# Just for the fun : 4 motors inline?



## Dalardan (Jul 4, 2008)

Just for the fun, while I was looking at Warp13 motors, I found that they're sold near $5000 and produces ~50 hp @ 72V. So I looked for a small Sepex motor and found that a D&D one can be found for ~$1000 and produces ~15 hp @ 48V. 

If I calculate well, you can get 4 6,7" sepex motors for the price of 1 13" series motor. Where it begins to be interesting is that each sepex motor comes with it's controller, not the Warp motor, which makes this choice even more expensive.

My idea is : Would it be interesting for a drag/pick-up/bigger car setup to put 4 sepex motors inline an go direct drive? This way, you could get a series configuration, a 4 parallel configuration and a 2 series, 2 parallel configuration, which would give the equivalent of a "3 speed gearbox".

You would also get a lot more brushes, but I don't remember why it is good. And you could go with a 48V battery pack, downsizing the battery pack (and maybe allowing to add an other row of batteries, enhancing range).

One of the drawbacks is that the sepex motors I pointed have a top speed of 3000 RPM at 48V in comparison to the 5500 RPM of the warp13 at 72V. Would it matter in a direct drive setup?

Thanks to think about it,

Dalardan


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## Qer (May 7, 2008)

I guess this would more or less only make sense if you connect them directly each to one wheel. If so 3000 rpm is PLENTY! If you ever reach 3000 rpm you're a speed demon and will probably have every available police car chasing after you. Luckily drag will stop you from turning THAT suicidal. 

Very nice price considering it's with a controller. Too bad they don't have any curves over torque and horse power etc, it would be nice to be able to compare them to, for example, Warp 9.


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## Jeremy (Jul 12, 2008)

I've been doing much the same, looking at using multiple, smaller motors. In my case I'm looking at making an electric paramotor as my next EV project and have been exploring the world of big RC model brushless motors.

The same principle seems to apply, in that two smaller motors and controllers are cheaper than one big one of the same power. The only penalty is some extra weight.

Jeremy


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## TX_Dj (Jul 25, 2008)

My first worry would be that 48v would A) draw far too many amps for reasonable acceleration on direct-drive, and B) not provide enough potential for achieving and maintaining a high speed.

I do like the idea about the series/parallel switching, ala Wayland's "Siamese 8" configuration, but I'm not sure that can be done w/ SepEx? I know almost nothing about SepEx though.

I think you would achieve this goal far more effectively if you had 120+v and dual larger series-DC motors such as a pair of ADC 8's or 9's.

I also don't think that 48v or even 72v is going to give the kind of performance necessary to direct drive each hub without sucking major amps from the pack(s), which of course will cause far more voltage sag than you probably want.

There was a car someone built years back, I can't remember who or what they called it, but I do recall it was a Ford Taurus with 4 wheel motors and a fairly high voltage pack, they took it up to about 200 mph on the salt flats and set a world record for EVs


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## Dalardan (Jul 4, 2008)

I've found that Thunderstruckmotors have got a power curve for this 48V D&D sepex motor there. Hope you have fun.

If we continue thinking about an inline configuration, if we get a 3:1 rear differential ratio, this would give at most a 1000 wheel RPM (probably more in the 750 ) is this suitable for a vehicule? (I've got lost trying to figure out...)

Also, 4x56lbs = 225 lbs instead of the Warp13's 367lbs. Is it worth thinking?

Dalardan


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## TX_Dj (Jul 25, 2008)

For the record, 750 rpm @ the wheels will be somewhere in the range of 60 mph depending on the diameter of your tire. For example, a 165/80-15 tire turns about 795 revolutions per mile, so if you can make it turn 750 RPM you will be going just under 60 mph.


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## Qer (May 7, 2008)

TX_Dj said:


> My first worry would be that 48v would A) draw far too many amps for reasonable acceleration on direct-drive, and B) not provide enough potential for achieving and maintaining a high speed.


