Phase 2 - Dual Massive hub motors driving a small EV

G

galderdi

1 kW
Joined
Sep 8, 2015
Messages
343
So firstly I know I haven't fully finished my current project: https://endless-sphere.com/forums/viewtopic.php?f=34&t=76189
But that was always a compromise to meet a specific set of requirements:
2 seater able to compete in motorkhana and khanacross. This means the frame and roll cage had to be significantly bigger and heavier, thus the motor and batteries also had to be bigger and heavier.
As a result I was always aware it would struggle to be competetive in both competitions.

I am starting to gather ideas for phase 2. This is probably a few years off but I want to plan it out and build it over a slightly longer period (not 11 months like the current car) The requirements would be significantly different:
A small and light as possible. Single seater. Just a single hoop for the roll over protection.
Considering my current project came in at 530KG I am thinking I can bring Phase 2 in at around 230KG.
The weight of the current car is approximately:
Motor 60KG
Seats 20KG
Frame 200KG
Rollcage 60KG
Controller 20KG
brakes, hubs, suspension, wheels and tyres 60KG
Batteries 70KG
Cables 15KG

Elliminate the gearbox -50KG
Single seat -10KG
Reduce the motor weight -40KG
Reduce the frame weight -120KG
Reduce the roll cage weight -40KG
Reduce the batteries -30KG
Reduce the controller - 5KG
Reduce the Cables -10KG

=approximately 230KG

To achieve this I am thinking of running two large hub motors (circa 5-7 KW each) on each of the front wheels. I am thinking of using the old style VW wheels because I think I could get them to mount on the hub motor effectively. I am not sure how I would run brakes but I guess I would get some sort of disc machined to fit alongside the hub motor. The wheels and tyres would need to be a compromise. Big enough to get some grip but not so big that they add stress to the motors and other components. I think 205s would be about the best.

The front frame is where most of the stress is. So it would continue to be steel. I would need to design a couple of primary members from front to rear to give the rear the torsional strength required. These primary members would somehow connect to the roll over protection and rear suspension. But otherwise the rear half of the car would be alloy and composite materials. Because I am planning on using hub motors I no longer need the space in the front for the motor, gearbox and driveshafts. So I will be able to reduce the structure surrounding these items and be more conservative with my suspension design and weight.

What are the biggest reliable hub motors available?
What sort of controller does everyone recommend to run these sort of motors?

I would also be mounting the batteries in the front, reducing the cable weight required and placing a larger percentage of the weight on the front wheels.
I would have a sensor on the steering so as you turn the wheel it sends less power to the inside wheel. Or maybe even a sensor on the dual handbrakes so it cuts the power to the inside wheel while continuing to power the outside wheel to drive the car around the obstacle.

I would keep my current car so I could still compete in the Khanacross. Running the new car in Khanacross would be too unstable due to the reduced wheelbase plus the impact protection is reduced.

Any thoughts
 
Phase 2.JPG

Something like this but without the full cage (single hoop behind the driver instead) and instead of inboard motors imaging hub motors on each front wheel.
 
What ae you hoping to do with this when completed..road registered, or just track use ?
What are your performance targets ?
Car sized hub motors ( cantilever/spindle mount) are limited choice and the few that i have seen used were very problematic. Finding enough Torque at those low rpm's is the basic problem.
Some motor info..http://www.hs-escooter.com/sdp/1012764/4/pd-4958252/11145969-2261373/8000W_Car_Hub_Motor_single_shaft_hub_motor_Electri.html
This was one of the better documented conversions.. ( curtesy of Ripperton and DIYelectric car.com)
http://www.diyelectriccar.com/forums/showthread.php?t=82349
 
Thanks Hillhater. That is exactly what I was after. Two of those motors should push 350kg (including driver) quite nicely. And they have even solved the disc issue for me.

