Pedal generator for lightweight car with all electric drive

[CharlesR]

I want to build a pedal generator for a lightweight vehicle.

I have a PMSM generator, from a small wind turbine (Rated power 300W, 600 RPM, 48 V), that I can run with a 1 to 5 gear ratio from the pedals.


Ideally, the generator should be used to charge the battery and control the drive-motors with speed and torque.

Is there a controller for this requirement?

Regards
Charles

 

[From-A-To-B]

Cannot comment on which controller you need, but I do suggest you search around for others experiences on similar projects.

For instance: Charging your battery with a bicycle electric generator

The general sentiment is that pedaling to charge a battery, then take the battery energy to drive a motor is both lossy and produces underwhelming results.

Likely, you’re better off building a pedal car (or car where your pedaling contribution runs directly to the drive), OR just charging a battery and using its energy to go forward.

There’s a reason why you don’t see ebikes where the cranks power a generator which charges the battery.

 

[DanGT86]

You can use any controller with adjustable regen to control the generator portion. You will need to have a wide range of adjustment on Regen power since human legs are particularly weak. The simplest way to do it would be to have this separate from the controller that is driving the wheels. So run this regen pedal generator power from that controller to the battery.

For Pedal assist you will need any controller that is capable of taking inputs from a torque sensor. Or you could use a Cycle analyst and a cheap controller.

I don't know of any controller that will handle both jobs at the same time. You would likely be better off just using one motor and controller and pedaling along to help it.

 

[CharlesR]

thank you for your answers.

As has DanCT86 written, it makes sense to separate the charging of the battery and the motor control.

The generator can also be bought in a bundle with a rectifier. If that worked, that would be an easy solution for battery charging. Could this work?

 

[TrotterBob]

This might give you some ideas. I havent tried it but I like the concept of being able to pedal at a standstill and charge vehicle batteries. Would also allow a separation between electric and human powered drivetrains. Also I think adding a flywheel to the generator side of this setup would make the pedal feel more natural.

 

[fechter]

As long as there's a diode between the generator and the pack, I don't think you really need a controller for it. It's unlikely you will overcharge your battery pedaling.

 

[Chalo]

I want to build a pedal generator for a lightweight vehicle.
[...]
Ideally, the generator should be used to charge the battery and control the drive-motors with speed and torque.

If you assume the use of a battery, then charging it by literally any method other than pedaling would be more effective and satisfactory. Is this just some proof-of-principle novelty gizmo, or do you aim to use it for some practical purpose?

Like fechter says, if you get the gearing right for the generator's RPM/volt, you only need a 3 phase rectifier and a power diode to prevent the battery from backfeeding the generator. (When I built a stationary generator cycle, I also put in a mechanical relay as a hard disconnect for the diode.) But trying to charge your battery this way will grind you down, with very little charge to show for your effort.

 

[TroySmith80]

I'm very interested in the same question as Charles asked in the original post. I'm not sure, but I think the reason he's asking maybe similar to my reason.

It's not about providing any meaningful amount of energy via my pedaling, it's more about using a natural, bicycle-like experience as a way to control the power delivery of the main power system... Instead of a throttle.

So in my case I would want 20 or 100 times the power I'm generating to be output from my main motor. It wouldn't even be that problematic to just use a resistive load and burn off the power I create as heat, it will be trivial in comparison to the total amount of energy being used. Does understanding that change anyone's answers or help to better understand the intent of the question? To the op, if I've got this wrong please correct me so I don't derail your thread.

 

[offGridDownUnder]

I would want 20 or 100 times the power I'm generating to be output from my main motor

I read this as you have another power source to provide the majority of the input to the main motor and thus the power output from the main motor to turn the wheels. You want the power generated by pedaling to serve as a modulation to control the input/output of the main motor, but not provide the majority of the power that the main motor consumes and transforms into motion.

If that's correct, then your controller does the job of a Pedal Assist Sensor (PAS). Depending on how the PAS is implemented, it might output a small signal of it's own which is read to determine the amount of assist, or it may modulate a small power source to provide that signal. Your approach simply limits the creation of the signal to the first of the two approaches - generation by the PAS.

