Comet Chassis Saga

[DCB]

6 minutes ago, jimwal said:

 

In the circumstances, good advice. 

 

The advice was given based on what I would have done. 

I would find it easier to fix the item than to repackage and write out a letter explaining the problem.

 

However I appreciate that for many (perhaps most?) people this is not the case.

 

I don't want to admit defeat!

 

On 30/03/2020 at 23:51, jimwal said:

Sounds like something metallic has got in the insulating layer between the nickel-silver tyre and the Mazak centre. A black mark must show where the burning was occurring. Try clearing it with something pointed and then check with a meter preferably, or wires from the power supply to each side of the wheel insulation.

When you are absolutely certain the damaged insulation is clear of burnt material, fill it with epoxy adhesive.

 

Jim

Thanks for the advice. I will give that a try

[afkent]

Could it be an MRRC motor that was intended for slot car racing? Similar to the Romford 'Bulldog but not compatable. - 1970'/80's

[hayfield]

57 minutes ago, afkent said:

Could it be an MRRC motor that was intended for slot car racing? Similar to the Romford 'Bulldog but not compatable. - 1970'/80's

 

Nothing like the MRRC motor which has both brushes on the top of the motor the same as the Bulldog and X03/4 motors

 

I think everyone has settled on either the D11 or D13, due to the distinctive brush screws 

 

Here is a link to the 005 slot car version, from memory had shorter shafts

 

They also did a  motor  called the Slimline had a shaft at both ends and in the same style of the early K's mk 1 & 2

[DCB]

I finally took the cow by the horns and found the area between the tyre and wheel centre blackened and under cut on the suspect wheel, the one the connecting rod drives on on the insulated side.  I tried to scrape the black carbonised gunge away but then the tyre fell off!

With less difficulty than I expected I removed the suspect driving wheel.    The con rod securing bush on the crank pin wouldn't come un-soldered but the crank pin unscrewed and came clear when I removed the rear wheel.    The insulated band was still intact though maybe a bit thinner than usual in one place.  Obviously as soon as I had the wheel off I refitted the rear wheel and tried the resulting 0-7-0 chassis.  It ran very well, a bit bizarre with the con rod and cross head moving without the wheel in place but it got round 20" radius curves with all 4 flanged wheels on the inside, so at last I am relatively confident I can get it sorted if I,

a) glue the tyre to the wheel centre with thick superglue, and b) make sure the brass wheel balance weight which fell off is away from the tyre.   Hopefully now its sorted, and when I reassemble it, the typical K's cock up straight framed 28XX with side window cab can re enter service.

[DCB]

It's back together,  with the body on but not the pony truck and it runs round 20" radius curves .

Doesn't go along the straights. Open circuit not shorting, Back to the kitchen table...

[Izzy]

Given that this was fitted with a D11 and the whole motor is ‘live’ to one polarity, could part of the problem be that therefore the chassis is also live and pickups are only on one side as well? I’m trying to think through why it works round the bend (is it sending you there as well?), but not on the straight.

 

Izzy

[DCB]

Its running!  New brush fitted to the motor, wires reattached and off it went. Thought I had fixed it.  Just a minor issue when the brake gear fouled a point blade and dragged the point open under it and the fact despite 8 pickups it only seemed to take power from 3 of them.

 Put the body on and the gears instantly went out of mesh. Oh well back to the bodging bench.

Edited June 2, 2020 by DavidCBroad

[DCB]

Gear mesh sorted well bodged with extra spacers under the motor mount, it really needs an extra bearing to support the front of the armature shaft. I nearly changed the DS 11 for a Triang XT 60. But the DS11 is now behaving itself.   I ran the chassis for over 30 minutes at around half speed, pushing as many wagons as it could manage without of the weight of the body and it started to free up nicely.

I oiled the gears and next thing that 18mm flanged Insulated Romford (Or Markits?) driving wheel was shorting again.  Between tyre and centre through the insulating band. Going round like a roman candle as the chassis crawled to a halt flat out.   

Oil was 3 in 1.   I have used Romfords for 40 years and never had anything like it before.  The tyre has previously been off and everything thoroughly cleaned and reassembled and ran for 30 minutes without problems until I oiled it.  Is oil the problem?  First time I used electrolube, next time I used ATF, today 3 in 1.  I just haven't had any problems with any of these oils before.

