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Old 07-26-2012, 09:34 PM
Torqueauto Torqueauto is offline
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Question High torque low rpm hub motor

Trying to dream up a diesel eletric rock crawler utilizing wheel hub motors to facilitate a wild suspension design. Is there a wheel hub motor with enough torque to operate on extreme rocky surfaces? Speed is not an issue as it will be a trailered rig. It will use a small diesel motor and minimal battery storage to make it as light as possible but enough to be able to run for as long as the diesel tank is full with absolutely no down time to charge.

Also, if anyone knows of a very, very short motor that could be used in place of a wheel hub motor let me know. It may be something to start with until i could afford the appropriate hub motor. A hub motor would be idea to keep the motors out of harms way when rock crawling.

I am a diesel mechanic and own my own repair facility but am a newbie when it comes to ev... However, the idea of being able to control each wheel independantly and to not have my design be restricted by driveshafts and axles seems very appealing. Skys the limit so-to-speak!
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Old 07-26-2012, 09:38 PM
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Default Re: High torque low rpm hub motor

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Originally Posted by Torqueauto View Post
Is there a wheel hub motor with enough torque to operate on extreme rocky surfaces?
Nope. Maybe look into hydraulics.
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Old 07-30-2012, 08:58 AM
Torqueauto Torqueauto is offline
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Default Re: High torque low rpm hub motor

Anyone else? Maybe someone with some actual constructive information like how much torque the current strongest motors have? Why they thought the current hub motors were not strong enough. Or possibly any news on something coming down the pike that may have more torque? Hydraulic motor buggys have been done. I like the idea behind them but want to avoid the many downfalls like weight/ heat/ leaks/ noise/ expense/ and way too complicated.

Since posting this i did find videos of a gas/ electric/ hydraulic buggy that did use electric for the wheels. However the motors seemed conventional but were awefully short. The hydraulics only operated the suspension and in my opinion added too much complication and weight to the design. Search green dawg rock crawling on youtube for some videos. My idea is much lighter as will have passive suspension instead of heavy hydraulic active suspension.
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Old 07-30-2012, 09:44 AM
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Default Re: High torque low rpm hub motor

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Originally Posted by Torqueauto View Post
Anyone else? Maybe someone with some actual constructive information like how much torque the current strongest motors have? Why they thought the current hub motors were not strong enough. Or possibly any news on something coming down the pike that may have more torque? Hydraulic motor buggys have been done. I like the idea behind them but want to avoid the many downfalls like weight/ heat/ leaks/ noise/ expense/ and way too complicated.

Since posting this i did find videos of a gas/ electric/ hydraulic buggy that did use electric for the wheels. However the motors seemed conventional but were awefully short. The hydraulics only operated the suspension and in my opinion added too much complication and weight to the design. Search green dawg rock crawling on youtube for some videos. My idea is much lighter as will have passive suspension instead of heavy hydraulic active suspension.
I gave you the short honest answer. You have electric wheelmotors or hub motors available for bicycles, scooters and huge mining trucks, but nothing in between. So if you are of mind, go ahead and do it. It likely will cost about $50,000 per wheel and you'll be disappointed with performance and durability. Search here or on the internet. Ref: http://www.diyelectriccar.com/forums...ght=wheelmotor

I have seen some experimental hub motors for military trucks which might come close to your dreams, but those would be even more costly. You say you want to go real slow.....just get a forklift motor and use a 200:1 reducer for each wheel. Just kidding, kind of

{edit} Thinking about it,,, just had someone tell me the newer JLG scissor lifts have switched from hydraulic to electric hub motors. Maybe you can take a look at one of those.

Last edited by major; 07-30-2012 at 10:00 AM.
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Old 07-30-2012, 10:00 AM
Batterypoweredtoad Batterypoweredtoad is offline
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Default Re: High torque low rpm hub motor

Like Major said, you are in a black hole in the size range you want. Hub motors are too heavy to work well in cars with the rapid suspension movements and direction changes required by street driven vehicles so nobody pursues them beyond the concept stage. Hub motors are just a short motor driving a planetary/sun gear setup. His forklift motor with gear reduction comment might be the only way to make what you want to happen, happen. Another option might be to explore the military or mining market and see if the smallest things they sell would work for you, but I doubt it.


Last edited by Batterypoweredtoad; 07-30-2012 at 10:03 AM.
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Old 07-30-2012, 10:47 AM
Torqueauto Torqueauto is offline
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Default Re: High torque low rpm hub motor

Thank you! If they are using them in scissor lifts then it is possible they could work for me. Scissor lifts generally weigh more than a car (upwards of 5k lbs) and move at a very slow rate of speed which should translate into some lower gearing. The one problem i see is that they use very small wheels which when paired with large offroad wheels would effectively up the gear ratio.

