Trade SDMP/Finney7 - Driving a Geep?

[SteveO]

Good and valid questions Mike.

Having spent half an hour thinking about it, the answer to B is no. The train is only ever going to be two coaches long, being a 2 coach DMU, so I could easily get away with one motor bogie, depending on the final weight of the train and the power of the motor.

The answer to A is more complicated. I'm a believer that weight in wagons will overcome most problems that compensation or springing solve – and is easier – so I'm aiming at around 200-250g per wagon, and my brake vans will probably be more like 300-350g (ABS white metal). Even a very small train is going to weigh 1.5Kg+. My 1824 motors are not very powerful so I'm not sure just one of them is going to move something like that on one bogie. I'm playing safe by assuming I'll need two powered bogies and have bought a bag of motors to achieve that. I think I've got about 10 or 12 of these things laying about somewhere.

I know my logic may seem slightly twisted to some but it works for me.

 

[Steph Dale]

Steve,
Makes some sense to me, I come from the 'all axles powered, all wheel pick-up' school of thought myself. So for smaller (Type1, Type 2) locos I'll be using your approach to get drive on all four axles, even if oodles of power isn't necessary to get the locos pulling scale-length trains.
As an aside, have another quick look at the pictures Mike posted, the trailing bogie shows the internal frame most clearly. The height in the Westdale power bogie comes from the motor mount(s), which appear to be separate.
Steph

 

[SimonT]

I hope that some of my experience may help. The two car DMU is powered by one power bogie in the guards compartment. Mashima 1833 motor, Branchlines gearbox (40:1 I think) and Delrin between the two axles. The drive bogie is weighted to 1450gms. This DMU can manage the 1:80 of the hill with ease.

To settle the question of drive on the three car we took Shaun's stand model and tried it up the hill on the plain track. The one power bogie slipped and there was little progress. So mine has two power bogies. The spec is similar to above but with not so much weight. Although both power bogies have chips with exactly the same CVs, there is a delay in one of the bogies starting and even on the flat the running bogie cannot pull the train alone. Steve W is going to tune the CVs on the three car DMU to achieve union.

All the locos have two power bogies (so four wheel drive, six wheel pick up) and weigh around 1600gm.

Simon T

 

[Steph Dale]

Simon,

Apologies, I've only just seen your post. I suspect your DMU will be using gears around the 13:1 ratio in my gearboxes; 40:1 with Mashima 1833 really won't go fast at all.

I'm always pleased to hear of people doing a bit of well-reasoned empirical testing and appreciate the issues with running your DMU with two decoders; have you tried dialing out some of the back EMF to stop the bogies fighting?

Can you also confirm that you've built the motor bogies in your DMU rigid? I suspect a little compensation or springing may have improved both the free-running of the trailing bogies and the adhesion/traction of the motor bogies, so I'll be interested to know how you've built yours.

Cheers,

Steph

 

[SimonT]

Steph,
my DMUs are not high speed vehicles! As I hinted before, I cannot really remember what ratios I am using; they work for me.

The back EMF reduction is something that I will try before Steve Weekes has a go at reprogramming the decoders. I'll let t you know how I get on.

All the bogies are rigid. At one time the 104 bogies had beam springs. I cannot remember why I took them off. I have a vague memory of endless troubles with the brass tube through which the springs ran. I didn't notice any difference in traction. I used Barry's outer works and made my own innards to do the business of bearings, motor mount and bolster. There is too much body rock on the 104; it's on my todo list to correct. The Easybuild bogies are built as Shawn designed other than I had to carve bits of the plastic bogie sides away to give clearance for the S7 wheels sets. I do not know what ratio Shawn provides. Your ideas at #104 look interesting and might be worth building into the 104 when I get around to it.

All the best

Simon

 

[Steph Dale]

Simon,

Very useful; thank you for taking the time to reply.

