Monthly Archives: October 2013

New testing platform – initial build

I’ve finally started bolting together my second electromagnet testing platform. This is built on an MDF base, attached to an old Elite Chrono Fluid trainer stand.

tp1

For the roller I’m just using an old dumbbell shaft, held in a couple of one inch pillow block bearings. Shaft collars hold the flywheel weights, and will also hold the brake disk once it’s added.

tp2

A first spin up with the bike has highlighted a lot of drag in the bearings, despite some attention with a grease gun. You get what you pay for I suppose, and these particular bearings were pretty cheap and agricultural. The drag might not be noticeable on a tractor, but in this configuration my PowerTap says it’s taking over 400 watts just to hold a steady 20 kph!

Hopefully this is just drag from the seals, so next I’ll pop those out and try it again…

v1 modifications

After using the v1 trainer on a regular basis for the last couple of months, there were a couple of minor usability issues that I wanted to address.

First up was the position of the motor assembly and electronics. As the standard resistance cable is designed to run up to the bar mounted lever, when everything is laying on the floor it extends beyond the front wheel by perhaps a couple of feet. Because of this, my makeshift servo mounting was forever getting kicked and trodden on, and just generally getting in the way.

enclosure7

So first job was to replace the original resistance cable with a shorter, slicker, cable run. This would get everything tucked away beside the front wheel, and potentially have the side effect of reducing any positioning inconsistencies introduced by the cable itself. At the same time, I’d get the electronics and the motor into the aluminium enclosure I’d previously bought for this purpose.

For the cable I used a stainless Jagwire shifter cable and compressionless outer housing. The shifter nipple was ground down to a 3mm diameter to fit the resistance unit, and for attaching at the pulley end I used a 4mm screw-on cable nipple from eBay. Fine tuning of the free play is provided by a cable adjuster at the entry to the enclosure.

enclosure5

The servo was mounted inside the enclosure using a section of right angle aluminium riveted to the base of the enclosure. The circuit board is mounted on nylon PCB stand-offs, with some extra insulating tape where it might touch the edge of the enclosure. Rather than upgrading to panel mounted connectors, I’ve just filed some recesses into the side of the enclosure for the cables, which are then lightly pinched in place by the lid when closed.

I’d also become a bit spoiled by quarter turn Garmin mounts, and wanted to use one for the handlebar mounted controls. In this instance, I happened to have a spare quarter turn adapter for a 705, which I simply hot glued to the base of the the control box.

quarter

With these simple modifications out of the way, and finally some free time on my hands, I will be turning my attention back to the v2 electromagnet testing platform. More updates on this soon…