FrontWheelDrive dual-hubbed KMX

[Xase]

What do you guys think about a build consisting of a KMX kart (trike) with dual hub motors up front and just leaving the rear wheel as is?

Theoretical advantages over a single, rear mounted, hubmotor trike:
1. more even weight distribution
2. improved traction
3. 3-wheel drive: rear wheel - human powered; front two - hub powered
more?

Theoretical obstacles (edited include posts):
1. lack of suitable single-sided axles
possible solutions: find suitable single sided (stub) axle hubmotors (according to HAL9000v2.0, Crystalyte has models available for car applications; if these are too heavy &/or powerful, request for a smaller/less powerful hubmotor may be necessary)
2. too much weight in the rear even with the frontal hubs mounted, hence not enough traction to be effective FWD
possible solution: placing some weights up front; using heavier frontal hubmotors
3. torque steer
possible solutions: use lower power motors; modify the suspension - dual wishbone, multi-link; use proper sidewall ply design tires
4. wheels spinning at different speeds during turning maneuvers
possible solution: take LSD and hallucinate that it's not really occuring thereby bending reality to your wishes (sorry Mathurin, I was asleep in all the suspension & drive train-related automotive technology classes. Lost all vocab and never really understood it or cared to anyway. I was more of a motor head back in the day. Lectures on engine theory were the only ones that could really keep me on the edge of my seat. Unfortunately, it wasn't until much later that I came to realize the importance of suspension. LSD = Limited Slip Differential, perhapes?)
5. lack of frontal disc brake real estate and/or compatability
possible solutions: customize a hub-disc combo and/or add a large, oversized brake to the rear wheel.
more?

 

[Drunkskunk]

looks like a great Idea. Mounting the front axle will be a real trick. I think you're going to have to build something custom to make that work with most hub motors.

Torque steer is going to be a real bitch too. 2 pumas would make about 160FP of torque combined, 80 each. your average 4 cylinder car only makes about 120, and it has the benefit of power steering.

 

[recumbent]

Can you find hub motors with a stub axle?

 

[diver]

Can you find hub motors with a stub axle?

that would be awesome if there were some .

 

[knoxie]

yo

Cant really see the point? you will loose the discs and you dont want to rely on the rear brake infact I took mine off and just use the front ones, the axles are single sided as well and yes it would torque steer really bad and 1 x Puma is more than enough in a KMX, most of your weight is over the rear on a KMX you would wheel spin and loose traction with front wheel drive, it makes no sense?

Knoxie

 

[CGameProgrammer]

The wheels won't rotate at exactly the same speed so it will be extremely dangerous as it weaves and veers wildly. Additionally, when turning you want the innermost wheel to rotate more slowly than the outermost, but it will not in this case. So the idea is effectively impossible to do properly.

The only time anything like this should be attempted is when there are already mechanisms in place that do it for you -- for example, converting a gasoline car to electric.

 

[Xase]

Wow... didn't think of all that! Thanks for all the imput.

Ok, next question then: Which model out of the new (2008) line-up looks most e-conversion worthy?

The reason I ask is because it seems as though behind the seat, where most KMX converters were placing their batteries, there's less space now. But it also says in the descriptions that the seat can be adjusted.
The Viper and the Cobra models use 24" wheels in the back and 20" up front. While the Typhoon uses 20"x16"s leaving what appears to be more room behind the seat. What do ya think? Do-able, or will I need panniers, or an older model???
Viper:

Cobra:

Typhoon:

http://www.kmxkarts.co.uk

 

[Mathurin]

Torque steer is going to be a real bitch too. 2 pumas would make about 160FP of torque combined, 80 each. your average 4 cylinder car only makes about 120, and it has the benefit of power steering.

The real problem I see is the same as in car games when you push too much power in a light FWD car with no traction control, it'll eat up it's front tires very fast.

The wheels won't rotate at exactly the same speed so it will be extremely dangerous as it weaves and veers wildly. Additionally, when turning you want the innermost wheel to rotate more slowly than the outermost, but it will not in this case. So the idea is effectively impossible to do properly.

The only time anything like this should be attempted is when there are already mechanisms in place that do it for you -- for example, converting a gasoline car to electric.

If you run both motors off a single controller, in this case for each motor a controller with very high amp limit, no LVC and 100% throttle, then control that with a brushed controller, you get either an open diff or a speed sensing LSD depending if you wire the motors series or parallel. The BMC's would make this a 1 way speed sensing LSD and it could probably be made a 2way by getting rid of the freewheel.

 

[tigger3015]

I wouldn't do it. I have a kmx - x class. and your idea will be more problems than you can imagine. Stick to a rear wheel drive

 

[Rassy]

Xase, I like your idea, and if its possible to try I'd do it. At different times I have had three motors on both a mountain bike and a delta trike. In both cases the motors were on the front wheel and on the two wheels of a trailer. There were never any issues with turning or traction. Since the motors were independent, but well matched by running from the same throttle and the same battery pack, they never seemed to fight each other, but rather complimented each other during acceleration, etc. Of course your biggest problem will be that stub axle issue. Good luck.

