Building a remote controlled yard helper (Bruno) out of an electric wheelchair

Thread Starter

mikej12

Joined Nov 14, 2018
12
Hi. My background is U.S. Air Force service and commercial construction. I just retired and want to work on projects to make my life a little easier. Here is this project: I have already modified the wheelchair to the pictured red framed "Bruno." I want to use Bruno to mow the yard with our battery powered lawn mower, and power rake, aerate, fertilize and haul yard stuff as the wife desires. Bruno will be remote controlled via the Spektrum transmitter and Spektrum flight controller (with receiver and GPS modules) and utilize the Sabertooth 2x32 motor controller. My plan is to eliminate the wheelchair joystick/controller (it is a no go anyway - multi error messages), but keep the balance of existing wiring. I ABSOLUTELY want to keep the wheelchair battery charger. What I desire to add is a lighted on/off switch and a pc type cooling fan for the Sabertooth. Where in the wiring do I add the on/off switch and the cooling fan? Thank much.
 

Thread Starter

mikej12

Joined Nov 14, 2018
12
Welcome to AAC. Nice pictures. What's it do? Is this just a plan or a functioning unit?
Hi. This is my first entry and I selected post without a description. I hope my reply description will get my message across. But if you have any suggested changes, please send them my way. Thank much, Mike
 

Mark Hughes

Joined Jun 14, 2016
404
Hi @mikej12,
Welcome to AAC! The trick to attracting attention is to call people out with the @ sign. The moderators are all very smart people, and what's more, they know who the smart people are on the site. So if the smart people currently in the thread can't help you, we'll ping one of them and they'll bring in some more folks.

So let me try to understand your problem. You need to add a battery charger to your circuit, and you want to eliminate the control joystick?

All wheelchairs are a bit different -- but one thing they seem to have in common is that the battery charger is a separate entity. It just connects through the control-box for convenience. Your robot will have two batteries tied in series -- 24V, and your charger will likely have 24V out. You should be able to find a connector that matches your charger's connector and hook it right up -- positive to positive, negative to negative. A lot of companies use an XLR type 3-pin connector -- you can start your search there.

It's typically better to have a separate charger for each battery. And if you replace your charger, that'll be the way to go. But the manufacturers don't seem to have a problem with it, so I don't see why we should.

Now my concern with that scenario is overcharging -- I really can't tell you if your charger will switch to trickle charging after the batteries are fully charged. If not, you might need a separate circuit that cuts off the current once the batteries are charged.

As for the joystick -- I'd open the control box up, take the joystick out, and throw the rest of the brains away. Those joysticks go for around $50 new, and you never know if you have a project where you can use it later.

Is that what you were asking? Or can you help me better understand the questions that you have?
Thanks!
Mark
 
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Thread Starter

mikej12

Joined Nov 14, 2018
12
Hi @mikej12,
Welcome to AAC! The trick to attracting attention is to call people out with the @ sign. The moderators are all very smart people, and what's more, they know who the smart people are on the site. So if the smart people currently in the thread can't help you, we'll ping one of them and they'll bring in some more folks.

So let me try to understand your problem. You need to add a battery charger to your circuit, and you want to eliminate the control joystick?

All wheelchairs are a bit different -- but one thing they seem to have in common is that the battery charger is a separate entity. It just connects through the control-box for convenience. Your robot will have two batteries tied in series -- 24V, and your charger will likely have 24V out. You should be able to find a connector that matches your charger's connector and hook it right up -- positive to positive, negative to negative. A lot of companies use an XLR type 3-pin connector -- you can start your search there.

It's typically better to have a separate charger for each battery. And if you replace your charger, that'll be the way to go. But the manufacturers don't seem to have a problem with it, so I don't see why we should.

Now my concern with that scenario is overcharging -- I really can't tell you if your charger will switch to trickle charging after the batteries are fully charged. If not, you might need a separate circuit that cuts off the current once the batteries are charged.

As for the joystick -- I'd open the control box up, take the joystick out, and throw the rest of the brains away. Those joysticks go for around $50 new, and you never know if you have a project where you can use it later.

