Plunger Pickups

I may have mentioned before that I really really hate fitting pickups to locomotives. It doesn't matter how well built the model is, if it can't reliably pick up poer than it's next to useless. Unfortunately I find making and fitting pickups really difficult. Sometimes it's a problem with the material either causing too much friction (a problem I had with the 24hp Hudson Hunslet prototypes) or that they aren't springy enough and end up loosing touch with the wheels.

When desiging the wheels for Ivor I made the decision to isolate one wheel from the axle, leaving the other live. This means that for one side I can pick up power from the chassis (i.e. it goes through the wheel into the axle, and then through the bearings into the chassis) leaving me with only two wheels that need pickups.

In the past the pickups I've fitted have all been of a similar design, using wire to rub on the rear or flange of a wheel. For Ivor though the kit was designed to use plunger pickups which I'd never even seen before let alone used. I bought a pack of 10 from Alan Gibson, and it's a good job that was more than I needed.

Essentially each pickup consisted of three parts. There is a small plastic insert which fits into a 2.5mm diameter hole in the chassis in line with the back of the wheel. You then fit a tiny spring to a small turned brass plunger and slide that into the plastic housing. With the body of the plunger just inside the housing you bend the thin end over. This means the plunger now can't leave the plastic insert and is springy. A wire can then be soldered to the bent end to provide the electrical connection.

Not sure how good that description was, but hopefully you get the general idea from this photo of them fitted to Ivor's chassis. Note the red wire soldered direct to the chassis to pick up power from the other side; I was originally going toput this underneath the chassis but it was a paint to get the iron in, hence scratching off some paint to solder it on the top.

With the pickups fitted I reassembled the chassis and temporarily wired the pickups to the motor for a test. Initially it was terrible. I think this was partly a lack of weight, but also I'd painted the rear of the balance weights and I think I'd strayed too far towards the edge of the wheels causing the pickups to loose contact with the metal surface. After removing a little of the paint (which you'd never see anyway) and adding blutak for weight we had this.

Clearly not perfect, but not terrible either. Hopefully once the wheels are quartered (the live wheels are slightly loose on the axle) and the coupling rod fitted to drive the second axles things should be a lot better, but given the struggle to get to this point I'm happy with that.