Steph

 

[Tim Humphreys ex Mudhen]

Simon T,
I don't know if my experience will help but on my Class 40 driven with delrin chains I found it essential to get the chain tension on each bogie as close to the same as possible and for it not to be overtight. Initially the chain on one was slightly tighter than the other leading to the problem of one bogie starting to move before the other. I solved this problem by adding one link to each chain making them a little loose. This resulted in no binding from the tight chain and them both moving simultaneously. I then needed to take up the slack and did this by fabricating a simple chain tensioner from some brass rod fixed across the chassis, two lengths below the chain a one length above it. This stops the chain from thrashing about loosely under the bogie. The bogies were then wired to a single dcc chip with the result that all runs very smoothly.
Tim

 

[SimonT]

Tim,
thank you for the suggestion. The delay is of the order of 3-5 seconds and for that reason I suspect the DCC rather than the mechanics.

Interestingly I initially put chain tensioners into my Delrin builds to get around the problems caused by the different diameter cogs and chain pitch not matching the bogie wheelbase. As an experiment I omitted this on a later build and allowed a little slop. This seems to be taken up very gently as the vehicle starts off and to date no one has commented about it. From now on I will be able to recognise WTers by the comments!

Simon

 

[Tim Humphreys ex Mudhen]

Simon,
That would certainly suggest an issue with the DCC. How about, as an experiment, wiring the two motors into one chip and seeing how that works?
Tim

 

[SimonT]

Steph, Tim,
just returned from a session on the DMU. Before fettling with individual Back EMF CVs I thought I would try the automatic calibration offered by the Loksound V4 chips one more time. So after two catapult launches I have two well behaved motor bogies and a DMU that seems to drive in a civilised manner. A weekend of work at the Leeds Show should test it out!

Steph, thank you for this hijack of your thread.
All the best

Simon

 

[Steph Dale]

Guys,
I'll be interested to know what you think of this 8'6" wheelbase compensated inner bogie. Shown with Mashima 1824 and a set of my drive components, it can also be used perfectly happily as a trailing bogie. It can also be assembled (with slight modification) for split axle pick up:

Background image is a Class 20 section. End beams (in blue) can be bent up, down or left sticking out straight. Their position can also be adjusted by a couple of mm in/out. Height to the top of the bogie mounting is 22mm above axle centres.
Steph

 

[SteveO]

Looks cracking, can't wait to see it's test build on here.

A couple silly questions; how does the compensation beam affect the gear train? I see the motor shaft is central along the bogie but the point of rotation is on the opposite bearing – is this correct?

 

[Steph Dale]

A couple silly questions; how does the compensation beam affect the gear train?

It doesn't - any movement of the motor+gearbox vs. the free gearbox is taken up by the c/v joints between the two units. These parts will be provided in with the bogie fret, as will bearings and the pivot unit (a 9mm snap fastener).

I see the motor shaft is central along the bogie but the point of rotation is on the opposite bearing – is this correct?

Kind of - unusually the compensation pivot is in the middle of one side (the beam is keyed directly to the yoke which acts as the pivot unit for the bogie). This gives a bogie which is stable (self supporting) and has better stability than conventional designs which pivot over one axle. It's a simple way to mitigate the small wheel diameters prevalent in modern traction locos whilst also being simple to assemble. As an aside it also means that the traction centre is low, so the haulage is good and the bogie remains stable under load (drive/weight).

Steph

 

[Steph Dale]

As an alternative (and slightly trickier to assemble, no doubt) here's a set of 8'6 sprung bogies with the same overall geometry as the above compensated bogie...

Again, thoughts are welcome...!

Steph

 

[SteveO]

Again, very nice, beautiful engineering. Definitely starting to move into claustrophobia in there...

 

[Steph Dale]

Again, very nice, beautiful engineering. Definitely starting to move into claustrophobia in there...

