Hst vs 225 set compatibility

Discuss Hornby Model Railway products and related topics here. This includes (Lima, Rivarossi, Jouef, Electrotren).
dan8400
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Re: Hst vs 225 set compatibility

Postby dan8400 » Sun Nov 12, 2017 7:16 am

Hairyhandedfool, I tried to double motor an hst power car but couldn't seem to make it fit in the body. Could have just been that loco (or my ineptitude). Definitely worth a second look


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MickleoverTestTrack
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Re: Hst vs 225 set compatibility

Postby MickleoverTestTrack » Tue Nov 14, 2017 11:34 pm

I'd guess by double motoring an HST it means one motor in each power car rather than two in one power car.

In regard to a 158 chassis I've found the following http://www.semgonline.com/model/159rev.html with some dimensions.
"Each model car is 304mm over couplings, 36 mm wide, 39mm above rail height, bogie wheelbase 34mm and distance between bogie centres 208mm. Wheels are 11.5mm diameter and are chemically darkened. Major dimensions seem to scale correctly."


The wheels are a little undersize but I think the original Hornby ones look oversize. I can't find any definitive spec for the real Mk4 wheel diameter, best I could find is page 45 of this report http://uctc.berkeley.edu/research/papers/114.pdf giving the coach dimensions.

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Re: Hst vs 225 set compatibility

Postby b308 » Wed Nov 15, 2017 9:02 am

The wheel diameter according to one website is designed to be between 860 and 920mm, so 900mm (about 3ft) seems about right if that's any help...

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Re: Hst vs 225 set compatibility

Postby Bigmet » Wed Nov 15, 2017 11:00 am

MickleoverTestTrack wrote:I'd guess by double motoring an HST it means one motor in each power car rather than two in one power car...

As a side note, if maximum traction is required, always best to make one unit all wheels driven, rather than spread the motor bogies over two units. This came as a great surprise to me long ago, when I first put two motor bogies in one model. I had hoped for double the traction, but actually got well over three times the traction (plain metal tyres, no traction tyres involved).

The reason is simple. If you drive one end of a twin bogie unit, then to make a well balanced vehicle with both good traction and good rail holding, a fair amount of the model's weight is on the unpowered bogie. The unpowered bogie weight is effectively part of the train load the motor bogie is pulling, and 'unseen' subtracts from the motor bogie traction. Putting two powered bogies into the one body gives double the traction alright, but the unseen drag from the unpowered bogies no longer exists, so the net pull the loco can exert on a train is more than doubled, compare to those same two motor bogies in separate locos. What's more, any added weight is all on powered wheels, so all contributing to traction. This is part of the reason for the success of the centre motor all wheel drive models, and why they don't require traction tyres.

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hairyhandedfool
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Re: Hst vs 225 set compatibility

Postby hairyhandedfool » Wed Nov 15, 2017 12:55 pm

dan8400 wrote:Hairyhandedfool, I tried to double motor an hst power car but couldn't seem to make it fit in the body. Could have just been that loco (or my ineptitude). Definitely worth a second look


Thanks
Dan


Not sure about the HST, though having had two motored power cars on a Lima HST, I'd recommend finding two similar power motors as the effect on the coaching stock of uneven motors could be disastrous.

For the 86 and 90, the chassis is essentially the same at both ends, so there's no real problem, but I think the 91 (225) should work with two motors in the same body.
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Re: Hst vs 225 set compatibility

Postby stuartp » Wed Nov 15, 2017 2:17 pm

The 91 is traction tyred is it not ? It should manage in theory if it's heavy enough. Try adding some weight inside before you try anything more drastic.
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Re: Hst vs 225 set compatibility

Postby hairyhandedfool » Wed Nov 15, 2017 2:39 pm

stuartp wrote:The 91 is traction tyred is it not ? It should manage in theory if it's heavy enough. Try adding some weight inside before you try anything more drastic.


Additional weight works to an extent, but too much works against the performance of the motor. When the traction tyres wear, the problem is magnified.