But a forklift motor meant to be mounted at the wheel without a driveshaft, diff, and axles would also be a liveable choice. I just had an idea where i flip a very wide deep dish wheel around so that the motor sits inside just like the mining truck design. It would turn a "normal" motor into a "hub motor". Now how would i make it act like a brake? reverse the polarity till i stop? then how about a parking brake?
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Old 07-30-2012, 11:49 AM
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Lightbulb Re: High torque low rpm hub motor

Just to get an idea of what to expect from a real hub motor, you might try: http://www.ebikes.ca/store/store_motors.php

http://www.ebikes.ca/simulator/
Using a low speed planetary drive hub motor with a 16" mountain bike wheel, I got 132 pounds thrust at 0 RPM with a battery power of 1850W. So with one on each wheel you should be able to get 520 pounds of thrust which might be enough for a crawler. And you might even try ganging two motors and maybe even two entire wheels on each axle. These motors cost about $350 each so it might be a reasonable investment to try $1400 and see what you get out of it. These are meant for spoked wheels but they can be pretty rugged for mountain bikes.

It might be cool to make an articulated crawler using several sections and six or more wheels, like some of the military vehicles. This wheel hub motor also comes in kit form on a 24" wheel for about $700 and here are the specs: 48V, 20A, 550W, 3.8kG.

This may or may not be practical but it gives you an idea of real performance of hub motors and you can scale up from this. There are larger hub motors for electric motorcycles and it seems like that would be another good place to start. You don't really need a lot of power for a crawler, but mostly torque. And you probably cannot rely on more than two wheels on the ground at any one time, so that adds to the required torque or thrust for each wheel.

Last edited by PStechPaul; 07-30-2012 at 11:51 AM. Reason: Remove pasted text
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Old 07-30-2012, 12:30 PM
Torqueauto Torqueauto is offline
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Default Re: High torque low rpm hub motor

Yes, you are correct that i cannot rely on more than two wheels on the ground at once and likely only one of those will have traction at any given time. That is one reason i am looking into this idea. With a conventional transmission/ transfer case set up you must have lockers at each axle to be able to go anywhere with only one wheel having traction.

Does a pound of thrust from an electric motor at the wheel truly equals a pound of thrust from a piston motor in a regular vehicle? Since a combustion engine's torque is multiplied by gearing in the trans, transfer case, and axle it is mulitiplied considerably which may be hard to do in a planitary setup at the wheel?

To put it in perspective, with the predicted weight of my crawler at only 2000-2500 pounds it would only require a combustion engine with 100 ftlbs of torque. This would equate to 500 to a 1500 ftlbs per wheel depending on the gear ratios used. At some point in that scenerio the max torque becomes irrevelant and the desired outcome is simply a lower constant speed. I believe i could get away with 500 ftlbs per wheel since the torque is instant and the speed could be kept low with no reduction in max torque. On the other hand, If you have a gas powered rig with too high of gearing you must throttle up to an unacceptable speed to get your max torque number, hence the super low gearing in dedicated rock crawlers.
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Old 07-30-2012, 01:05 PM
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Thumbs up Re: High torque low rpm hub motor

I think you need to start with how much thrust you need, which is the force applied to the ground in the direction of motion. For a 2000 pound crawler, you would need 2000 pounds of thrust to climb a vertical wall, 1000 pounds to climb a 45 degree (100%) slope, and 500 pounds to climb a 50% slope. If your tires are 24" diameter then that is also 500 lb-ft torque. So you could use the motors I found if you had traction on all four wheels, or on two if you use double wheels. But 16" wheels might be too small for serious crawling, so if you double the diameter for the same thrust you double the required torque.

Changing the torque with a transmission is simple if you have one motor and mechanical connections to all wheels. But when the motor is on the wheel, it's hard to build a transmission in it. But the bike motors shown in the ebike page have planetary drives, so it might be possible to build one with a higher ratio and get more torque with less speed.
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Old 07-30-2012, 10:23 PM
aeroscott aeroscott is offline
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Default Re: High torque low rpm hub motor

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Originally Posted by Batterypoweredtoad View Post
Like Major said, you are in a black hole in the size range you want. Hub motors are too heavy to work well in cars with the rapid suspension movements and direction changes required by street driven vehicles so nobody pursues them beyond the concept stage. Hub motors are just a short motor driving a planetary/sun gear setup. His forklift motor with gear reduction comment might be the only way to make what you want to happen, happen. Another option might be to explore the military or mining market and see if the smallest things they sell would work for you, but I doubt it.

looks like a LTI (Laturno International) product talked with them years ago they use switched reluctance motors for max stating torque without overheating the armature (inductive heating) . They cut big gear teeth in the armature . This reduces the inductive heating . They also said controlling a SRM motor does not follow motor theory, if he told me he would have to kill me .LOL , the highest preforming motors out. :talked with the tesla motor guy when tesla R was in development he said it was all in the armature . Leading me to think SRM motors are where they are headed .

Last edited by aeroscott; 07-30-2012 at 10:37 PM. Reason: added:
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diesel electric, offroad, rock crawling, torque, wheel hub

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