ideal for this sort of application. Huge amounts
> of starting torque are available; as much as the traction allows.
>
> I would also think that all wheel drive would be desirable, so you could
> put all the vehicle's weight to work. Maybe use two axles from a couple
> fork lifts, motors and all.
>
> Traction control is just a feedback loop that senses wheelspin, and
> adjusts the throttle accordingly. It isn't an AC vs. DC thing. You can
> have it (or add it) to any controller.
>
> --
> Lee A. Hart | Ring the bells that still can ring
> 814 8th Ave N | Forget the perfect offering
> Sartell MN 56377 | There is a crack in everything
> leeahart earthlink.net | That's how the light gets in -- Leonard Cohen
>
> _______________________________________________
> | REPLYING: address your message to [email protected] only.
> | Multiple-address or CCed messages may be rejected.
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Discussion Starter · #4 ·
Hi Bob; Thsnks for sharing the RR pix! The RR is really where my heart lies.
Cars are a necessery evil! I ALWAY alwaranted to build an EV speeder. A
LIGHT one. aluminam frame, light wheels, etc? DOES it med to weigh over 1200
lbs for prealeasure riding??IF you running , say? Golf olfd badderies I
think you would hsve plenty ecight for trsction?? Controlling wheeslip would
be a seat of the pants thing?Sd it eas/ IS in GG-1's and HPP8's. You aren't
pullingg TONS of MWO stuff?The silent clickiclay ride would be pleasure! I
was thinking a contacter or ALTRAX controller? The NOCOARA Group are kinda
picky what they will let you run, though?They are the ORG. that sanctions RR
trips. You don't kont pop one of these rigs on your local RR's!!THEY set up
trips! I can't spell with a shit on here @#$%^!!!Stroke condition. MABE i'm
getting better??ok? Sigh.?? Loosing your MIND is the worst thing in getting
older!!!

keeping in training!

sea, ya

Bob
----- Original Message -----
From: "Robert MacDowell" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Tuesday, August 31, 2010 3:41 AM
Subject: [EVDL] Design challenge: Low speed + traction control


>I am trying to design an battery-electric drive for a railroad "track
> speeder" (the large Fairmont A4/A5 gang car, if you follow speeders).
>
> I'm trying to figure out the right motor/controller package for it.
>
> At first glance it seems like it calls for a small motor and the
> simplest of Curtis controllers. Except for one thing: Traction
> control would be so stupendously useful that I'd like an opinion on AC
> drive.
>
> The drivetrain layout is same as a rear-drive car.
> http://picasaweb.google.com/WoodingsCBI/A5CRebuild#5321700282597265458
> Reverse is integrated into the rear axle, so we don't need to design it -
> yay!
>
> It was built with a 35hp engine, for 60 mph, but we only need a top
> speed of 25.
>
> The machine weighs 2000 pounds. Adhesion is very limited due to being
> steel on steel. Fortunately so is rolling resistance. The machine is
> intended to drag trailers loaded with tens of thousands of pounds of
> material out to work sites. That means it has to pull hard at low
> speeds for long periods or continuously while climbing a steep hill.
> That'll require sizing the motor differently.
>
> Wheelslip is a nightmare, so traction control is a BIG win.
>
> In long trains of trailers, we put a speeder on each end, so we're
> always pulling. That means half the time, a speeder is "dead in tow".
> My crews aren't smart enough to take them the trailing car out of
> gear. Therefore, resilience to back EMF is essential. I'm OK with
> having a power contactor on the motor side.
>
> Would it be worth simplifying the car by using direct drive?
>
> What do you think? Is there an affordable AC drive that would attack
> the wheelslip problem? Traction control on a speeder would be simply
> amazing.
>
> Robert
>
> _______________________________________________
> | REPLYING: address your message to [email protected] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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> | OPTIONS: http://lists.sjsu.edu/mailman/listinfo/ev

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Discussion Starter · #5 ·
----- Original Message -----
From: "Zeke Yewdall" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Tuesday, August 31, 2010 11:30 AM
Subject: Re: [EVDL] Design challenge: Low speed + traction control


