New Behotec e-Tract electric gear
06-08-2013, 01:19 AM
#1
Thread Starter
New Behotec e-Tract electric gear
Hello everyone.
I have recently received the electric gear for the Scorpion Mk2.
It is a very, very nice set and I wanted to share the discovery of this little jewel with you:
http://www.ultimate-jets.net/blogs/j...ract-gear-line
Here are a few pictures:
The screw jack system and trunion:
The complete set:
The control unit:
and a video of the gear operations:
[link=https://vimeo.com/67937096]Scorpion Mk2 e-Tract gear[/link]
I have recently received the electric gear for the Scorpion Mk2.
It is a very, very nice set and I wanted to share the discovery of this little jewel with you:
http://www.ultimate-jets.net/blogs/j...ract-gear-line
Here are a few pictures:
The screw jack system and trunion:
The complete set:
The control unit:
and a video of the gear operations:
[link=https://vimeo.com/67937096]Scorpion Mk2 e-Tract gear[/link]
06-08-2013, 03:09 AM
#3
Thread Starter
RE: New Behotec e-Tract electric gear
ORIGINAL: smchale
Btw, the video also shows nice evidence of the new and much improved quality of the scorpion's finish. [8D]
Btw, the video also shows nice evidence of the new and much improved quality of the scorpion's finish. [8D]
06-08-2013, 03:17 AM
#4
RE: New Behotec e-Tract electric gear
ORIGINAL: olnico
And of the level of mess in my workshop at the moment...
ORIGINAL: smchale
Btw, the video also shows nice evidence of the new and much improved quality of the scorpion's finish. [8D]
Btw, the video also shows nice evidence of the new and much improved quality of the scorpion's finish. [8D]
06-08-2013, 04:21 AM
#5
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RE: New Behotec e-Tract electric gear
Why don't electric retract producers use square threads on the lead screw? They will have less friction and have less of a tendency to lock in the fully up or down position. Also as the screws get worn square threads are less likely to cause a problem. As the guys a Behotec are no fools I guess there is a reason why normal threads are used but other than difficulty in getting square threads of that size I can't see what it would be
Jason
Jason
06-08-2013, 09:13 AM
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RE: New Behotec e-Tract electric gear
The thread formation you are refering to is an ACME thread Jason!
It does take greater loads as compared to the more conventional thread types, I think the diameter is more of an issue with producing this type of thread against the cost! But you are spot on, although with any exposed lead screw, will be subjected to FOD!
I still think BEHOTEC have the best system!
It does take greater loads as compared to the more conventional thread types, I think the diameter is more of an issue with producing this type of thread against the cost! But you are spot on, although with any exposed lead screw, will be subjected to FOD!
I still think BEHOTEC have the best system!
06-08-2013, 03:12 PM
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RE: New Behotec e-Tract electric gear
Thanks John, now I know what it called I have managed to find a supplier that does stainless M3 to M100 Acme threaded rod. Problem is that the minimum order is 3 tons..
http://allfasteners.en.made-in-china...GR-AT335-.html
http://allfasteners.en.made-in-china...GR-AT335-.html
06-08-2013, 03:29 PM
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RE: New Behotec e-Tract electric gear
It is a matter to grind the tool to the square shape. The issue would be how to do the female part.[
]
In the pic you see a triangular shape tool performing a M-4x70 on my lathe. The thread rod is for convert a BVM gear to electric one
Total cost of the conversion 110 € included the electronics
Sorry, the thread is M-4x70
The issue would be how to do the female part.[]In the pic you see a triangular shape tool performing a M-4x70 on my lathe. The thread rod is for convert a BVM gear to electric one
Total cost of the conversion 110 € included the electronics
Sorry, the thread is M-4x70
06-09-2013, 03:27 AM
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RE: New Behotec e-Tract electric gear
Nice work Aviojet!
Internal screw cutting is not that bad, even on an M4 ACME thread, when using Brass/Bronze of good quality! It’s nice to do as the material chips away and less likely to dig in!
So Jason, when does the stock arrive! LOL
JT
Internal screw cutting is not that bad, even on an M4 ACME thread, when using Brass/Bronze of good quality! It’s nice to do as the material chips away and less likely to dig in!
