TIG advice/services sought

[addjunkie]

I know you are looking to build something, but have you considered modifying something like this, a ride on golf buggy. My father had one before he died, and it would whip round 27 holes of golf on an undulating course, powered by a new fangled lithiuom battery.

You quite often see them used for sensible money!

 

[DTS]

Switching to rigid axles, even if just the rear, will save you hours.

 

[D5meister]

Reading through its clear there are so many design ideas its difficult to go ahead with one.

To help get more info out there - will you be alone or will you be being pushed by an able bodied chum?? - as you mention 'wheel chair', but also - "I've omitted the drive" ... I took this as it may be self powered.

Also for collective wisdom of readers, as I am not mechanical but I am an engineer -

What are the extremes of of usage - where, how bumpy, how fast, what impacts, will you get air! Will there be solid cornering forces at speed etc.

What is your mass?

what is the max size this can be? (e.g. for transporting it about / storage)

Apologies if you have this info already.


The design as it stands looks like one of the better designs from the Red Bull Soap Box series. Some mech lads on there make some pretty slick amateur 'karts'.

One thing that does crop up regularly is wheel folding on cornering - esp large wheels - they have super strength radially but not laterally.

The COG is a big player here, as drawn your mass is more up than down. It will feel faster and safer and you more integral to the machine if a bucket seat can be integrated into the chassis so your butt is about level with the axles.


Steve

 

[Benpointer]

Thanks all. To answer Steve's questions:

I do not normally expect to be alone but equally not looking for my wife to have to push me.

"I've omitted the drive"... from the pictures. My aim, and this is tricky, is to have manual drive either by hand cranks or by levers but with electric assist like an e-bike pedelec. I'd like to get a bit of ecercise but realistically, I am not a paralympian (!) I was thinking of incorporating a Bafang mid-drive unit, which will also require a differential.

'Extremes of usage' is hard to define precisely but I would say not too extreme... I want to stick to walking pace generally so 3-4mph normally say 7 mph tops downhill under braking. I'd want to be able to climb some steepish inclines under power assist, say 25% max. I'd also like to be able to handle cambers of up to 20% without tipping and to handle typical farm tracks, canal paths and bridalways (not footpaths - the styles look like a challenge too far!)

My mass is just shy of 100kg, 15st 7lbs in old money.

As for maximum size of the wheelchair, well ideally, I'd love to be able to pop the wheels off (using quick release wheelchair style atttachments) and put it in the back of our Passat estate but realistically, I am expecting to need a trailer, especially considering the added weight of a motor and batteries. Width wise I was aiming for an 800mm track (compromise between lateral stability and getting through pdestrian gates). and about 1100-120 wheel-base.

Regarding large wheels folding, I have been concerned about this, but I am thinking that with low speed cornering that may not be a problem. I might however revert to 20" BMX wheels all round. (It was just that larger wheels on the back somehow 'looked right' - irrational, I know.)

@DTS - switching to solid rear axle is certainly an option I will consider.

@bR39Da - I think selecting the right tube sizes is an area where I might get some benefit from a Uni hook-up. I am not knowlegable enough to calculate the right sizes.

For info, I attach a picture of my Varna handcycle which I converted to an e-handcycle. This is made very simply from (I assume) chrome moly tubing and although it's for fast(ish) road use rather than walking pace off-road it has proved pretty robust, despite a simple 1" tube cantilevered rear axle. Makes me think I might be over-engineering.

Anyway thanks everyone for the comments, questions and suggestions - much food for thought!

