Danlov said:
Bryan Ratcliffe has just released a dirt ebike podcast https://podcasts.apple.com/ru/podcast/dirt-ebike/id1488285332#episodeGuid=Buzzsprout-3453370 with me talking about the SurRonShop in general and clearing out the situation with our race motor that recently happened. Here is an important text cut out from my talk. I want to spread this information to as many people as possible, would appreciate the help!
My name is Daniel and I am from Moscow, Russia. I got my first sur-ron in 2018 and I fell in love with this bike right away. Riding it every day felt amazing and after a couple of months I started to see it’s big improvement potential from suspension and brakes up to a controller and battery swap. I ended up upgrading every part of the bike except the frame and the motor.
By the time I had my 16kw sur-ron project finished, I found out that we have a lot of different electric bike workshops here in Russia that were not focused on sur-ron upgrades or could not find demand for their sur-ron products due to the language barrier or simply were unfamiliar with how to use social networks. This gave me an idea of why not to connect these different manufacturers with worldwide sur-ron communities. The first product I came out with were the seat extenders in summer 2019 for better sitting position and leg seat gripping while standing on the bike. This is by far our most popular product.
Surronshop is developing day by day and now we have a wide variety of upgrades for everybody like peg and seat extenders, stainless steel bash guards, peg spacers, chain dampers, suspension mudguards, custom decal kits, stronger progression links, batteries and battery cases, controllers and finally the race motors that were introduced in spring.
Many people already know about that recent incident with one of the supplied motors. I want to give my comments on this again and focus on the important points of the failure and clear our position as a supplier of the product. These high-performance motors are manufactured by Roman YTW200 since 2016 for different electrified motorcycles builds. The bigger magnets and better windings technology let this motor be much more powerful than the stock one and last significantly longer before overheating while having quite similar formfactor and weight. A sur-ron equipped with such motor in Moscow showed crazy performance: not only it was not possible to overheat the motor riding the bike with full throttle, but also it had more torque on the same power settings.
Now moving on to the incident, our customer Travis (http://facebook.com/to.schneider.1?tsid=0.9797496387528122&source=result) wanted the race motor that won’t overheat and give him the maximum possible performance out of his sur-ron on a track. We first sent him the high torque motor version at a self-cost price so that he could stress test it and give us the feedback as well as some advertisement as for a sponsor. He noticed that the bike performance was better with the new motor but the mountings were not strong enough to hold his 64-sprocket torque. Of course, Travis was offered a stronger mountings manufacturing and shipment for free but we needed to receive his old mountings for material to make new ones. What happened after that - Travis got the top speed motor version which was shipped with stronger mounts. When he was installing the motor, I was being hospitalized with pneumonia and couldn’t control properly the installation and setup process of the motor. So, the key thing that was wrong here is that Travis turned out to have launched the motor in SENSORLESS MODE which is like an emergency mode that is the way to go only if you have something wrong with the motor and you need the bike to just get you back home applying throttle gently. This mode is used for hall sensors setup process and not for normal riding. It’s important to note that one of the riders in Russian Sur-Ron community launched his original sur-ron motor in sensorless mode ending up breaking all of its magnets and having to fully recover the motor after a single ride.
So, what happened next in the backyard with Travis - the motor blew up after he applied full throttle. This is a terrible situation and I bring excuses to Travis again from me, the motor developer and the SurRonshop in general. We are sorry for what he had to go through after and I am glad he recovered from the incident. Returning to the motor explosion back again, this could only happen if the motor had a third-party metallic object inside like a nut between the stator and magnets which shattered into shrapnel after a good throttle input. I will now bring several arguments as to why other forces do not have an influence on the explosion.
First, using simple physics formulas, it is clear that when you apply full throttle on such 10.000 rpm motor, a force level of 355 Newtons occurs inside which is equal to just 77 pounds. So, even the force at full throttle cannot break or tear metal of the motors’ stator. And we are not even sure if Travis could reach that full throttle rpm speed riding in the backyard.
Second, I saw another possible explanation that because the magnets rub the stator from chain loads, the pileup of mag fragments caused the crash. This is not the case since the bearings are located in a way that the load on the motor axle cannot bend or twist the rotor.
Third and final doubt in our third-party object inside the motor explanation is that a detached or an un-glued magnet could cause the crash. This is again not the case since in the outrunner motor type the magnets are inside the ring… or I should say inside the circle. Centrifugal forces would strongly press back even a detached magnet preventing it from reaching the center where the motor stator is located. You can understand this my imagining yourself on a carousel. It is quite difficult to pull yourself to the center while it’s spinning.
After the incident we refunded all Travis payments for the motors. The issue was - we received payments in Russian currency from him and our currency exchange ratio dropped significantly. This resulted in a fact that when we fully refunded him all his motor payments, he lost 392$. After the situation became public, I could not contact him anymore on Facebook but I sent an email offering a refund of the rest of the sum out of my pocket. It would be great if we at least could get that motor back for investigation after a crash and maybe provide better proofs for our explanation other than the theory.