> Do have you have a differential? Unless I'm mistaken, trains don't have
> differentials, so it's slip of BOTH wheels that you are concerned about,
> not
> one? Right?
> DIGHT! RR's DON'T use diffys! WE sepend on wheel slippage to burn
> turns!. I would think it would be gardder to spin your wheels on a solid
> sxle setup up?
Bob, in training.
> Z
>
>
Lee Hart <[email protected]> wrote:
>
>> On 8/31/2010 2:41 AM, Robert MacDowell wrote:
>> > I am trying to design an battery-electric drive for a railroad "track
>> > speeder" (the large Fairmont A4/A5 gang car, if you follow speeders).
>> > I'm trying to figure out the right motor/controller package for it.
>> >
>> > At first glance it seems like it calls for a small motor and the
>> > simplest of Curtis controllers. Except for one thing: Traction
>> > control would be so stupendously useful that I'd like an opinion on AC
>> > drive.
>>
>> A series motor would be ideal for this sort of application. Huge amounts
>> of starting torque are available; as much as the traction allows.
>>
>> I would also think that all wheel drive would be desirable, so you could
>> put all the vehicle's weight to work. Maybe use two axles from a couple
>> fork lifts, motors and all.
>>
>> Traction control is just a feedback loop that senses wheelspin, and
>> adjusts the throttle accordingly. It isn't an AC vs. DC thing. You can
>> have it (or add it) to any controller.
>>
>> --
>> Lee A. Hart | Ring the bells that still can ring
>> 814 8th Ave N | Forget the perfect offering
>> Sartell MN 56377 | There is a crack in everything
>> leeahart earthlink.net | That's how the light gets in -- Leonard Cohen
>>
>> _______________________________________________
>> | REPLYING: address your message to [email protected] only.
>> | Multiple-address or CCed messages may be rejected.
>> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
>> | OTHER HELP: http://evdl.org/help/
>> | OPTIONS: http://lists.sjsu.edu/mailman/listinfo/ev
>>
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Discussion Starter · #6 ·
Here's an idea...

As a kid, I had electric trains. My first EVs. Isn't it interesting that
all model trains and slot cars are electric? Gets 'em started on EVs
early) :)

One of my locomotives had magnetized axles. It made it stick to the
track much better, providing more traction than weight alone could provide.

Could you do this in your rail car? It wouldn't be hard to put a big
electromagnet on the axles that you switch on when you need more
traction. It's not hard to generate 1000 lbs of force with an electromagnet.

--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Discussion Starter · #7 ·
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Discussion Starter · #8 ·
Lee Hart <[email protected]> wrote:

> Could you do this in your rail car? It wouldn't be hard to put a big
> electromagnet on the axles that you switch on when you need more
> traction. It's not hard to generate 1000 lbs of force with an electromagnet.

It sounds a bit like the plot of "The Philadelphia Experiment" ;)

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Discussion Starter · #9 ·
What about using a motor with a more constant speed characteristic -- like a
shunt or PM, instead of a series motor -- then you would be setting the rpm
level more, instead of the power, and it wouldn't slip like a series motor
would. But.... could you get enough torque from that?

Z

Evan Tuer <[email protected]> wrote:

> On Tue, Aug 31, 2010 at 4:03 PM, Lee Hart <[email protected]> wrote:
> > On 8/31/2010 2:41 AM, Robert MacDowell wrote:
> >> I am trying to design an battery-electric drive for a railroad "track
> >> speeder" (the large Fairmont A4/A5 gang car, if you follow speeders).
> >> I'm trying to figure out the right motor/controller package for it.
> >>
> >> At first glance it seems like it calls for a small motor and the
> >> simplest of Curtis controllers. Except for one thing: Traction
> >> control would be so stupendously useful that I'd like an opinion on AC
> >> drive.
> >
> > A series motor would be ideal for this sort of application. Huge amounts
> > of starting torque are available; as much as the traction allows.
>
> The advantage that an AC drive might have is torque control.
>
> So, the driver can easily avoid slippage just by opening the go lever
> to a known point, and the train will accelerate at a constant rate
> until limited by some other factor.
>
> Much more difficult with a forklift DC controller where the smallest
> throttle opening can suddenly result in maximum motor current and
> torque, and the driver has to be part of the feedback loop if you want
> to limit the torque.
>
> Traction control (sensing the speed of a non-driven axle and comparing
> it to the driven one) might solve this problem for the DC drive of
> course, but the devil is in the detail, implementing that.
>
> Also with a cart where all 4 wheels are driven, you'd need to have an
> extra idler wheel somewhere to sense the actual track speed.
>
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Discussion Starter · #10 ·
> > with a cart where all 4 wheels are driven, you'd need to have an
> > extra idler wheel somewhere to sense the actual track speed.
>
> Yes, it would be more difficult. Perhaps it could be done by comparing
> front and rear axle speeds, and backing off the current on whichever one
> tries to turn faster (i.e. starts to slip first).
>
> I think that's how most cars with traction control do it -- by comparing
the four wheels' speed
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Discussion Starter · #11 ·
Of course! We ALL hsd Laonel trains in our deformative years? saled as
"Magnatraction?" Modern lliatraill stuff lite this for emergerency
stopping.
----- Original Message -----
From: "Evan Tuer" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Tuesday, August 31, 2010 12:25 PM
Subject: Re: [EVDL] Design challenge: Low speed + traction control