Is that what you were asking? Or can you help me better understand the questions that you have?
Thanks!
Mark
@jpanhalt,
Oh -- I haven't given up on the two of us just yet. Let's put our two heads together and see if we can't come up with an idea or two once we hear the problem laid out.
Hi @mikej12,
Welcome to AAC! The trick to attracting attention is to call people out with the @ sign. The moderators are all very smart people, and what's more, they know who the smart people are on the site. So if the smart people currently in the thread can't help you, we'll ping one of them and they'll bring in some more folks.

So let me try to understand your problem. You need to add a battery charger to your circuit, and you want to eliminate the control joystick?

All wheelchairs are a bit different -- but one thing they seem to have in common is that the battery charger is a separate entity. It just connects through the control-box for convenience. Your robot will have two batteries tied in series -- 24V, and your charger will likely have 24V out. You should be able to find a connector that matches your charger's connector and hook it right up -- positive to positive, negative to negative. A lot of companies use an XLR type 3-pin connector -- you can start your search there.

It's typically better to have a separate charger for each battery. And if you replace your charger, that'll be the way to go. But the manufacturers don't seem to have a problem with it, so I don't see why we should.

Now my concern with that scenario is overcharging -- I really can't tell you if your charger will switch to trickle charging after the batteries are fully charged. If not, you might need a separate circuit that cuts off the current once the batteries are charged.

As for the joystick -- I'd open the control box up, take the joystick out, and throw the rest of the brains away. Those joysticks go for around $50 new, and you never know if you have a project where you can use it later.

Is that what you were asking? Or can you help me better understand the questions that you have?
Thanks!
Mark
Hi @Mark Hughes Thanks for the quick response. I realize I did not do the best job in describing my problem. My problem is this: add on/off switch and add cooling fan. I have a wheelchair base with a build in battery charger that is working just fine ( photo above of Red Bruno, charger plugged in, indicator light on). I want to add a lighted on/off switch that will permit me to shut off all power and utilize the existing battery charger. I plan on snipping the joystick wiring just at the joystick, thus giving me access to wiring for motors, DC power, and brakes to connect to the Sabertooth 2X32. I will also be wiring in the Spektrum flight controller (photo above) to the Sabertooth 2x32. I don't know where in the wiring to add the on/off switch. I also don't know what Brand and type of switch would be best. Lastly, I am down here in Southern Mississippi and it gets hot. I feel adding a cooling fan to the receiver and driver case (approx. dimensions will be 6x6x3) is necessary. The case will be mounted vertically above the wheelchair base approx. 12 inches (GPS module reception). Where do I add the fan in the wiring and what Brand and type fan is best to use? Thanks much, Mike
 

jpanhalt

Joined Jan 18, 2008
8,346
Hi Mike,
I am not familiar with motorized wheelchairs, except to have seen quite a few. First, I would like to step back to your design and the mower function per se. I am assuming your electric mower is battery, not mains operated. Your description reminds me of a commercial mower called "Grasshopper." It bills itself as the 1st zero turn mower. The mower "deck" is in front, steering wheels are on the sides, and casters are in back for balance:
upload_2018-11-17_6-39-49.png

That image is not me. I am assuming your electric mower will be in front and the wheelchair drive will be in the rear. I happen to have a Grasshopper with a 60" deck, and it is a joy to drive. In fact, so much fun that I cannot appreciate the desire for RC.

Based on that successful design, here are some features to consider:
1) The only non-castering wheels should be the drive wheels. Otherwise, turns will take a lot of room and the tires will skid. That will not be nice to the grass at a minimum. You need a castering wheel in the rear (one or two) to prevent wheelies. I guess the mower deck could have 4 casters, but I would remove the rear two.

2) One of your questions has to do with switches. I think the mower blade power needs a way to be disconnected under any condition. If gasoline power, a clutch is used. If electric, I would recommend a shut off safety -- in your case controlled by radio and some sensor(s) such as for tilt or obstruction. Main power needs a switch, and you may or may not want a switch for the radios. With RC aircraft -- something I am familiar with -- aircraft with ignitions usually have separate switches for radio and ignition. Non-ignition aircraft will have a throttle off position for shut-down. Electric aircraft frequently have a switch for radio and an arming switch for power. Low power units will get by with only one switch or by just unplugging the battery. Bigger units almost always have a separate arming switch. I have some Spektrum equipment, and the receiver is pretty good at tolerating just a single plug for on/off and power in an airplane I did not build. Airplanes I have built have a switch for radio and an arming switch for power. The need to ensure positively turning off a blade or prop is incorporated in our safety code and is strictly followed. Radio switches can be just be a typical toggle, plug, or slide type. Slide types are most common as they offer more protection than toggle switches from being accidentally turned off. A plug type uses a switching power plug and receptacle. Typically, when the plug is in place, the switch is open (off). When removed, the switch is closed (on). Of course, if you drop and lose the plug, you can't turn the radio off easily. For motor power, a contractor or solid-state equivalent is used. Some people use a shorting plug in a power connector. I don't know what currents will be switched so cannot make any specific recommendation.