A controller then accepts the signal from the PAS, and modulates the power the controller provides to the main motor according to the signal from the PAS.

 

[Chalo]

It's not about providing any meaningful amount of energy via my pedaling, it's more about using a natural, bicycle-like experience as a way to control the power delivery of the main power system... Instead of a throttle.

I don't know if you've ever pedaled a generator bike or anything comparable to that, but trust me when I tell you it's not a natural bicycle-like experience. Yes, your feet go around and it uses effort, but that's as far as the similarity goes. To me, it feels more like pedaling against nothing, but still getting tired from it.

I guess you could set up a DC motor with some reduction to give you a 0-5V output without any real resistance, and then you'd get a direct cadence-proportioned throttle signal. With any load on the pedals it will just feel like pedaling bread dough.

 

[amberwolf]

I suppose you could use the generator's controller to load it variably based on the torque the wheel's motor requires to move the vehicle. (vaguely worded because it's probably something that would need to be experimentally tuned, probably by using an MCU of some type to monitor and control this).

 

[beemac]

I'm very interested in the same question as Charles asked in the original post. I'm not sure, but I think the reason he's asking maybe similar to my reason.

It's not about providing any meaningful amount of energy via my pedaling, it's more about using a natural, bicycle-like experience as a way to control the power delivery of the main power system... Instead of a throttle.

So in my case I would want 20 or 100 times the power I'm generating to be output from my main motor. It wouldn't even be that problematic to just use a resistive load and burn off the power I create as heat, it will be trivial in comparison to the total amount of energy being used. Does understanding that change anyone's answers or help to better understand the intent of the question? To the op, if I've got this wrong please correct me so I don't derail your thread.

Isn't that a complicated and energy-wasting torque sensor?

 

[TroySmith80]

yes.

The reason a normal torque sensor won't work is because i can't really couple my pedals to the drivetrain because i would need a full-range gearing allowing me to pedal from 5-40mph in a drivetrain that can take 10kW. That doesn't exist (as far as i know), not at any reasonable price anyway.

Maybe it would be easier to just put some kind of adjustable friction brake on the cranks with a torque-sensing bottom bracket?

 

[offGridDownUnder]

The reason a normal torque sensor won't work is because i can't really couple my pedals to the drivetrain

I read this as meaning you don't need any mechanical connection between your pedals and drivetrain. If that's not the case, perhaps you could clarify so we can reason about what you want.

If this is what you mean, you are effectively 'ghost pedaling' except that in your case it's physically true that there is no mechanical connection between the pedals and the driven wheel. I can do what you want now by using my stock Grin Baserunner, Cycle Analyst, and hub motor by taking the chain off. The PAS on the cranks signals what I'm doing, the Cycle Analyst and Baserunner tell the motor what to do based on that signal.

Some of the time, I'm doing this now with the chain on - I can pedal and hear the freehub ratchet clicking as the wheel turns faster than the input from the cranks - the signal tells the controller to spin the motor faster than I am pedaling.

I have also set the Cycle Analyst with 20 levels of pedal assist, and I use an up-down rocker (stock equipment) to move up and down through the levels, so that it's like selecting a 'gear' for the motor - the same pedaling will offer different levels of assist and speed/climbing for each. Roughly, think of an electronic push-button gear shift. There are other modes to interpret the signal-to-motor-output which I haven't explored yet.

I do not have, but Grin also sells an 'infinitely' variable dial controller that does the same, but not in jumps. You can set the amount of motor output on the fly to match whatever pedaling speed you cared to use.

This is off the shelf - just don't connect your pedals with a chain to your drive. Does this meet your needs?

 

[JackFlorey]

The reason a normal torque sensor won't work is because i can't really couple my pedals to the drivetrain because i would need a full-range gearing allowing me to pedal from 5-40mph in a drivetrain that can take 10kW.

That's an 8:1 range. A Schlumpf bottom bracket plus a Rohloff or equivalent gearhub will give you 13:1.

 

[Hillhater]

Maybe it would be easier to just put some kind of adjustable friction brake on the cranks with a torque-sensing bottom bracket?

