2020-01-13, 04:07 PM
[quote pid='11720' dateline='1578879718']
7.5 watts is a huge amount of power just for a clutch. The pi zero uses about 1 watt, and often the average motor consumption is less than this. What about using a resistor and capacitor in series with the clutch? This can limit the power it consumes (to hold) but still allow a larger current to lock. The usual clutch current of raymarine drive is also around 6 watts so this is really a lot of power consumption.
If you are using a motor which can actually be driven from the L298N: "2) Large output current, the instantaneous peak current can be up to 3A" it isn't enough for the motor.
Why do you have toothed pulleys and belts if you are using planetary gears?
Also, the cheap ballscrews on amazon may work but are usually 400 grade stainless which means they will rust a lot more than normal stainless. I am not sure where to find 316 ballscrews, or other alloys though. I think these ballscrews may work well if there is enough grease and they can stay covered.
I am still not sure which tillerpilot you want to replace... The belowdecks units such as raymarine type 1 and 2 linear drives using ballscrews have a much larger brushed dc motor than what you selected. This is a much more powerful and efficient motor. It uses something like a 3.5:1 reduction from this motor using a toothed belt to the ballscrew and magnetic clutch. In raymarine units, these toothed pulleys wear out especially if the autopilot is stressed a lot and eventually this belt skips which acclerates the wear of the toothed pulleys. I would consider this and either use hdt5m belts at least 15mm wide, gearbox which is rated for 4x the torque you will ever drive it, or have the magnetic or other clutch capable to slip before the the gearbox or belt would.
[/quote]
Thanks for the input Sean.
My goal is to build something out of readily available items and try to keep the cost down making it worth the effort. That has driven many of the choices made to this point. I am certainly no expert, just have always thought about giving it a try.
Definitely will try to lower the clutch draw and adding a capacitor and resistor sounds like a good start.
The electomagnetic clutches that I can find are either very expensive or very inefficient. This made the $25 eBay surplus clutches the most reasonable choice at this point. With that in mind it limits what the unit can be and how it is constructed. If anyone has any suggestions that could work better that would be great.
The L298N was just something I had laying around. Will uses something more robust for sure. Again another thing I'm no expert at. Just started messing around with motor controllers and Arduino for that matter.
The toothed pulleys are just what the clutch came with. It could certainly change, but just wanted to make sure that it could handle the power that was desired. I tried spur gears below the clutch at first (lower set of gears) but there was too much resistance and it caused a much higher resistance to movement of the piston when the clutch was disengaged.
I bought that motor with the planetary gears because it had enough torque to get the job done and turned at the right RPM allowing the proper hard over to hard over time. This motor was also fairly inexpensive for the amount of torque it produced. Any recommendations?
The belts are HDT5M 15mm wide.
At this point the actuator is more of a proof of concept than an actual usable unit so any input is greatly appreciated.
7.5 watts is a huge amount of power just for a clutch. The pi zero uses about 1 watt, and often the average motor consumption is less than this. What about using a resistor and capacitor in series with the clutch? This can limit the power it consumes (to hold) but still allow a larger current to lock. The usual clutch current of raymarine drive is also around 6 watts so this is really a lot of power consumption.
If you are using a motor which can actually be driven from the L298N: "2) Large output current, the instantaneous peak current can be up to 3A" it isn't enough for the motor.
Why do you have toothed pulleys and belts if you are using planetary gears?
Also, the cheap ballscrews on amazon may work but are usually 400 grade stainless which means they will rust a lot more than normal stainless. I am not sure where to find 316 ballscrews, or other alloys though. I think these ballscrews may work well if there is enough grease and they can stay covered.
I am still not sure which tillerpilot you want to replace... The belowdecks units such as raymarine type 1 and 2 linear drives using ballscrews have a much larger brushed dc motor than what you selected. This is a much more powerful and efficient motor. It uses something like a 3.5:1 reduction from this motor using a toothed belt to the ballscrew and magnetic clutch. In raymarine units, these toothed pulleys wear out especially if the autopilot is stressed a lot and eventually this belt skips which acclerates the wear of the toothed pulleys. I would consider this and either use hdt5m belts at least 15mm wide, gearbox which is rated for 4x the torque you will ever drive it, or have the magnetic or other clutch capable to slip before the the gearbox or belt would.
[/quote]
Thanks for the input Sean.
My goal is to build something out of readily available items and try to keep the cost down making it worth the effort. That has driven many of the choices made to this point. I am certainly no expert, just have always thought about giving it a try.
Definitely will try to lower the clutch draw and adding a capacitor and resistor sounds like a good start.
The electomagnetic clutches that I can find are either very expensive or very inefficient. This made the $25 eBay surplus clutches the most reasonable choice at this point. With that in mind it limits what the unit can be and how it is constructed. If anyone has any suggestions that could work better that would be great.
The L298N was just something I had laying around. Will uses something more robust for sure. Again another thing I'm no expert at. Just started messing around with motor controllers and Arduino for that matter.
The toothed pulleys are just what the clutch came with. It could certainly change, but just wanted to make sure that it could handle the power that was desired. I tried spur gears below the clutch at first (lower set of gears) but there was too much resistance and it caused a much higher resistance to movement of the piston when the clutch was disengaged.
I bought that motor with the planetary gears because it had enough torque to get the job done and turned at the right RPM allowing the proper hard over to hard over time. This motor was also fairly inexpensive for the amount of torque it produced. Any recommendations?
The belts are HDT5M 15mm wide.
At this point the actuator is more of a proof of concept than an actual usable unit so any input is greatly appreciated.