So Jason, when does the stock arrive! LOL
JT
06-09-2013, 05:03 AM
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RE: New Behotec e-Tract electric gear
Having spend a year or so designing and working with colleagues on this 'electric' gear thing on our Stinger jet electric gear does pose a few challenges the main 'issue' which presents itself in electric gear is the management of locking up at each end of the travel.
If you drive the threaded rod to the lock position it generally requires slightly more current to do this and once locked ideally you want to be able to stop the motor instantly, in the real world this does not happen, inertia drives the thread hard into the end stop before the electronics can stop the motor (unless you have a painfully slow retract unit and most dont want that).
I know from experience that one fix was to provide a cushion at each end of the travel, usually in the form of a rubber/silicone washer, we used this method and I notice that so do Electron, I cannot speak for others. This dampens and slows the end stop 'crash' which gives time for the electronics to detect the current spike and shut the motor down (even reverse it momentarily too to get it ready for the return journey and to also remove some resistance).
I did not experiment with ACME threads, and it may well help, but key is the electronics (and a decent motor/gearbox) - I am sure as electric retracts develop all these things will be overcome.
Just thinking about the threaded rod maybe also a square rod with the threads on each corner would allow FOD to be scraped into the flat sections and not pose an issue with locking the thread up.......
marcs
If you drive the threaded rod to the lock position it generally requires slightly more current to do this and once locked ideally you want to be able to stop the motor instantly, in the real world this does not happen, inertia drives the thread hard into the end stop before the electronics can stop the motor (unless you have a painfully slow retract unit and most dont want that).
I know from experience that one fix was to provide a cushion at each end of the travel, usually in the form of a rubber/silicone washer, we used this method and I notice that so do Electron, I cannot speak for others. This dampens and slows the end stop 'crash' which gives time for the electronics to detect the current spike and shut the motor down (even reverse it momentarily too to get it ready for the return journey and to also remove some resistance).
I did not experiment with ACME threads, and it may well help, but key is the electronics (and a decent motor/gearbox) - I am sure as electric retracts develop all these things will be overcome.
Just thinking about the threaded rod maybe also a square rod with the threads on each corner would allow FOD to be scraped into the flat sections and not pose an issue with locking the thread up.......
marcs
06-09-2013, 07:08 AM
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RE: New Behotec e-Tract electric gear
ORIGINAL: marc s
Having spend a year or so designing and working with colleagues on this 'electric' gear thing on our Stinger jet electric gear does pose a few challenges the main 'issue' which presents itself in electric gear is the management of locking up at each end of the travel.
If you drive the threaded rod to the lock position it generally requires slightly more current to do this and once locked ideally you want to be able to stop the motor instantly, in the real world this does not happen, inertia drives the thread hard into the end stop before the electronics can stop the motor (unless you have a painfully slow retract unit and most dont want that).
I know from experience that one fix was to provide a cushion at each end of the travel, usually in the form of a rubber/silicone washer, we used this method and I notice that so do Electron, I cannot speak for others. This dampens and slows the end stop 'crash' which gives time for the electronics to detect the current spike and shut the motor down (even reverse it momentarily too to get it ready for the return journey and to also remove some resistance).
I did not experiment with ACME threads, and it may well help, but key is the electronics (and a decent motor/gearbox) - I am sure as electric retracts develop all these things will be overcome.
Just thinking about the threaded rod maybe also a square rod with the threads on each corner would allow FOD to be scraped into the flat sections and not pose an issue with locking the thread up.......
marcs
Having spend a year or so designing and working with colleagues on this 'electric' gear thing on our Stinger jet electric gear does pose a few challenges the main 'issue' which presents itself in electric gear is the management of locking up at each end of the travel.
If you drive the threaded rod to the lock position it generally requires slightly more current to do this and once locked ideally you want to be able to stop the motor instantly, in the real world this does not happen, inertia drives the thread hard into the end stop before the electronics can stop the motor (unless you have a painfully slow retract unit and most dont want that).