Since it won't take many rpm's to drive insanely fast you probably don't need high voltage. However, you'll need some packs in parallel rather than in a string to provide the amps. But hey, what could POSSIBLY go wrong?


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## skullbearer (Jul 9, 2008)

If you connect them strictly 'in-line' by hooking their shafts end-to-end, you'd deal with some major torque effects on the back two motors and the last in particular which would likely damage if not destroy those motors.

If you connect them all to a single sprocket via identical output/input gears though, you've got yourself a setup.


Better to go with 4 96 or 120v motors that do lower torque but 6k+ rpm and use gear reduction to achieve the desired speed, if you were adamant about a single axle with all the motors driving it. The higher the system voltage (as long as it doesn't arc) the higher the efficiency of overcoming resistance inherent in the system.

Higher amps will heat wires and require bigger thicker cabling, which adds weight and removes space.


One way I've seen in some custom audio setups of running massive wattage subs without 1/0 cable everywhere was to use micro-transformers that doubled or quad the voltage, one system was running 48v rather than 12v (its actually 13-14v x 4 with the alternator). What matters in subs is watts not volts, but volts are generally fixed without a more complex control system. What those systems could do though was run smaller cables for massive drivers. Like with wall powered systems, they don't run fat 1/0 cables to everything because they run at 120v from the wall in high power cases.


So I personally would opt for a greater gear reduction.

As for driving all 4 wheels, running equal power on all four would not optimize your grip for acceleration, particularly in corners (I'd rather spin the rear than the steering wheels in a turn). Slap motors of same rpm or geared for same final rpm on the front that are a third of the rear wheel motors in terms of output power, and you should have a fairly balanced drive system I'd think.


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## Dalardan (Jul 4, 2008)

You're bringing an interesting point, Skullbearer. I don't know up to whitch point these shafts are overdesign, but it a realistic assumption that the last motor's shaft may break.

A possibility would be to build twice double motors, this could reduce the needed space for the motor and maybe allow a row of batteries over the motors. Why I'm thinking about inline setup is that with a rear wheel drive car, it may be possible to cut the driving shaft and place the direct drive motors in that place (with appropriate protection against water, dust and hits and with appropriate cooling) so it would leave the ICE motor space empty for batteries and may reduce the number of trunk batteries.

Something important for a daily-driven direct-drive car is the ability to reverse. If I understand well the principes of motor advance, when you advance the brushes, the motor may handle higher voltages and spin faster, but may not be reversed. Maybe with the 84V Sepex motor from the site I pointed above we can get something interesting (4500 top rpm).


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## skullbearer (Jul 9, 2008)

It absolutely boggles my mind that nobody seems to be building motors with centrifugal or hydraulic advance!

In my very very limited experience of actually tearing apart (small) DC motors for fun, the brushes were always right at one end, and it seems to me fairly simple to use a ball weight centrifugal advance system like on centrifugal clutches or older centrifugally advanced distributors.

The hardware exists for a very broad range of rpm, and in many cases simple calculations and swapping of weights will allow you to 'tune' the advance and rpm.

This would be an issue if you have a high motor vs wheel rpm because it would begin the advance (with centrifugal) even in reverse and 'cancel' your reverse, if that is an issue as you point out, otherwise I see it as such an advantage to have such a system...

And not nearly as difficult as going to a computer controlled brushless DC motor.

I must be wrong in the case of larger DC motors though, since I don't really see or find mention of this.


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## Qer (May 7, 2008)

skullbearer said:


> And not nearly as difficult as going to a computer controlled brushless DC motor.


Well, if you have a good way to control the advancement of the brushes (with a small servo motor for example), it would be fairly simple to let the same microcontroller that runs the PWM control the advancement as well and especially make sure it's not running higher voltage than the advancement can handle.

A totally nutty way to control it would be to let the accelerator move the advancement through a wire and then the microcontroller matches it with a voltage. Not very practical though.


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