Really interesting stuff, this -
As a total newbie to the electric bike world, I had thought that the Agni brushed motor represented some sort of "state of the art" standard .... but, costs must be cut somewhere, and maybe the brushes and their holder are the place where it happened ...... ?
No question in my mind (degree in geophysics ..... ) that your iron mining locality could produce copious dust which would just love to cake an air-cooled electric motor with crud. One thing I'm starting to think about here in droughts-ville (norCal) is the effect of water on the high-current motor control electronics.
Mike
It would appear that the brush carriers are the weak spot in the motor. After looking at this motor I have come to the conclusion that the Bakelite design is just not up to the task and that the current path through the brushes, is too long and results in brush heating. I am thinking about trying copper brush guides, to both carry current closer to the tip of the brush and to dissipate heat better from the brushes.
I found an interesting quote about running the Agni motors in a dual configuration. That tends to cause them to burn up, the thing is it is the carrier that tends to fail... According to Giampiero Testoni of the eCRP (Energica) team: “We used to show up to the races with a pallet of motors – swapping them out as they burned up.†On one particular occasion, even with the help of the master himself – Cedric Lynch – it was nigh-on impossible to keep the motors from burning out when pushed to race tolerances. A well-known builder and racer in the Australian community is fond of referring to the dual-Agni race bikes as “…the twin Indian smoke machinesâ€. The motors
typically failed around the brush assemblies, but also, because of the long, narrow armature design, could fail with the armature warping to one side or the other.
The quote from above, would tend to indicate that if this type of motor is going to fail when problems occur, then it will likely be the carrier burning up. The individual pig tails can't manage the current when things go wrong, they act more like heating elements, or even filaments... The springs end up taking current too and the whole lot burns up.... It is interesting to note that on other motors, that I have researched, that it is more common to use metal to hold the brushes, at least at the business end of the brushes. I really don't think any kind of plastics are a good option close to the commutator arcs. I am fast running out of time for my experiments. What I have learned though, is that the motors should really be getting filtered air. Magnets trap dust and shorts in the commutator slots increases current consumption and heating. Copper fragments from drag over can also cause problems with armature shorts.
The other thing that I would look at with this motor if I was going to keep it, would be to add an advance function. I have some old central locking door actuators that look like they would be good to adapt for the job. It would allow for advancing the timing a few mm on the motor on the fly. More power for less current at low and high speeds, rather than a compromise setting, it would act like an "overdrive" for highway use. The need for "matched" brushes in the Agni is being exacerbated by the design of using an insulated tube to hold the brush. Any uneven resistance of the brushes exacerbates individual brushes to end up carrying more or less load and subsequent failures when pushed harder as a pair may end up taking most of load and fail.
Cam
Author
Topic: Acme sensor for Agni brush temperature. (Read 1146 times)