Tuesday, April 29, 2014

How added suspension to my railmotor

A couple of years ago, I constructed a two-car railmotor based on a couple of Andel resin freelance coaches (see How I constructed a railmotor). Since her construction, she has been through quite a few reincarnations as I have sorted-out a series of problems. Whilst this has at times been frustrating, the solutions have also provided me with opportunities to develop knowledge and experience in a range of different fields.

Problem: Erratic radio control
Initially, she was controlled with a keyfob controller using a circuit from a gadget for dimming LEDs.
Solution: After trying various modifications, I eventually discarded this control system and installed a Deltang receiver/controller (see An evaluation of the Deltang r/c system)

Problem: Lack of power
 Initially, the railmotor was powered by an IP Engineering motor and gearbox assembly. The 16:1 gearing on this mechanism meant that there was insufficient power from the motor running on 12 volts to take the power car and trailer up the 1:40 gradients on the railway.
Solution: The original motor/gearbox was discarded an MFA gearbox motor was mounted beneath the chassis powering the wheels through bevel gears. (see  Progress Report 48)

Problem: Regular derailment
Whilst sometimes she would run round the track without problems, on other occasions she would regularly become derailed as she negotiated some pointwork.
Solution 1: My first diagnosis was that she needed more weight over the front wheels - to keep her nose down. Some strips of lead flashing were trimmed to fit into the cavity beneath the bonnet and, with fingers crossed, I gave her a trial.

Some sets of points she negotiated without problem, but others she refused to take without derailment. Close scrutiny of her progress showed that one wheel was riding up over the check rail, thereby causing the other to foul the frog.

 Solution 2: My next attempt was to widen and deepen the flanges of the Tenmille wheels with plasticard as I had done successfully with other finer-flanged wheels (see How I improved the compatability of IP Engineering wheels with LGB pointwork)
Tenmille wheels
Plasticard 'washers' roughly shaped
Superglued to the back of the wheels before being filed to shape
 Whilst this has been successful with other rolling stock, this was not so with the railbus. I then tried some LGB spoked metal wheels which have wider treads and deeper flanges and of course are designed to be compatible with LGB pointwork. No success. Clearly the problem was more deep-rooted.

I studied her closely again as she went through the points and realised that, as her wheelbase is quite long (in comparison to most of my other locos), she was unable to flex her chassis if the rail dropped slightly. This meant that in certain places, not all four wheels were in contact with the rail. Whilst this was less of a problem on straight track, it was disastrous on the curves of points which were not perfectly level.

Solution 3: What was needed was some simple form of compensated suspension - to allow the leading wheels to follow the contours of my uneven trackwork. After considering (and rejecting) a range of complex hinged systems, I eventually opted for the simplest - a U-bracket which was loosely mounted so it could rock from side to side.

 A bracket was made from 64thou brass strip, with two fixing-holes along the centre-line.

Between these holes a short length of 2mm diameter brass rod was soldered.

The bracket was then bent into shape and fixed in place with self-tapping screws as, unlike nuts and bolts, these could be screwed-in without me having to dismantle the bonnet assembly (a fiddly process).

Another test-run showed that this solution was successful. The wheels now remained in contact with even my most irregular trackwork.

A few more test-runs showed I needed to adjust the back-to-back distances on the wheels on the powered axle, but the railmotor will now trundle around the railway at a sedate pace with only the occasional mishap - usually explained by overhanging vegetation or twigs which have fallen on to the track.

I spruced her up by giving the radiators and headlamp surrounds a couple of coats of brass paint and painted the underframes and steps with matt black.

And then, of course, she needed extensive test-running ......

And then, although she will never need to traverse R1 pointwork (the only R1 points I now have on my railway are in the copper mine sidings), I decided to see how she would fare through the most challenging trackwork on my railway.

No trickery involved (apart from editing out the manual changing of the points) - I even tried her flat-out through the points without mishap. However, she struggled to get through two R1 points connected in tandem to form a cross-over. But this was because the buffers between the two cars locked rather than any problem with the suspension system.

So, I feel very pleased with my applied problem-solving in this instance. This is one of the reasons I find railway modelling so rewarding - each day presents a new challenge which requires ingenuity and sometimes dogged persistence to overcome.

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