All wheel pickup for P&D brass Blomberg trucks

[Bob]

Over the years I've tried many different ways to get reliable all wheel electrical pickup with P&D's beautiful cast brass Blomberg trucks. From P&D only half the wheels pick up power from the rails, and that goes through a torturous path involving rotating and sliding parts. How can one add reliable all-wheel pickup wipers?

There's not a lot of room in the trucks, since they are very close models to an equalized and sprung Blomberg B truck. Yes, one of the cross bars at the left end of the truck is still sitting in a jar waiting for installation.

Reminder: Click on a photo to enlarge it in a new window.



Just before the 2023 Denver O Scale Convention I purchased some excellent photo etched wipers from Rod Miller, but didn't have time to do much with them. These wipers are 3mm tall and etched from 0.008" phosphor-bronze. Over the last couple days I've been designing and milling wiper mounting blocks from raw 1/4" Delrin bar stock.

Here's a first "dry fitting" assembly. Two 0-80 screws hold down the wipers, which were right angle bent using an etched metal bending tool. A single 2-56 screw runs up the bottom through the spring plank center oval hole to keep the block in place. All screws are 1/4" long, and the 0-80 screws stop just shy of exiting the Delrin, so no short circuits.



The wipers still need to be formed and cut to length. Just past the edges of the Delrin block I plan to bend them outward to produce the primary spring tension. They will wipe on the back of the wheels approximately at axle height. Because of the contact position, friction will want to raise one end of the wiper and lower the other end. To counter this, the wiper sits in a 3mm deep x 0.1" wide rabbet that supports the wiper edge and prevents it from twisting or rocking up and down. A little shelf below the wiper's edge keeps it from shorting to the spring plank. If my calculations are correct, there should be about 0.040" of clearance above to the next potential short circuit surface.

Bends were made using a new/never used etched metal bending tool.

Because I make lots of mistakes while manual machining, I started with 40 Delrin blanks and spoiled 4 before I got into the flow over several days. 36 survived the process. To be honest, after hand tapping two 0-80 holes 1/4" deep I was dreading the future of my wrist. Then it dawned on me to grab a cordless drill and power tap. All 72 0-80 holes were tapped in a jiffy! Normally I wouldn't try to power tap in metal, especially gummy aluminum, even with a 2-flute "gun" tap that shoots chips forward and out the other side of the hole. Delrin is ultra-machinable, and not once did the 3-flute tap come close to jamming.

Thanks to Rod Miller for sharing the Mouser part number for the tiny crimp lugs. I think I'll solder some very flexible Adafruit black silicone insulated 26 AWG wire into the lugs.

Now it is time to start painting some trucks and frames.

[Bob]

Finally, these wipers were installed in David's lone F3B that shoves hoppers at the Brookstone coal Loadout. This engine is receiving a new paint scheme, and an ESU decoder upgrade.

[Bob]

David finished repainting/weathering his F3B. With a new Loksound 5L DCC decoder and the new all-wheel pickup, stalling is a thing of the past and it creeps very slowly in the slowest speed steps.

For best operation the engineer can use the slow increment/decrement buttons on an NCE ProCab to precisely set just the right speed. Four or five different speeds should be suitable for continuous flood loading of coal hoppers.

[Bob]

Found a need for 8 more trucks worth of wiper blocks. Instead of setting up the saw and mill for a short run, I decided to 3D print them. The design and printing took less time than subtractive machining in Delrin. The parts are not as precise and a little rough in finish, but they are fully functional.

[Bob]

Here's an application of the 3D printed wiper blocks for one of David's F7B units. I tore into it because there was an out-of-gauge wheel that caused frequent derailments. The wiper screws are 0-80 and the mount to the spring plank 2-56. These holes were hand tapped since my FDM printer can't print useful threads at these miniature sizes.



And the final installation. I really like Rod Miller's wipers.



An astute observer may notice that the right side gear box is not tightly screwed together. I discovered that some of the wheel axle gear profiles changed between early and late models. When the screws were fully tightened, there was a once-around bind with the brass worm. Loosening the screws a tad allows the two gearbox halves to slightly move relative to each other. I applied Loctite to the 4-40 gearbox screws to keep them from loosening.