It would be purely for motorkhana. It would not be road registered and would be unlikely to ever go faster than about 60Kmph.
But I would want it to get to 60 in about 2 or 3 seconds.

I am fairly sure combined torque and power from two of these hub motors should pull 350kg from 0-60 in a couple of seconds.

Ripperton's Mira was around 500KG plus the driver and still performed well enough for a commutor. So I figure half the weight should = great performance. I am also hoping half the weight would elliminate the need for all those mods Ripperton experimented with. I am thinking just bolt the wheels on the hubs, use two adequate controllers and away I go. I wonder if Ripperton still has his components.
 
I little inspiration for you.. :wink:
If you can lay your hands on a pair of these EMZ motors, they would do nicely !
Neat video also to give you a few ideas maybe ..
http://www.gizmag.com/electric-car-world-record-acceleration-eth/34563/
 
Very nice. Although in my sport I am limited to 2 wheel drive. But yes it certainly shows what is possible.
 
Hillhater said:
Another thread you may not have spotted which uses those 8kW hub motors..
https://endless-sphere.com/forums/viewtopic.php?f=7&t=73888&p=1114735#p1114735
Click to expand...

Wow, yes that is awesome. Its not quite the same as my phase 2 concept but as a road car it sounds great.

Try this. But just imagine it with hub motors instead of that lump out in front.


mini special.jpg
 
Fair point.

Yes weight is a consideration. For a car needing to do higher speed it would be more of an issue due to the unsprung weight.

For this specific objective I think it will be fine as the top speed is only around 60kmph. The overall weight would still be lower as it would elliminate the need for a gearbox, driveshafts and much of the structure usually required to mount all these components. It would free up the space between the front wheels to allow more efficient structure for the front suspension. That space in the front would also allow the batteries to be up front. Bringing all the weight forward would give better grip in the front and allow the back to swing around during handbrake turns. Elliminating the driveshafts and narrowing the front structure should allow the front wheels to turn further allowing a tighter turning circle. I know some of this isn't related to the weight but I am capturing my thoughts so I can include these in the eventual design.
 
Thanks guys, I am getting more and more enthusiastic as I think about it more. I think will will focus 2016 on developing my current project so its as competitive as posible for 2017. But in the mean time I will still keep gathering ideas. In 2017 I think I will start the serious design. In 2018 I will build it with a plan to compete in 2019.

My current car is 650kg including driver. I get the acceleration I need when pumping about 150amps at 150v into the motor. I figure that to be about 22Kw. My target weight for phase 2 would be 350kg with driver (maybe even lighter). So maybe I don't need to go with the biggest hub motors available. But the real unknown for me is the torque. The torque i have currently is excellent but I can't quantify it. So I have no point of reference to decide how much torque I need for phase 2. Maybe once its all working right I will book some dyno time. Any other ideas?
 
I would have a sensor on the steering so as you turn the wheel it sends less power to the inside wheel. Or maybe even a sensor on the dual handbrakes so it cuts the power to the inside wheel while continuing to power the outside wheel to drive the car around the obstacle.
Click to expand...

Completely unnecessary. I'm driving a 2WD tadpole vehicle now, front wheels steer and also are powered, there is no problem with powering around corners. The mistake here is thinking about two independent front motors as if they were locked together by a differential, then the rest of the thought process follows down from this error.

Hub motors turn independently. They also do not turn at constant speed - they produce torque, not locked to a specific speed. Your hall sensors tell the controller when to commutate based on the current speed of the motor, whatever that may be. If you are on full throttle, and one wheel is turning at 1 hz and the other at 10 hz, they both add full torque at whatever speed they are going. The inside motor is producing torque, it moves the vehicle forward. The outside motor is producing torque at a different speed, it moves the vehicle forward. No mechanical connection, the motors could be running at wildly different speeds and they'd still both move the vehicle forward.

Don't make it complicated. No reason to do so.

