Gone are the days in which bulky, cumbersome wheelchairs are the norm. Older individuals and those with limited mobility who depend on wheelchairs have a plethora of options available to them, including folding electric wheelchairs. These types of mobility support items make it easier than ever to exert independence and live life to its fullest. Let's look at how folding electric wheelchairs are providing users with better portability and convenience.
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Benefits of Folding Electric Wheelchairs
Electric power chairs with convenient folding mechanisms can make travel and transport much easier for users and their caregivers. Quickly and easily fold and lift these folding electric wheelchairs to simplify loading and unloading in cars, trains, planes and buses. These types of wheelchair's smaller capacities make them ideal when there is limited storage space. Many folding electric wheelchairs fold with the touch of a button and others disassemble in seconds. Miracle Mobility's 4N1 Ultra Lite Electric Walker Wheelchair features a convenient joystick controller and folds in three seconds to the size of a large suitcase. The Golden LiteRider Envy GP162 is a fun electric wheelchair, boasting unparalleled maneuverability. What's more, this electric wheelchair is available in multiple, fun colors and has a comfortable stadium-style seat. It also boasts a generous footplate and larger 22-amp batteries, so you can go even further than before.
Lightweight Designs
Traditional electric wheelchairs were often heavy. Although these power chairs offered better convenience and maneuverability for the users, they weighed more due to the individual components, most notably the battery and their steel frames. However, with the advent of newer, more lightweight materials, today's electric folding wheelchairs are lighter than ever. This makes them even easier to take with you on the go! Journey Air's Lightweight Folding Power Chair weighs only 35 lbs. (without the battery), and its joystick operation makes it responsive and quick. Ideal for shopping, dining and running errands, this electric wheelchair device is FAA-approved.
The Comforts of Home
Electric wheelchair manufacturers have listened to their users' needs and requests, implementing accessories and add-ons tailored to their active lifestyles. Padded seats offer superb comfort during use, available trays offer secure places for activities and ample storage means that you can take your must-have items with you while on the go. Pathway Mobility's Geo Cruiser LX has an adjustable backrest, footrest and a pressure-relief seat cushion for added comfort. This compact, lightweight and foldable electric power chair has a tight turning radius. It travels up to 15 miles with a top speed of 4 MPH. Tailor your folding electric wheelchair to your needs with additional wheelchair accessories available at Senior.com.
The Best Manufacturers at Low Prices
If you're shopping for a folding electric wheelchair for yourself or a loved one, Senior.com is the place to be! We offer dozens of folding electric wheelchairs from top manufacturers, including Golden Technologies, Merits Health, Miracle Mobility, Ewheels and many others! Shop with confidence and enjoy a price-match guarantee on every foldable wheelchair in our inventory. We want to ensure that you find the perfect folding electric wheelchair for your needs, and our Customer Care Specialists are available seven days a week during business hours to assist you in your purchase. Financing is available. Visit our Senior Help Center to learn how to reach us.
Dear Hajj,
I'm glad your still working on this and pleased to see pretty clear specification of what kind of controller you need. I think that there are three avenues you might explore, so I'll take them up one by one. There'll be two messages because this will take more than the 9500 characters allowed in a single message.
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**(1) Do it yourself. ** This seems to be what want to do, but I think it may not be the best way to go. You wrote:
- A PWM module is a must, because acceleration and deceleration need to be well controlled.
- The motors used require peaks of 60 amps for a couple of seconds and 20-30 amps while cruising on a slope.
As wheelchair controllers go, that is a basic level of output suitable for a chair going no more than say 7-8 km/hour on relatively smooth terrain. Many wheelchairs do use controllers of this type, but faster chairs, chairs for heavy users, and chairs that have to handle the outdoors often have more powerful controllers - top-of-the-line commercial controllers at the moment provide up to 90-110 Amp for several seconds, adequate for 10 km/hr with a heavy user and perhaps 12-13 km/hr with a very lightweight driver.
However, even a 60 Amp PWM controller is not an easy thing to engineer, especially when the person riding that chair can't get off and walk away if something goes wrong. Not only must it have low resistance MOSFETS and enough of them to handle the current, at a minimum it needs run-away protection, brake control (about 1Amp at 24V for each brake), overheat protection, under and over voltage protection and you CAN NOT use the chair frame as part of the battery circuit as you would in a car and you MUST make sure that there are no low-impedance connections between the electronics and the frame. The PWM is going to be switching high currents to (and from) an inductive load. Transient protection is not trivial for this, nor is keeping electrical noise to a reasonable level so that it doesn't drive the microcontroller crazy. Even the circuit boards are very different from the 1 oz copper boards used for low power circuits. You need lots of copper, good isolation and excellent heat sinking if you expect it to work for any length of time. You already have a controller that doesn't work, you don't need to create another one, so a lot of study is going to be needed if you want to go this route.
