Would like to lock out my friction drive based on speed

[Kepler]

I am trying to make my friction drive more idiot proof by keeping it locked out until a minimum safe engagment speed has been reached. I am finding the friction drive works incredibly well if operated under the correct condtions. However, engaging the drive at very low speeds needs to be avoided. This is easy for me ride around who knows the setup but can be a problem for someone that isnt useto the setup.

Is there any way I could use my Cycle Anaylist to intercept the 0-5V signal from the throttle to carry out this task?

 

[tritonwow]

Not sure about the CA. How about hacking a bicycle computer (speedo)?

 

[evblazer]

Is there any way I could use my Cycle Anaylist to intercept the 0-5V signal from the throttle to carry out this task?

I've been trying to read the documentation on the feature. Here is their wiring diagram for trying to keep a controller at the speed.

It also mentions only being able to work in the ma range on the throttle override which killed my ideas involving contactors and such.

According to evlogix post over http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=11682&hilit=evlogix.&start=30 the throttleizer will go to zero throttle if the throttle is disconnected so could that be a start? (could be what tritonwow was eluding to)
I wonder if running one of the throttle signals through a reed switch and something to hold the connection a ms or so (small cap across 5v and ground?) while the wheel rotated on a two wire speed sensor would blow up the throttleizer :? I mean going to zero in case the cord gets unplugged is one thing doing it over and over might be completely different. The cap if I'm using it right might help lesson the constant on off once you got up to speed and proper sizing might allow it to give you a minimum speed to engage, I did change majors in college to get away from this stuff though so this could be a really bad idea . I wouldn't be willing to guinie pig my setup at least without a little blessing from evlogix at least.
I may use that throttle disconnect info to implement a brake throttle off though.

 

[rkosiorek]

the problem is that you need to reverse the signal from the CA. the CA acts like a speed limiter to set the maximim speed of the vehicle. you need something that will not let the motor to start operating until a certain speed is reached. which is the opposite.

you would need some external circuitry to make this work.

rick

 

[amberwolf]

You could use a 555-timer based circuit, which is fairly simple. Basically have the sensor on your wheel you're using for counting wheel revs for speed also resetting a timer or one-shot that's the first stage. As long as the time between pulses is long enough (slow enough speed) it does not reset the first stage, so the first stage keeps the output held in whatever state inhibits your friction drive.

Then once the time between pulses is short enough to keep the first stage reset, it'll allow the output stage to uninhibit the friction drive.

There are some circuits out there on many 555 timer websites that could be modified to do this easily enough. Most use another 555 timer as the source of the pulses, but in your case you will replace that with the pulses from your wheel rev sensor.

 

[mr.electric]

Zappy scooters turned the motor on and off with a relay. It would not turn on until you hit 2-3 mph. It was a very simple circuit. I can't remember the name of the transistor like component wired to the relay. Fechter would know how that circuit worked. The way the circuit functioned was voltage in from the motor spinning at a certain minimum rpm enable the relay to turn on. Some people would solder two leads of the transistor like component together to over ride the rolling start function.

The zap roller drives evolved from solid knurled steel to a piece of roughly splined steel with an aluminum core to finally a piece of aluminum shaft with a donut of grinding stone glued on. The stone rollers worked great even worked ok when wet. The best part was they never wore out because the stone would not ever get smooth like a worn knurled roller.

 

[amberwolf]

The way the circuit functioned was voltage in from the motor spinning at a certain minimum rpm enable the relay to turn on.

It probably is just a transistor, with the base lead tied to the motor voltage, and the emitter tied to the battery negative, collector tied to negative end of the relay coil.

Soldering across collector/emitter would override the function.

I suppose that really is a simple way to do it for any brushed motor it'd be really easy. I guess it'd be ok on a brushless, too, just hooking the base to one phase wire.

The only thing you'd have to be sure of is to use a reasonably high-voltage transistor; one that could take a base-emitter voltage that is as high as whatever the back-EMF of the motor phase might be. Alternately, a resistive voltage divider can be put on the base so that it only gets a portion of the BEMF. If a potentiometer is used for this, the trigger point can be adjusted easily.

 

[evblazer]

The friction drive on Kepler and a few others doesnt' touch the wheel when not on so using the drive motor as a triggering device wouldnt' work. A cheap bottle dynamo with minimal pressure on the rim might work? I used to be able to get one for a few bucks at the mart.

You could use it only when other people ride your bike since you know to pedal first. Have a switch to enable to pedal first option or straight off and the bottle dynamo (or homemade device to the same purpose) can easily swing on/off the rim.

 

[mr.electric]

What if you used a crank sensor or wheel sensor to trigger an enable circuit. You could build it on the same board as some other function like a precharge resistor or 12v light system.