Steve,
Yeah, it's getting a very tight; the issue is keeping the height down, which means the motor has to go in with the flats horizontal. But it definitely all fits. I've made a couple of small changes this evening, the spring is now under slightly greater tension, which should improve the ride quality and I've simplified the bogie pivot too. One final thing was to put a 'fence' on the bearing holders to keep the spring in place.
Both (along with another couple of things floating around here) will now be turned in to artwork as the next stage. From that test etch I'll part things out, write the instructions and all should be available early in the New Year.
Steph

 

[Dikitriki]

Yippee!

I'll have 2 complete power bogie kits please

Richard

 

[lancer1027]

Hi Steph,

Been lurking over this thread watching with interest. But for a simple lad like me i tend not to ask too many questions as i dont really know enough about motors/gears etc.

However i feel the time is right to ask a question.

8' 6" DMU bogie.

Firstly with your power bogie ( un-sprung ) what motor would you recomend to suit smooth running but with a scale speed of about 70mph for my radio controlled set-up?.

Secondly when will these go into production and how much would one of these beauties be.
Do they come ready assembled ( how much) or in a kit form (how much )

Rob

 

[Steph Dale]

Hi Rob,

I'm still generally of the opinion that the best way to drive a DMU is prototypically, with the inner axle of each bogie driven from an under-floor mounted motor. Assuming you're working from a kit it requires the least modification of bogies and running gear.

However, from discussions we've had already, I understand you want the underframe space for your r/c gear and batteries, so you need a self-contained motor bogie.

To be honest with you, I think you may be better looking at an alternative for a DMU than either of the bogies I've designed here. I've been looking at fitting a drive set in to a Wayoh 8'6" bogie etch for another client, which results in this compact little layout. The top bearing surface of the bogie is 30mm above track height. This has some advantages over the bogie designs I'm suggesting above; it's slightly more compact, can be made up on carriage wheelsets (axles sleeved up to 3/16" in the gearbox area). The conversion of the Wayoh parts involves modifying the bolster assembly to clear the motor and incorporates the anchor for the rear of the motor.

Here's a quick illustration to show you what I mean. The Wayoh etched bogie outline is shown in magenta.


In terms of your other questions I'm aiming for a mid Q1/2014 production run for the new bogies, with hopefully a couple of prototypes from the test etch available for people to see and handle at the Bristol show.

Prices are not yet worked out as the price of the etch is calculated from area and I've not completed the parts layout. They will be available both as a kit and r-t-r but I'll have to work prices from the build time for the r-t-r option. In any case, the gearboxes are available now in kit or ex-works, prices as on the website. Motor is a Mashima 1824 to allow the parts to actually fit within the wheelbase of the bogie.

I hope that helps, feel free to email or PM me if you want some more specifics,

Steph

 

[Steph Dale]

Guys,

Here's one way to drive a DMU - this set is destined for an Easybuild 'Bubblecar' and shows just one bogie's worth, the aim will be to drive the inner axle of each bogie using a centrally-mounted Mashima 1833. The wheels are Slater's 3'1" Disc Power Bogie (B7837), with 2mm extension journals (7317) mounted instead of the supplied fixing screws. The 2mm bearings (1211) will replace the normal top hat bushes in the bogie frame. As the Easybuild bogies are plastic I can happily use split axles (which has been done, although the wheels haven't been wired yet (I'm about to crack on with that particular job now); but even metal bogies could be modified. This is a slightly pricey way to get 3'1" wheels on 3/16" axles; an alternative would be to use carriage wheels and a sleeve, which Evergreen do (1/8"- 3/16" tube), Eileen's also stock a brass tube of the same dimensions. Slater's also seem to have used the same die for both the 3'1" carriage wheels and these - so a mixed set could be employed without it being noticeable.



I've also had a set of Peartree DMU wheels across the workbench recently; these too are mounted on 3/16" axles, but have standard size journals for the normal top hat bearings so are a possible solution; although the wheel has to be pressed off (and back on) an insulated bush to fit the gearbox.

Steph