 

[Xase]

I wouldn't do it. I have a kmx - x class. and your idea will be more problems than you can imagine. Stick to a rear wheel drive

I appreciate your imput, especially since, unlike myself, you own and ride one of these machines. But could you possibly be a bit more specific on said 'problems'?
...or are you just emphasizing your agreement to the theoretical problems that might arise which have already been mentioned in previous posts? Thanks.

 

[cerewa]

did you mention the disadvantage that a trike with two hubmotors is going to be heavy? Probably weigh double what my lightweight e-bike weighs.

 

[Xase]

did you mention the disadvantage that a trike with two hubmotors is going to be heavy? Probably weigh double what my lightweight e-bike weighs.

Actually, at only 19.5 kg without the motors, I think it's reasonably light for a trike to begin with. Of course with a couple of hubs I'm not going to be picking the thing up and hiking up any flights of stairs.
I think this also depends on the choice of the hubs involved. If I choose a couple of smaller, less powerful ones I don't think weight will be a big issue. Battery type & amount also factor into this equation, of course.
The KMX website claims the trike can handle 135 kg of load on road. I can't imagine two hubs, batteries, controller, lights, etc. and my personal body weight coming to that total any time soon.

 

[paultrafalgar]

All this talk of 2 wheel drive reminds me of this, 3 wheel drive machine (only human power, though):
Russian trike
http://www.eland.org.uk/s327.html
http://www.trike.ru/en/english.phtml

Maybe you could adapt some of those engineering ideas to your KMX?

 

[Xase]

Hey, thanks a lot Paul!!! Those trikes look awesome! Aluminium & titanium frame - only 16kg in total; centre-point steering; etc. Peter's customizations look pretty cool too. Thanks for the links!

Do you own one yourself? Or is that a Catrike in your avatar?

It's too bad that site looks a bit old... like it hasn't been updated in a couple of years. I haven't bought the KMX yet; maybe I should save my pennies some more, try to contact this company and attempt to score one of these instead. ...leave it 3WD human power, plus a rear mounted hubmotor... mmm tasty!

 

[Drunkskunk]

nice!

the website says they aren't in production right now, but they will be 2000-2500 euros. Not bad for a high end trike, especialy an all wheel drive.

But there's enough pics to build one of your own.

 

[HAL9000v2.0]

Can you find hub motors with a stub axle?

that would be awesome if there were some .

Crystalyte have them. I have 4 for my car project. It is basicly x408. IMHO to heavy for recumberant...

 

[Xase]

Can you find hub motors with a stub axle?

that would be awesome if there were some .

Crystalyte have them. I have 4 for my car project. It is basicly x408. IMHO to heavy for recumberant...

Cool, how much do they weigh & cost?

IMO,the heavier the better for this project. I think the machine would need more weight up front for it to work right on the KMX. Not sure though. KMX claims that the trike can handle 135kg.

If they're too much, do you know if Crystalyte have lighter ones available?

Thanks Hal! With each knowledgable and well-researched post the naysayers seem to be losing ground! Could this still be a viable project?

 

[Xase]

nice!

the website says they aren't in production right now, but they will be 2000-2500 euros. Not bad for a high end trike, especialy an all wheel drive.

But there's enough pics to build one of your own.

Yup... or even modify a KMX accordingly...

 

[HAL9000v2.0]

Cool, how much do they weigh & cost?

11,4 kg that is ~25lb each.
4 pieces with discount and after 9 month waiting (not in standard production) =10000kn app. 2300$

 

[paultrafalgar]

Hey, thanks a lot Paul!!! Those trikes look awesome! Aluminium & titanium frame - only 16kg in total; centre-point steering; etc. Peter's customizations look pretty cool too. Thanks for the links!

Do you own one yourself? Or is that a Catrike in your avatar?

No, I don't own one, my trike is a British built Trice T from here:
http://www.ice.hpv.co.uk/
Costs a lot more than a KMX!

 

[paultrafalgar]

... and here's a Lithuanian one:
http://www.velomobiles.eu/

 

[Jozzer]

The KMX frames is not sooo strong..mine snapped right in the middle (under the seat). THey fatigue very easily under a lot of weight, very thin steel.

 

[Xase]

Hey, thanks a lot Paul!!! Those trikes look awesome! Aluminium & titanium frame - only 16kg in total; centre-point steering; etc. Peter's customizations look pretty cool too. Thanks for the links!

Do you own one yourself? Or is that a Catrike in your avatar?

No, I don't own one, my trike is a British built Trice T from here:
http://www.ice.hpv.co.uk/
Costs a lot more than a KMX!

Awesome, yeah I was looking at those too. They're foldable, right?
I really like the 'side pod' bags they've designed for 'em. Looks like thye have tons of room for batts.

 

[Xase]

The KMX frames is not sooo strong..mine snapped right in the middle (under the seat). THey fatigue very easily under a lot of weight, very thin steel.

Oh shit... how'd you manage to do that?