Now, electrically, the two motor controllers should see the same throttle signal. Any noise that appears on one throttle signal and does not appear on the other signal will cause minor steering errors. I kept the electrical path between the two throttle signals short and identical length, mounted the controllers adjacent, grounded them both to the same, short cable. I sense very minor, in fact negligible, steering errors due to noise.
 
llile said:
I would have a sensor on the steering so as you turn the wheel it sends less power to the inside wheel. Or maybe even a sensor on the dual handbrakes so it cuts the power to the inside wheel while continuing to power the outside wheel to drive the car around the obstacle.
Click to expand...

Completely unnecessary. I'm driving a 2WD tadpole vehicle now, front wheels steer and also are powered, there is no problem with powering around corners. The mistake here is thinking about two independent front motors as if they were locked together by a differential, then the rest of the thought process follows down from this error.

Hub motors turn independently. They also do not turn at constant speed - they produce torque, not locked to a specific speed. Your hall sensors tell the controller when to commutate based on the current speed of the motor, whatever that may be. If you are on full throttle, and one wheel is turning at 1 hz and the other at 10 hz, they both add full torque at whatever speed they are going. The inside motor is producing torque, it moves the vehicle forward. The outside motor is producing torque at a different speed, it moves the vehicle forward. No mechanical connection, the motors could be running at wildly different speeds and they'd still both move the vehicle forward.

Don't make it complicated. No reason to do so.

Now, electrically, the two motor controllers should see the same throttle signal. Any noise that appears on one throttle signal and does not appear on the other signal will cause minor steering errors. I kept the electrical path between the two throttle signals short and identical length, mounted the controllers adjacent, grounded them both to the same, short cable. I sense very minor, in fact negligible, steering errors due to noise.
Click to expand...

Based on an intent to drive around a normal corner I accept you statements. But my intent behind the steering sensor isn't to allow the wheels to turn at individual speeds. It is to drive one side of the car much faster than the other side. This will violently spin the car at low speed. This is a fairly unusual requirement that is unecessary outside the sport of motorkhana. A handbrake will almost get the same effect but a handbrake turn requires speed leading in and is dificult to get any more than 180 degrees out of the turn. The steering sensor idea would enable a full 360 degree turn at very low speed.
 
Sounds an interesting concept, but you would likely need a large torque capability in each motor to be effective.
It maybe simpler and less power demanding (= motor, controllers, batterys, weight, etc + $$$'s) ..to just go with 4 wheel steering ?....or front wheel drive and rear wheel steering :shock: :lol:
 
Hillhater said:
Sounds an interesting concept, but you would likely need a large torque capability in each motor to be effective.
It maybe simpler and less power demanding (= motor, controllers, batterys, weight, etc + $$$'s) ..to just go with 4 wheel steering ?....or front wheel drive and rear wheel steering :shock: :lol:
Click to expand...

4 wheel steering is against the rules unfortunately (unless the car came from the manufacturer with 4 wheel steer). Rear wheel steer is an interesting proposition. It would be an interesting proposition to learn to drive that way. Our sport also includes reversing so advantages in one direction are sometimes reversed in the other direction. One of my competitors considered building a car where you sit sideways. I think it would kill my neck. The same guy builds his cars with passive rear steering (passive is within the rules). As you load up one side of the rear suspension it subtally turns that wheel out.

Soooo many options, so little time to try them all.
 
Learn rear steering ?
Volunteer at the local golf course to mow the greens on one of those "zero turn" mowers ! :D
Or.. Ask the local farmer if you can play on his Combine Harvester !
Or have you seen the "drift trikes". Front wheel drive with ultra low friction rear tyres !....a sort of passive steering !
 
Ah yes, and don't forget Maccas trays under the rear wheels. Sooo much fun to be had.
 
Interesting project Greg,

I think you are right torque to pull you out of the corners is what you need. Also you get Regen from hub motors which will help braking.

