2 Speed Gearbox

Open for any sort of non-technical discussion regarding EVs
User avatar
EV2Go
Senior Member
Posts: 2059
Joined: Wed, 16 Jul 2008, 00:21
Real Name: Paul
Location: Brisbane 1963

2 Speed Gearbox

Post by EV2Go »

Electrocycle wrote: yes, if you use two controllers supplying the same current to the motors, the one with less load on it (outside wheel is trying to go faster) will increase in rpm.

If you're using DC motors, wiring them in series and running them from one controller will behave exactly like a normal open diff (no drive if you get a wheel in the air)
Running two series wound DC motors in parallel from one controller should also work ok - and will be a bit more like an LSD.

If you used two permanent magnet DC motors in parallel it'll act like a spool at anything above crawl speed due to back EMF.


Ok think I am starting to understand theory... but would turning slowly into a corner provide sufficient weight transfer to cause one motor to unload allowing higher RPM?

Also wouldn’t turning left load up the right side? I am just thinking about a truck sign showing a truck going around a sharp left hand corner, the signs always show it tipping to the right. If we want the outside wheel to be unloaded to allow it to rev higher it would seem to do the opposite.

How are Warp DC motors normally wound serial or parallel?

Squiggles
Senior Member
Posts: 742
Joined: Wed, 22 Apr 2009, 03:19
Real Name: Neil
Location: Newcastle NSW

2 Speed Gearbox

Post by Squiggles »

Electrocycle wrote: yes, if you use two controllers supplying the same current to the motors, the one with less load on it (outside wheel is trying to go faster) will increase in rpm.

If you're using DC motors, wiring them in series and running them from one controller will behave exactly like a normal open diff (no drive if you get a wheel in the air)
Running two series wound DC motors in parallel from one controller should also work ok - and will be a bit more like an LSD.

If you used two permanent magnet DC motors in parallel it'll act like a spool at anything above crawl speed due to back EMF.


I think you are right...almost.
Generally in a car turning the outside wheel will have more load due too weight transfer, what actually happens is the inside wheel tries to spin and go as fast as the outside wheel. Your theory may well account for this phenomenon just the same.

All this assumes we are using non synchronous motors of course.

I don't think the variable speed calculation would be all that difficult actually if it where required, the hardest thing would be determining the desired radius of the turn.

EEV
Noobie
Posts: 21
Joined: Wed, 15 Oct 2008, 04:07
Real Name: John
Location: Sydney

2 Speed Gearbox

Post by EEV »

If you use two motors to do the work of one there are some benefits:

Each motor is smaller and lower cost, possibly half or better

No differential is needed, if provided in electronic format it will be compact and lower cost

Current demands will be lower

Controllers will be smaller in capacity and less costly.

And of course it may be appropriate to extend the advantages and drive four wheels, possibly better efficiency and economy.

Hopefully research put into wheel motors will produce a motor that will be suitable to direct drive a wheel through an axle without a gearbox and differential and hopefully not placed in the wheel.

Motors in wheels are only suitable for vehicles that operate on good uniform tarmac conditions.

User avatar
EV2Go
Senior Member
Posts: 2059
Joined: Wed, 16 Jul 2008, 00:21
Real Name: Paul
Location: Brisbane 1963

2 Speed Gearbox

Post by EV2Go »

I’m with you EEV on that one. I don’t like all that unsprung weight sitting in the wheel. If I ever went for two motors I think it would be east - west with a drive shaft off both.

Cost wise... I don’t know about two smaller motors being cheaper, two of anything is seldom cheaper than one big one. i.e. two Warp 7 or 9’s wouldn’t be cheaper than a Warp 11

But the great thing about 2 motors would be serial – parallel switching.

EEV
Noobie
Posts: 21
Joined: Wed, 15 Oct 2008, 04:07
Real Name: John
Location: Sydney

2 Speed Gearbox

Post by EEV »

If you must have a gearbox the planetry is the simplest.
Changing gear is as simple as locking a brake band as happens in some automatic gearboxes and the T-Model.

antiscab
Senior Member
Posts: 2513
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

2 Speed Gearbox

Post by antiscab »

EEV wrote: If you use two motors to do the work of one there are some benefits:

Each motor is smaller and lower cost, possibly half or better


No.
The size of a motor is determined by its torque, not its power.

