Tracking the Movement of a Hand-Lever

[HyperSpeed]

Hi guys,

I'm looking for some potential newfound creativity concerning a project of mine, hope you don't mind me seeking it here.

What I am trying to do, more or less, is track the movement of a hand lever. It is the lever style as would be used for braking/clutch on a motorcycle. It is not cable-actuated, but hydraulic. I need to come up with some sort of minimally-invasive assembly that could monitor the lever movement without impeding the movement at all, in order to gather telemetry data. As for resolution, the lever movement that's used is about 25–30°, and ≤0.1° data points will likely be sufficient (I realize this might be a meaningless bit of info to include, as other variables will determine the final available resolution of the system as a whole). Anyways, I will probably run a Raspberry Pi unit to track sensor data, just sort of left scratching my head as to what may be appropriate types of sensors to look at, in order to devise a mounting strategy and finally track the lever movement.

Any suggestions?

I appreciate any help with this, thanks!

 

[KC3KNM]

String pot? Might be able to attach to the lever with little modification.

Edit: probably too expensive to be useful here, but you can find them in smaller sizes for under 100$.

 

[David_Stack]

is there a way to affix a circular potentiometer to the lever assembly (assuming the lever pivot shaft moves in concert with the brake/clutch lever itself)? I picture the potentiometer shaft tapped into the lever pivot shaft, and then the outer potentiometer housing secured to the clutch/brake lever housing...

 

[Funkworks]

Does it have to be mounted on handle bars?
Would you keep the present pivot point and just add a device?
Or can you replace the pivot assembly with something else?

 

[Grog6]

https://www.amazon.com/Acceleromete...t=&hvlocphy=9013402&hvtargid=pla-817395333973
This is the complicated way; I'd attach a stick to a pot and to the lever and digitize it, it would be easier.
This is a high res pot; it's not wirewound, it's continuous
https://www.mpja.com/Precision-Angle-Sensor-0-360Deg-Analog-Output/productinfo/36215+MI/

 

[mikec]

Depending on operating conditions (lighting, motion, etc) it might be feasible to use machine vision on the output of a small camera.

If you have to leave the assembly completely alone and not incorporate an encoder or something, that's a significant constraint.

If you can attach a magnet to the lever a magnetometer might work since you only have one DOF you need to determine.

 

[HyperSpeed]

This is indeed interesting, thanks for input so far guys! My brain is a churning now.

I just thought about something else. There's another set of data which could be more useful to measure in this situation; the amount of pressure which the fingers themselves are applying to the lever at any given time. Since there is a spring rate that's constant against the clutch basket, there would be a corresponding pressure profile that essentially models where the clutch basket is itself along it's full path of travel. For example, if the basket spring feeds its rate back to the lever, and 5lbs of force is required against the hydraulic master cylinder piston to begin causing the basket to lift, then possibly somehow a pressure sensor could be placed between the lever and the back of the piston. It could then be possible to interpret the action of the manipulating fingers, since it is not actually a linear correlation to lever movement in degrees. By monitoring the data this way, it then becomes possible to derive total force the fingers have exerted to manipulate the lever, which could be summed over time. The reason I feel this is far more important data to have is because as this force accumulation occurs, the rider's muscles in the hands and forearms saturate with blood, swell, and the rider becomes less able to manipulate the levers as effectively. "Arm pump" occurs. Seeing that a lever moves X degrees a number of times really doesn't provide any useful data about the force accumulation that causes the arm pump to occur. (Yes, I caught my own mistake about monitoring the process. ) Things like ambient temperature, clutch fade, brake fade, etc, could better be observed on how they change the forces at the levers, which act against the rider's body, by monitoring the forces applied through the lever instead of the lever movement alone. Now with that being said, how might a form of pressure sensor be implemented somewhere between lever contact with hydraulic piston, and slave piston contact potentially as far down the system as the final mechanical interface which the hydraulic forces are applied to? Would it make sense to possibly monitor hydraulic line pressure itself, and convert that into a digital reading? Though I feel like this way could be done, maybe even more easily than other methods, if the reading was internal to hydraulic pressure, it could depend where the reading was taken at that best corresponds to pressure against the lever. So it would seem to me that the best place for the sensing to take place, would be nearest the lever, right between lever and master piston (external to fluid pressure, then.)