 

[amberwolf]

The wheel rev sensor triggering/resetting a 555 is what I first suggested.

 

[EVTodd]

Kepler,

I can't recall what voltage you're running your system at but perhaps consider simply raising it a bit so you have more power down low.

I'm running at 36 volts and can start from a dead stop without much drama. I'm sure it's a bit hard on the controller so I really try to pedal first anyway but it does work.

 

[Kepler]

Thanks for the input guys. At first I thought this would be a simple addition but has proven to be quite a bit more involved than I first anticipated. The 555 circuit could be a solution and I have made a couple of these for throttle control purposes. However, my electronic skills only go as far as building a simple circuit from a wiring diagram and custom modification as suggested by amberwolf is a little bit out of reach at the moment.

Using the available signal from the CA still seems to be a possible solution but as mentioned, would need to essentially operate in reverse. From what I understand, the CA cruise control function works by applying a 0-5V signal to the controller and is wired to intercept and override the signal from the throttle. Speed below the cruise set point will increase the voltage and speed above the set point will decrease the voltage. I am thinking this may be a usable signal for me to work with.

The Throttleizer has a brake switch input with a normally open action. Closing the contact will shut down power as if you just put on the brakes. My thoughts are that I need to convert the Analogue 0-5V signal from the CA to a digital signal so that I can open and close the brake circuit as required. Let’s say the cruise control is set to 10kph. A speed below this setting is going to drive the CA cruise control output to 5V. A speed above 10kph is going to drive the output to 0V.

With the above in mind I believe what I need is an Analogue to digital converter that can be programmed to switch a contact at a set voltage. I am thinking that at anything below 3V output and the contact is closed. Anything above 3V output and the signal is open.

So does this sound like a possible solution and if so, is there a simple device or circuit available to carry out this task? (I am searching at the moment)

 

[Kepler]

Kepler,

I can't recall what voltage you're running your system at but perhaps consider simply raising it a bit so you have more power down low.

I'm running at 36 volts and can start from a dead stop without much drama. I'm sure it's a bit hard on the controller so I really try to pedal first anyway but it does work.

I run mine either 5S or 6S (18V to 25V). Also my motor is smaller then yours. I think your setup is a little more robust then mine too. Low speed starts (below 5kph)are very hard on my setup especially considering my motor is 320KV and has a ratio of 14:1. Good for speed, not so good for low down torque. Other issue for me is that the bike tube sleeve works really well under most conditions. However, low speed starts tend to rip the sleeve to peices. There are always compromizes but I am more then happy to work with these compromizes as the rest of the system works so well.

 

[evblazer]

How long ago did you get that Throttleizer and was it one with the dual current limit function? I just got one and I noticed it didnt' have the e-brake wires shown in the manual I'm wondering if the dual current limit replaced the e-brake.

I'm also interested in what you come up with for this. I've only been a few test rids on my bike but would love to make it so it can't start when it really shouldn't. I have my amp limit low but even low amps at near zero speed is probably really harsh on the controller and motor, and will eat that nice tube sleeve.

 

[Kepler]

I got mine at the start of the year. It has the dual current limit function and the ebrake input. I suppose if you dont have the ebrake feature on yours, just breaking the circuit from the throttle will lock the controller out.

I think a circuit like this might be of use for a quite a few RC applications, not only friction drives like ours.

 

[amberwolf]

However, my electronic skills only go as far as building a simple circuit from a wiring diagram and custom modification as suggested by amberwolf is a little bit out of reach at the moment.

If I find the page that has the circuits you need I'll post them up; there is a page (lots actually) that has just about all the possible 555 circuits, shows what they do, and gives a calculation and/or table of values to get different frequencies and/or delay times. You'd just calculate how long you need things to wait and build it with the parts from the table/calculation.

With the above in mind I believe what I need is an Analogue to digital converter that can be programmed to switch a contact at a set voltage. I am thinking that at anything below 3V output and the contact is closed. Anything above 3V output and the signal is open.

You can use an op-amp (comparator) circuit for this simply enough; there are lots of pages on the web showing the components and diagram for it.

Even simpler is an optocoupler, if you find one that inverts the signal. So you have the resistor to the LED side of the opto set to bias the LED inside to On above 3V. Use a pot so you can play with the current needed to do that. WIre the transistor output of the opto across the switch. (assuming the switch input is grounded on one end--if it's not, you can use the opto transistor to turn on a relay and have it's contacts close the switch instead).