3) Battery charging: If you are set up for dual 12V chargers fine. However, many 24V systems made from series connected batteries use just one charger and regulator. I second the need for a regulator to switch to trickle charge.

@mikej12
I don't know where in the wiring to add the on/off switch.
I am not familiar with that specific controller. After checking it out, it seems there are some options with the DIP switches, but not a hard disconnect for the battery or motor drives. Admittedly, I did not read the entire 57 page manual carefully, but a few things stuck out:
1) It shows the RC receiver powered by 5V from the controller. In modeling terms, that is a battery eliminating circuit (BEC). That is fine, so long as there is a separate motor cutoff so the receiver will always have power if the voltage drops too low.
2) From what I saw in that brief review, "motor off" depends on the DIP switch settings. If radio control, that "off" is the servo center-position pulse width. THAT is not a reliable off in my opinion.

One solution would be to run the receiver from a separate BEC (e.g., Castle Creations) or battery (I would prefer a BEC). Then, you can put a hard disconnect in the power to the Sabertooth controller. An battery disconnect switch is a durable way to do that. Alternatively a starter solenoid and typical automotive wiring will work too. My choice for simplicity would be a disconnect switch like this:
upload_2018-11-17_7-55-23.png

If you have a separate BEC, that should be wired around it. Start sequence would be something like radio switch on, throttle off, motor power on. Stopping would be the reverse. Again, there are design options so specifics are vague. But to emphasize again, I feel drive and blade hard disconnects are essential.
 
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Thread Starter

mikej12

Joined Nov 14, 2018
12
20181111_170615.jpg 20181012_094215.jpg 20181111_170615.jpg 20181012_094215.jpg
Hi Mike,
I am not familiar with motorized wheelchairs, except to have seen quite a few. First, I would like to step back to your design and the mower function per se. I am assuming your electric mower is battery, not mains operated. Your description reminds me of a commercial mower called "Grasshopper." It bills itself as the 1st zero turn mower. The mower "deck" is in front, steering wheels are on the sides, and casters are in back for balance:
View attachment 163946

That image is not me. I am assuming your electric mower will be in front and the wheelchair drive will be in the rear. I happen to have a Grasshopper with a 60" deck, and it is a joy to drive. In fact, so much fun that I cannot appreciate the desire for RC.

Based on that successful design, here are some features to consider:
1) The only non-castering wheels should be the drive wheels. Otherwise, turns will take a lot of room and the tires will skid. That will not be nice to the grass at a minimum. You need a castering wheel in the rear (one or two) to prevent wheelies. I guess the mower deck could have 4 casters, but I would remove the rear two.

2) One of your questions has to do with switches. I think the mower blade power needs a way to be disconnected under any condition. If gasoline power, a clutch is used. If electric, I would recommend a shut off safety -- in your case controlled by radio and some sensor(s) such as for tilt or obstruction. Main power needs a switch, and you may or may not want a switch for the radios. With RC aircraft -- something I am familiar with -- aircraft with ignitions usually have separate switches for radio and ignition. Non-ignition aircraft will have a throttle off position for shut-down. Electric aircraft frequently have a switch for radio and an arming switch for power. Low power units will get by with only one switch or by just unplugging the battery. Bigger units almost always have a separate arming switch. I have some Spektrum equipment, and the receiver is pretty good at tolerating just a single plug for on/off and power in an airplane I did not build. Airplanes I have built have a switch for radio and an arming switch for power. The need to ensure positively turning off a blade or prop is incorporated in our safety code and is strictly followed. Radio switches can be just be a typical toggle, plug, or slide type. Slide types are most common as they offer more protection than toggle switches from being accidentally turned off. A plug type uses a switching power plug and receptacle. Typically, when the plug is in place, the switch is open (off). When removed, the switch is closed (on). Of course, if you drop and lose the plug, you can't turn the radio off easily. For motor power, a contractor or solid-state equivalent is used. Some people use a shorting plug in a power connector. I don't know what currents will be switched so cannot make any specific recommendation.

