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Thread: Power chair with cambered wheels. What do y'all think

  1. #1

    Power chair with cambered wheels. What do y'all think

    Hello,
    I play wheelchair tennis and use a power chair due to limited strength and grip in my hands.

    I am looking to have a local welder put together a frame for me which will accommodate cambered drive wheels. The guy, Travis makes custom BMX bike frames and his work is renowned in the city and commendable.

    I found an older power chair on Craigslist from which I can use the motors, control module, batteries and Joystick.

    I was thinking to start with a manual tennis chair and essentially follow the same design for the frame, but use beefier members to support the extra weight of the batteries and motors (approx 150 lbs). Of course different wheels will be needed to handle the weight and angular forces.

    Any pitfalls, comments, questions or concerns would be appreciated.

  2. #2
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    Interesting.

    Negative camber has been used on performance vehicles for as long as I can remember. Racers sometimes resort to extreme camber angles to get the handling the want. All of today’s cars use at least a small amount of negative camber to improve the way their vehicles perform. An electric wheelchair is just another powered vehicle.

    If you have someone who can do the job, I say go for it. Of course you can expect an increased amount of uneven tire wear. But toe-in/toe-out is the most important thing that will need to be controlled. Changing camber usually amounts to a change in toe. Good luck.

  3. #3
    Quote Originally Posted by ala View Post
    Interesting.
    If you have someone who can do the job, I say go for it. Of course you can expect an increased amount of uneven tire wear. But toe-in/toe-out is the most important thing that will need to be controlled. Changing camber usually amounts to a change in toe. Good luck.
    The first time I ever sat in a sports chair, was a revelation. Of course the benefits of Negative camber are undeniable. Quicker turn in and stability being the biggest of them.

    Did not know about the toe in/out issue. I will have to stress that the welder pay close attention to these measurements.
    Tire wear I think I can live with. Will need to make wheels removable as well.

  4. #4
    The camber will help. If it is a chair used only for tennis. I would try, lowering the battery, you and any other parts before I cambered the wheels, Maybe smaller diameter wheels. Like a lawn mover or go kart. This would change the gear ratio and make it quicker.
    We built a racing electric chair once. Went 42 mph. Used a Lear jet starter motor. Tooo much fun.

  5. #5
    Quote Originally Posted by baldfatdad View Post
    The camber will help. If it is a chair used only for tennis. I would try, lowering the battery, you and any other parts before I cambered the wheels, Maybe smaller diameter wheels. Like a lawn mover or go kart. This would change the gear ratio and make it quicker.
    We built a racing electric chair once. Went 42 mph. Used a Lear jet starter motor. Tooo much fun.
    Tell me more about this chair y'all built. any build thread/details I could glance at? Small wheels and 42 mph is impressive. How were durability and power consumption??? 12v or 24v?

    Indeed, i'll try to keep the batteries as close to the ground as possible. I want to implement a Panther drive system which will use a gear connected to the wheel axles, that way I can put the motors close to the ground as well.

    Why the smaller diameter wheels? If I can use smaller gears, that would serve the same purpose right? These electric motors seem to have plenty of torque. I was thinking I would use larger wheels for stability.

    I want to be as high of the ground as I can possibly be so I can Increase my vertical reach for better serves and smash shots. I have good trunk control so I could really increase my range of shots. I saw a guy at a tournament where he was literally kneeling in his (custom) chair. Most unique setup i ever saw.

  6. #6
    I was thinking of a go kart tire. Wide and low. Good start and stop grip. You can get them as narrow as 3 inches and as wide as 6. With or without tread and some pretty sticky compounds. Might be cheaper than gears. I would try to go with one battery and be able to do a quick change between sets if necessary.
    If you change the gear ratio on the chair, you may find yourself, spinning skinny wheelchair tires.
    The thing we build was for road racing. 20 inch bike wheels. The driver was laying on his back. Not at all like what you want.

  7. #7
    The purpose of camber is to make the chair turn quicker/easier and bring the tops of the wheels closer to the person pushing. Thus making the chair easier to operate.

    In a powerchair, there is no need to bring the tops of the wheels closer to the person. Also, turning on a powerchair is achieved by speeding up one of the drive wheels while slowing down or reversing the other drive wheel. So, there is no need to make it easier to turn.

    If I was going to scratch build a power tennis chair..... I would be focused on low center of gravity, maximum acceleration from one side of court to other and the ability to make a full throttle turn with no chance of flipping.