But even simpler is just an NPN transistor with a voltage divider on the base, and your input voltage at the top end of the divider. Bottom end of the divider goes to ground, as does the emitter of the transistor. Base of transistor goes to center tap of the divider. Collector of transistor goes to one side of the switch input, other side of switch is assumed to be grounded. If not, use the transistor to trigger a relay to close the switch. Use a pot for the voltage divider, with wiper on the base, to make it easy to set the trigger point.

If either of the triggering methods won't work because it's inverted from how you need it to operate, then using the relay as the final stage makes it easy to invert, by using the other set of contacts on it (if it is a relay with both NO and NC contacts).

 

[Kepler]

Could this circuit do the trick?

Simple Analog to Digital Converter Click here for the circuit diagram

Normally analogue-to-digital con-verter (ADC) needs interfacing through a microprocessor to convert analogue data into digital format. This requires hardware and necessary software, resulting in increased complexity and hence the total cost.
The circuit of A-to-D converter shown here is configured around ADC 0808, avoiding the use of a microprocessor. The ADC 0808 is an 8-bit A-to-D converter, having data lines D0-D7. It works on the principle of successive approximation. It has a total of eight analogue input channels, out of which any one can be selected using address lines A, B and C. Here, in this case, input channel IN0 is selected by grounding A, B and C address lines.
Usually the control signals EOC (end of conversion), SC (start conversion), ALE (address latch enable) and OE (output enable) are interfaced by means of a microprocessor. However, the circuit shown here is built to operate in its continuous mode without using any microprocessor. Therefore the input control signals ALE and OE, being active-high, are tied to Vcc (+5 volts). The input control signal SC, being active-low, initiates start of conversion at falling edge of the pulse, whereas the output signal EOC becomes high after completion of digitisation. This EOC output is coupled to SC input, where falling edge of EOC output acts as SC input to direct the ADC to start the conversion.
As the conversion starts, EOC signal goes high. At next clock pulse EOC output again goes low, and hence SC is enabled to start the next conversion. Thus, it provides continuous 8-bit digital output corresponding to instantaneous value of analogue input. The maximum level of analogue input voltage should be appropriately scaled down below positive reference (+5V) level.
The ADC 0808 IC requires clock signal of typically 550 kHz, which can be easily derived from an astable multivibrator constructed using 7404 inverter gates. In order to visualise the digital output, the row of eight LEDs (LED1 through LED8) have been used, wherein each LED is connected to respective data lines D0 through D7. Since ADC works in the continuous mode, it displays digital output as soon as analogue input is applied. The decimal equivalent digital output value D for a given analogue input voltage Vin can be calculated from the relationship

 

[Kepler]

The above circuit needs a 550khz clock signal which they say can be easily derived from an astable multivibrator constructed using 7404 inverter gates. Sounds simple enough :? Would anyone know of a simple circuit for this?

 

[amberwolf]

That ADC is a pretty overcomplicated way to do what you want to do.

The 555 timer would be a better choice to use for the oscillator in your case since there are schematics already available on many 555 pages showing exactly how to make it and calculate the resistors/capacitors for a particular frequency.

However, if you really want to try it, the 7404 inverter oscillator is simple; just put a resistor between the input and output of one inverter on a 74HC04 chip, connect that output also to the input of another inverter on the same chip, put a nonpolarized capacitor between the input and output of that same second inverter, then connect that second inverter's output to the first one's input. The frequency will be approximately 1 divided by the Resistance times the Capacitance, IIRC.

Used to use that kind of oscillator a lot in my sci fi props for blinky lights and sound effects.


Really, though, the other circuits I suggested will be much simpler to build, and cheaper.

 

[Kepler]

Thanks Amberwolf, simpler and cheaper sounds good to me

Anyway, I have a few options now so time to get some bits and start experimenting.

 

[amberwolf]

I found a couple of resource pages:

http://www.national.com/an/AN/AN-31.pdf
http://www.national.com/analog/amplifiers/application_notes
http://www.ecircuitcenter.com/Circuits.htm

http://home.cogeco.ca/~rpaisley4/LM555.html
http://www.kpsec.freeuk.com/555timer.htm
http://www.doctronics.co.uk/555.htm#Images_swf/555_pins

Some of the links on this page:
http://www.talkingelectronics.com.au/projects/50%20-%20555%20Circuits/50%20-%20555%20Circuits.html
show you good info on how it works and some circuits and things, without buying the ebook.

This site you'll have to scroll down, as it may not show anything relevant on the "first" page.
http://www.josepino.com/circuits/?555_circuits1.jpc
http://www.josepino.com/circuits/?555_circuits2.jpc

http://www.talkingelectronics.com.au/projects/200TrCcts/101-200TrCcts.html

 

[Kepler]

Great stuff. Appreciate your help.