3) Battery charging: If you are set up for dual 12V chargers fine. However, many 24V systems made from series connected batteries use just one charger and regulator. I second the need for a regulator to switch to trickle charge.

@mikej12

I am not familiar with that specific controller. After checking it out, it seems there are some options with the DIP switches, but not a hard disconnect for the battery or motor drives. Admittedly, I did not read the entire 57 page manual carefully, but a few things stuck out:
1) It shows the RC receiver powered by 5V from the controller. In modeling terms, that is a battery eliminating circuit (BEC). That is fine, so long as there is a separate motor cutoff so the receiver will always have power if the voltage drops too low.
2) From what I saw in that brief review, "motor off" depends on the DIP switch settings. If radio control, that "off" is the servo center-position pulse width. THAT is not a reliable off in my opinion.

One solution would be to run the receiver from a separate BEC (e.g., Castle Creations) or battery (I would prefer a BEC). Then, you can put a hard disconnect in the power to the Sabertooth controller. An battery disconnect switch is a durable way to do that. Alternatively a starter solenoid and typical automotive wiring will work too. My choice for simplicity would be a disconnect switch like this:
View attachment 163948

If you have a separate BEC, that should be wired around it. Start sequence would be something like radio switch on, throttle off, motor power on. Stopping would be the reverse. Again, there are design options so specifics are vague. But to emphasize again, I feel drive and blade hard disconnects are essential.
@jpanhalt I like your suggestions. The frame for Bruno (full picture attached) has a easy disconnect on the front crossmember for the battery powered lawn mower to roll into the frame. I have not completed the supports for the lawn mower to attached to Bruno but my plan is to build a L shaped slider bracket that will attach to the rail and easily move; thus allowing easy mounting of lawn mower, lawn aerator, etc. I have researched several YouTube RC Lawn Mower designs and I don't like not being able to adjust the cutting height or use the grass catcher.

The suggestion of a simple on/off switch on the battery positive is now on my list of definitely do. I will research Castle Creations BEC configuration for the receiver 5v power disconnect and add that to my list of definitely do. I agree 100 percent with your emphasize on hard disconnects for power and blades. The Spektrum transmitter with a servo might do the trick - more research. Any recommendations on the cooling fan? Thank much, Mike
 

jpanhalt

Joined Jan 18, 2008
8,346
You mower creates suction when running. A small duct (1" to 2" SCAT ) to the deck might suffice. The receiver doesn't need cooling. The motor driver probably does. Fresh air across it should suffice. A low voltage computer fan on top of the box with screened holes around the edges would probably work.
 

Mark Hughes

Joined Jun 14, 2016
404
Hi @Mark Hughes Thanks for the quick response. I realize I did not do the best job in describing my problem. My problem is this: add on/off switch and add cooling fan. I have a wheelchair base with a build in battery charger that is working just fine ( photo above of Red Bruno, charger plugged in, indicator light on). I want to add a lighted on/off switch that will permit me to shut off all power and utilize the existing battery charger. I plan on snipping the joystick wiring just at the joystick, thus giving me access to wiring for motors, DC power, and brakes to connect to the Sabertooth 2X32. I will also be wiring in the Spektrum flight controller (photo above) to the Sabertooth 2x32. I don't know where in the wiring to add the on/off switch. I also don't know what Brand and type of switch would be best. Lastly, I am down here in Southern Mississippi and it gets hot. I feel adding a cooling fan to the receiver and driver case (approx. dimensions will be 6x6x3) is necessary. The case will be mounted vertically above the wheelchair base approx. 12 inches (GPS module reception). Where do I add the fan in the wiring and what Brand and type fan is best to use? Thanks much, Mike
@mikej12,
I think I have a better idea now. Once I got off of mobile and onto a PC -- I got a better idea of what's going on. BTW -- nice build!
First -- some unsolicited advice -- since I wrote the wheelchair article, I discovered a stash of Anderson Powerpole connectors at a surplus store and I've been adding them to everything I own that has DC in it. They have a series that can handle high current demands that you'll have and make it very easy to connect/disconnect things for maintenance and tinkering. If you can get some at a good price, you might want to add them to your project. See this catalog (http://www.andersonpower.com/_global-assets/downloads/pdf/cat-ppmp.pdf) page 64/65 for a way to turn them into a switch -- you mount one connector to the frame and add a handle to the mating connector.

