Introducing The SkateHitch! A Passenger board for Chairs

[DrewDigital]

Check out the SkateHitch that I've been working on: http://www.Skatehitch.com
It's a passenger/companion skateboard that is towed behind power wheelchairs. This one has folding wheels for a low profile and a grip to stow the board. It's now available to buy on Etsy!

[Burgerman]

The boards cool. More interesting to me are the drive tyres. Do you know the brand? Or where from? Those are what I am after for my BM2 chair at the moment.

[DrewDigital]

SUNF tires: https://a.co/d/adp1evI They're the same size as the knobby tires on the Frontier.

Do you think people will be able to get the skateboard installed? The hitch tube has to be bolted to the bottom of the battery box. Or rig up a bracket from the tie downs or seat frame...

[shirley_hkg]

Fleetwood Mac : Never Going back again

The design concept is totally wrong.

[Burgerman]

Do you think people will be able to get the skateboard installed? The hitch tube has to be bolted to the bottom of the battery box. Or rig up a bracket from the tie downs or seat frame...

A few will. The vast majority cant or wont. Especially if it means drilling anything. Or lifting anything.

[biscuit]

Could I ever find such a thing suitable for my ancient mother? This wouldn't do. But my nephew might enjoy it, if his sense of balance is excellent.

I suppose it would kill my batteries to tow a passenger.

What do you see wrong with the design, Shirley?

[shirley_hkg]

They are skate wheels , not casters. That means the joint will break when doing sharp turn.

If the joint is a swivel joint , it can't reverse. Look how much skill is need for a trailer truck diver to reverse.

Just in case you've missed it, biscuit

https://www.wheelchairdriver.com/board/ ... 4&start=30

[Burgerman]

In case you dont grasp the HK english translation, he means the following.

If you reverse as you do endlessely in a powerchair or turn in place then it will get wrecked or jacknifed,

He is saying that a better way is to have no left right hinge like a typical tow hitch, but just a board that only lifts up and down. With casters under it. So that you can safely turn in place, reverse, etc and the thing just stays in line with the chair. Which is correct. Basically a fixed but hinged board that only moves in the vertical plane with casters under it.

[DrewDigital]

Lateral Stability (side to side control) is the issue with these boards. A trailer with straight (fixed) wheels has superior Lateral Stability compared to a swivel caster board.

This skateboard isn't meant to go backwards or turn in place. It's meant to go fast and far.

Imagine a truck towing a trailer full of bricks and the trailer had swivel casters instead of fixed wheels. (and a rigid joint to the truck.) What would happen when you go around a corner? Without fixed wheels, nothing is stopping the centrifugal force of the bricks and it would overcome the traction of the truck tires and the truck/trailer would spin out of control.

Same concept applies to these boards.

Swivel casters may work with rear wheel drive chairs (where the driver is in front of the drive wheels and the passenger is right behind the drive wheels so it's balanced), but with mid and front wheel drive chairs, the passenger mass is too far behind the drive wheels and the chair will spin out of control.

[Burgerman]

Thats the problem wih front drive and to a smaller extent with mid drives anyway, even without the board on the back.

[AgGuy]

I admire your engineering to fit a need. Very well done.
Those here that are hung up on not being able to reverse, seem to forget that your passenger still has functional legs and can stow the board when needed.

[Burgerman]

Not me! I have no need of one at all. I had a 19 year old carer called kristen years back that had shoes with flip out wheels. That worked pretty good too. She was a little strange though. Favorite food was garden pea and salt sandwiches. She managed to get these in pubs and resturants all over the place.

[acid_coke]

First of all: That board looks really cool. I like it. Maybe you could sell another version with casters?

Lateral Stability (side to side control) is the issue with these boards. A trailer with straight (fixed) wheels has superior Lateral Stability compared to a swivel caster board.

That's true but you could mitigate it somewhat by adding some caster to the casters i.e. tilting them a little.

Have you thought about adding some kind of suspension?

[shirley_hkg]

Lateral Stability.
This skateboard isn't meant to go backwards or turn in place. It's meant to go fast and far.

You have records to break.


https://www.wheelchairdriver.com/board/ ... start=3150

[Burgerman]

What would worry me, having already destroyed rather a lot of motors of many brands is that towing increases load. That increases the heat. That also makes it feel to the motors as if you are going uphill all the time. So I wouldnt do this actually up a hill! That would really hammer them. So only 4 pole motors should even attempt this. Or brushless.

You may also run into thermal rollback issues. Certainly it will happen sooner. I do that anyway if I am abusing the chair without an extra human in tow quite frequently as it is.

Make sure your passenger is a small person!

[shirley_hkg]

I had the same concern at first. It is 17--18 years now and nothing happened.