>
Lee Hart <[email protected]> wrote:
>
>> Could you do this in your rail car? It wouldn't be hard to put a big
>> electromagnet on the axles that you switch on when you need more
>> traction. It's not hard to generate 1000 lbs of force with an
>> electromagnet.Made shipddidapearapaer!
>
> It sounds a bit like the plot of "The Philadelphia Experiment" ;)Worked
> greast as a time cmine!chane!Great flick! Off course the Navy denighed it
> story line!
>
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Discussion Starter · #12 ·
Cor van de Water <[email protected]> wrote:
> So it would not be a problem to carry a *heavy* pack of floodeds....

Not a problem at all :)

> BTW, traction control is not a function of AC or DC drive,
> it often is integrated with a car's ABS system as it needs the
> same sensors to detect wheel slip from braking or acceleration.
> Since you have a single driven axle here (and hopefully a limited
> slip diff, otherwise the *first* wheel to slip will remove *all*
> of the traction) you would need to compare wheel speed on the
> unpower with the powered wheels and automatically throttle back
> if there is a significant difference.
> If it is not simple to get a limited slip diff, then you might
> consider using two motors, each driving one wheel and thereby
> maintaining maximum traction. The traction control can then
> even be doubled up, each powered wheel should maintain approx
> the same speed as the unpowered wheels (slight variation in a
> curve must be allowed).

That rear axle "pig" that was in the pictures -- does not contain a
differential. That's a solid axle going right through it. What it
contains is two "ring gears" on either side of the pinion. Reverse is
accomplished by engaging one ring gear or the other.

Of course the axle "skiffs" around curves. That's not a big deal
given the gentle curves on the railroad and the poor adhesion (35%
with a tailwind).

Apropos to nothing, the front axle is unpowered on most speeders and
has a rudimentary differential. This is so you can pick up the
lighter rear end and pivot the car on the front axle. The car has
"lift handles" for that purpose. On an A-type gang car, it takes 4
men, but the car is balanced to put the weight over the front axle for
this reason (and better tracking).

> You may want to look into ripping a set of ABS sensors from a
> car that has ABS and experiment with putting the assembly on
> the speeder's wheels. I have seen people experiment with some
> logic to detect improper tire inflation, which can be seen
> from getting slightly different circumference and thus a faster
> pulse from the wheel that has low pressure.
> http://autos.groups.yahoo.com/group/Prius_Technical_Stuff/message/16003
> This means that you could take the ABS sensors and use some
> logic (or SW) to detect wheel slip like the ABS computer does.

That would be cool... but I fear, also outside the scope of this
project. It would work as an after-project addon, though.

> Note that an easy way to double the traction is to convert the
> speeder to have two powered axles. This does not change the
> amount of batteries, but it may require double the number of
> motors to allow independent traction front and rear.

That's an interesting notion; fit a rear axle from another car onto
the front axle of this one, and power both with 2 motors. That would
be an easy hack.

> I do not understand why you'd need two speeders, unless the
> cars and speeder are not hooked to each other, as each speeder
> should be able to push equally well as pull. Many trains have
> a loc always on the same side and will push or pull, depending
> on which direction it goes.

You're right, mechinically they can push and pull equally well. That
seems to be a universal characteristic of rail equipment.

However a) the operator needs to be up front on the first car for
visibility. It's an insurance thing, since this railroad (the
Southern Michigan Railroad Society) often hauls passengers on
speeders. The prospect of remote controlling the powered car is an
interesting one, and certainly has plenty of precedent in the rail
industry. Do you use digital controls (M.U.) or an analog current
loop like BART does in manual mode?

However b) These cars are linked with fairly informal drawbars.
Pushing leads to uglier accidents than pulling.