1) Switch: I'd install two switches. Power, and e-stop. You could actually install several e-stops around the device in case it goes nuts. If you have them configured NO (normally open), you would connect them in parallel. If you have them configured NC (normally closed), you'd wire them in series. Power switches get a little pricey when dealing with >50A. In fact, if you're comfortable with it, I'd instead recommend a relay/contactor , perhaps even from your local auto-parts store.
The e-stop gets connected to some of the accessory screw terminals on the sabertooth. I think I showed which one in one of the wheelchair articles you've already found.
The power relay interrupts the connection between the positive end of the battery and the sabertooth, preferably close to the battery. You'd then add a much smaller and much cheaper switch between the battery, the coil, and the switch.

2) Fan: Digikey and Mouser have a nice selection of every fan that you'll ever want. I imagine you'll want a 24V DC fan, so you can connect it straight to the wheelchair batteries. The dimensions are listed on the page, as well as the air-flow (in CFM). Find a 2-wire lead package that is at least 20 CFM (feel free to go higher, this is only ballpark guess). If you are going to install a filter to keep debris out of the fan and electronics (recommended), you should get a fan with a higher CFM, as the type of filter mesh, mesh density, and surface area of the filter will derate the airflow through the device.

I've got a few things to do today -- but if you need it, I can likely lay out a drawing for you sometime this weekend.
 
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Thread Starter

mikej12

Joined Nov 14, 2018
12
@mikej12,
I think I have a better idea now. Once I got off of mobile and onto a PC -- I got a better idea of what's going on. BTW -- nice build!
First -- some unsolicited advice -- since I wrote the wheelchair article, I discovered a stash of Anderson Powerpole connectors at a surplus store and I've been adding them to everything I own that has DC in it. They have a series that can handle high current demands that you'll have and make it very easy to connect/disconnect things for maintenance and tinkering. If you can get some at a good price, you might want to add them to your project. See this catalog (http://www.andersonpower.com/_global-assets/downloads/pdf/cat-ppmp.pdf) page 64/65 for a way to turn them into a switch -- you mount one connector to the frame and add a handle to the mating connector.

1) Switch: I'd install two switches. Power, and e-stop. You could actually install several e-stops around the device in case it goes nuts. If you have them configured NO (normally open), you would connect them in parallel. If you have them configured NC (normally closed), you'd wire them in parallel. Power switches get a little pricey when dealing with >50A. In fact, if you're comfortable with it, I'd instead recommend a relay/contactor , perhaps even from your local auto-parts store.
The e-stop gets connected to some of the accessory screw terminals on the sabertooth. I think I showed which one in one of the wheelchair articles you've already found.
The power relay interrupts the connection between the positive end of the battery and the sabertooth, preferably close to the battery. You'd then add a much smaller and much cheaper switch between the battery, the coil, and the switch.

2) Fan: Digikey and Mouser have a nice selection of every fan that you'll ever want. I imagine you'll want a 24V DC fan, so you can connect it straight to the wheelchair batteries. The dimensions are listed on the page, as well as the air-flow (in CFM). Find a 2-wire lead package that is at least 20 CFM (feel free to go higher, this is only ballpark guess). If you are going to install a filter to keep debris out of the fan and electronics (recommended), you should get a fan with a higher CFM, as the type of filter mesh, mesh density, and surface area of the filter will derate the airflow through the device.