 Next plan change the insulated band for one off another 18mm insulated wheel, which means taking the rods off again.  Has anyone else had these issues because it's very very annoying.

[Michael Edge]

Don't use 3 in 1 oil - it could well be that which has broken down the Romford wheel insulation. I use car engine oil, it doesn't harm any plastics. Electrolube should be OK though.

[t-b-g]

This thread reminds me of why I have a policy of not trying to "sort out" something that somebody else has built!

 

The number of times people have said "It just has a tight spot" or "It isn't running as smoothly as I would like", "Will you have a look at it for me?"

 

In most cases making a new mechanism would have been quicker and easier!

 

So I don't offer or agree to do them any more, unless it something obvious and easy to sort, like a pick up that has come off or a crankpin nut missing.

Edited June 5, 2020 by t-b-g

[DCB]

Finally a bit of luck, it has generic Romfords not the correct 28XX wheels, so I had one or five in my scrap box. I changed the wheel, changed over the balance weight and its looking good again.   However there doesn't look like there is much wrong with the old one.  Yet there was an orange flame revolving last time it ran. Very odd.  Next job outrigger bearing for the armature shaft to keep the gears in mesh.

[hayfield]

David

 

Perhaps the tyre came off at some point in the past and a small speck of metal contaminated the insulation material, or the insulating material was contaminated when built. If it runs true treat it as an uninsulated wheel

[DCB]

It's now ready for a test run.  Latest mod is the outrigger bearing for the armature shaft to hopefully cure the chassis flexing and losing the gear mesh.  The bearing is from an ancient long dead motor with the same armature shaft diameter,   mounted  in a housing carved from a Caravan 6 pin connector socket  and the mounting a bit of brass cut with scissors and soldered in.  All pure bodgery.  Next bit of applied bodgery will be cab windows and a new boiler back head a bit further back than it should be as it now has a longer motor a DS 11 I believe instead of a DS 10. Apologies for the picture, the one after cleaning up  and painting doesn't show the bearing support at all well. 

[t-b-g]

Your new motor looks more like a D13 to me. It was the same general design as the D11 apart from a bigger magnet, which made it much more powerful. The DS10 was quite a bit smaller and a different type of design.

 

If your Romford wheel tread came away like that, then the insulation material has been damaged, possibly contaminated with some non insulating oil, like "Electrolube". If the insulation is intact and undamaged, it is most unlikely that the tread would come away from the centre. 

[DCB]

On 07/06/2020 at 19:09, t-b-g said:

Your new motor looks more like a D13 to me. It was the same general design as the D11 apart from a bigger magnet, which made it much more powerful. The DS10 was quite a bit smaller and a different type of design.

 

If your Romford wheel tread came away like that, then the insulation material has been damaged, possibly contaminated with some non insulating oil, like "Electrolube". If the insulation is intact and undamaged, it is most unlikely that the tread would come away from the centre. 

Thanks, it does look like a D13 for sale on eBay recently, It sold for £27 plus postage.

I reckon you're right about the wheel insulation becoming soaked with non insulating oil.  Odd it was only one.  Last evening I had a 16mm Romford where the tyre was loose and the insulation had broken into several pieces.  I made a new insulator with good quality Brown paper soaked in superglue 100 or 120 gsm I reckon.  I found as long as there is a hole in the paper near the wheel centre the tyre will force on nicely. If no hole it tears.  Might try it with the offending 18mm now its consigned to my scrap box.

[t-b-g]

6 minutes ago, DavidCBroad said:

Thanks, it does look like a D13 for sale on eBay recently, It sold for £27 plus postage.

I reckon you're right about the wheel insulation becoming soaked with non insulating oil.  Odd it was only one.  Last evening I had a 16mm Romford where the tyre was loose and the insulation had broken into several pieces.  I made a new insulator with good quality Brown paper soaked in superglue 100 or 120 gsm I reckon.  I found as long as there is a hole in the paper near the wheel centre the tyre will force on nicely. If no hole it tears.  Might try it with the offending 18mm now its consigned to my scrap box.

 

I had a similar problem with a pair of wheels, now 74 years old, on one of the Buckingham locos. The insulation had just disintegrated. I smeared Araldite round the centre and forced the tyre back on. I think I got lucky and your paper might be more easy to keep an even layer. I couldn't even put two new wheels on as they are now 19.6mm diameter and I needed them to match. That is what 74 years of running does to a Romford 20mm wheel!