Thats a bad idea…you would just be wasting your energy directly to friction/heat .
i assume you are aware that even the best system will only produce <200W on average from your legs…..if you are fit !

 

[TroySmith80]

I read this as meaning you don't need any mechanical connection between your pedals and drivetrain. If that's not the case, perhaps you could clarify so we can reason about what you want.

If this is what you mean, you are effectively 'ghost pedaling' except that in your case it's physically true that there is no mechanical connection between the pedals and the driven wheel. I can do what you want now by using my stock Grin Baserunner, Cycle Analyst, and hub motor by taking the chain off. The PAS on the cranks signals what I'm doing, the Cycle Analyst and Baserunner tell the motor what to do based on that signal.

Some of the time, I'm doing this now with the chain on - I can pedal and hear the freehub ratchet clicking as the wheel turns faster than the input from the cranks - the signal tells the controller to spin the motor faster than I am pedaling.

I have also set the Cycle Analyst with 20 levels of pedal assist, and I use an up-down rocker (stock equipment) to move up and down through the levels, so that it's like selecting a 'gear' for the motor - the same pedaling will offer different levels of assist and speed/climbing for each. Roughly, think of an electronic push-button gear shift. There are other modes to interpret the signal-to-motor-output which I haven't explored yet.

I do not have, but Grin also sells an 'infinitely' variable dial controller that does the same, but not in jumps. You can set the amount of motor output on the fly to match whatever pedaling speed you cared to use.

This is off the shelf - just don't connect your pedals with a chain to your drive. Does this meet your needs?

In that case, you just have cadence sensing, right? Because there's no resistance on the pedals, so there's no torque in the cranks.
That would meet my needs if there was some (adjustable) drag on the cranks so that I'd get some exercise and there would be torque to be sensed.

 

[TroySmith80]

That's an 8:1 range. A Schlumpf bottom bracket plus a Rohloff or equivalent gearhub will give you 13:1.

In theory maybe possible. Very expensive and you can't combine a schlumpf and a torque sensor, can you? Also, probably dont want to put a ton of power (like 8kw+) through an expensive rohloff.

 

[TroySmith80]

Thats a bad idea…you would just be wasting your energy directly to friction/heat .
i assume you are aware that even the best system will only produce <200W on average from your legs…..if you are fit !

Right, that's the point, my 200w is pretty inconsequential if we're talking about a 6-12kw system so it doesn't really matter if I just waste that power out to heat.

I just want the exercise and a "natural" feeling riding experience.

 

[offGridDownUnder]

I just want the exercise and a "natural" feeling riding experience.

Perhaps I've misread above, but this seems to me to be the first time I've read this aspect of what you want.

All up, I gather now that the only connection between the movement of the vehicle and you is that your pedaling decides how it moves forward. How fast, although you may have some other idea in mind.

A cadence sensor or a torque sensor on the pedals can provide this input for the main motor.

Another system entirely can provide the physical experience you want - a generator, or an energy sink.

Apart from the pedals being the origin of both, there is no connection - you can do whatever works for each.

Unless you want a physical way to pedal and move the machine without any power source, such as if it breaks down.

 

[Chalo]

Right, that's the point, my 200w is pretty inconsequential if we're talking about a 6-12kw system so it doesn't really matter if I just waste that power out to heat.

I just want the exercise and a "natural" feeling riding experience.

Well, include an effective flywheel in your system, or else couple it to the vehicle's forward motion. Because if you don't do one or the other, the feeling at the pedals will be anything but natural.

 

[JackFlorey]

Also, probably dont want to put a ton of power (like 8kw+) through an expensive rohloff.

Keep in mind that they don't care about power - they only care about torque. You can get 8kw with very little torque with the right gearing/wheel size etc. although then pedaling might get tougher.

I just want the exercise and a "natural" feeling riding experience.

Well, spinning a generator is pretty much the opposite of a natural feeling riding experience.

 

[Chalo]

Here's a thought. If you couple the pedals separately to both a geared-down 2-wire DC motor that gives back EMF of 4.2V at whatever your comfortable maximum pedal cadence is, and a geared-up magnetic resistance unit from a stationary trainer, you could have both "natural feel" and a throttle signal that makes sense to the controller.