I've got a few things to do today -- but if you need it, I can likely lay out a drawing for you sometime this weekend.
@Mark Hughes. Thanks much for pointing me in the right direction. Electronics is like me visiting a foreign country: I will find my way around, but I will get lost from time to time. I reviewed your wheelchair article and see you have the e-stop switch connected to A1 and A2 on the 2x32. Run just the 2 wires, I can handle that. One e-stop switch works for me, I will see what Digikey has to offer. For the main power switch you are correct they do get pricey above 50 amps. My existing wheelchair battery wiring has two 70 amp fuses, one on positive side and one on negative side. I don't know if I would need a 70 amp switch or what. I don't have a problem at all with installing a relay/contactor. Installing one puts me back in a foreign country: what type/model and connect positive wire to what terminals on the relay? I then add a simple 12 volt on/off switch between the relay and the 2x32 positive ? Cooling fan: I will research what Digikey has to offer around the 30 CFM; install with fan to pull cooler air through filter and exhaust out. Logically I can connect the fan directly to the positive and negative connects on the 2x32 ? Thus the main power switch will turn it on/off directly. Mark I don't need a response immediately - Thanksgiving activities next week. Thanks again, Mike
 

jpanhalt

Joined Jan 18, 2008
8,346
Thanksgiving activities next week. Thanks again, Mike
Ditto here. Will be with my daughter in VA and her wonderful family. Happy TG to you. Will be back late Saturday, weather permitting. Always worry about the PA mountains -- Somerset and Breezewood in particular. I have driven that route many times in college (50 years ago), and it is still trying.

John
 

Thread Starter

mikej12

Joined Nov 14, 2018
12
Ditto here. Will be with my daughter in VA and her wonderful family. Happy TG to you. Will be back late Saturday, weather permitting. Always worry about the PA mountains -- Somerset and Breezewood in particular. I have driven that route many times in college (50 years ago), and it is still trying.

John
@jpanhalt. Safe travel and Happy TG to you. While I was in the Air Force, I lived in Dale City, VA for the 4 year tour. Enjoyed the seasons, but hated the DC traffic. From time to time, I would vacation back in my home state of Minnesota, traveling through rural PA. Always was summertime travel; beautiful scenery.
 

Mark Hughes

Joined Jun 14, 2016
404
@mikej12,
You might try going down to your local auto-parts store/scrap yard and see if they have a guy who can help you. Look for the unkempt one, with a scraggly beard and an unironed shirt. If you've got a kid who only can help you if he knows the make/model of your vehicle, you're out of luck. But if you get an old-timer, you can tell him what you're doing and he can tell you exactly what part you need. From there we can tell you how to hook it up properly.

Happy Thanksgiving and I can't wait to see a video of this thing tearing around the yard!
 

jpanhalt

Joined Jan 18, 2008
8,346
@jpanhalt. Safe travel and Happy TG to you. While I was in the Air Force, I lived in Dale City, VA for the 4 year tour. Enjoyed the seasons, but hated the DC traffic. From time to time, I would vacation back in my home state of Minnesota, traveling through rural PA. Always was summertime travel; beautiful scenery.
Agree. The best description I have heard of PA is that the mountains do not obstruct the view. It is the only place I have lived where I would just got out on a Sunday for a few hours and drive with no destination. Each little town along the Susquehanna had its own character.

Daughter is in McLean, VA. Lived in SE MN for many years, but even"tropical" Minnesota was way too cold for me. (California native here.)
 

Thread Starter

mikej12

Joined Nov 14, 2018
12
@mikej12,
You might try going down to your local auto-parts store/scrap yard and see if they have a guy who can help you. Look for the unkempt one, with a scraggly beard and an unironed shirt. If you've got a kid who only can help you if he knows the make/model of your vehicle, you're out of luck. But if you get an old-timer, you can tell him what you're doing and he can tell you exactly what part you need. From there we can tell you how to hook it up properly.

Happy Thanksgiving and I can't wait to see a video of this thing tearing around the yard!
@Mark Hughes. Thanks again. I used to work with a crusty, grumpy, old mechanic who said he voted for Truman. I will chat with him after Thanksgiving. Happy Thanksgiving Mark. Video will most likely be uploaded to YouTube in early Jan when I complete the project.
 

ericgibbs

Joined Jan 29, 2010
9,116
hi mike,
From what I have read from your posts, this multi function 'bruno' has at least two modes of operation.?
Lawn mowing, which I assume is autonomous and a general purpose manually guided work horse function.?

What is the auto work area and the positional accuracy required.?

Eric
@jpanhalt
 
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