The differential is almost always geared (i have yet to see one that is not).
replacing a single motor and differential (with 4:1 ratio) with two true direct driven motors, requires the sum of both motors to be 4x bigger than the one replaced.


Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

EEV
Noobie
Posts: 21
Joined: Wed, 15 Oct 2008, 04:07
Real Name: John
Location: Sydney

2 Speed Gearbox

Post by EEV »

An interesting parallel?

Most early IC cars were single cylindered.

The same for electric cars, electric motors are mostly cylindrical.

One day the EV-V16?      Brmmmm

EEV
Noobie
Posts: 21
Joined: Wed, 15 Oct 2008, 04:07
Real Name: John
Location: Sydney

2 Speed Gearbox

Post by EEV »

Not necessarily bigger
but with different torque and power characteristics.

User avatar
EV2Go
Senior Member
Posts: 2059
Joined: Wed, 16 Jul 2008, 00:21
Real Name: Paul
Location: Brisbane 1963

2 Speed Gearbox

Post by EV2Go »

This whole two motor thing has got me to thinking...

2 x Warp 8’s vs 1 x Warp 11

8” diameter, series wound DC motor
Weight, approx. 106 pounds
44.7 HP (72 Volts, 463 Amps)*
70 Ft. pounds torque*
5,500 RPM's

vs

11.45” diameter, series wound DC motor
Weight, approx. 229 pounds
43.7 HP (72 Volts, 453 Amps)*
135 Ft. pounds torque*
5,500 RPM's

Lighter per unit for better weight distribution (thinking back of a Mini) mounted side by side with a single 3:1 cog and chain reduction on both sides. Output roughly in the middle with a drive shaft off each side to wheel.

Could be wired for serial - parallel through a single Zilla or equivalent.

antiscab
Senior Member
Posts: 2513
Joined: Mon, 26 Nov 2007, 05:39
Real Name: Matthew Lacey
Location: Perth, WA

2 Speed Gearbox

Post by antiscab »

sure you can change the torque characteristic of the, you just cant change the continuous torque output.

This is a current density limit, based on max heat disipation.
The current density * surface area determines the field strength of the magnet. the strength of the two opposing fields determines the torque output.

you can change the arrangement of the copper (thus changing the torque output characteristic) but the thermal enforced current density limit remians.

case in point, a adc x-91 6.7" has the same torque constant (outside of saturation) as a adc 9" fb4001.
the 9" weighs almost twice the 6.7".
The 9" continuous current limit is twice that of the 6.7" and so is its continuous torque.

in the ACIM world, for a specific continuous torque output, there is only a minor (~10%) difference in weight for the same continuous torque output between the pole counts. all that is changed is the torque and power characteristic.

If you want more continuous torque out of a motor, it needs to be bigger (or the conducting material needs to have a far lower resistance).

Matt
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells

EEV
Noobie
Posts: 21
Joined: Wed, 15 Oct 2008, 04:07
Real Name: John
Location: Sydney

2 Speed Gearbox

Post by EEV »

Maybe a planetry gearbox to the end of each motor instead of the chains and sprockets.
There may be an opportunity to achieve direct drive and a 5:1 or other reduction.

EEV
Noobie
Posts: 21
Joined: Wed, 15 Oct 2008, 04:07
Real Name: John
Location: Sydney

2 Speed Gearbox

Post by EEV »

Do you know of any good wheel motors, two or four to drive a Mira or Charade?

User avatar
EV2Go
Senior Member
Posts: 2059
Joined: Wed, 16 Jul 2008, 00:21
Real Name: Paul
Location: Brisbane 1963

2 Speed Gearbox

Post by EV2Go »

EEV wrote: Maybe a planetry gearbox to the end of each motor instead of the chains and sprockets.
There may be an opportunity to achieve direct drive and a 5:1 or other reduction.


EEV I think your talking about something like this which was discussed several pages ago...

The problem with this is that you cant get a 5:1 reduction through only one planetary set and then it would still need to offset by cogs or gears when the motors are side by side. It would be a different story if the motors were end to end but then there isn't enough width.

