..........Driving Trolley

This is not going to be a blow by blow account of how to build a trolley but merely a brief description with a few pictures. It's a pretty simple trolley based on ones I've seen at various rallies and I claim no originality for the design. It was built very quickly (in about a week) as I needed one to use at a running day at North West Leicester SME's track in early July. Since then I've stripped it down again to finish it off (e.g. fit some brakes!) and give it a coat of paint. It's designed for use on raised track but could be adapted for ground level tracks by fitting a box to sit on and straight footrests instead of the long ones.

The chassis is 24" in length and constructed from 3/4" square mild steel tube of 16swg thickness all MIG welded together. It's a long time since I've done any MIG welding and it shows! Still, it doesn't look too bad now it's painted. I don't think it will fall to pieces in a hurry.

The 'buffer beams' are 1/8" steel plate again welded on. The towing brackets are bits of 3/4" x 1/8" steel angle drilled with five sets of holes so that the coupling links can be positioned to give a straight pull on multi-gauge tracks. The coupling links can also be set at different heights to suit different gauge locos. The beams extend to just above track level so that the trolley will rest on them if it derails rather than tip up (in theory anyway!)

Various views of the chassis

The suspension is by swinging arms pivotted to the chassis at the outer ends with coil springs at the inner ends, the axles being in the middle. The swinging arms are nothing fancy, just lengths of 1"x1/2" mild steel.

Underside of chassis showing anchor points for the swinging arms

and pivot pins for the brake calipers

Swinging arms

The springs need to be quite strong and the ones I've used are only temporary as they are the clutch springs from a motorbike I am rebuilding! (the only ones to hand at the time) They're a bit too short really so I turned up some spacers to make up the length required. I'll replace them with longer springs when I get chance. Each spring assembly has a bolt running through the middle anchored through the chassis at the top and a nut under the swinging arm. This holds the spring in place and stops the swinging arm dropping completely.

Springs, bolts, and spacers

The wheels and brake discs are turned from mild steel blanks rather than castings. Apart from the fact that steel seems to wear better than cast iron it works out much cheaper. All six blanks only cost £14 and there's not really any more work involved than machining castings. The only problem was that the blanks had been sawn with quite a wedge shape so a fair bit had to be machined off before they were flat! The axles are tubular and are fitted with needle roller bearings at each end which run on fixed silver steel axles. The wheels are loctited onto the tubes but the brake discs are welded on for security. Welding these was right at the limit of my welder, consequently the welds are a bit 'blobby'! The faces of the brake discs were skimmed with the wheel assemblies mounted between centres in the lathe to make sure they ran true to the axles. One wheel is drilled to take a rare earth magnet to operate a reed switch on a digital cycle speedometer which will enable me to keep a record of mileage covered by the locos pulling the trolley. I can also see how fast I'm going!

Wheel assemblies

Axles and swinging arm pivots

The footrests are simply lengths of 5/8" square by 16swg tube cut, bent, and then welded at the joints. These fit into a 3/4" square cross tube welded to the trolley chassis. Unfortunately the 5/8" square tube was slightly too big to fit straight inside the cross tube so the ends had to be ground down before they would fit easily. If I had used 18swg tube for the cross tube I think the footrests would have fitted without any grinding. I wasn't quite sure how long to make the footrests but 'guesstimated' at 12" which seems to be about right. Too long and they catch on the ground, too short and the riding position is uncomfortable.

Detachable footrests

The brakes will utilise ordinary alloy brake calipers which are easily and cheaply available for mountain bikes etc. They will be operated by a brake lever on the top 'handlebar' of the trolley. Both axles will be braked and I've got to devise some sort of compensation device to balance the braking on both pairs of calipers. I've an idea that may work using just a single inner cable to operate both sets of calipers but we will see.

Brake calipers off mountain bike etc.

08/08/2007

The trolley was quickly put back together for the rally at Little Hay but is now more or less finished.

I still need a decent piece of plywood for the top but made the chipboard one a bit more presentable by covering it with some black vinyl. A couple of lengths of aluminium angle were fastened onto the top at the back to locate the 5 litre plastic container which will serve as the water container until something better comes up. This is held in place by a strap tensioned by a spring enabling it to be quickly fitted or removed. A plastic pipe runs from the water container at the back to a valve at the front which controls the output to the loco.

Due to lack of time I only fitted one set of brake calipers but I think that is probably adequate at the moment. I don't envisage pulling loads of passengers just yet! The brake lever is a short cycle type which is originally designed to clamp around a handlebar. To fit it I cut off the round clamp and drilled the body to take a bolt which holds the lever onto the top bar of the trolley. A spring is fitted between the two brake calipers to push them apart when the brake is released but I think it may be necessary to fit some other springs to centre the calipers in the off position as at the moment they tend to be a bit lop-sided.