Robert

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Discussion Starter · #13 ·
From: Robert MacDowell <[email protected]>
> That rear axle "pig" that was in the pictures -- does not contain
> a differential... the front axle is unpowered on most speeders and
> has a rudimentary differential. This is so you can pick up the
> lighter rear end and pivot the car on the front axle. The car has
>"lift handles" for that purpose. On an A-type gang car, it takes 4
> men, but the car is balanced to put the weight over the front axle
> for this reason (and better tracking).

Do you mean they designed it with most of the weight on the non-driven *front* wheels, and then complain about poor traction? And, that they want to lift the driven wheels off the tracks by hand, and then move it around like a wheelbarrow off the tracks? This seems like a very strange way to do it.

Why not make the *driven* wheels carry most of the weight, and lift the undriven end to move it around. Include a differential on the driven axle, so it won't fight you for off-the-track turns. Heck, make the front axle pivot like a wagon, so you could push or tow it around with all its weight on its own wheels.

--
Those who say it cannot be done should not interrupt the one who is
doing it. -- Chinese proverb
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart-at-earthlink.net

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Discussion Starter · #14 ·
Lee Hart <[email protected]> wrote:
> On 8/31/2010 11:22 AM, Evan Tuer wrote:
>> The advantage that an AC drive might have is torque control.
>> So, the driver can easily avoid slippage just by opening the go lever
>> to a known point, and the train will accelerate at a constant rate
>> until limited by some other factor.
>
> This is a function of the controller, not the motor. Motors (both AC and
> DC) generate a predictable torque determined by the current. If the
> controller limits the current, it limits the torque. Many controllers
> (AC and DC) use the throttle to set the current limit as well as the
> speed limit.

Well, part of what i'm asking about AC drive is if the price points
have improved. Last I looked (5 years ago) it seemed like an
automotive-sized AC control was north of $5000 and required a 200+
volt battery pack.

While at the other end of the spectrum, you had these AC controls for
R/C model airplanes for under $100 which seemed to carry incredible
amounts of power for their cost and size.

And I wonder if there's been any convergence there. Notably my pack
is going to be between 24 and 72 volts, not a range I know of any AC
drives operating in.

>> Much more difficult with a forklift DC controller where the smallest
>> throttle opening can suddenly result in maximum motor current and
>> torque, and the driver has to be part of the feedback loop if you want
>> to limit the torque.
>
> No; for example, barely moving the throttle on a Curtis controller
> commands a low PWM ratio (low speed) *and* low current limit (low torque).

I'd be keen on some controller reco's ...

> You sometimes encounter a crude or old DC motor controller that has a
> fixed or no current limit. In this case, it does go straight to full
> torque. You may also have too big a motor on a given controller, so its
> current limit can't work properly. This was the case with the old Curtis
> 1221B and ADC 9" motor, for example.

How big a motor do you think I need? Should I direct drive it with a
bigger motor and let it lug? Or retain the transmission and have
operators use 1st gear for pulling?


>> with a cart where all 4 wheels are driven, you'd need to have an
>> extra idler wheel somewhere to sense the actual track speed.
>
> Yes, it would be more difficult. Perhaps it could be done by comparing
> front and rear axle speeds, and backing off the current on whichever one
> tries to turn faster (i.e. starts to slip first).

In the 70's, they tried to have locomotives compare axles, but found
consensus only led to mass hallucination, rather like many things in
our society today. Every few years I see photos go around of a
section of rail with 12 deep scallops cut in it, where such a
locomotive labored for a good long time under the impression that it
was moving. Ultimately, they went with ground radar units to get a
speed reference. They later found that with accurate speed, they
could deliberately slip the wheels slightly for better traction.

Fortunately my cars have only 2 powered wheels. It wouldn't be real
hard to stick a hall-effect near one of several points to give speed
sensing on any wheel. Of course, all this is wildly out of scope for
the project.

On Tue, Aug 31, 2010 at 1:08 PM, Lee Hart <[email protected]> wrote:
> From: Robert MacDowell <[email protected]>
>> That rear axle "pig" that was in the pictures -- does not contain
>> a differential... the front axle is unpowered on most speeders and
>> has a rudimentary differential. This is so you can pick up the
>> lighter rear end and pivot the car on the front axle. The car has
>>"lift handles" for that purpose. On an A-type gang car, it takes 4
>> men, but the car is balanced to put the weight over the front axle
>> for this reason (and better tracking).
>
> Do you mean they designed it with most of the weight on the non-driven *front* wheels, and then complain about poor traction? And, that they want to lift the driven wheels off the tracks by hand, and then move it around like a wheelbarrow off the tracks? This seems like a very strange way to do it.