I know from experience that one fix was to provide a cushion at each end of the travel, usually in the form of a rubber/silicone washer, we used this method and I notice that so do Electron, I cannot speak for others. This dampens and slows the end stop 'crash' which gives time for the electronics to detect the current spike and shut the motor down (even reverse it momentarily too to get it ready for the return journey and to also remove some resistance).
I did not experiment with ACME threads, and it may well help, but key is the electronics (and a decent motor/gearbox) - I am sure as electric retracts develop all these things will be overcome.
Just thinking about the threaded rod maybe also a square rod with the threads on each corner would allow FOD to be scraped into the flat sections and not pose an issue with locking the thread up.......
marcs
Lead screws you see on CNC machines where speed and power is the driving factor.
You need a thread pitch double that of a regular screw thread at least. Often these are cut with 2 or three starts, ie 2 or 3 different "grooves", running in parallel. In the case of M4 the fine pitch is 0.5mm and coarse is 0.7mm. A M4 leadscew could have a 1.5 to 2.5 mm pitch for e-tracts. These threads are also more efficient with less friction. They move of course faster for a given RPM and require proportionally more torque. So they need a higher gear reduction ratio. Also more expensive unless you CNC them.
A cheap source to play with is the position lead screw (Acme often) in a stiffy disk drive.
For your electronics if you use current as your trip that is too late. The current will only peak after the innertia of the motor has already locked the thread. You need to detect a change in RPM instantly and brake the motor with a pulse of reverse.
Andre
06-09-2013, 07:43 AM
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RE: New Behotec e-Tract electric gear
You need to detect a change in RPM instantly and brake the motor with a pulse of reverse
With current sensing which is still not ideal I admit you can dial in some 'allowance' and therefore avoid some cases of hung gear.
In an ideal world what is actually required is a limit switch at each end of the retract unit, positioned so it trips the electronics and allows the unit to avoid the 'crunch zone' - on big retracts this I doubt would be a problem if they were designed/made to accommodate this, smaller units pose problems simply due to being small.
marcs
06-09-2013, 07:59 AM
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RE: New Behotec e-Tract electric gear
ORIGINAL: marc s
Easier said than done..... often the gear will encounter 'resistance' at different stages of its travel from cycle to cycle, maybe retracting gear at different speeds following take off etc so 'when' exactly do you tell the motor to stop as there is a strong chance it will stop mid cycle?
With current sensing which is still not ideal I admit you can dial in some 'allowance' and therefore avoid some cases of hung gear.
In an ideal world what is actually required is a limit switch at each end of the retract unit, positioned so it trips the electronics and allows the unit to avoid the 'crunch zone' - on big retracts this I doubt would be a problem if they were designed/made to accommodate this, smaller units pose problems simply due to being small.
marcs
You need to detect a change in RPM instantly and brake the motor with a pulse of reverse
With current sensing which is still not ideal I admit you can dial in some 'allowance' and therefore avoid some cases of hung gear.
In an ideal world what is actually required is a limit switch at each end of the retract unit, positioned so it trips the electronics and allows the unit to avoid the 'crunch zone' - on big retracts this I doubt would be a problem if they were designed/made to accommodate this, smaller units pose problems simply due to being small.
marcs
The current is irrelevant. The speed of the motor is the only reliable no cost sensing option.
The best solution is to change the thread and pitch so that there is no locking.
Generally a helix pitch angle of more than 22 deg is enough.
Any capable CNC operator can cut you such a thread and nut/camblock.
06-09-2013, 08:33 AM
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RE: New Behotec e-Tract electric gear
Way back in 1986 I bought a set of electric retracts from Mick Reeves which had normal size lever arm micro switches at both ends of travel. You can buy much smaller micro switches nowadays. By use of a spring touching the leg they staggered the start time so they did not travel perfectly together. The switches were mounted in a way that you could alter their position a little to allow for slightly different than 90 degree angles. All done without any electronics.
06-09-2013, 08:59 AM
#15
Thread Starter
RE: New Behotec e-Tract electric gear
ORIGINAL: marc s
Having spend a year or so designing and working with colleagues on this 'electric' gear thing on our Stinger jet electric gear does pose a few challenges the main 'issue' which presents itself in electric gear is the management of locking up at each end of the travel.