Here is an idea 4 QS hubs 2 mounted together on each front with 2 rims with motor bike tires on each front corner, Mercedes did this a few years back and it dramatically improved handling and grip.

Oatnets tow rail VW conversion proves that light weight of 1000 lbs doesn't mean a faster acceleration by the same reduction of weight.
You have the laws of physics to overcome which normally means KW and Nm

Heers Kiwi
 
galderdi said:
4 wheel steering is against the rules unfortunately (unless the car came from the manufacturer with 4 wheel steer).
Click to expand...

Won't you be the manufacturer seeing your drawings? So everything you build is from the manufacturer... :D
 
kiwiev said:
Interesting project Greg,

I think you are right torque to pull you out of the corners is what you need. Also you get Regen from hub motors which will help braking.

Here is an idea 4 QS hubs 2 mounted together on each front with 2 rims with motor bike tires on each front corner, Mercedes did this a few years back and it dramatically improved handling and grip.

Oatnets tow rail VW conversion proves that light weight of 1000 lbs doesn't mean a faster acceleration by the same reduction of weight.
You have the laws of physics to overcome which normally means KW and Nm

Ceers Kiwi
Click to expand...
 
Unfortunately all wheel drive must have been a standard feature on a production vehicle. It is specifically against the rules for my category.

4 x hub motors is certainly an idea. I will weigh up the pros and cons when I start getting serious.

Yes I agree weight reduction is not the be all and end all. I still need to maintain decent power/torque to weight figures.

I figure I am using about 130amps worth of torque at the moment. I was using about 200amps worth of torque and that was giving me great acceleration on my 650KG total weight. So I figure I need about 100amps worth of torque to get the same acceleration from 325KG total weight.

For me reducing size has the added benefit of being able to navigate between flags a better angles and greater speed. It is a noticable advantage in my competition.
 
Its looking like I am changing direction. I might be buying another Advanced DC motor. This time its the little brother (8 inch). But that should be perfect for a 300kg car.

This time around I am aiming to be sub 300kg (minus driver). The car would be slightly bigger than a gokart but with car sized wheels and tyres.
Another key difference from last time where I had a gearbox, I am thinking of running a chain from the motor to a solid / live rear axle (hopefully with a ratio of around 5:1). I think I will have trailing arm suspension. The motor will be mounted with the centre of the motor aligned to the front mounts of the trailing arms. The idea being the distance from motor to the drive shaft should remain constant and chain tension won't be an issue.

That all works if both sides are under equal strain. IE left and right tyre swing up at the same rate. But that won't be the case. What I am struggling with is how to allow for vigerous cornering where one wheel has all the weight and the other almost none. I haven't thought of a good way to allow for that twist. Normally by running the motor through a diff the diff takes care of the twist. But running the motor via chain to the drive shaft means that any uneven suspension travel would result in a twist in the chain.

A couple of my unconvincing thoughts include:
1.Somehow separating the whole back end so the back end (including the motor) can twist as much as needed. then have extra shocks/springs to restrict the twist and retain some cornering control.
2.Another thought is to not allow the twist at all. Only allow both sides of the suspension to lift and drop at the same rate. This sounds like an achievable option but it would impact my level of grip.
3.Run a central axle secured with bearings and with a CV on each end out to the hubs.
 
You must log in or register to reply here.

Similar threads

Desertprep
"Almost" hub motors
Replies
4
Views
273
Hillhater
H
M
    • Like
1,500 lb eTrike???
2 3
Replies
66
Views
2,103
Diggs
D
T
    • Like
My first scratch build: 30kw full suspension tandem velomobile.
Replies
20
Views
975
thebeachtoday
thebeachtoday
Mongo
2022 Velo Orange Neutrino minivelo, Nine Continent RH212 rear hub motor
Replies
0
Views
228
Mongo
Mongo
Skyler
Wheel building for hub motors.
2
Replies
31
Views
2,634
D Alan Stewart
D
Back
Top