You wrote:
- The maximum speeds and accel/decel profiles need to be adjusted for each individual, depending on their case, handicap and overall mobility requirements.
This would be handled in the microcontroller, again with a lot of attention to safety, but it is not nearly as difficult an engineering challenge as the motor controller. Other things to consider for the algorithm are how to mix X and Y joystick outputs to get left and right motor power, an adjustable deadband for users that might have a hand tremor, different speeds in forward and reverse, turn rate, turn acceleration and deceleration, variable exponential curving so you can have fine control near stick center and increased response with large joystick deflections. There's a good discussion of chair programming on the WheelchairDriver web site. As noted there, the best control for those who have good hand coordination comes with turn accelerations/decelerations maxed out, but turn rates reduced way down. If acceleration is turned down, the delay between control input and response can make the chair very difficult to control and easy to over-control. It sets you up for what in aviation is called a "pilot induced oscillation".
Lastly, you wrote
- More thinking needs to go into controlling the wheelchairs on upward and downward slopes as this will impact the control algorithm.
Most wheelchair controllers do this by using what's called IR compensation. As mechanical load on a motor increases, the current flow increases as does the back EMF. That back EMF, which is current x (motor + wiring) resistance is then used as FORWARD feedback to increase PWM on time. Notice that this is a potentially unstable situation; the more PWM is boosted, the more current flows, when PWM increases current goes up, then PWM again increases and so on. Hence, a fraction of the motor resistance is experimentally found that gives enough boost for decent control, but not so much that the chair is "nervous" (or in the worst case actually takes off on its own). One might start out with 0.7 * resistance (in the 50-300 milliohm or so range) * motor current, and then adjust in small increments to get the response needed. If you don't know the motor resistance, you have to start with a very low value, and work cautiously up from there. Set up well, motor compensation will let a chair go at fairly constant speed as slope changes, and keep going reasonably straight if one wheel hits a bump -- at least until your controller runs into its Amp limit or the motor just can't produce the needed torque. The only hardware needed is a good way to measure actual motor current: voltage across a shunt or (better) a Hall-effect current sensor. Take a look at the data sheet for the Allegro ACS758 family of current sensor ICs, particularly the board layout, to get an idea of the engineering involved in working with these kinds of currents.
A less common scheme is to use sensors (gyroscope, or shaft encoder etc.) and closed loop control. This can give very constant speed and direction, but is more complex and more expensive.
(2) Use a commercially available generic motor controller and add your own microprocessor control. I think that this is a more feasible approach, but might still not be the best way to go. MarkT suggested looking at Robot Power OSMC Project Info, and I agree that would be a good idea. What you will see is that very few the control boards they sell would be workable for you. First off, none of the controllers for "up to 28V" are suitable, even though the battery is nominally 24V unless you block regeneration - the motor acting as a generator when decelerating or going down hill. Voltages generated during regeneration can easily go to 32V or more, and you really don't want to prevent regeneration because it is what gives a chair controlled deceleration and also adds to efficiency. So, the OSMC store controllers that can handle 60Amps are just two: the Vyper and the OSMC. Both have far more current capacity than you need, and they are not cheap. Each one is just one channel, so you'd need two, hence $400 for two Vypers, or $440 + fans for two OSMC. Even then, you would have to design and engineer the safety controls that are needed on a wheelchair controller.
Another possibility, are some Roboteq products. http://www.roboteq.com/index.php There are a few people using these on wheelchairs because they want higher power than commercial wheelchair controllers produce, or want to move to higher voltage LiFePO4 batteries, or want open-source programming (and can't, as individuals, get full access programmers for standard WC controllers). The Roboteq NextGen series of controllers already has many of the safety features built in, or programmable, though at least an external high-current contactor has to be added to meet the minimum safety requirements for a wheelchair. Most people experimenting with these for wheelchairs are using the HDC2540 which is a dual channel, 150 Amp for a full minute controller that costs $645. At least one person is experimenting with brushless motors and a Roboteq dual channel brushless controller. For your specs, the MDC2460 (60A/channel for 1 minute) costing $395 is one to consider. You can download their user manual, spec sheets and software to get an idea of the work involved in making safe use of these for a wheelchair.
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