Controlling the acceleration of the motor

hi,

the throttle has a potientiometer and varying the voltage signal of the throttle changes the speed of the motor.

so how do you control and vary the acceleration of the motor? can advise?

thanks
regards
brian

i think the new Cycle Analyst v3 will do that for you. ask justin.

how? throttle input to acceleration???

i don't have the manual so you should go see if you can read up on it at justin's website.

CAv3 provides current throttle and power throttle in addition to speed throttle. It's not acceleration (doing literally that would be obviously unfeasible: set a given acceleration, wait long enough, and voila' you are at supersonic speed) but practically quite near and probably what the OP meant. I am very satisfied with current throttle.

all the throttle i see are potentiometer so it's voltage signal throttle. how does CA3 convert it to current throttle or power throttle?

what are the advantages of current throttle over typical potentiometer voltage signal throttle?

quamau said:

CAv3 provides current throttle and power throttle in addition to speed throttle. It's not acceleration (doing literally that would be obviously unfeasible...

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The OP did not say he wished to control the acceleration with the throttle. The V3 throttle ramping function effectively limits acceleration.

Acceleration is the rate of change of velocity. V3 throttle ramping indirectly addresses acceleration by clamping the rate of throttle change so that throttle (PassThru, Current, Power, or Speed) cannot change at greater than the specified rate - up or down. This is not motor/bike acceleration per se, but the effect is similar.

The feature can be used to limit the rate of change of throttle application so that getaways are smooth and wheel-spin-free even if WOT is applied off the line - effectively avoiding rapid bike acceleration. Small throttle excursions (small rates of change below the configured ramping limit) are unaffected.

brianLEV said:

all the throttle i see are potentiometer so it's voltage signal throttle. how does CA3 convert it to current throttle or power throttle?
what are the advantages of current throttle over typical potentiometer voltage signal throttle?

Click to expand...

As suggested above, you might be best served by examining the V3 Unofficial Guide. In particular, see sections "1.2.6 Throttle Enhancements", "5.2 Closed-Loop Throttle Modes", and "4.8 Adjust Throttle Ramping"

brianLEV said:

all the throttle i see are potentiometer so it's voltage signal throttle. how does CA3 convert it to current throttle or power throttle?

what are the advantages of current throttle over typical potentiometer voltage signal throttle?

Click to expand...

First off, the voltage and current we talk about are motor voltage and motor current. Any voltage from the throttle or pot is just a signal and could be 0 to 10V, or 1 to 5V, or even 4 to 20 mA. It is just a signal used for a reference in the logic of the controller.

teklektik explained the operation of the CA. I am not familiar with it as I haven’t used one yet. But I do have experience with EV controls and motor controls in general. I maybe I can help you understand.

With motors and controllers on loads consisting of mass, the formula of interest thanks to Sir Newton is F = ma. Force translates thru the wheel radius and chain ratio to motor torque. Motor torque must be proportioned to the amount needed to overcome drag on the vehicle and gradient (I call this road load) and torque used to accelerate the mass. When the road load consumes all the torque output of the motor, acceleration stops and the vehicle continues at a steady speed (condition of equilibrium).

So to control acceleration, motor controllers can do a fairly good job by controlling motor torque. Without going too technical, motor torque can be controlled by motor current. Current is easier to sense than torque. So the throttle device can supply a reference signal representing a desired motor current and the controller will sense the actual motor current and adjust the PWM such that actual moves toward the reference. So if you want to accelerate faster, you increase the reference. If you don't want to accelerate, you set the reference to the point where the torque is just enough to equal the road load. And you get varying degrees of acceleration in between maximum current request and the point of just enough to maintain steady speed.

i see. thanks for the explanation.

so the rate of change of voltage in the throttle signal is proportional to the current going into the motor, hence acceleration. to clarify.

but how does the system know how fast the voltage should change. by how fast u change the throttle position? what if u hold the throttle at the same spot so how does it know how much acceleration needed to maintain constant speed?

thanks

brianLEV said:

so the rate of change of voltage in the throttle signal is proportional to the current going into the motor, hence acceleration. to clarify.

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No, that is not what I said. The throttle signal is a fixed voltage dependent on the position of the twist or lever. That signal voltage is used by the controller to set a fixed reference for motor current which will cause motor torque which will cause acceleration. That level of motor torque and motor current resulting from that fixed throttle voltage signal will accelerate the vehicle until the programmed speed limit is reached or until the entirety of motor torque is consumed by the road load and equilibrium is reached.

Here is a simplified example. The controller uses an 0 to 5V throttle. The rider twists it to 60%. It sends 3V to the controller. The controller sets a current reference at 60% of the maximum current. The motor then produces torque which starts increasing the speed of the vehicle. As the vehicle speed increases, the throttle stays at 3V. The motor current stays the same. The torque produced by the motor stays the same. The RPM and mph increase. As the mph (vehicle speed) increases, the road load increases so less and less motor torque will be there to accelerate the vehicle. Eventually all the motor torque is being use to overcome aerodynamics and friction (road load) and none is left to accelerate the vehicle. So equilibrium is reached at 20 mph for instance. Now, if a faster speed is desired, a further twist to 80% will cause 4V sent to the controller and it will reset the reference to 80% current and the motor torque will increase causing acceleration to 25 mph or so (the new equilibrium).

This is just an example of how a motor controller produces acceleration from a throttle signal. There are other methods. And I have simplified the process for clarity. I hope this helps the basic understanding.

I control my acceleration by going wot from the start if I want fast acceleration, or slowly increasing the throttle if I don't. The same as I do with my car.

brianLEV said:

.... how does it know how much acceleration needed to maintain constant speed?

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That's an interesting question. I'd say, constant speed infers zero acceleration. Acceleration is the rate of change of speed. Constant speed is no change in speed, so no acceleration.

In answer to "how does it know"; it knows by feedback through the rider. He will adjust the throttle position depending on his sense of speed and how he desires to change it. If he wants to maintain a constant speed, he holds the throttle at a position giving him just enough torque to equal the road load. If the road load increases, like due to a hill or wind, then he'd slow down but he will sense that and increases the throttle position to increase the motor torque to maintain a constant speed.

How all this is accomplished inside the controller can be seen in a thread I noticed today. http://endless-sphere.com/forums/viewtopic.php?f=2&t=61004