[DCB]

I am on plan D now. I have a K's motor Mk2(?)  for my Dean goods to replace the Airfix MRRC which has awkward brush gear on the right side of the motor which stops the body going on straight.  I then realised the K's 28XX body was designed around the K's motor, and is too narrow for an XO4 so I will be fitting the K's to the 28XX.  I can't stop the Anchoridge motors commutators sparking  and  taking the temper out of the brush springs.  I guess its because the chassis runs so stiffly.   I bought a D11 for spares and ruined those springs as well.  Plan E is extra brush springs for the Anchoridge and put it in the Dean. Its just far too awkward to get to the motor in the Comet chassis to try fancy brush gear.    Now my 28XX with a big fat computer motor on a H/D 8F chassis has been happily running round the shed all evening  with 22 Hornby Dublo wagons in tow. Effortlessly,  The wheels revolve the same speed up hill down dale or when it it's overloaded and slips. 4 minutes a 50 ft lap it looks good but its only a scale 12 mph!.  Unfortunately That Motor is also too fat for the K's body....

[PenrithBeacon]

The thread title seems to imply that the problem is with the Comet chassis as bought, but this isn't so. The problems lie elsewhere.

[DCB]

1 hour ago, PenrithBeacon said:

The thread title seems to imply that the problem is with the Comet chassis as bought, but this isn't so. The problems lie elsewhere.

I don't know how to rename the thread.   It's been a long and extremely frustrating saga but currently its the Comet design giving me problems.

There is design problem with the chassis as built in that the motor can't be removed without first removing the worm from the armature shaft. and the motor mount is not sufficiently robust to stop the gears de meshing under load.  I can't fix the worm issue but the outrigger bearing cured the de meshing.  I had to move the K's armature shaft so it's longer one end to suit and adapt a Triang bearing as an outrigger to suit the larger shaft.  Next problem, no access to attach the wire to the lower brush on the K's motor, and no clearance to attach them before fitting the motor. The Anchoridge has one insulated and one non insulated brush holder so its not an issue, except you have to use 8 insulated drive wheels if using DCC.   I will not be beaten. I might end up with a Tender mounted  motor and shaft drive to the loco if I can find a K's 3500 gallon tender.  

[hayfield]

1 hour ago, DavidCBroad said:

I don't know how to rename the thread.   It's been a long and extremely frustrating saga but currently its the Comet design giving me problems.

There is design problem with the chassis as built in that the motor can't be removed without first removing the worm from the armature shaft. and the motor mount is not sufficiently robust to stop the gears de meshing under load.  I can't fix the worm issue but the outrigger bearing cured the de meshing.  I had to move the K's armature shaft so it's longer one end to suit and adapt a Triang bearing as an outrigger to suit the larger shaft.  Next problem, no access to attach the wire to the lower brush on the K's motor, and no clearance to attach them before fitting the motor. The Anchoridge has one insulated and one non insulated brush holder so its not an issue, except you have to use 8 insulated drive wheels if using DCC.   I will not be beaten. I might end up with a Tender mounted  motor and shaft drive to the loco if I can find a K's 3500 gallon tender.  

 

Firstly to change the title just go to the first post and one of the edit options will allow you to change the title

 

I could be very wrong, but I cannot remember Comet producing a motor mount for the D11/13, if they did I assume it was a generic motor mount for any chassis, rather than one specifically designed for the 28xx. I to have difficulty with early design motor mounts, I was told by one supplier they need tweaking first to get the meshing correct prior to fitting into the chassis.

 

If the Anchorage motor is suffering under load then it will either be due to the motor mount or chassis, if its the former then the issues will be resolved by a new motor and motor mount/gearbox, if its the latter then the problem will continue

 

You can short out the lower K's armature tag on the body or just solder a wire to it first

 

If the wheels are free running I would opt for a modern gearbox and motor, as motor mount gears and gearbox gears have moved on a lot in the past few years in both meshing and efficiency. I has been reported often about the poor performance of older style gears with large metal worms, few mesh properly etc 

[t-b-g]

I have honestly never heard of anybody taking out a motor and installing a Ks one in an effort to improve the running of a loco. Not in 40 years of modelling.

