Fechter's Throttle Interface for RC controllers

[fechter]

Am an nnamed John Tetz has been able to eliminate that current spike. You can find his info on the WISIL site that hosts my recumbent build.

Matt

The current limiting function of my circuit is intended to eliminate (or at least limit) the startup spike. That's why it's there.

I designed the circuit that John Tetz is using. It is the same concept, only I opted for using the Allegro sensor instead of a shunt.

 

[MitchJi]

Hi Richard,

The current limiting function of my circuit is intended to eliminate (or at least limit) the startup spike. That's why it's there.

I designed the circuit that John Tetz is using. It is the same concept, only I opted for using the Allegro sensor instead of a shunt.

Sorry I'm so electrically challenged but will it eliminate the spike when shifting gears?

Thanks!

Mitch

 

[fechter]

Sorry I'm so electrically challenged but will it eliminate the spike when shifting gears?

Thanks!

Mitch

Yes. That's the idea anyway. It may take a bit of tweaking to get the loop response matched to the controller, but I'm hoping it will be pretty universal. I think you would still want to back off on the throttle when shifting.


The problem is most RC controllers are designed for very low inertia loads and the current spike on acceleration is typically short enough for them to survive. They are also set at a level that is intended to keep the FETs from blowing, which might be way higher than what it takes to snap a motor shaft or strip some gears. On a bike, the acceleration takes much longer and on a hill, you could be at the limit for minutes at a time. If the current limit is set too low, you will just not get the full rated power. On a bike, it's handy to be able to adjust this as it greatly affects your range and performance.

 

[dontsendbubbamail]

Fechter,

Could you give us a walk through on how the circuit works? The one you or Goodrum did on the BMS was very helpful.

Bubba

 

[fechter]

Start with the schematic again:


R1, D1 and Q1 are a pre-regulator for U1 (up to 100 volts). U1 is a 5v regulator. The 78L05 also acts as a current limiter to help protect the rest of the circuit from shorts. Everything runs on 5 volts.

U2 is a dual cmos version of a 555 timer. The left side uses R2 and C2 to generate a square wave at 50hz. This gives the 20ms time frame for the RC pulses. Output from the left side passes through C3 which shortens the pulse so that the second timer does not get a trigger signal when it's time to turn off. R4 discharges C3 on the other part of the cycle.

The right side of U2 produces the actual 1ms to 2ms pulses. R5 and C4 are the basic timing elements. Changing either of these can be used to adjust the pulse width at zero (1ms).

Pin 11 of U2 is the control voltage input. The pulse width of the output will be controlled by the voltage on this pin. Resistors R3 and R7 are used to scale the throttle voltge to the correct range to get the desired span (full throttle pulse width). R6 is a pull down resistor to pull the throttle down in the event the throttle cable gets disconnected (safety feature).

U3 and U4 make up the current limiter circuit. The output of U4 with no current is 2.5v. At maximum current, the signal from U4 is around 4.5v. R9 and C7 are used to filter out the controller PWM noise from the signal. R10, R11 and RV1 make up a voltage divider to set the desired current limit which can vary from near zero to 100% of the sensor rating. U3a compares the signal from U4 to the setting from the voltage divider. As soon as the current signal exceeds the divider setting, the output of U3a goes low, pulling the control voltage down, decreasing the throttle signal to the controller. C6 and R8 provide a proportional range and slew rate limit to the output of the amplifier so the signals do not change too quickly. C6 and R8 will adjust the speed of the loop response.

 

[northernmike]

SO when can I purchase one?

 

[swbluto]

The basic idea behind this is so much easier to implement on a microcontroller and the code makes it inherently easier and quicker to upgrade/modify. But, this should be good enough for bikes, I suppose. As far as scooters go, it seems the amount of "torque" on start-up is crazy enough to buck the rider off so implementing a custom current ramp is essential.

By the ways, we could all say "bubba" foresaw this. Well, anybody who actually tries to convert RC use to e-bike or other uses would see a need, anyways. I know I did. :lol:

 

[fechter]

The basic idea behind this is so much easier to implement on a microcontroller and the code makes it inherently easier and quicker to upgrade/modify.

Maybe for you :wink:

I don't do code so well. There are some other advantages to analog also, but it would be cool if someone made a micro based one.

 

[GGoodrum]

SO when can I purchase one?

Maybe as soon as next week, but certainly the week after. The proto boards should show up on Wednesday. Richard will get his by Friday. We just need to test it with several controller brands (I have a pile of different controllers here...), and see what values need tweaking. Should know something by next weekend. Anyway, once we get it tested, it won't take long after that. Four days for the PCBs and two days for parts.

Before you ask, I have know idea what this will cost yet. It depends on what everything ends up costing.

-- Gary

 

[swbluto]

The basic idea behind this is so much easier to implement on a microcontroller and the code makes it inherently easier and quicker to upgrade/modify.

Maybe for you :wink:

I don't do code so well. There are some other advantages to analog also

There is?

I'm kind of ignorant of the analog "real world"(and my school doesn't want to allow me to use an oscilloscope because my current electrical class is not "advanced enough".), although I understand the basic concepts behind almost all the parts in the schematic. I take it one advantange is nearly instant response as opposed to the ~100 nano-seconds a microcontroller would take?

