If you are talking about the slot to slide the wheel forward and back, there shouldn't be much torque there. A pic would be helpful.

 

An impact socket?

 

300 nm converts to about 225ft/lbs. Not much torque at all

 

4340 chromoly is about as tough as you'll get. In reality if things are designed properly, regular old mild steel (A36) should be sufficient. 225ft/lbs isnt really a huge amount. I have a feeling stress cracking and shock damage are going to be a bigger problem in your design, depending on how fast you intend to hit peak torque. I'm guessing if your using electric that you will have a motor controller to ramp up the output so you arent breaking things all the time.
Just for comparison, I can manage over 500ft/lbs on a breaker bar if I'm motivated and a little pissed off without sweating too much 600+ if I get my legs involved

 

Some seem to say you can weld chromoly to mild steel, interesting. I was under a different impression.

I am not sure what to take a picture of. I attached a drawing. The idea is that this material is what the axle slides into. An electric motor can splay this slot if it isn't tough enough.

Electric motors seem to generate torque differently than gas motors, I don't know how to explain this deeply.

Domex 100 seems like it may be a viable option, but I don't really know for certain.

 

In most cases, you would use ER70S-2 for filler on chromo as the weld stays more ductile, and does gain some of the chromo qualities that it fuses with.
For a 4340 shaft, you would be looking at a 4130 filler, and a slow cool down process to keep it from getting too brittle.

While Oldendum has a point, the 4130 or 4340 WILL have a greater resistance to radial deflection. It will stay true longer. BUT- when it comes back, it will come back with more authority.
So, maybe expect a snap from the backlash. Not in the shaft, but in whatever is attached to it- drive hub, shear pin, splines, etc.

 

If you think a better steel alloy is going to be "stiffer", guess again. A better or heat-treated piece may flex and return to the original position without permanent deformation, but it will still flex.

If it needs to be rigid, you need a larger diameter or thicker piece of steel, depending on the loading.

 

If you are anchoring the motor to the axle mount, you need to re-think your design. Some type of torque arm needs to be added.

 

The goal or idea is to start with an ideal material, then work out the dimensions of the material. Obviously, if I used a 2" diameter 1/2" thick piece of steel alloy and it splayed, I'd need to bump it up to larger diameter and thickness. I am not a materials engineer with a history in metallurgy, maybe I need to seek one out. But I am under the impression that if I used a material that had very high toughness, it would take an awful lot of energy to deform it.

The dropout (part holding the axle) will be the torque arm entirely, that is the idea or purpose of this part. Slipping the wheel on and off with nothing more than loosening the axle nut is definitely radically more ideal than closed mouth torque arms. Most of my experience with closed mouth torque arms involve struggles that I want to avoid.

 

@ bowlingofsunshine - you're into EV cycles. Check? Then you're aware of the stellar http://www.d1g1taldr1ve.com/d1-tech-specs/. Check? The sled's motor has a CPO and CTO of 60kW and 600-850 Nm, respectively. Above your torque requirements, but perhaps factors in the "systems design criteria" you seek.

We know nothing of your overall design intent, not to mention the motor specs. Weldments are generally designed for strength only, rigidity, and no load. The design process/formulae factor in the load, member properties, and stress/strain. If any two are known, the third can be calculated. All you've cited is a "torque." Is it continuos torque output? Maximum torque output?

True that e-motors and ICE develop torque "differently". Electrically, in a near-sinusoidal ouput with maximum (theoretical) torque at/near 0 RPMs. And ICEs, at a much higher RPM due to the time required to buildup (air, fuel, rotating mass) and generate power.

So you want a material selection and mounting schema for your e-motor based soley on a torque value? What's the mounting boss (drop out) connected to? A frame made of 4130, dragon skin, or ademantium? Lots of environmental and O&M aspects to consider.

Suggest you contract a PE and contact the builders in Portland to see what they'll disclose. Form, for the sake of personnel safety, needs to flow from function.

 

The material selection influences the design, and the design influences the material selection.

You can make something out of plain 1010 mild steel that could work, or you can make something out of heat-treated 4340 steel that could work.

The devil is in the details though.

btw, "tough" in steel or metallurgy terms generally refers to the material will "yield" (start to permanently deform) waaaay before it finally breaks via fracturing or pulling apart. In this word usage, an opposite of "tough" is "brittle". A fully quenched piece of high(er) carbon steel can be very "strong", but when its final material limit is reached it will shatter (brittle failure). The difference in stress between the yield point and the final failure point is not very great. Your part in that instance is very "strong", but if/when it fails it would be sudden and could be rather catastrophic.

Example: take a piece of plain mild steel and put it in a vise. Pull/push on the steel and it will bend, permanently if you pull/push hard enough. You have exceeded the yield limit of that piece of steel and caused a permanent deformation. Put a hardened piece of steel (maybe a nice hard file could do as an example) in your vise. Pull/push (carefully now) on that hardened piece of steel. You would pull/push much more than you did with the mild steel piece before you get any permanent deformation, but more likely you would just suddenly snap the hardened steel (file). It fractured and didn't bend (permanently) much at all.

second btw, ALL steel 'flexes' the same amount, up until the yield point That 'flex' is called the "modulus of elasticity". The difference between 'hard' steel and 'soft' steel is that the yield limit for the hard/strong steel can be much higher than the yield limit for the soft steel. For tensile loads, the modulus of elasticity is also called "Young's Modulus", which for steel is 29,000,000 psi (often used to one significant decimal place is 30,000,000 psi). Note that I said for "steel", as the modulus is independent of specific alloy or hardness and is a metallurgical property of the material itself and not the alloy or heat treatment or 'hardness'.

http://en.wikipedia.org/wiki/Modulus_of_elasticity

Take two pieces of steel, exact same size and shape just different hardness (could even be the same alloy, maybe one fully annealed piece of tool steel and one hardened but not quenched piece of the same tool steel). Load the 'soft' piece, could be bending or torsion or tension loading, just until it starts to permanently deform (load it a little bit and it bends/stretches but comes back to its original size/shape/form/position when you release the load, keep loading it a little bit more until it -just- no longer comes back to its original size/shape/form, congratulations you have just reached the yield limit for that sample. Hopefully you kept good charts/tables/records of what you just did, because now you are going to duplicate the experiment but with the harder/stronger piece of steel. Start the experiment with the hard/strong piece of steel and note that you can get to the same load condition where the softer/weaker sample started to permanently deform (yield), the hard/strong piece of steel still returns back to its original size/shape/form. If you continue the experiment, you will find that you can apply a higher load on the harder/stronger piece of steel and it keeps coming back to its original size/shape/form, but eventually it too will start to permanently deform (yield).

If you chart/graph the load (force, or torque, or whatever load 'type' you applied) versus the deflection of the sample, you will find that both samples had the same chart/graph up until the yield limit was reached.

See also

http://en.wikipedia.org/wiki/Strength_of_materials

If you want to make some part 'stronger', you can use a 'stronger' material or a 'stronger' design.

If you want to make a part 'stiffer', you can use a different 'stiffer' material (note that all steel is still steel, as far as the Modulus of Elasticity is concerned, but "steel" is stiffer than "aluminum") or a 'stiffer' design.

We have not even considered fatigue in our design discussion so far, as that is yet another factor in successful machine/mechanism design.

And saying "225 ft-lbs of torque" is not quite enough info to determine a design. It's a start, for sure, but not enough info. Apply 225 ft-lbs of torque to a 1" Grade 8 bolt head and you have not done much at all. Try to apply 225 ft-lbs of torque to a 1/4" bolt and you'll rip the head right off.

:drinkup: