I was realllyy looking forwards to seeing proper graphs of torque arms failing too from this test jig, and I can tell you that they don't disappoint!
...a squashing the cable in the process = back to the drawing board.
A larger ID on the bearing would be great, but this requires re-working the planetary gear system the motor might use, which is sized to fit over a 17mm axle. For any geared motor, this is prohibitively expensive - plus, you don't have much room on the non-drive side of a rear hub motor due to the disc rotor attachment. Also, a torque arm integrated into the motor (which would be awesome!) is very difficult to pull off with a modern rear hub motor due to the disc brake on one side, and gear cassette on the other.fechter wrote: ↑Apr 03, 2018 10:11 am...Ideally, the motor should have a larger ID on the bearing to allow a larger axle diameter so you don't need a hollow axle and you have a larger diameter shoulder to grab onto. I liked the old Hienzmann motor style where the arm is integrated into the motor. ...
Wow! That's a very secure torque arm assembly. How long did it take you to install? The goal with this project is to have an effective torque arm with a streamlined installation, and that doesn't run into the disc rotor spacing issues described in Justin's first post.electricwheels.de wrote: ↑Apr 03, 2018 10:49 am...Here a torque arm fitted with a Crystalyte HS3540:
The torque arm is made from 4 mm thick alloy 7075 T6 and is used with 4 additional torque washers:
They are connected with 2 pieces dia 3 x 18 mm steel dowels, which go through all 5 layers and turning it into a solid block.
Similar principle on the reku torque arm on the opposite side...
The arms are made from 2 parts, so that a preload can be applied. Using so-called RIPP screws, they won't loosen even under vibration.
The torque arm rests in a piece of POM against the frame tube, and is always parallel to the tube...
For sure, but the drawing board is not a sad face, that's a happy face place to be. This kind of challenge in product development and testing is fun and exciting!
This is true, but part of our design goal was also that the spline modifications be relatively easy for the hub motor companies (MAC motors, Crystalyte, eZee, MXUS etc.) to do with the same CNC equipment that produces the axles. We thought that a rounded spline like this allow for it to be machined either with live tooling coming in from the end of the axle, or with a ball-end mill on the side of the axle. To do trapezoidal teeth profile could require EDM or custom tooling.Instead od using rounded teeth, try using trapeziod teeth with a slightly negative angle. The rounded section at the top of each tooth acts as a ramp aiding the downwards movement. A negative angled flat does the opposite, the shaft wants to go towards the closed end.
Oops, I didn't see this post when I just submitted mine. It's true that the motor simulator shows 120 Nm, but I suspect that we're into non-linear and demagnetization realm of the MAC motor at that level of phase current, so the actual torque is likely to be less than this. We just today received a 150A 40V 6kW power supply from ebay that will let us repeat the tests here with more modern equipment.
At this stage that's exactly what we're shooting for, 200 Nm. The fact that we could just about hit this with a machined 6061 aluminum arm surprised me. And this is with a plate that is 3/16" thick, but our next sample of custom MAC axles will have the splines going to a depth of 1/4", which would mean even 33% more metal and torque.Ideally, the torque arm wouldn't show any signs of failure at that torque, and really higher to get a margin of safety. What do you think is a reasonable design goal of torque applied without any sign of failure? 200 N-m? More?
Exactly. As I mentioned in the first post, the reason that we were using aluminum was so that we could be sure it was the torque arm that failed and the steel axle and axle splines would remain unscathed for additional tests. It wasn't because I thought that the final arms would necessarily be from aluminum, but if it turns out that they could then that would be awesome. Lighter, faster/cheaper to machine, minimal corrosion concerns.
You went from elastic to plastic deformation. Remove the TP at that point and check the dimensions.
There's the leverage affect.
Thinking back to AmpedBikes TAs - perhaps the skewing could be reduced if the inner edges of the U were shaped to engage a matching filler plate. Unlike the shaft, the TA parts are laser cut, so there are many shaping options for the serrations to minimize redirecting forces in undesirable directions.
I agree with Buk 100% on this one. The splines are cute and if I were a splined lever I might even ask yours out on a "splined-date."Buk___ wrote: ↑Apr 04, 2018 5:26 am...........
I have serious reservations about the benefits of splines over flats. The idea is sound -- spreading the load -- but it would require specifying such tight tolerances and a level of accuracy of machining for both parts that it would be hugely expensive to achieve if axles and TAs were manufactured as matched pairs (triples); and impossible if they are to be manufactured by different companies/countries.
The primary benefit of the splines on that design is it allows it to used at any of 24 different position -- every 15°-- and the same part can be used on both sides, so an effective way to have one part that will fit both sides of many bikes.teklektik wrote: ↑Apr 04, 2018 10:52 amThinking back to AmpedBikes TAs - perhaps the skewing could be reduced if the inner edges of the U were shaped to engage a matching filler plate. Unlike the shaft, the TA parts are laser cut, so there are many shaping options for the serrations to minimize redirecting forces in undesirable directions.
The reference is about using the laser cut serration concept in flat stock to create parts that interlock to resist movement. It has nothing to do with the specific use of that idea in the the AmpedBike TA and has nothing to do with resisting rotation - it is about pressing that idea into service for linear rather than rotary motion to address the skew problem.Buk___ wrote: ↑Apr 04, 2018 2:58 pmThe primary benefit of the splines on that design is it allows it to used at any of 24 different position -- every 15°-- and the same part can be used on both sides, so an effective way to have one part that will fit both sides of many bikes.teklektik wrote: ↑Apr 04, 2018 10:52 amThinking back to AmpedBikes TAs - perhaps the skewing could be reduced if the inner edges of the U were shaped to engage a matching filler plate. Unlike the shaft, the TA parts are laser cut, so there are many shaping options for the serrations to minimize redirecting forces in undesirable directions.
It's still the flats of the insert that take the load first.