DIY Electric Car Forums banner

41 - 47 of 47 Posts

·
Registered
1996 Toyota Land Cruiser
Joined
·
141 Posts
@eUKenGB You are misremembering Colin's quote or something else. And yes, if you drop a name like that as your argument from authority, you better be able to back it up.

"The type of suspension used is not important as long as it fulfills a number of basic requirements. These are minimum unsprung weight, minimum change of roll center height, correct camber change, minimum angularity of the driveshafts, and elimination of sliding splines. Another essential is to select the correct spring rate, which in effect means deciding on the softest possible spring, one which will give maximum bump absorption with reasonable wheel travel-that is, without increasing ground clearance from a minimum of 4 in. for the sprung mass of the car. On current (1960) racing cars anti-roll bars are needed to obtain the required handling characteristics, but are not necessarily an essential feature of suspension design."
-Colin Chapman


It seems that Mr. Chapman thought unsprung weight important enough to put it first on his list of basic requirements.
 

·
Registered
Joined
·
47 Posts
I am not misremembering anything. I just cannot be bothered with all this doom and gloom to try and remember where I read it and since I am not about to waste the time finding corroboration for the quote, obviously I'm lying. Have it your way. I didn't come here to argue about stuff like this.

I thought in a forum such as this we should be supporting everyone's attempt to convert to electric propulsion. Sadly, as in so many other forums, there are always those who simply want to criticise others without actually adding anything of any value.

Pour all the hate you want on the idea of in-wheel motors, but for some of us, in some circumstances, it makes sense and quite frankly, I couldn't give a toss about what Colin Chapman or anyone else says.

What I would like to discuss is e.g. getting coolant out to the motors and other actually interesting technical details of the OP's project.
 

·
Registered
1996 Toyota Land Cruiser
Joined
·
141 Posts
Alright sorry, @eUKenGB, I won't interact with you anymore. You brought up CC so obviously you do "give a toss." Unsprung weight is one part, mechanical advantage, vibration, water and debris, etc are all other reasons

Go ahead and build your EV with hub motors, should be an excellent vehicle, right.
 

·
Registered
1996 Toyota Land Cruiser
Joined
·
141 Posts
@eUKenGB I lied, I will pester you some more. I've done a modicum of searching on the subject and find lots and lots of talk by Colin on unsprung weight. Mostly, that all types of weight should be kept to an absolute minimum, I mean that is his mantra. Secondly, the part you are probably mis-remembering, is that there is an important relationship between unsprung weight and suspension springrate, he called it "suspension frequency." Basically unsprung weight isn't the be-all, end-all of suspension, but it is extremely important.
 

·
Registered
Joined
·
47 Posts
@eUKenGB I lied, I will pester you some more. I've done a modicum of searching on the subject and find lots and lots of talk by Colin on unsprung weight. Mostly, that all types of weight should be kept to an absolute minimum, I mean that is his mantra. Secondly, the part you are probably mis-remembering, is that there is an important relationship between unsprung weight and suspension springrate, he called it "suspension frequency." Basically unsprung weight isn't the be-all, end-all of suspension, but it is extremely important.
I am not averse to continuing a civil discussion, so no problem.

I will clarify one point. The comment I read in relation to unsprung weight was quoted specifically in relation to the use of in-wheel motors and originally emanated from Lotus. I had in mind it was Colin Chapman, but it may have been his son or just Lotus, who may have been involved in development of that project. I realise now that I apparently attributed it to CC himself, but that wasn’t what I was trying to say. My apologies for being unintentionally misleading. The essence though is that while not actually desirable, more unsprung weight can be successfully dealt with by suitable suspension design.

Having said that, I am not convinced any major changes to suspension will be required as in my experience, such subtleties are invariably lost when not attempting to minimise lap times on track. For example, I have a Honda FireBlade based motorcycle and although racers and other owners will wax lyrical about the benefits or otherwise of altering suspension height by even one mm, for my own specific reasons, I dropped the rear of the bike by nearly 2 inches and I am unable to tell the difference on the road. Would I have done that to a track bike? No. But this is a naked road bike and in the use for which I have adapted it, I defy anyone to tell the difference.

I am not necessarily saying that fitting a couple of M700s in the rear wheels will be undetectable in all circumstances, but for its intended usage, I am satisfied they will not prove noticeably detrimental to my car. When considered in conjunction with the advantages that an in-wheel motor offers, in particular for my project the huge increase in available battery space and elimination of gear noise, they become a very attractive proposition.

When I stated I don’t give a toss what CC or anyone else thinks, what I mean is that in my use case, those aforementioned advantages of the in-wheel motor trump any so-called disadvantages for different usage. I have the greatest respect for Lotus and CC’s legacy, but they are not trying to do what I am. Their current electric idea is a £2m hypercar that will I am sure be stupendous and no doubt have wonderfully low unstrung weight, but while the Eviya is interesting, it is irrelevant to me. The only reason I raised the issue of their comment about unsprung weight of in-wheel motors was in response to the negativity I was reading here, targeted specifically at that facet of in-wheel motors. However, no, their opinion on the matter is irrelevant to me on this particular project.

I would still be interested in a more technical discussion about this use of in-wheel motors and let’s not get bogged down in having to justify why this particular course of action has been chosen.
 

·
Registered
1996 Toyota Land Cruiser
Joined
·
141 Posts
Fair enough. Hub motors are the "popular mechanics" of the EV world. Every person I tell my conversion plans to asks "will you put a motor on each wheel?" To which I always reply no. It's the "it's so simple why isn't everyone doing it?!" of the EV world.

Well there happen to be many reasons why it's not been done. You are right that it frees up lots of space and you could possibly do torque vectoring and yes you probably wouldn't notice the change most of the time. All of these benefits are clear to everyone and still the automotive industry has not pursued them in production vehicles.

I believe the OP of this thread has been trying to get his hands on M700s for several years now without success. Perhaps because what works on paper isn't good enough for real roads.
 

·
Registered
Joined
·
47 Posts
I think you're right and that in-wheel motors are not the panacea many believe. But, they are a great solution in some circumstances for space reasons and also the possibility to convert to 4 wheel drive which although not necessarily simple, is basically impossible any other way. Swings and roundabouts.

I also have another project for which I plan to use a Tesla (or similar) motor, centrally mounted and with traditional drive shafts which better suits that particular case. I guess I could summarise that as 'horses for courses'.

The only important factor is that whoever is attempting the work understands all the potential pitfalls.

Designing an EV from scratch is a different proposition and makes in-wheel motors less attractive, except in specific cases for e.g. specialist utility vehicles as being suggested by some hub motor manufacturers. As to why it is taking so long to obtain the M700s? Have you tried buying ANY new modern tech motor. So many great new motors one can read about, but they are all still in development so in-wheel motor development seems no different in that regard.

In any case, the manufacturers only want to sell to 'large' organisations which is disappointing for those of us wanting to convert an existing vehicle as it leaves very little choice. This I believe is THE big problem facing prospective converters. Tesla motors are most commonly used simply because they are the most readily available, but there will soon be better options availalble - just not to us. 😖
 
41 - 47 of 47 Posts
Top