Image

User avatar
Electrocycle
Senior Member
Posts: 985
Joined: Sun, 19 Oct 2008, 20:23
Real Name: Andrew
Location: Sydney
MSN: dumhed@dumhed.com
Contact:

2 Speed Gearbox

Post by Electrocycle »

Squiggles wrote: I think you are right...almost.
Generally in a car turning the outside wheel will have more load due too weight transfer, what actually happens is the inside wheel tries to spin and go as fast as the outside wheel.
Oh yeah sorry, I meant load as in rotational load - not weight.
The outside wheel is pushed faster in a turn, so it has less load (torque) - therefore will increase in rpm.

The inside wheel has more torque load even though it has less weight on it.

Of course this is assuming drive power in a forward direction. Slowing down via regen will cause more torque load on the outside wheel (being pushed faster, but against the motor torque)
The Engine Whisperer - fixer of things

User avatar
woody
Senior Member
Posts: 1715
Joined: Sat, 21 Jun 2008, 02:03
Real Name: Anthony Wood
Location: Mt Colah

2 Speed Gearbox

Post by woody »

EV2Go: 2 Warp 8s with chain reduction in the back of a mini sounds great to me :-)
do the bug harleys have belt drive? Is that more efficient and will it carry the load? Chains you could double or triple up for extra strength and noise.
Series / parallel switching sounds great too.

What happens with parallel DC motors when there is uneven load?
Planned EV: '63 Cortina using AC and LiFePO4 Battery Pack

User avatar
Electrocycle
Senior Member
Posts: 985
Joined: Sun, 19 Oct 2008, 20:23
Real Name: Andrew
Location: Sydney
MSN: dumhed@dumhed.com
Contact:

2 Speed Gearbox

Post by Electrocycle »

PM DC motors tend to lock together electrically when they're connected in parallel.

Series wound motors don't have their rpm as closely related to the input voltage, so they will vary speed much more with load (independently, even with motors wired in parallel)
The Engine Whisperer - fixer of things

Sparky Brother
Groupie
Posts: 95
Joined: Sun, 30 Mar 2008, 05:20
Real Name: Angel T.
Location: Melbourne

2 Speed Gearbox

Post by Sparky Brother »

I know I`ll be condemned for that but will say it any way Image

Just picture this. One big enough motor (AC or DC would not be an issue) coupled to a variable displacement hydraulic pump feeding one, preferably two hydraulic motors that by simple pressure regulator will achieve the differential effect. If hydraulic motor is one then you keep the diff.

Please note there will be no gain in weight in such a set up just like there will be no such gain if you originally planned to put one big11.45” diameter, series wound DC motor
Weight, approx. 229 pounds hoocked up to the diff. then you say change your mind and get rid of the diff by installing two this time Warp 8’s that you now have to figure out what sort of frame will accomodate them (more weight) and throwing in two controllers in the mixture making it equally complex

The only reason why I am speculating on the Idea of Electro-hydraulic transmission is that the variable displacement hydraulic pump gives you the same multiplication of the torque we need but with smoother variation between let`s call it for convenience "gear change"

User avatar
EV2Go
Senior Member
Posts: 2059
Joined: Wed, 16 Jul 2008, 00:21
Real Name: Paul
Location: Brisbane 1963

2 Speed Gearbox

Post by EV2Go »

The 8” Warps only weigh 106 lbs each compared to 223 lbs for a Warp 11, but unfortunately they are no longer available. Just looking at the 6.7” Advanced DC motor at 97lbs each.
At only 15.2” (38.6 cm) long each or 30.4” (77.2 cm) end to end, and 194 lbs (86.6 kg) for the pair...

Push both motors hard up against the back seat to keep the weight as forward as possible. Could chain or gear drive off the middle coupling giving an equal axle length, and serial – parallel switch off a single Zilla controller.

User avatar
Electrocycle
Senior Member
Posts: 985
Joined: Sun, 19 Oct 2008, 20:23
Real Name: Andrew
Location: Sydney
MSN: dumhed@dumhed.com
Contact:

2 Speed Gearbox

Post by Electrocycle »

Sparky Brother wrote:One big enough motor (AC or DC would not be an issue) coupled to a variable displacement hydraulic pump feeding one, preferably two hydraulic motors


I've thought about this, and I've talked to people who design hydraulic stuff.