 

The mechanism has to be free running with no motor in at all. If it is free running, then any problems are down to the motor and gears.

 

The best motor and gears in the world won't turn a stiff mechanism into a good one. A poor motor and gears will turn a good mechanism into a bad one.

 

My test is to push the mechanism along a flat level track, from the back putting no downwards pressure on it. If the wheels and coupling rods turn freely, I move on. If they don't, I investigate and fix the fault before I move on. Problems with brush springs usually mean they are old, sticky, full of muck or not in their sockets properly. It can also mean the mechanism is so stiff that the motor is drawing a high current to try to overcome the stiffness. The tiny springs are made from very thin wire and if the draw too much current, they can heat up, which can spoil their springiness.

 

If the mechanism is free running, I would give any motor a good test, run for a long time to see if it is overheating or not running smoothly when worn. Especially if it is an old motor. Trying to get good running using motors that might already be 40 years old and are quite crude compared t modern motors, is always going to be harder than using a modern, newer one. In my duties as a loco building tutor at Missenden Abbey, people often bring along kits that have been "stashed away" for many decades. They still want to use the 40 year old motors and gears, which have probably not moved in all that time and have corrosion and stiffness problems that are not easy to get rid of.

 

If it was me, I would be looking at ow the motor mounts and getting a nice new High Level gearbox and motor. The DJH ones are good quality bu a fixed shape and size and sometimes not easy to hide.

 

I would add that there is always an answer to any problems in a model loco mechanism, so you will get there. 

 

 

[DCB]

7 hours ago, 313201 said:

Hi Everyone

 

Would I be right in saying that you possibly intend to have a drive shaft between the loco and tender if you do a tender mounted motor.

 

It sounds very much like an idea that was done by a member of the pendon museum who built a GWR 28XX 2-8-0 where the motor was mounted in the tender with drive shafts connected by universal joints to the locos driving wheels.

 

This also had the benefit that it left a lot more space for weight to be added therefore allowing the loco to haul much heavier anx longer trains.  The pendon loco I believe hauls 100 of their 4 wheel coal wagons all loaded aswell as a break van.

Yes, Guy Williams built it and I remember it hauling 80 or 100 wagons across the Pendon viaduct years ago.

The fall back position is a drive shaft from loco to tender mounted motor not quite like he did it but pretty much.  

[Barclay]

Can I ask if you have removed the motor to see if the chassis is free running? As some of the others have said, if it's stiff then changing the motor won't help. If it won't roll under gravity something's up - try reaming the bearings or maybe ease the coupling rod holes if they are a little tight? Or perhaps the chassis is a little too wide and the wheels are rubbing on the bushes or there are too many spacing washers in there.

 

Given that it has Romford wheels a full dismantle would not be too hard and may provide the key.

[DCB]

On 17/06/2020 at 08:30, Barclay said:

Can I ask if you have removed the motor to see if the chassis is free running? As some of the others have said, if it's stiff then changing the motor won't help. If it won't roll under gravity something's up - try reaming the bearings or maybe ease the coupling rod holes if they are a little tight? Or perhaps the chassis is a little too wide and the wheels are rubbing on the bushes or there are too many spacing washers in there.

 

Given that it has Romford wheels a full dismantle would not be too hard and may provide the key.

Hi Barclay.  No I didn't remove the motor to test it initially as I didn't build it, it was running badly when I had it, very gutless and needed  the controller turned right up.    It runs as stiff as hell now I have 8 instead of 3 pickups working, it doesn't have any tight spots but it fails the tow test, as in do the wheels revolve when I tow the bare chassis around the layout but passes with the body on.  This is only the second competed Comet chassis I have worked on.

The problems may well stem from the axles and bearings being tight, but there isn't enough clearance in the brake gear or slide bars for much slop the chassis looks square with the wheels parallel to the chassis.  I Hope to get the K's Motor fitted for Sunday.

Meanwhile my own Wrenn Chassis Computer Motor Hornby 28XX keeps bending its con rods when they snag in its temporary cylinders as it has so much power, sadly the computer motor s too fat for the Comet Chassis K's Body combo.

[micklner]

Pick ups dragging ?

 

Good luck with a K's motor = 99% total junk in most cases.

 

Buy yourself a decent motor and gearbox as already said.