And believe it, dooooooood, programming has become much easier than the days of Assembly and Fortran yore! Apart of that is due to the explosion in memory density which allows one quite a bit of memory on a chip for a program, which allows for easier-to-use languages and easier abstracting functions.

(But, yeah, I could be pretty biased here. I guess the fact I started programming when I was 12 might have something to do with its seeming simplicity. I'm sure years of practice has made designing analog circuits quite easy?)

By the ways, how do you slow down the response time of the current limiting op-amp? Is it possible to divide the voltage being negatively fed back to the negative input to a lower value to slow down the adjustment rate? Or is a certain capacitance increased? I should read your detailed post first before asking questions, I guess.

 

[voicecoils]

I'm kind of ignorant of the analog "real world"(and my school doesn't want to allow me to use an oscilloscope because my current electrical class is not "advanced enough".)...

Very strange, we were immediately required to use a CRO in my first first-year EE subject at Uni. :?

'scope days are far from over IMHO

 

[j3tch1u]

fechter, would it be possible to integrate a motor brake signal into your design? i'd like to enable brake regen but don't want it to kick in on low throttle when coasting. ideally, your interface would cut throttle and send a 1ms pulse to esc when a switch is toggled on the brake lever.

 

[fechter]

The brake switch input shown on the schematic will pull the throttle signal down a bit lower than zero throttle. You could adjust the pulse width at zero throttle by trimming with a resistor. My guess is it will work the way it is.

 

[j3tch1u]

perfect! your throttle circuit is exactly what i'm looking for.

 

[northernmike]

Soooooo ....

When 'sit coming?

I almost bought a servo tester a minute ago.

 

[swbluto]

Is anyone planning on offering a product? if so, what kind of product? Offer the PCB and then the components would have to be purchased and installed by the customer? Or is the PCB and components offered and then the customer has to install them?

As far as I understood, it seemed like Gary's famous BMS was offered in the "PCB only" format and parts had to be ordered separately and customer installed(And it seems installation instructions had to be further awaited on... hah. hah.).

 

[GGoodrum]

Is anyone planning on offering a product? if so, what kind of product? Offer the PCB and then the components would have to be purchased and installed by the customer? Or is the PCB and components offered and then the customer has to install them?

As far as I understood, it seemed like Gary's famous BMS was offered in the "PCB only" format and parts had to be ordered separately and customer installed(And it seems installation instructions had to be further awaited on... hah. hah.).

I just got the first test boards yesterday, and sent one up to Richard this morning. We need to do at least a little testing first, and I suspect that will result in a few tweaks, here and there. I have the first cut at a "production" board ready-to-go, as shown below:

We will try and offer these as completed units, but we'll see hw it goes.

 

[nieles]

this is the kind of throttle circuit i have been looking for.

will it work with this hall trottle?
http://tncscooters.com/product.php?sku=101100

if not could someone post a link for me?

 

[deecanio]

Hi Nieles,

i think richard said that it would work with any hall or 5k pot throttle so i would assume so unless anyoneknows differently?

Cheers,

D

 

[fechter]

this is the kind of throttle circuit i have been looking for.

will it work with this hall trottle?
http://tncscooters.com/product.php?sku=101100

if not could someone post a link for me?

Yes, should work fine with that one.

 

[nieles]

thanks for the heads up 8)

the copper traces for the high power, will these be thick enough to transfer 50-100A?
the traces will get hot if there is not enough copper right?

and for the caps to be most effective they need to be as close to the controller as posible,
mabye an seperate pcb for the caps near the controller?

Niels

 

[MitchJi]

Hi,

and for the caps to be most effective they need to be as close to the controller as posible,
mabye an seperate pcb for the caps near the controller?

Niels

Why not just mount it very near the esc?

 

[swbluto]

Is anyone planning on offering a product? if so, what kind of product? Offer the PCB and then the components would have to be purchased and installed by the customer? Or is the PCB and components offered and then the customer has to install them?

As far as I understood, it seemed like Gary's famous BMS was offered in the "PCB only" format and parts had to be ordered separately and customer installed(And it seems installation instructions had to be further awaited on... hah. hah.).

I just got the first test boards yesterday, and sent one up to Richard this morning. We need to do at least a little testing first, and I suspect that will result in a few tweaks, here and there. I have the first cut at a "production" board ready-to-go, as shown below:

We will try and offer these as completed units, but we'll see hw it goes.

Gotcha. Testing is definitely needed for electronics.

Btw, what kind of PCB program do you use to create the PCB layout? Are there any you'd recommend for a cheap-skate beginner?

 

[swbluto]

Interestingly, I just noticed that there wasn't a provision for a temperature sensor. Any particular reason?

(it's a little hard to implement w/o a microcontroller? *nudge* *nudge* )

 

[fechter]

Interestingly, I just noticed that there wasn't a provision for a temperature sensor. Any particular reason?

(it's a little hard to implement w/o a microcontroller? *nudge* *nudge* )

Actually, the other half of the op-amp can be used for that. I did not include that for simplicity and the fact that you need to settle on a 'standard' temperature sensing device.

Maybe on the next revision...