Sunday, November 3, 2013

Drive Train and Brake Drive Design

This weekend there was a lot of progress in the drive train design as well as in the trailer brakes.

We arrived at a motor decision, we'll be using the LMC-170 motor.  It is a bit smaller than the motor used in the eSuperbike but it is still an axial flux PM DC motor, it can give us a lot of power (...a lot). We ran some simulations to determine the gear ratio we should use.

Speed Time curve for Trike at 0% grade

Speed-Time for 10% grade

screenshot of simulink model (made by Abraham, Roberto and Nigel)
The plots above are at a voltage of 50V (duty cycle of ~50% in the controller), also at the speeds shown above our speed is limited by the no load speed of the motor (which is of course dependent on the voltage) this means we have the freedom to increase our speeds considerably if we increase the voltage a bit. We'll be limiting the motor speed via the motor controller output voltage to stay within legal limits.

From the data shown and practical considerations of the size of the sprockets we arrived at a gear ratio of 8. Erich and Alex are currently busy designing/buying the sprockets using the #35 chain specs. Jacob and Will were busy all day yesterday CADdding out the mounting of the motor. Here is a picture of the current design.

notice the eccentric motor mount that allows for tensioning the chain
We have put in the order for the motor and as soon as we get some more detailed cad for the motor we can go ahead and manufacture the mounts.

The brake team had a very productive day, we decided to try out some work-gear driven motors (like windshield wiper and car window motors) to actuate the brake cables. These motors have huge gear reductions which makes them very hard to back drive which is great for us. The simplicity of the motor will allow us to drive it open-loop to open and close the brake calipers.
c-clamp holding the motor for testing

jack and j-rod testing out the motor driven brakes

We powered the motors from a power supply and the mechanism worked well. The addition of these brakes will give us lots of stopping power and keep us safe in the road.

The EE team also had a big day yesterday but I'll let them give you guys an update in a separate blog post.

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