If we are talking about a full 2+8/9 coach rake, then I think a standard 91, even with additional weight, will really struggle on sharp bends and gradients.
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dan8400
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Re: Hst vs 225 set compatibility

Postby dan8400 » Wed Nov 15, 2017 5:26 pm

It will indeed be a full length hst. I also have curves (not sharp) and gradients (maybe medium steep).

No problem for modern stuff.

Would an alternative be something like thisx2:

https://goo.gl/images/DHZFB4

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Dan
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Re: Hst vs 225 set compatibility

Postby GWR_fan » Wed Nov 15, 2017 7:19 pm

hairyhandedfool wrote:.......................... but I think the 91 (225) should work with two motors in the same body.


I converted several class 91 to dual motor configuration and these were quite successful. Traction tyres were fitted to one motor bogie only and additional pickups were fabricated for the geared wheels without tyres on the second motor bogie to help with reliability.

A downside of the conversion is the lack of compensation in the chassis with two drive bogies. When the loco enters a curve with all the power pickups on the outer diameter of the curve then running is perfect. Alas, with the power pickup wheels running on the inside rail (traction tyred bogie on the outer rail) then erratic running may happen. The cause is lack of compensation resulting in the inside wheelsets lifting slightly with resultant loss of power pickup. It seems that one bogie wants to lift an inside wheelset on the curve causing loss of pickup.

If one could overcome the compensation issue then the conversion would be fine. The standard configuration relies on the compensation of the non-powered bogie (trailing bogie on the class 91) to allow all wheelsets to remain in contact with the rail in a curve so two power pickups each side of the loco are sufficient. With a dual motor chassis there is basically no compensation and in a curve the loco shifts it weight to the outside rail losing power pickup momentarily on the inside rail.

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Re: Hst vs 225 set compatibility

Postby GWR_fan » Wed Nov 15, 2017 7:23 pm

dan8400 wrote:It will indeed be a full length hst. I also have curves (not sharp) and gradients (maybe medium steep).

No problem for modern stuff.

Would an alternative be something like thisx2:

https://goo.gl/images/DHZFB4

Thanks
Dan


Olivia's Trains does a dual motor conversion on the Hornby APT power car using the Railroad Blue Rapier motor blocks which are similar to that in your linked image.

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Re: Hst vs 225 set compatibility

Postby MickleoverTestTrack » Wed Nov 15, 2017 9:39 pm

Bigmet wrote:
MickleoverTestTrack wrote:I'd guess by double motoring an HST it means one motor in each power car rather than two in one power car...

As a side note, if maximum traction is required, always best to make one unit all wheels driven, rather than spread the motor bogies over two units. This came as a great surprise to me long ago, when I first put two motor bogies in one model. I had hoped for double the traction, but actually got well over three times the traction (plain metal tyres, no traction tyres involved).


I agree with what you are saying.

I've not had experience with the Lima version but have had lots with the original Hornby ones. The first problem I find is that there isn't enough space to get a ringfield in where the front bogie sits. I know there is more space in the 91 and I have seen it done. The second problem I have is the adding extra weight; because of the way weight in the plastic chassis sits onto the bogies, adding extra weight inhibits the ease with which the bogies can turn in the chassis so you can get away with adding a bit but not loads, certainly not close to a modern centre drive chassis weight, though adding a power bogie you are adding the weight to the bogie not the chassis.

I have my own Mk4 and a cheap 158 chassis to play with (was 2/3rds of a 159 being sold as a 158 so I picked it up cheap for this purpose) when I get the time. It certainly has the best potential performance of any remotor option.

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Re: Hst vs 225 set compatibility

Postby GWR_fan » Wed Nov 15, 2017 11:13 pm

As a thought what about a powered coach from a Bachmann class 221 Super Voyager. The sideframes are a reasonable match for the coach bogie (overall wheelbase/length unknown). The non-tilt class 220 would be better but you would need to adapt Hornby Mk4 sideframes. I did this with ease to a class 221 missing a bogie sideframe.

The only downside would be the class 220/221 chassis are not particularly 225 km/hour record breakers.

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Re: Hst vs 225 set compatibility

Postby b308 » Thu Nov 16, 2017 8:51 am

The originals are, though, I've been on one at 137mph which is close enough! ;)


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