I'm back at the chin scratcher point now, how small of pressure sensing "pads" do they make, to possibly either be placed between the two, or a lever modification could occur, so that something like a small cylinder could be inserted into the lever, that directly acts against the master piston base--I do like the thought of that, since it would be secured and highly protected that way.

Can't wait to see where this might go from here, now that a better goal has finally been established.

 

[OverTheTop]

Pressure transducer? Would need to be careful to not introduce failure modes in the pressure line though.

 

[HyperSpeed]

Pressure transducer? Would need to be careful to not introduce failure modes in the pressure line though.

Ok, what would be the proper type of sensor that has little to no movement (I.E. is a relatively rigid sensor) and is capable of being found in very small versions? Electric in nature, not hydraulic. Would this be some sort of micro piezoelectric sensor? Say around the size of a cylinder ≤9mm OD and ≤20mm length.

I do feel like the more useful route would be to sense force rather than movement, now that I have had some time to think about it. So the goal has slightly changed, but the end application has not changed.

 

[OverTheTop]

Ok, what would be the proper type of sensor that has little to no movement (I.E. is a relatively rigid sensor) and is capable of being found in very small versions? Electric in nature, not hydraulic. Would this be some sort of micro piezoelectric sensor? Say around the size of a cylinder ≤9mm OD and ≤20mm length.

There are a few sensors around, and most are based on MEMS technology so displacement of the sensor would not be a problem. Compatibility with the brake fluid would need to be checked. Once you have the sensor a circuit can be designed to read the pressures from the sensor. You need to check the sensor is rated to the required line pressure too. I suspect there are industrial pressure sensors with the electronic front-end built in that might suit your needs.

 

[HyperSpeed]

There are a few sensors around, and most are based on MEMS technology so displacement of the sensor would not be a problem. Compatibility with the brake fluid would need to be checked. Once you have the sensor a circuit can be designed to read the pressures from the sensor. You need to check the sensor is rated to the required line pressure too. I suspect there are industrial pressure sensors with the electronic front-end built in that might suit your needs.

Check it out, I'm not putting the sensor in the fluid. I described that above, as to the reasoning, but I came up with the idea where the lever uses a bolt to push against the back of the primary piston, the front of the piston is inside the hydraulic system, the rear is outside. I want to take a reading outside the fluid, so that I minimize variables. This way, only actual hand pressure force is measured. So the sensor only needs to work in atmosphere pressure, using actual pressure the sensor has applied against it from a bolt that's already there. I wish I was next to the bike right now. Would show you. But just imagine a wired bolt, and you want to know how much force is on the bolt tip when you push it against a metal plate. That's what's effectively going to happen.

 

[OKTurbo]

What you’re describing is called a load cell. Most use a strain gauge to measure force. Finding a miniature one that will work will in your application will be a challenge.

 

[Sandy H.]

I may be completely misunderstanding, but if you measure the hydraulic pressure, you should be able to calculate the force required on the lever to get that pressure. The master and slave cylinders are constant piston size, so if you knew the pressure somewhere, you could figure out how much force had to be applied to get that pressure. Depending on the linkage/method that the lever is actuating the master cylinder, it could be simple and fairly linear or it might be more complex/less linear, but I would think its just kinematics or worst case a regression/polynomial equation to relate hydraulic pressure to lever force.

As I said, I could be completely missing what you're trying to accomplish.

Sandy.

 

[OzHybrid]

Is this a bench setup for prototyping? Is it on the real thing? Draw us a sketch so we don't have to guess. The best answer will depend on what the parameters are. What's your budget? Blue Sky? Bleeding Edge? Garage Bubblegum? This will stop people wasting time on your behalf if there's not an appropriate budget.