Yup, that's what they did. And I plan to correct this deficiency with
battery placement.

However I believe it is more elegant than it seems. These cars were
designed to haul burly maintenance crews to the jobsite. Most models
could seat a crew that weighed more than the car. The better seats
are over the rear axle, so the weight disadvantage is promptly
corrected when the crew sits down. And of course, the ballast removes
itself when turning the car :)

Robert

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Discussion Starter · #15 ·
Lee Hart <[email protected]> wrote:
> On 8/31/2010 11:22 AM, Evan Tuer wrote:
>> The advantage that an AC drive might have is torque control.
>> So, the driver can easily avoid slippage just by opening the go lever
>> to a known point, and the train will accelerate at a constant rate
>> until limited by some other factor.
>
> This is a function of the controller, not the motor

Of course. But I'm not aware of any car-sized DC controllers for
series wound motors which have this feature. Are you? Maybe some of
the modern Curtis microprocessor controlled range, but they tend to be
lower power.

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Discussion Starter · #16 ·
On 9/1/2010 4:46 AM, Evan Tuer wrote:
>
Lee Hart<[email protected]> wrote:
>> On 8/31/2010 11:22 AM, Evan Tuer wrote:
>>> The advantage that an AC drive might have is torque control.
>>> So, the driver can easily avoid slippage just by opening the go lever
>>> to a known point, and the train will accelerate at a constant rate
>>> until limited by some other factor.
>>
>> This is a function of the controller, not the motor
>
> Of course. But I'm not aware of any car-sized DC controllers for
> series wound motors which have this feature. Are you? Maybe some of
> the modern Curtis microprocessor controlled range, but they tend to be
> lower power.

My 10-year-old Curtis 1231C will do this. I'm using it with an ADC L91
series motor, which has enough inductance so the Curtis current limit
works. Barely crack the throttle, and it creeps forward at low torque.
The throttle is controlling current at low speed settings, and
transitions to control voltage at higher settings.

--
Lee A. Hart | Ring the bells that still can ring
814 8th Ave N | Forget the perfect offering
Sartell MN 56377 | There is a crack in everything
leeahart earthlink.net | That's how the light gets in -- Leonard Cohen

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Discussion Starter · #17 ·
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Discussion Starter · #18 ·
Sounds like a need for a good sander setup??I see Nocoua REQUIRES sanders
on some of their trips? I've walked along locos with a bucket to "sand"
slick rails, on leafy daze!

Bob
----- Original Message -----
From: "Robert MacDowell" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Tuesday, August 31, 2010 3:41 AM
Subject: [EVDL] Design challenge: Low speed + traction control


>I am trying to design an battery-electric drive for a railroad "track
> speeder" (the large Fairmont A4/A5 gang car, if you follow speeders).
>
> I'm trying to figure out the right motor/controller package for it.
>
> At first glance it seems like it calls for a small motor and the
> simplest of Curtis controllers. Except for one thing: Traction
> control would be so stupendously useful that I'd like an opinion on AC
> drive.
>
> The drivetrain layout is same as a rear-drive car.
> http://picasaweb.google.com/WoodingsCBI/A5CRebuild#5321700282597265458
> Reverse is integrated into the rear axle, so we don't need to design it -
> yay!
>
> It was built with a 35hp engine, for 60 mph, but we only need a top
> speed of 25.
>
> The machine weighs 2000 pounds. Adhesion is very limited due to being
> steel on steel. Fortunately so is rolling resistance. The machine is
> intended to drag trailers loaded with tens of thousands of pounds of
> material out to work sites. That means it has to pull hard at low
> speeds for long periods or continuously while climbing a steep hill.
> That'll require sizing the motor differently.
>
> Wheelslip is a nightmare, so traction control is a BIG win.
>
> In long trains of trailers, we put a speeder on each end, so we're
> always pulling. That means half the time, a speeder is "dead in tow".
> My crews aren't smart enough to take them the trailing car out of
> gear. Therefore, resilience to back EMF is essential. I'm OK with
> having a power contactor on the motor side.
>
> Would it be worth simplifying the car by using direct drive?
>
> What do you think? Is there an affordable AC drive that would attack
> the wheelslip problem? Traction control on a speeder would be simply
> amazing.
>
> Robert
>
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