Most people say it'd be massively inefficient, but then I also talked to someone who was developing a hydraulic "gearbox replacement" to be used in normal cars which was apparently 95% efficient.
The Engine Whisperer - fixer of things

Sparky Brother
Groupie
Posts: 95
Joined: Sun, 30 Mar 2008, 05:20
Real Name: Angel T.
Location: Melbourne

2 Speed Gearbox

Post by Sparky Brother »

Well I would not say the efficiency is the least of my worries but for the practicality`s sake I am living it aside for now. And what doesn`t create inefficiencies?

Just check this out! The hydraulics work even in this crazy application http://www.youtube.com/watch?v=1n1O5GSIug4        http://www.youtube.com/watch?v=t6G_YrGu ... re=related

I realize this sort of transmission would require more maintenance than a single direct drive 3 phase set up but for now I kinda like the idea of fiddling with something like that

Edit:

I can even imagine I could install the 3 Ph motor with the hydraulic pump hooked on to it with shorter hoses and the hydraulic motor bolted down onto the diff all together underneath the boot space which effectively free lots of space in the gear box tunnel and the ICE compartment.

Sorry I got carried away Image
Last edited by Sparky Brother on Tue, 01 Sep 2009, 15:32, edited 1 time in total.

Sparky Brother
Groupie
Posts: 95
Joined: Sun, 30 Mar 2008, 05:20
Real Name: Angel T.
Location: Melbourne

2 Speed Gearbox

Post by Sparky Brother »

I just can`t help it Image

What if instead driving the hydraulic pump by the E motor we have properly sized hydraulic piston solenoids pulsating the fluid directly to the H. Motor at the diff?

If I`ve gone too far just let me know guys Image

User avatar
Electrocycle
Senior Member
Posts: 985
Joined: Sun, 19 Oct 2008, 20:23
Real Name: Andrew
Location: Sydney
MSN: dumhed@dumhed.com
Contact:

2 Speed Gearbox

Post by Electrocycle »

nah go a solenoid piston engine driving the hydraulic pump :P
The Engine Whisperer - fixer of things

EEV
Noobie
Posts: 21
Joined: Wed, 15 Oct 2008, 04:07
Real Name: John
Location: Sydney

2 Speed Gearbox

Post by EEV »

We're becoming very inventive which is very good.

Einstein said that imagination is 90% of genius or something similar.

It would be good if something new is developed which allows the gearbox and diff to be dispensed with for electric drive.

I guess we're heading in that direction.

Sparky Brother
Groupie
Posts: 95
Joined: Sun, 30 Mar 2008, 05:20
Real Name: Angel T.
Location: Melbourne

2 Speed Gearbox

Post by Sparky Brother »

Ok. Let`s live the solenoid piston engine driving the hydraulic pump alone.Image

I`ve been doing some thinking Image recently and just came back from my shed. It appears that if I block one of the axles of the front diff of my Feroza and drive the tail shaft it gives me approximately (did not calculated it, just counted) reduction of 2.6:1 output to the other one. In theory If I can control and regulate the braking power applied to one of the axles the other one shold be able to produce a variable ratio output that can be used to drive the rear diff. which on its own is supposed to overcome the problem with a low torque 2 pole motor.

This theory looks confusing to me too but decided to throw it in and see if someone would find something viable in it.

User avatar
Electrocycle
Senior Member
Posts: 985
Joined: Sun, 19 Oct 2008, 20:23
Real Name: Andrew
Location: Sydney
MSN: dumhed@dumhed.com
Contact:

2 Speed Gearbox

Post by Electrocycle »

that's still going to be wasting a large amount of power in the braking setup (around 50%!)

There is a way you can use basic differential gearing and a small (low torque) CVT to make a +-2:1 infinitely variable transmission.
The problem is that it works in "speed mode" so your "gear stick" ends up being your speed setting, and you can easily decelerate hard enough to lock up the wheels (and / or break the gearbox)

The other problem is that using a diff in a way that results in a large speed difference between its two output shafts continuously will wear it out very fast.

Incidentally, this system is actually how the Prius transmission works, but instead of a CVT adjusting the diff "ratio" is has the two motor / generators - which gives it a soft connection and allows more flexibility.
The Engine Whisperer - fixer of things

Post Reply