[biscuit]

Overcoming the inertia when pulling off, and any slope uphill - not so? I can easily keep a boat on a dolly (or in water) moving, if it is already moving, with my little finger. Devil is stopping or turning the drifting boat, in fact.

[slomobile]

I think you did a fantastic job with the look, branding, and presentation. The basic idea is great. But I think Shirley is right about the drive kinematics. I think simply adding a rope with loops at both ends, fit over your caster bearing towers, and slipped under the platform would hold it off the ground. Eliminating the requirement for extra wheels all together. Should allow normal backing up, and less pivoting of the board when you turn. That will put less sideways strain on your attachment joint, which has too much angular moment to survive very long with wheels. Less pivoting means you can enlarge the platform (if you want to) for your passenger as it is less likely to hit the casters in a sharp turn. You can select rope with varying amounts of elongation (1-10% for climbing ropes) to serve as a bit of a shock absorber for your passenger.

Lateral Stability (side to side control) is the issue with these boards. A trailer with straight (fixed) wheels has superior Lateral Stability compared to a swivel caster board.

This skateboard isn't meant to go backwards or turn in place. It's meant to go fast and far.

Imagine a truck towing a trailer full of bricks and the trailer had swivel casters instead of fixed wheels. (and a rigid joint to the truck.) What would happen when you go around a corner? Without fixed wheels, nothing is stopping the centrifugal force of the bricks and it would overcome the traction of the truck tires and the truck/trailer would spin out of control.

Fixed wheels only advantage for lateral stability is by virtue of their wider base of support than central casters. The chair's stock casters have an even wider base of support than your fixed wheels. And should offer greater lateral stability.
Your analogy to a trailer of bricks may feel true, but isn't. If you have a "rigid joint to the truck", that rigid joint resists roll, and yaw. In the case of SkateHitch it does not resist pitch.

I think your intuition is correct about the average users' ability to mount SkateHitch. If they have the ability to mount it, they also have the ability to make a deck. However, probably not as beautiful as what you've made. It really does look good.

You could really make it much easier for your users by collecting and compiling some measurements on a variety of chairs.

I suggest offering the hinge and deck for sale. With or without wheels. But offer a 50% refund after the user provides a measured drawing, photo, and video in use of the mounting solution they used on a chair that is not yet in your database. You could initially just publish the data, then as you have time, make mounting kits for the most popular chairs.

[Burgerman]

Fixed wheels only advantage for lateral stability is by virtue of their wider base of support than central casters. The chair's stock casters have an even wider base of support than your fixed wheels. And should offer greater lateral stability.
Your analogy to a trailer of bricks may feel true, but isn't. If you have a "rigid joint to the truck", that rigid joint resists roll, and yaw. In the case of SkateHitch it does not resist pitch.

He is correct. The further back the CG of the chairs load is behind the drive wheels the greater the tendency to icrease any turn and try to spin. Thats why front drive chairs steer so crap. Thy need a gyro to take away your control authority and use the power module to actively stop it from accelerating into any turn. And it feels distincly dangerous to me. You are never in full control at speed. Addig a board + heavy weight with no steering hitch so that it is fixed in direction just makes a mid drive into a front drive as far as physics is concerned. Casters do nothing to change stability in any way as they go wherever the forces send them.

[DrewDigital]

I know from experience how dangerous swivel caster boards can be. Years ago, I let my friend ride on the back of my chair, standing on the rear caster stems. He thought it was funny to shift his weight to the side and it would send me into a 180 degree spin! Having a board with swivel casters would be worse because the passenger mass would be even farther back.

With the trailer style, he can't do that. (ok, he was twice my weight, so there was a major imbalance, but you get the point..)

As for suspension, I'm experimenting with different wheel sizes for a smoother ride.

[shirley_hkg]

Doing this on a mid wheel drive is a mission impossible.

Appreciate your devotion.

[Burgerman]

I know from experience how dangerous swivel caster boards can be. Years ago, I let my friend ride on the back of my chair, standing on the rear caster stems.

In my opinion, if a chair even has rear casters then its designed wrong. All chairs where the G is behind the CP (Cente of Pressure being the drive wheels) which includes most mid drives are an unstable platform. Its not marked enough on mid drives to actually cause problems at the low speeds we travel at as the difference between GG and CP is just a few inches. But of front drives it is. Or on a mid drive if you stand on rear casters. Or a non "hitch" type board.

Rear drive chairs are naturally stable. If they get moved from a straight line, they naturally correct this and go straight on their own. In the same way as the tail feathers on a dart keeps it pointing forwards. The opposite to the other two layouts.

If you really want a decent board you need one with casters, that can lift up/down but doesent have any left/right hitch type movement of a REAR drive chair.

Whatever you design for a front or mid drive chair is going to be flawed in one way or another. You cant beat physics.