I've come here as a long time Arduino and ESP32 user with a problem with my latest robotics project:
I need to control the unwinding of a winch (that a brushless motor will later pull back in.)
My engine braking is working fine so far.
For further braking and holding it in place I want to use a hydraulic disc brake, preferably from a small car.
Now here is the problem:
I've never worked with these parts. How would you actuate such a braking system? What parts would you suggest to get to control the brake force (i can base the control-loop on the winch speed)?
I don't want to MacGyver and press on a pedal with a linear actuator though
Any suggestions welcome! If you already have done something similar, please reach out.
Why hydraulic? Why from a small car? Why not a mechanical disk brake from a go-cart? Avoids all the mess of hydraulic fluid, master cylinder, fluid reservoir.
Do you have the shop skills to mount a disk brake and associated mechanical structure to your winch?
Unless you are for some reason bound on hydraulic disc brake I would be thinking a magnetic particle brake. Hydraulic brake if you want controlled braking in addition to a hydraulic pressure source you will need to maybe PWM a proportional solenoid valve. A magnetic particle brake is a much cleaner way to go. They come in all sizes and shaft dimensions.
Again if you need controlled braking you can use hydraulic but it is a messy solution.
Ok, I'm blind to find the quote function so I'll wirte my thoughts up this way:
First of, a big thank you all for your help and knowledge!
@DrDiettrich: Not quite sailing... lets say it's complicated. Worst case scenario are around 10 kJ of energy (100 kg falling from around 10 m height). I have to brake it to a complete stop and hold it there. I can do it with my Motor (around 10 kW of peak power), but i want/need a backup, especially when i cannot recuperate.
The braking occurs (worst case) every 5 minutes once.
If you have an exampe for a "brake by wire" solution feel free to post it. I couldn't find anything good. Of course i'd love to use that.
@DaveX:
Thanks for your suggestion. Didn't think of the easy way, but tbh i want to stick to standard parts (like from cars or bikes, that i can reorder if needed). But i'll definitly look into that, maybe i can get something standard to buy.
@Paul_KD7HB:
I thought of hydraulic because i knew the difference in pressure on the lever needed on my MTBs. The hydraulic brakes are far superior. Never had a mess with my brakes so I stopped thinking there
But Go-Karts is a nice niche. I'll look into that and see if i can use something off of them.
Do you think that they could handle the 10 kJ energy dissipation? But i guess i can calculate that over the weight and speed of carts.
How would you actuate the brake? Using a Servo?
@Ron_Blain
No, I'm open to any kind of brake, but i want to buy it and not make it myself.
If i calculated correctly the (worst case) power of the brake needed is around 7kW to stop in 3 seconds. I couldn't find any magnetic brake under $1000 for those requirements
@everyone:
Yes, i have the tools and engineering and hands-on knowledge to adapt any braking system.
I'm asking for your help and ideas so that i can include the brake into the winch as early as possible.
Thanks again for all your feedback.
Please, if you have more knowledge or questions, feel free to add it!
Since they are designed to use a cable between the brake pedal and the caliper, A servo or a solenoid could work. If you need something other than OFF or ON, you need an adjustable force mechanism. Same would be needed by hydraulic brakes!
Yea, i hope to get around the "force measurement" part.
Thought about controlling the braking power with the delta_speed as input for the control loop.
I it's not slowing down, apply more force and vice versa.
Yea, i just ran some numbers of the energy and force needed for the braking proces and it should work well with the go-kart brakes. Thought they were hydraulic, too, but if i can get them to work with a wire i can add a powerful servo.
Nope. Unless you're a natural or do them frequently, they're kind of a pain. Look at the diameter of the roller of the wench and how many pounds it'll be supporting. That'll give you in/lbs or whatever your preferred torque measurement. Scale that to your disc break size and use the friction material contact area times its coefficient of friction to get its holding force.
If I'm remembering how to do that correctly that is.
Would be ok, but the brake needs to come on very fast. Gear motor would be great for controlling and "working the brake" but if i need the brake it's more like a "slam on the brakes, but still controll the speed" kinde of movement.
Thanks for the idea though
Sorry!
if the controller decides that motor braking isn't working (there are several reasons) it needs to switch to the normal brake within the least amount of time (i'd like to get it below 250 ms).
If 100% brake force is applied and the weight is only 50kg (instead of worst case 120kg), the braking would be to strong. The mass must decent with around 2 m/s so i'll have to control the brake depending on the weight (and other conditions, ofc.)
I defenitely need a controllable brake, so i guess a servo will be best way.
Maybe a solenoid; controlling the current should work well
I'm thinking you want an appropriately sized DC gear motor with a relay. One contact is a 1 megaohm resistor that allows the motor to free spin easily, and the other shorts the motor for maximum back EMF braking.
That’s worth thinking more about. If the winch itself is driven by a gear motor, the descent could be controlled by varying the speed of the gear motor and then varying levels of braking could be controlled by reversing it.
-- image from https://emce.com/about-winches