Now, despite how it all ended, Travis if you are reading this, I know you are a great person and I am again terribly sorry for this incident with our product. I take responsibility as a manufacturer for what has happened since the unit was supplied without strict installation instructions and precautionary actions that have to be taken before mounting. We already took the lesson from this situation and will provide precautionary actions as a self-checklist for installation process of the future motors. We are also working on a new design of enclosed mounting for the motors that will be made out of thick stainless-steel using water and laser cutter equipment. We could have already introduced the new mountings frame or at least a 3-d model but due to the coronavirus self-isolation restrictions here Russian non-medicine or food production organizations cannot work otherwise they get big penalties.
I want to mention again that the first delivered motor that Travis tested normally in FOC mode (not sensorless) gave him an advertised performance. We also provided the customer with a full refund of his payments even though the motor was not setup correctly and we did not control the installation process.
In conclusion, I hope this cleared the race motors situation and I want to thank each and every one who supports me on facebook and forums dedicated to sur-ron or ebikes in general. This means a lot to me and every SurRonshop customer is crucially important. We are doing our best to maintain a 24 by 7 individual tech support for each client who purchased our production. A couple of new Sur-Ron products will be released soon and I know many people are waiting for them so please follow my facebook. This project is not just a money-making source for me, I am excited to help electric bikes community develop with the rare and unique products like SinTech and Nucular controllers. I love to see when a person who was skeptical on a controller purchase since he is not very good with electronics gets it installed and setup himself with my support and enjoys the new riding experience.
serious_sam said:
Danlov said:
First, using simple physics formulas, it is clear that when you apply full throttle on such 10.000 rpm motor, a force level of 355 Newtons occurs inside which is equal to just 77 pounds. So, even the force at full throttle cannot break or tear metal of the motors’ stator. And we are not even sure if Travis could reach that full throttle rpm speed riding in the backyard.
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#1 Please explain the three apparent cutouts in the rotor in the attached image.
#2 Please show (in detail) your simple physics formulas, showing the 355N and where this force is
applied inside the motor.
1.
I'd also like to know why a larger rear sprocket somehow increases the forces on the motor/motor mounts. The motor has an output power/torque... that is the source of forces in the system... a larger / smaller sprocket has no effect on these forces
on the motor only on parts 'downstream' of the motor (ie chains and sprockets, and by extension, the rear wheel). Please explain how the mount deformed 'purely' because of larger rear sprockets.
2.
"First, using simple physics formulas,... "
paragraph directly contradicts
"...that a detached or an un-glued magnet could cause the crash."
If the centrifugal forces are small such as to not deform the motor at 10krpm, then the 'pushing out' forces are small... because they are the same forces. One being of benefit because its 'small' can not be also of benefit because its 'not small'.
case in point...
F=m*v^2/r, with v = ω * 2 * π * r
I CBF doing the maths myself right now but using an online calculator a 150mm radius rotor weighing just 1kg at 10krpm has a centrifugal force of 160 000N... not 300. Thats over 15 tones distributed around the face of your rotor. if your rotor is >150mm radius or >1kg in weight, then these forces are even larger. Take a shock load into account and you may well have enough deformation in the rotor to loosen a magnet or strike the stator. You also use different magnets around the rotor - if they are (say) 100g lighter, then at 10krpm you have a variance in force around your rotor of about 1600N/1.6T less force wherever you have one of these smaller magnets. IE 3, 4, 5 etc points where the forces are unevenly distributed and this likely to cause deformation, particularly at high rpms. Any deformation will also change the radius, causing more variance in the forces...
even at 3000 rpm, its a 150kg variance in force for 100g variance, or 1.5T/1500N of force. 300N is passed at just 430rpm, again, assuming your rotor is 1kg. Note - 3mm thick steel tube at 150mm radius and 100mm 'long' is about 1.8kg - so I suspect your rotor weighs more than 1kg...
Now I'm an electrical engineer not a mechanical engineer - so feel free to correct me if im wrong here but I dont think the physics are so complicated as to be significantly off in my calculations.
3.
" This is not the case since the bearings are located in a way that the load on the motor axle cannot bend or twist the rotor. "
It'd be good if you can post a photo of the bare stator and the inside of the rotor, as im not (entirely) convinced that it cant deform in this way - though i dont think it'll be as significant as centrifugal forces.
I've little doubt about your regret for this incident and the pain caused. But im also in doubt that you fully understand the forces within the motor and the probable cause of the incident, due to the inconsistencies mentioned above. I'm also unconvinced that the large holes in the sprocket side of the motor will not cause debris to be scooped into the stator/rotor interface and caused exactly what we've seen - a simple flyscreen for instance would prevent small stones from falling in while allowing airflow (as has been seen in some modified hub motors
). Perhaps something is 'lost in translation' though your English seems quite good - if you can answer the above 3 issues it'd be much appreciated.
magnets to n52 