If you drive the threaded rod to the lock position it generally requires slightly more current to do this and once locked ideally you want to be able to stop the motor instantly, in the real world this does not happen, inertia drives the thread hard into the end stop before the electronics can stop the motor (unless you have a painfully slow retract unit and most dont want that).
I know from experience that one fix was to provide a cushion at each end of the travel, usually in the form of a rubber/silicone washer, we used this method and I notice that so do Electron, I cannot speak for others. This dampens and slows the end stop 'crash' which gives time for the electronics to detect the current spike and shut the motor down (even reverse it momentarily too to get it ready for the return journey and to also remove some resistance).
I did not experiment with ACME threads, and it may well help, but key is the electronics (and a decent motor/gearbox) - I am sure as electric retracts develop all these things will be overcome.
Just thinking about the threaded rod maybe also a square rod with the threads on each corner would allow FOD to be scraped into the flat sections and not pose an issue with locking the thread up.......
marcs
Having spend a year or so designing and working with colleagues on this 'electric' gear thing on our Stinger jet electric gear does pose a few challenges the main 'issue' which presents itself in electric gear is the management of locking up at each end of the travel.
If you drive the threaded rod to the lock position it generally requires slightly more current to do this and once locked ideally you want to be able to stop the motor instantly, in the real world this does not happen, inertia drives the thread hard into the end stop before the electronics can stop the motor (unless you have a painfully slow retract unit and most dont want that).
I know from experience that one fix was to provide a cushion at each end of the travel, usually in the form of a rubber/silicone washer, we used this method and I notice that so do Electron, I cannot speak for others. This dampens and slows the end stop 'crash' which gives time for the electronics to detect the current spike and shut the motor down (even reverse it momentarily too to get it ready for the return journey and to also remove some resistance).
I did not experiment with ACME threads, and it may well help, but key is the electronics (and a decent motor/gearbox) - I am sure as electric retracts develop all these things will be overcome.
Just thinking about the threaded rod maybe also a square rod with the threads on each corner would allow FOD to be scraped into the flat sections and not pose an issue with locking the thread up.......
marcs
The resolution Behotec is working at is 35mm/7600= 0,0046 mm per step or 4,6 thousands of mm. Needless to say that the trunion machining must be accurate. This is working extremely well on the new gear and the positioning of the trunion assembly is very consistent.
The electronics still have a amp tripoff and timeout function, but this is more a safety feature than anything else.
In practice the gear always stops at the stop step ( positioning stop ) and not from current tripoff. The menu on the GSU allows to see that. Every time the trunion is right into the end of the groove.
Brilliant design.
06-09-2013, 09:45 AM
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RE: New Behotec e-Tract electric gear
Nice to see the 'next' level of positional metering achieved already, hopefully the 40% increase in price will be rewarded with complete reliability.
marcs
marcs
06-09-2013, 11:43 PM
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RE: New Behotec e-Tract electric gear
ORIGINAL: olnico
Behotec has bypassed all these problems by using stepped motors. The gear is programmed with a start step and end step. The problem in that case is to get a very consistent position of the trunion for a given motor step.
The resolution Behotec is working at is 35mm/7600= 0,0046 mm per step or 4,6 thousands of mm. Needless to say that the trunion machining must be accurate. This is working extremely well on the new gear and the positioning of the trunion assembly is very consistent.
The electronics still have a amp tripoff and timeout function, but this is more a safety feature than anything else.
In practice the gear always stops at the stop step ( positioning stop ) and not from current tripoff. The menu on the GSU allows to see that. Every time the trunion is right into the end of the groove.
Brilliant design.
ORIGINAL: marc s
Having spend a year or so designing and working with colleagues on this 'electric' gear thing on our Stinger jet electric gear does pose a few challenges the main 'issue' which presents itself in electric gear is the management of locking up at each end of the travel.
If you drive the threaded rod to the lock position it generally requires slightly more current to do this and once locked ideally you want to be able to stop the motor instantly, in the real world this does not happen, inertia drives the thread hard into the end stop before the electronics can stop the motor (unless you have a painfully slow retract unit and most dont want that).
