Here is the update I sent to Warren to load on teh web site; :wink:
I have put about 200 miles one the E-Cumbent since building it and I am having a blast with it! I have, however, encountered a few problems. A couple of them are simple issues, not worth discussing here. However, one problem has been nagging from the beginning;
The AXI motor has an odd issue. The Back EMF (magnetic pulse the controller uses to "Read" the motor armature position) is not consistant. Basically the motor can resonates at one specific RPM which confuses the controller and make the motor eminate a loud screaching sound. When that happens, I get off the throttle, let the controller read the motor RPM properly, then get back on the throttle. I did alot of research into this. It is not a controller problem, it is a specific issue unique to AXI motors. It is rarely discussed because the motor is designed for airplane use. As such, it does not affect its operation in an RC plane. However, in my application, it is an issue.
So, I began looking into replacement motors. None that I found is a direct replacement. One, however, looked fantastic, but would not fit my bike without serious modifications. That is the Plettenberg Terminator 30-8 heli motor. I have run Plettenberg motors in RC helis for years. They are the best outrunners money can buy. Well, I e-Bayed a LARGE amount of RC stuff to buy this motor and it was worth every cent!
The issue mounting it is related to the diameter (among other things). It is 14mm wider than the AXI. The AXI was already a tight fit. This thing just barely fits and only after a large amount of machining. Here's what I did;
I removed the power unit and the AXI motor. Im then removed the motor front plate. That was done to drill and tap two 4mm holes to fit the 1.75 inch AXI mount hole locations. This was done to eliminate the need to maching a new plate on the power unit. This step was far quicker.
Next, I completely disassembled the power unit. Every screw and aluminum piece was removed, machined (if needed), cleaned, drilled, tapped, etc, etc, etc. Very few parts were not modded for this conversion.
Once I began disassembling the power unit, I removed a center divider wall in the power unit to provide clearance. Next I machined the heck out of the power unit sides. I removed every bit of aluminum I could from the power unit to make the motor fit. It is such a tight fit that the sticker on the can was too thick and got rubbed off in one spot! The fit is so tight, in fact, that I had to make a new chain idler bracket for clearance, and I only have 3mm fore/aft movement of the motor for belt adjustment, and that 3mm is only possible by moving the entire power unit back 3mm.
I spent a total of 7 hours on it. Now, how does it run? Wonderful!
Here's the scoop on its performance;
The back EMF screach is totally gone. No problem at all! It accellerates perfectly smooth all the way from 0 RPM to full throttle. This motor has very little sound compared to the AXI. It does not groul and whine like the AXI. It makes a sonderful muffled whistle that is pleasing to the ear. It also is more tractable at very low speeds (5mph pulling my kids in the Burly trailer). This motor is also more powerful. The AXI is rated at 4,000 watts. This Plettenberg is rated at 6,000 watts! However, I only pull 3,000 watts from it most often (hard accellerating). I have the slipper clutch set to protect the driveline. But, it is obvious the Plettenberg is less stressed when pushed hard than the AXI was. The AXI never really seemed to like being pushed really hard. It would run well, but always felt like it was unhappy with the use. Not so with the Plettenberg!
The only downside is a slight reduction in efficiency. This motor is larger with a lower efficiency rating. I have not alculated it axactly (been pulling the kids in the trailer). But, it is taking a touch more amp hours to recharge after our typical ride. With the AXI, I averaged roughly 16 watt-hours per mile. If I had to guess, I would say this motor is more like 17 or 17.5 watt-hours per mile. Not a bad drop, but it does seem to be a touch lower than the AXI. I will calculate it exactly and get back to you with the numbers. What I find odd about the drop in efficiency is the motor heat. I would expect an increase in motor heat with a drop in efficiency. However, that is not the case. This motor runs the same temp as the AXI. Again, I will have to check the efficiency exactly and get back to you.
Well, that's it for now!
Matt
