Electric Bike Attachment to Manual Wheelchair – Not Fit For Purpose.

Les79

unforeseen wrote: »

What do you mean the incline was 3-1?

The bike brake would never have held it on an incline because all the weight would be on the back causing the front to lift and TBH you are lucky the whole thing didn't tip backwards since you had to lean forward when trying to go up just to put weight on the wheel.

I suspect that it means *1 unit vertically VS 3 units horizontally*

So if the horizontal distance is 3 metres, you go up vertically by 1 metre.

(if it was the opposite, 3 units vertically VS 1 unit horizontally, then that would be very steep indeed!).

My A-level Physics is failing me right now, and Google is only coming up with Physics problems which tackle acceleration DOWN a plane, but it would be very interesting to crunch the numbers using Pythagorean-based equations here!

We've got the speed value (20kph), we can have an educated guess at the distance (using pythagoras if needed) and the friction coefficient. This would help us work out the subsequent rate of deceleration (and whether the optimal values, ie the one a consumer expects to experience, produce a result whereby you make it up the bank).

Rubbish the things you forget when you get a bit older.

Aylesbury_Duck

A 1:3 incline is incredibly steep. It would be a struggle on a bicycle and on foot. I don't think the salesman understood what he was saying.

To put that in context, I have a 1:8 hill near me that needs to be taken in second gear in a car and is a hard climb on a racing bike. No way would I contemplate climbing it in a powered scooter or wheelchair.

ScorpiondeRooftrouser

Aylesbury_Duck wrote: »

A 1:3 incline is incredibly steep. It would be a struggle on a bicycle and on foot. I don't think the salesman understood what he was saying.

To put that in context, I have a 1:8 hill near me that needs to be taken in second gear in a car and is a hard climb on a racing bike. No way would I contemplate climbing it in a powered scooter or wheelchair.

I would agree with this...but I would also suspect that as he says he has done it regularly on a mobility scooter, maybe it isn't 1:3.

"Which"

https://www.which.co.uk/reviews/mobility-scooters/article/mobility-scooter-faqs

says

"Generally, they can cope with a small slope – the same gradient used for wheelchair access ramps (1:12). Some can cope with a slightly steeper slope (1:8) but any steeper and they are likely to cut out."

So unless he has some kind of super mobility scooter adapted to hill climbing, I suspect we are not talking a 1:3 incline here.

unforeseen

Maybe it can cope with a 1 in 3 bank. They tend to be pretty short compared to a hill.

Aylesbury_Duck

unforeseen wrote: »

Maybe it can cope with a 1 in 3 bank.

Sounds like the new name for TSB, based on the chances of being able to log in to internet banking.

ElefantEd

A 1 in 3 slope has an angle of about 18 degrees. If the chair + occupant weighs 100kg (=1000N) in total, this means the component down the slope is about 320N. At 20mph (=9 m/s), the energy required would be 2.8kJ every second, ie the power of the motor would need to be 2.8kW. This doesn't even allow for frictional losses. I suspect the OP's motor is rated at less than this, hence the difficulty in getting up. A 1 in 3 slope is pretty steep, many cars wouldn't be able to cope -it's about the steepest gradient on a road in the UK (somewhere in Yorkshire I think?).

Aylesbury_Duck

ElefantEd wrote: »

A 1 in 3 slope has an angle of about 18 degrees. If the chair + occupant weighs 100kg (=1000N) in total, this means the component down the slope is about 320N. At 20mph (=9 m/s), the energy required would be 2.8kJ every second, ie the power of the motor would need to be 2.8kW. This doesn't even allow for frictional losses. I suspect the OP's motor is rated at less than this, hence the difficulty in getting up. A 1 in 3 slope is pretty steep, many cars wouldn't be able to cope -it's about the steepest gradient on a road in the UK (somewhere in Yorkshire I think?).

I love a bit of physics. Thanks.

Les79

ElefantEd wrote: »

A 1 in 3 slope has an angle of about 18 degrees. If the chair + occupant weighs 100kg (=1000N) in total, this means the component down the slope is about 320N. At 20mph (=9 m/s), the energy required would be 2.8kJ every second, ie the power of the motor would need to be 2.8kW. This doesn't even allow for frictional losses. I suspect the OP's motor is rated at less than this, hence the difficulty in getting up. A 1 in 3 slope is pretty steep, many cars wouldn't be able to cope -it's about the steepest gradient on a road in the UK (somewhere in Yorkshire I think?).

Love it

Out of curiosity, do you have a link to a formula which is related to this? I had a look and could only really find acceleration down an incline from rest!

its_all_over

Keep_pedalling wrote: »

I would be worried about any electric bike claiming that top speed, the maximum allowable is 25kpm (15mph), anything over that sounds a very dodgy product.

I think it's even worse than that, a wheelchair used on the pavement shouldn't be able to go faster than 4 mph which is only 6 kph.

This is from the Highway Code

Rule 36
There is one class of manual wheelchair (called a Class 1 invalid carriage) and two classes of powered wheelchairs and powered mobility scooters. Manual wheelchairs and Class 2 vehicles are those with an upper speed limit of 4 mph (6 km/h) and are designed to be used on pavements. Class 3 vehicles are those with an upper speed limit of 8 mph (12 km/h) and are equipped to be used on the road as well as the pavement.

I found the page on gov.uk at this link https://www.gov.uk/guidance/the-highway-code/rules-for-users-of-powered-wheelchairs-and-mobility-scooters-36-to-46

I Think apoole might get into bother doing 20kph in a motorised wheelchair on any public pavement.

ElefantEd

I just did a diagram and worked it out from first principles, I teach physics so it's second nature to me! Everything rounded off to make the numbers easy.

But it boils down to P = Wv sinx where W = Weight (in Newtons ie 10 x mass in kg), v = steady velocity, x = angle of slope. You can get the angle from tan x = 1/3 (for a 1 in 3 slope) if that's the way the info is presented. But you'll need a calculator for the tan and sin functions.

Obviously if you start off going fast enough you can get up a short, steep, slope but only by trading off your kinetic energy and losing speed.