I know from experience that one fix was to provide a cushion at each end of the travel, usually in the form of a rubber/silicone washer, we used this method and I notice that so do Electron, I cannot speak for others. This dampens and slows the end stop 'crash' which gives time for the electronics to detect the current spike and shut the motor down (even reverse it momentarily too to get it ready for the return journey and to also remove some resistance).
I did not experiment with ACME threads, and it may well help, but key is the electronics (and a decent motor/gearbox) - I am sure as electric retracts develop all these things will be overcome.
Just thinking about the threaded rod maybe also a square rod with the threads on each corner would allow FOD to be scraped into the flat sections and not pose an issue with locking the thread up.......
marcs
Having spend a year or so designing and working with colleagues on this 'electric' gear thing on our Stinger jet electric gear does pose a few challenges the main 'issue' which presents itself in electric gear is the management of locking up at each end of the travel.
If you drive the threaded rod to the lock position it generally requires slightly more current to do this and once locked ideally you want to be able to stop the motor instantly, in the real world this does not happen, inertia drives the thread hard into the end stop before the electronics can stop the motor (unless you have a painfully slow retract unit and most dont want that).
I know from experience that one fix was to provide a cushion at each end of the travel, usually in the form of a rubber/silicone washer, we used this method and I notice that so do Electron, I cannot speak for others. This dampens and slows the end stop 'crash' which gives time for the electronics to detect the current spike and shut the motor down (even reverse it momentarily too to get it ready for the return journey and to also remove some resistance).
I did not experiment with ACME threads, and it may well help, but key is the electronics (and a decent motor/gearbox) - I am sure as electric retracts develop all these things will be overcome.
Just thinking about the threaded rod maybe also a square rod with the threads on each corner would allow FOD to be scraped into the flat sections and not pose an issue with locking the thread up.......
marcs
The resolution Behotec is working at is 35mm/7600= 0,0046 mm per step or 4,6 thousands of mm. Needless to say that the trunion machining must be accurate. This is working extremely well on the new gear and the positioning of the trunion assembly is very consistent.
The electronics still have a amp tripoff and timeout function, but this is more a safety feature than anything else.
In practice the gear always stops at the stop step ( positioning stop ) and not from current tripoff. The menu on the GSU allows to see that. Every time the trunion is right into the end of the groove.
Brilliant design.
http://en.wikipedia.org/wiki/Leadscrew
I am surprised since this is well known principles to any fitter/turner.
All the systems I have seen have this issue. All use screw type threads designed to have extreme friction to not come loose from reversal. Basically trying to build an electric screwdriver that does not tighten screws.
Really not rocket science people....
06-10-2013, 12:13 PM
#18
Thread Starter
RE: New Behotec e-Tract electric gear
ORIGINAL: Turbotronic
Certainly overengineerd. Too complicated and unnecesarily so. Its all in the thread design and helix angle.
Certainly overengineerd. Too complicated and unnecesarily so. Its all in the thread design and helix angle.
This was the case of the Jets-Munt XBus and all digital link recently. Was it necessary? No. Why do we go ahead and progress? Because we can do it. It is in our essence and our pride.
Now there is a very good reason for using stepped motors in that application: variable detection gain.
The reason behind being that most of the time, the resistance of the gear during motion is not linear. Thus the consumed current.
Factors like struts+ wheel weights, ram effect of the latter, ram effect of possible doors, foreign object/ dust in the screw tend to increase the load applied to the motor during retraction.
With a current triggered retract, there is a possiblility of tripping off the system during motion due to these factors.
With stepped units, the detection gain is reduced during motion to only trip off if one gear gets seriously jammed. The detection becomes more sensitive near the stops to accurately detect when the trunion reaches the end poosition and the current starts to increase.
We have been developping and using the previous generation of electric retracts for the last 4 years with GZ retracts:
http://www.ultimate-jets.net/pages/e...tom-conversion
This new system is very welcome and a big step ahead in this field. A 40% conversion cost is in practice what we charge for previous generation electric systems.