The bracket for the cycle speedometer simply clamps around the end of the top bar and the sensor is mounted on one of the swinging arms using small cable ties.

 

Side view of trolley

Front view

Sensor for speedometer

Speedo and water valve

Brake calipers

The only thing missing now is a nice soft cushion!

17/04/2018

Although the driving truck has been fine for use with Helen, I've noticed that for smaller locos it seems to drag quite a lot and they struggle to pull it around sharp curves. It is quite a long wheelbase for a fixed axle trolley and this does cause drag on curves. Also, the axle bearings seem to be getting a bit rough and noisy.

I did strip the wheel/axle assemblies down at the end of last year and noticed that the axles were getting worn and pitted where the needle roller bearings were running on them. Two of the bearings seemed a very tight fit on the axles and I think I may have made the bearings too tight a fit in the housings which compressed them too much causing the damage. At the time I just cleaned up the bearing surfaces of the axles, reassembled everything and carried on using it.

For some time now I have been planning on building a new truck based on the design by David Hudson which features self steering axles and rubber suspension. David wrote several articles in Model Engineer in 2003 describing the theory behing his design and the construction of a driving truck and also twin bogie passenger cars. We have two of his design driving trucks at the club and they are extremely free running. I have used them on many occasions and the difference they make for a small 2½" gauge loco is amazing. We also have six passenger trucks made to his design and they are also excellent. One member of the club, now sadly no longer with us, made a driving truck to the Hudson design and took it to a rally at the Burton Upon Trent club. For a laugh at the end of the day, another member gave the truck a good push to see how far it would go on it's own. It did a complete lap of the Burton raised track and was still going strong!

I took Ayesha to a rally at Tingley a week ago and used my truck there. The poor old girl really struggled to get round (the track has a very steep climb at one point) so I decided it was time to do something about it. I also want to reduce the weight of the truck as it is far too heavy to carry around!

A friend at the club has recently built a lightweight truck from mostly aluminium and this features the self steering axle design. He very kindly gave me some of the aluminium angle that he had left over from building his truck. I will eventually build a completely new truck but for now I'll just modify the existing one.

Rod had his truck at the club last week so I took the opportunity to take a few photographs of his axle assemblies to help decide how to redesign mine.

 

 

How the design works is that the axle is mounted on a plate separate to the frame of the trolley. This plate is suspended by four long bolts from brackets fixed to the trolley via sets of rubber blocks. The rubber acts as the springs and the bolts allow the plate holding the axle to move independently of the frame. This allows the axles to turn and follow the curve of the rails. In the original Hudson design, the wheel treads have a special wheel profile which is not a straight taper but I'm going to leave the treads as they are and see if it will still work. It will be easy enough to reprofile the treads if necessary.

The first job I did was to machine some material off the wheel assemblies to try and reduce the weight a little. The front of the wheels was recessed a little deeper than before and another recess machined in the back of the wheel. The brake discs were also considerably reduced in thickness and just the centre left at the original thickness to act as a boss. This meant machining the complete wheel/axle assembly so one wheel was gripped in the 3 jaw chuck and the other end supported by the axle held in the tailstock chuck. Not a very rigid setup but fine so long as small cuts are taken.

 

 

The machining needed the tools to extend from the tool holder quite a long way so that the toolpost cleared the wheels and brake disc. The topslide was also rotated to give more clearance. The wheel recesses were machined using a carbide tipped threading tool as this gave a nice chamfered edge to the recess. The brake disc was machined with an ordinary carbide facing tool extended out as far as it would go.

I had decided to replace the needle roller bearings with ordinary sealed ball races as I think they may be better suited to this application. I was limited in the maximum size of the bearing by the diameter of the housing that I could machine in the end of the tubular axle so I bought some 6282RS bearings which have an outside diameter of 24mm and a bore of 8mm. I went for top grade bearings rather than the budget grade as they will have quite a high load on them when running. They weren't expensive anyway.

The old needle roller bearings were knocked out of the axles with a drift but one of them was really tight in there and this was probably the one that had badly damaged the axle. It wasn't much use for anything when I finally got it out!

The ends of the tubular axles were then bored out to take the new bearings. Once again, one wheel was gripped in the 3 jaw chuck, but this time I had to use the fixed steady to support the other end. Care was taken to get the wheel running as true as possible before boring out the recess for the bearing.

 

 

20/04/2018

I reused the existing axles and just reduced the ends to fit the new bearings (8mm) and reduced the length of the full diameter part to fit between the bearings. When I machined the housings in the ends of the tubular axles, I made one of the ends slightly deeper and an easy fit for the bearing so that the bearing could slide to adjust it's position to suit the length of the axle. This prevents side load being put onto the bearings if the distance between the bearings does not exactly equal the length between the shoulders on the axle.

 

 

I've still got to rethread the ends of the axles to take the securing nuts when I've decided how long the end section needs to be.

