since the recent most epic of fails, the future of Brems-Chopper was unclear. It sat in MITERS for a couple of days with its toasted-rotor heart removed.
it wasn’t until the amazing KOUTTRON, master of electromechanical contraptions, offered a Baldor treadmill motor that there was hope once more.
soon after Dane brought it over to MITERS, I removed the peripherals and measured its characteristics.
On the bench I attached a piece of tape to the shaft and applied voltage. MMM, nice quiet motor. I used the MITERS Strobotac (a strobing tachometer) to measure the shaft speed. Dividing shaft speed by voltage gives Kv, measured here in RPM/V. It is measure of how fast a motor spins given a certain voltage.
the framerate here doesn’t sync up right so the effect is not very visible. When the strobe pulses exactly once every motor shaft revolution, the tape appears to not move. The dial to adjust frequency on the Strobotac is graduated such that a rough measurement can be taken.
The baldor measured out at about 30 RPM/V – about a 50% gain over the previous No Name treadmill motor.
I inspected the brushes to get the necessary pre-Brems analysis.
By some miracle of motor standards (NEMA?) the can diameters of the new and old motors were identical. This saved a ton of potential work that would have been making new motor mounts. Praise be to moter jeesus.
but the first boot after the BremsFire incident was silent. The contactor wasn’t getting power and the green light on the 12V brick was out. I pulled the brick and found it to be dead. Strange. The thing is pretty much hermetic so it would be a stretch to call water/snow damage. The rest of the controller was totally fine, so I don’t think it was related to any nastiness flowing backwards through the Big Power side of things. It could be that this power brick doesn’t like being run absurdly out of spec for long periods of time. Oh well.
I went on a quick Stata techno-trash gathering run and harvested another inverter based 12V brick. These things are certainly not in short supply. With it installed, the BremsVehicle booted just fine.
Well I dragged the thing outside into the beginnings of Boston’s second major snowfall this winter. it felt kind of… weak. an inaugural tiny puff of smoke emerged from the pristine Baldor. No damage, just uhh, warming up those brushes.
Oh right, derp. It takes shittons of torque to plow through the snow, plus this motor is 50% higher Kv than the last one and the thing is geared for speed.
I hauled the clunky contraption back inside to Revise My Gearing. a quick search of 25 pitch sprockets in MITERS yielded promising results. I found a 24 tooth as well as a tiny 14 tooth. Stepping down to 24 teeth from 32 would approximately match the pre-BremsFire top speed with the new motor. I figured running near stall in the snow was probably a cause of sadness for the old motor, so it would be worthwhile to step it way down for future snomoBrems action.
Not wanting to painstakingly hand-file another keyway like I did on the 32 tooth sprocket, I opted to use set screws with turned ends to engage with the motor shaft keyway. Shud be fine. Drilling and tapping was done on the bridgeport.
The tiny 14 tooth sprocket only had a 3/4″ dia. boss attached to it. That wouldn’t have left much thickness for a set screw to engage with. I turned out a chunky adapter doodad with some chamfers on it to be welded to the small sprocket.
Here’s partway through TIG welding. I bored both parts to 1/2″ and put a piece of 1/2″ rod through them to hold concentricity while welding. I ground the tungsten to a sharp point to try to get down into the 45 degree channel. The weld has to be low-profile so that the chain doesn’t rub against it. This was an exercise in heat control on the TIG. It was easy to dump too much heat into a tooth and melt out some undercut.
overall, it came out OK. I finished the bore out to 5/8″
As was feared, the chain rubbed a bit on protruding filler material. I popped the part back on the lathe and took down the excess with a parting tool.
Well then we had some good fun for a few days. Brems-Chopper is actually a decent snow vehicle. It’s best on hard packed snow where the ski and rear wheel can get some bite.
It wasn’t until the evening after some late night unfilmed deep snow action that the brushes decided they’d had enough.
It was a confusing debugging process at first. Controller spat out pack voltage — good, motor measured about 2 ohms — good. Oh wait, JK. When I jiggle the wires the motor looks like an open circuit.
I went so far as soldering the crimped connections inside the motor before noticing that one of the brushes had split in half and was no longer making good contact with the braid.
Whoops. Must have run it too hard somewhere in there.. I ebayed some spare brushes for cheap. Till they arrive, we’re snowbound.