Difference between revisions of "The drive mechanism"
(New page: The drive mechanism is both the strength and weakness of the 2000X. Positive: # It reduces weight by many pounds over the conventional chain driven system (like the i-ped). # It splits th...)
Revision as of 12:31, 11 February 2009
The drive mechanism is both the strength and weakness of the 2000X.
- It reduces weight by many pounds over the conventional chain driven system (like the i-ped).
- It splits the load between two motors, allowing for use of (relatively) cheaper motors and some measure of redundancy
- It also allows for a longer running board by placing the motors to the side of the motor, rather than in front or on top (like the i-ped. One of the biggest complaints of the go-ped i-ped is that the motor is where you would want to hold the board in a balanced fashion. The other is that you need to stand on the i-ped with feet side-by-side).
- It also makes the motors less conspicuous, which is very important in situations like public transportation where a large motor and wires make other people nervous.
- The drive mechanism has an optical wheel which gives feedback to the electronics how fast the motor is turning. This is a great safety feature preventing the motorboard from accidentally starting while been moved from place to place (as in public transportation).
- Overheating is a big problem with DC motors. You want to provide vents for heat dissipation, but vents bring dust. Roth's solution was to have the motors enclosed in a large air space. (The i-ped mounts a huge heat dissipater on top of the motor which is both ugly and hot if touched by accident).
- The friction between the motor drive shaft and the motor can slip if the motorboard hits a bump in the road. This can cause the motor to spin out and carve a notch into the wheel. I assume that the optical wheel sends a signal to the PIC16F73 microprocessor to cut power to the motor if it detects a sudden increase in speed (spinout).
- The friction is also very dependent of the width of the wheel. After a month of driving (say 150 miles) the wheel is too thin (not to mention possible cracked or damaged by the road) to provide adequate traction causing frequent spinouts and this in turn cause the electronics to shut down.
- Production of the wheels seem to vary by several millimeters, with other defects. It seems that the requirements of caster wheel manufacturers (that's what the Roth wheel is) are not used to the precision required by the 2000XR
- Overheating is a big problem with DC motors. It doesn't appear to me that Roth provided any protection against overheating, although they included a buzzer on the electronics board which may have been meant to sound some kind of warning.
Roth mentions several times in the manual to watch out for a "clicking noise" which indicates that the tires should be replaced. This can be caused by notches, in which case it is correct to replace the wheel. Or it can be cause (as in my case - see thread "Loss of power") by the DC motor brushes not functioning.
In my opinion the 2000X would be better (and much cheaper) than i-ped if the drive system could be modified. I have some friends that can build anything in metal, if I know what to ask for. I was thinking of:
- Some kind of metal harness for each motor that could adjust the tension of the motor on the wheel. This could allow the motor to be moved closer to the wheel as it wears down, or completely away from the wheel if the battery has died and you want true free wheeling.
- Caps that would fit over the cones to provide increased traction
- Plastic disks that could be fitted on the wheel to provide increased traction.
- A true mechanical connection that would not rely on friction, such as a notched hub which fit on the wheel and was driven by a motor with matching sprockets.
One of the biggest problems with Roth Motors is the lack of support. But in truth, I would prefer a motorboard that I could service myself. I don't want to send my board to California to get it repaired. But to do this, the motorboard needs to indicate what is wrong. Additional sensors would be helpful
- A thermocouple could be added to each motor to sense heat buildup.
- A magnet could be embedded into the wheel to provide a Hall sensor with the actual speed and distance of the motor.