02/05/2018

Now that the DRO job on the mill is finished, it's back to the driving truck.

I need the truck this coming Sunday for a rally at Nantwich so I'm not going to have time to make a start on the new one. In any case, I can't get the suspension rubbers, cups and cones for the new design yet as the supplier, Dave Noble, is on holiday at the moment.

So, it was a case of putting the old truck back together. I threaded the ends of the axles to take the securing nuts and redrilled the swinging arms to take the smaller diameter. I could have made bushes to fit the existing holes but I wanted to move the wheels further inwards to decrease the wheelbase and reduce the friction on curves a little so I drilled the new holes one inch further along the arms. This will reduce the wheelbase by two inches overall. Incidently, the ends of the tubular axles have worn quite deep grooves into the sides of the swing arms as the original needle roller bearings did not control any sideways movement of the wheel assemblies and there must have been quite a significant sideways force when the truck was going around curves. I should have fitted bronze or even brass thrust washers to take the load but I didn't think at the time.

 

 

There must have been quite a bit of friction between the ends of the axles and the swingarms which wouldn't have helped the free running of the truck. The new ball races will prevent any sideways of the wheel assemblies and take care of any sideways thrust.

I quickly fitted everything back together as I want to take the truck to the club tomorrow to give it a quick push around the track to see what it is like. The wheels certainly rotate much more smoothly and quieter than before.

10/05/2018

I took the truck to Nantwich and it seemed as bad as it was before I made the modifications! I don't know what the matter with it is. It went around our track at Coalville ok but at Nantwich it seemed very tight again. The track there does have some very tight curves and the truck did not like them at all. I gave up on it and borrowed one from one of the other chaps and used theirs instead. Time to make the new truck I think!

17/05/2018

The suspension rubbers and cups and cones arrived from Dave Noble today so I can now make a start on the new wheel assemblies.

 

 

06/06/2018

Back to the driving truck again!

Rod had made the frames that holds the axles from a single piece of 3mm steel plate but I wasn't convinced that it would be stiff enough. I didn't have any suitable plate anyway so opted from making frames built up from some of the 1 inch by 1/8" thick aluminium angle that Rod had given me. The frames would consist of two side pieces and two cross members held together with countersink screws.

 

 

The Hudson design, and also Rod's, uses external bearings for the axles mounted in blocks attached to the frames but mine has the bearings in the wheel assembly so the axle can be simply bolted to the side pieces.

So, out came the hacksaw and I cut four pieces of angle for the side frames and four more for the cross members. The ends of the pieces were squared up in the mill and trimmed to the correct length at the same time. I did all the sides together and all the cross members together by stacking them on top of each other and milling them all in one go. That meant that they would all be exactly the same length. It was also quicker than doing them one at a time!

The side pieces needed a cut out milling in them to clear the wheels and this was done with a 1/2" endmill. I set the first one up with the end of the angle level with the end of the vice and then set up the cut using the DRO. Once one was done I could take it out and put the next one in, again with it's end level with the end of the vice, and mill it using the same settings as the first. Thus, I only had to set everything up once to cut all four cutouts.

 

Milling the cut out in the side pieces to clear the wheels

 

The next job was to drill all the holes. There's a 1/2" diameter hole to take the nylon cups that hold the rubber blocks and four holes around this to take 3mm countersink head bolts that hold the cross members to the sides. This was an ideal opportunity to use the DRO to locate the centre of the 1/2" hole and then use the circular array feature to position the other four holes. I used nothing but the DRO to locate and drill all the holes in the sides and the cross members and never had to measure or mark out anything. Brilliant!

 

Using the edge finder to locate the edges of the angle

 

Using the circular bolt hole function

 

All holes drilled with no marking out needed at all.

 

When drilling the holes I did the same as when I was milling the cut outs i.e. I set the end of the angle level with the end of the vice jaws. After drilling the holes in one end of the angle I simply took the piece out and replaced it with the next one so it was only necessary to do one set up for each end of the angles. I must admit that I find 'mass production' like this a bit tedious but it all went fairly quickly so it wasn't too bad a job.

Once all the holes were drilled everything was deburred. The holes in the cross members were countersunk to take the fixing bolts and the corresponding holes in the side pieces tapped 3mm.

Time for a trial assembly and it all fitted together perfectly. All the holes lined up and the fixing bolts went in with no binding.

 

 

I've still got to make some spacers to go between the bearings and the side frames so I've just used a load of washers for the time being. Also I haven't shaped the side frames yet or cut down the cross members to suit. I wanted to see if it would all work first.

I thought that I would fit the suspension parts to see how it all looked and noticed the rubbers didn't have holes all the way through them so I had to drill them out. They are a very tight fit on the bolts that go through them so that will have to be sorted.