 

[D5meister]

My neighbour is always into some project or other and has a haibike (fat bike) and loves it. He rates Bafang and is going to convert a Halfords donor MTB with the 1kW Bafang. He got a 56V I think - clearly more juice than standard - I read that they do an 8inch self powered wheel - be good if you had 2 up front if the drive could do 2 wheels. Probably too small and 250W per wheel may be a little pokey.

https://www.bafang-e.com/en/components/component/motor/fm-d410250d.html

 

[Aesgarth]

I can't help much with what you have so far, but this may be relevant...

http://www.mountaintrike.com/blog/personalised-mountain-trike-for-global-trials-rider-martyn-ashton

 

[DTS]

These guys sell some awesome bike kit. https://em3ev.com/shop/em3ev-triangle-battery-bag/

 

[gaz_moose]

from what ive seen on 'go karts' like the ones they race around tarmac circuits with the tyre wall around the perimeter of the track they make the steering arms out of a plastic like delrin as absorbs some of the

i was under the impression you were building a 4 wheeled 'down hill' mountain bike.
didn't realise it was an electric propelled cross country jobbie you had planned.
I wouldn't delve too much into material selection. just look at what other stuff of this kind is made from and copy that.

how do you find that one you have? is it to bumpy with no suspension?

trying to transmit manual propelled drive from the handle bars to the rear wheels sounds tricky.

 

[Benpointer]

@gaz_moose The handcycle I have is primarily for road use - off-road it is very bumpy. Being a three-wheeler it is prone to tipping over on adverse camber and as the drive is through the front wheel it loses traction uphill on slippery ground - so not really suitable for off-road at all! It's fine on the road though!

 

[Benpointer]

@Aesgarth I was aware of the Mountain Trike, which does look like an awesome bit of kit. They have the non-self-propelling version at Stourhead Gardens, which we often visit (though I haven't tried one of those as I don't like being pushed around haha!).

There doesn't seem to be a battery assist option at the moment for the self-propelling one and I honestly don't think I would be able to drive them up any very steep hills on arm power alone. I have thought about buying one and converting it to e-assist mode... but more challenging to do my own design

Interestingly, given the conversation earlier on this thread, the Mountain Trike seems to have very little triangulation - rather, it relies on large section aluminium tubing for stiffness.

 

[gaz_moose]

id be building a powered version of this,,

first time I saw one I wanted to have a go.

 

[D5meister]

I cant beleive any of them lived. Thats intense.

This level of kit is a bit guy martin

 

[Benpointer]

Yes, something like that, maybe less extreme, would be my aim - adding the power is tricky though.

 

[sako243]

Have you considered reusing existing MTB components where possible? I was initially thinking of the front side of things but sure it can be extended further and the design refined as you go, after all that's the benefit of metalworking, need it cut apart, grinder to the rescue, need it stuck together then welder it is.

Anyway the idea was rather than design a completely new front steering design what about reusing the headstock and front forks from a mountain bike. You have lots to choose from and can immediately get a decent suspension setup and braking built in if you desire. All you'd need to do is join the two forks together and come up with a steering linkage. Can even go quick release to make fitting it in a car easier.

You could almost go the whole hog and simply get two mountain bikes and weld the two together with a nice comfy seat on between. OK not as refined but a good starting point and would allow you to get out and refine it as you go. As they say no plan survives contact.

 

[sako243]

Also I think the wall thicknesses you're talking here are ridiculous if I'm honest, OK design of the chassis plays a huge part. But consider the thickness (in ali) that most mountain bike frames are, I'd be surprised if they're much over 1mm.

I mean come on a Defender chassis is only 1.6mm wall or thereabouts and you don't see many of them snapping or breaking up due to fatigue and abuse. 3mm wall CDS is the spec for Ultra4 roll cages and much as I admire the ambition I don't think you're quite in the same leagues as those guys yet.

 

[HughF]

I'm in Dorset.... but I'm furiously busy at the moment

 

[Benpointer]

@sako243 The thought of welding two mountain bikes together had crossed my mind and if I came across a matched pair going relatively cheap I might give it a go, or possibly buy them to reuse components.

In any event, I do plan to used off the shelf MTB parts wherever it make sanse to. Re the wall thicknesses, I am sure you are right - we just bought an ally sack-truck come trolley from screwfix which is made of what seems to be very thin walled sections but it's got a capacity of 350kg! As an aside it's mainly riveted with a few tube to box section welds that definitely look like MIG not TIG. https://www.screwfix.com/p/3-in-1-hand-truck-350kg/4114p

@HughF - Thanks, I will get in touch if/when I get to the stage of actually being ready to have something stuck together! At the moment I am busy proving that 'procrastination is the thief of time' sadly - too many options!