    I would take a center-wheel drive style platform with the smallest drive wheels (probably 10"). Front and rear swivel single anti tippers welded on with 3" rollerblade wheels. If you are playing on tournament style courts, you should have level surfaces and not need to worry about ground clearance or high-centering.

    Just my thoughts......

  8. #8
    Quote Originally Posted by baldfatdad View Post
    I was thinking of a go kart tire. Wide and low. Good start and stop grip. You can get them as narrow as 3 inches and as wide as 6. With or without tread and some pretty sticky compounds. Might be cheaper than gears. I would try to go with one battery and be able to do a quick change between sets if necessary.
    If you change the gear ratio on the chair, you may find yourself, spinning skinny wheelchair tires.
    The thing we build was for road racing. 20 inch bike wheels. The driver was laying on his back. Not at all like what you want.

    Go kart tires would work great for straight line travel, or making turns on a track when you have steering. I am interested in neither.
    I need cambered wheels to make quick turns on the courts.

    I love your idea about the modular batteries. About using only 1 battery, most wheelchair motors are wired for 24 V. I wonder if I can use big rig batteries.

    Did it have bicycle wheels or motorcycle wheels? I am worried about weight bearing. Motors and batteries are HEAVY and that combined with cambered wheels could be hazardous. I want to look into dirt bike wheels made by Spinergy. The wheels shouldn't be unnecessarily heavy, else they will slow me down and consume to much juice.

    Road racing huh, sound cool. Did y'all have one starter motor from the Lear connected to both wheels? Any kind of transmission??? Rear end??? CVT? Posi track? I'm intrigued and really hope you will share some details.

  9. #9
    Quote Originally Posted by jakeyboy1 View Post
    The purpose of camber is to make the chair turn quicker/easier and bring the tops of the wheels closer to the person pushing. Thus making the chair easier to operate.

    In a powerchair, there is no need to bring the tops of the wheels closer to the person. Also, turning on a powerchair is achieved by speeding up one of the drive wheels while slowing down or reversing the other drive wheel. So, there is no need to make it easier to turn.

    If I was going to scratch build a power tennis chair..... I would be focused on low center of gravity, maximum acceleration from one side of court to other and the ability to make a full throttle turn with no chance of flipping.

    I would take a center-wheel drive style platform with the smallest drive wheels (probably 10"). Front and rear swivel single anti tippers welded on with 3" rollerblade wheels. If you are playing on tournament style courts, you should have level surfaces and not need to worry about ground clearance or high-centering.

    Just my thoughts......
    You are right about those advantages of cambered wheels in chairs. Also about how turning is achieved.

    One advantage of cambered wheels you failed to mention is quicker/sharper turns. While my daily use power chair also has 0 turn capability (thanks to its center drive style) turning is quite slow compared to my 5.5 mph straight-line speed. This may be a safety feature for stability, but regardless, it makes it tougher for me to get in position for fast balls fats enough. If I can't get in position fast enough, I have to rush my shot and that increases the chances of wild hits.

    Agreed, I will try to make the CG as low as I can. Especially the batteries will be inches of the ground. Depending on frame style and whether or not I use gears, motors may be mounted a bit higher. Regardless, the cambered wheels and weight of the batteries should allow for WOT turns.

    Yes, I do play on courts and while on court I don't have to worry about clearance. Thing is, getting the chair to the courts may involve going over some rougher terrain and may necessitate some additional ground clearance.

    I am wondering why you are recommending smaller wheels? I realize larger wheels are easier to push manually via the hand rims from the torque being applied at a greater distance from hub/axle. Top seeded players have moved to 27" wheels on manual chairs and those extra 1-2 inches make a significant difference.
    One advantage of smaller wheels would be I could get solid rubber tires or tires with rubber inserts and not have to worry about air pressures. Those would also make the chair a tiny bit more responsive.
    Don't get me wrong, I am in no way interested in 27" wheels, but I don't understand how 10" wheels would be better than say 15" or 17" ones. Larger diameter wheels would lend more stability in straight-line and wide arc turns.

    I would really like you to tell me more about smaller wheels.

    Yesterday, I had the idea to use fixed gears so I can better control the wheels better and slow down without needing a braking system.

  10. #10
    Senior Member grommet's Avatar
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    If you are going to use a powerchair while playing tennis, why do you want cambered wheels? What is the advantage you are hoping for?

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