 

 

The idea was to fit a length of angle along both sides of the existing truck frame at the bottom between the front and back plates which would support the bottom of the suspension but unless I use longer bolts between the rubbers I think there may be a problem with clearance between the angle and the bottom of the side frames. I have ordered some longer bolts just in case but I may have to rethink this as I'm not sure how fitting longer bolts will affect the self steering qualities of the axles. I could take some off the bottom edge of the side frames which would give more clearance. It probably isn't necessary to have a lot of clearance as putting a load on the truck i.e. sitting on it, will cause the truck to drop relative to the axles and increase the clearance anyway. I suppose it depends how hard the rubber blocks are and how much they will compress under load.

14/06/2018

I spent Friday and Saturday working feverishly to try and get the truck finished for the rally on Sunday but failed miserably!

I dismantled the axle frames and tapered the bottom edge of the side frames as per the drawings. I also reduced the depth of the angle on the cross pieces to suit. This was necessary to get enough clearance for the axle frames to move about without catching on the supporting angles. I fitted the two angles along the bottom edge of the trolley as originally intended but instead of supporting the ends of the suspension directly on these, I fitted cross angles which removed a lot of the clearance problems with the original design. The height of these angles had to be reduced as well to get enough clearance between them and the cross pieces of the axle frames.

It was then time to fit the axle assemblies into the trolley frame and I then discovered that the new brakes on the axle assemblies fouled the old cross support for the previous brake arrangement! It was now late on Saturday night and I decided to call it a day as things obviously weren't going to be finished for Sunday. I don't think the neighbours would be happy with me sawing away in the early hours of the morning!

The rally on Sunday went well and the weather was gorgeous. I took Ayesha for a run and used the trolley that belongs to the Association. That thing weighs a ton but seems to run fairly well. I was pleased to see that Ayesha's lubricator seemed to be working ok now. It had been a bit hit and miss the last few times that I had run her. I think the spring in the check valve was too strong so I fitted a weaker one.

I returned to the truck on Tuesday and got it finished up, well at least to the point where it could be used. I sawed out the crossbeam that fouled the brakes and everything fitted nicely after that.

I had made a bit of a mistake when drilling the holes to take the nylon suspension cups. I had drilled them clearance size for the spigots on them but really they need to be a press fit to stop them falling out of the holes when the trolley is lifted up and the weight taken off the wheels. There is no guarantee that they will go back in the holes when you put the truck back down again. As it happens, the axle frames can't drop enough to allow the cups to fall out of the holes as the bottom of the axle side frames sits on the two angles that run the length of the truck. It wasn't planned to work like that but very fortunate that it does!

 

Axle assemblies supported by the two longitudinal angles and the four cross angles

 

Top and bottom views of the completed trolley

 

Brake Assembly

The brakes are virtually the same as before but the brake levers pivot on a 10mm bolt screwed into the cross member of the axle frame rather than a cross beam fastened to the trolley frame. This is necessary as the brake assembly needs to move with the axle.

I'm not overly happy with these brakes as they are very cheap and the clamps don't secure the brake blocks very securely. I'll probably replace them at some point. They could do with some centreing springs as well to keep the brake blocks from rubbing on the brake disc when in the off position.

I also modified the seat so that it can be removed. It was permanently fastened before with screws through the frame into the underside of the seat.

I took the completed truck to the club today and tried it on the track. It really is free running now and rolls a good distance given a good push. It's very smooth running, much quieter than before, and the rubber suspension seems to absorb all the bumps in the track. I sat on it and it rolled all the way down a slight incline at a nice slow speed with no problems at all. I would say that it is now as free running as the two club driving trucks. The real test will be behind Ayesha though but I've high hopes that this new truck will be very successful. There's another running day at Nantwich on July 8th and that will be a very good test for it!

The standard straight coning on the wheel treads seems to work fine so I may not bother remachining them to the Heumann profile as described by David Hudson in his articles. I have a feeling that this profile will probably only be effective on correctly profiled aluminium rail anyway. Most of the tracks that I run on consist of plain steel bar with a flat top and square edge so the profile is probably not as important and straight coning will be fine.

I had originally intended to make a complete new trolley with an aluminium frame but there doesn't seem much point now. It would only save a bit of weight and the truck seems quite a bit lighter now anyway so I think I'll just leave it as it is.

That's another project out of the way. Only 9,999 to go!

09/08/2018

We had a 2½" gauge running day at the club on July 22nd and so that gave me the chance to try out the new truck behing Ayesha. Unfortunately, Ayesha was not at her best that day (I think the lubricator is playing up again) but I still managed a few laps before deciding to call it a day. The new truck is a world apart from the old one and Ayesha had no trouble at all pulling it around the track so I think I can say that the new truck is a resounding success. Quite a few other people have asked for details etc. and where to get the suspension components so I expect to see a few more trucks of this design in the near future.

 

 

 

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