Member postings for Roy Vaughn

No offence taken Dave. I've ordered the bits for an STP cable to replace my existing screened-but-non-twisted pair cable and we'll see how they compare. I can't provoke any interference at all today so I expect it will be inconclusive, but extra margin would be beneficial.

Thanks for the information SoD. As an ex-professional programmer (many years ago now) but latterly a user of microcontrollers for hobby purposes, I am familiar with Cat5/6 cabling but never in non-standard (non-balanced) usage you propose or using STP rather than UTP. The idea that solving a hardware problem in software is possible mad comes as a surprise, in the microcontroller world the software often (usually) has to work around and protect against "hardware" artifacts, that is, the real world. For example, contact debounce is simple in software and saves one or two components, which can be worthwhile if you are pushed for space or weight as my projects mostly are. I agree that curing interference at source is preferable and will definitely try your recommendation. However, seeing the lead screw take off in high gear is hard to forget and I will be keeping the software fix in place in case the hardware defence is ever breached.

The fix hardly deserves a mention on Github, it's simply a jump around the input reading statements in the Userinterface.ccp module if the spindle speed is greater than zero. Pm me if you want further info. As well as defending against interference, the fix also protects against finger trouble on those little keys. A refinement, if you really want to alter settings with the spindle in motion but still provide some protection against the worst consequences, would be to disallow change in more specific circumstances, e.g. to disallow switching between feed and thread, to inhibit the up/down buttons unless in feed mode, by making changes dependent on the rpm (I think there is some stuff on Github along these lines), etc.

Thanks all for your thoughts. Off to Ebay now to buy an Ethernet patch lead.

Roy

I have just got my implementation up and running on the lathe, all is operating as it should. During the build I found that screened cable was needed to stabilise the display even without obvious sources of interference nearby. As the control panel is not yet permanently mounted I can move it around to test its residual susceptibility to interference. I've found that when the cable is passed close to either the lathe's motor or the stepper, there is still occasional interference. It gave me a fright the first time it happened with the lathe turning and the feed engaged, when the system switched itself unbidden from a slow metric feed to coarse tpi. Obviously I will arrange the final installation to minimise the chance of interference but the fact that it could still occur with potentially unfortunate results convinced me that something needed to be done. I've therefore made a small modification to the code to disable keypad input when the spindle is turning. Has anyone else made any safety mods to the software?

Jimmeh

I have the same setup. I haven't tried those tests. Maybe the behaviour of the stepper controller could be changed so let the software take control by doing something over the data port. Probably in the all too difficult category.

Apologies for the junk in the end of my last email, I can't get rid of it now.

The odd missed step isn't crucial except when screwcutting, but it shouldn't happen, so the root cause (overspeed or overload) needs to be fixed by the operator. A lot of missed steps leading to a crash is another matter. If it's due to operator error that's exactly equivalent to the geared lead screw situation with the same consequences and solution. If it's due to electronics failure I imagine that the banjo will be back on the lathe in short order. The lead screw will track the spindle even after the emergency stop button has been hit, but what if there's a power cut? Put the ELS on a UPS? It all gets a bit complicated. So I agree the software best solution is to signal the alarm on the display and leave it at that.

Roy

Since it should never happen the only corrective action is to fix the source of the problem, e.g. overspeed or overload.

I envisage alarms arising from the odd missed step due to over-speed or overload, hard to notice otherwise and only important when screwcutting . If something major happens, e.g., the lead screw stops while the spindle carries on, leading to a crash, I imaging the whole lot being decommissioned and sold for parts on Ebay!

Thanks Martin, I'm familiar with the hardware requirement, it's what I have. My question concerns the software handing (or not) of an alarm signal. Roy

Nearing the finishing post now and starting to think about detailed functionality. It would be useful to see a visual indication of a stepper driver alarm on the control panel. James has included support for the input from the interface but I can't see any functionality attached to it in the code. Does anyone know any different?

Stay safe, Roy

Dias, connect +5V to the + terminals of each signal as shown in the wiring diagram. Yes, ignore GND from the interface board. Hope this helps. Roy

Hi Phil

Thanks for confirming the pinout, I see the markings on the board now but I wanted to be sure. Good news that it's all working on the bench. Now for the bigger job of engineering the installation. I wonder if anyone has finished their ELS yet and how they got on?

Cheers, Roy

Hi Phil

Can you confirm the order of the screw terminals on the PCB please? I imagine they are the same as Clough42's but I'd like to make sure, I've blown up too much kit this past year getting power connections wrong!

Cheers, Roy

Graham, fit of the first piston sounds fine so long as the liner is not too tapered and the contrapiston doesn't leak. Check the fuel and that you have the compression up high enough. I'm intrigued as to why you made a new piston when you could have simply lapped the original a bit.

Roy

Tug, thanks for the offer of drawings for Rob M's stunt motor but that would be far beyond my capabilities! So far I have managed an ML Midge and an Atom Minor. My plan is to build a standard Nalon Viper next and then an update on its design with more modern porting. I like to fly my motors so something like a C/L Weatherman should do as a testbed.

One new to me feature of the Viper is the broached transfer porting. My impression is that broaches are expensive and fragile. Is it worth a try or might I be better off just filing the ports out?

Looking forward to the tether car thread.

Roy

Ordered all the bits end-November and nothing took more than 10 days or so to get here.

Roy

John, you seem to be suggesting that the rear outer race should be free to move in the housing. This is exactly the condition that must be avoided at all costs with this type of motor. As Rob M says in his article, the hammering the rear bearing gets will eventually loosen the outer race if it not securely fitted, friction will build up and performance will be lost. High performance motors which use standard ball races often use a nut to secure the inner to the shaft. The philosophy nowadays is to clamp everything up so it can't move. The expense of shimming is the price to be paid.

Tug, thanks for the tip, plenty of C3s to choose from. As to the spelling of Metkemeijer, I recommend copy-and paste!

I believe that the current top motor in pylon racing is the MB, also a Rob Metkemeijer design, so it's bearing setup may illustrate the state of the art for front induction motors. I found some maintenance instructions online which give some clues:

http://bmpra.bmfa.org/mb-service-sheet-2

LINK

I'd be interested to know where high clearance bearings can be obtained in one or two off quantities.

Roy

Edited By JasonB on 22/12/2019 10:03:56

John, I can assure you that "those guys" certainly knew of high clearance races, one at least of which is needed for the rear race in an aluminium housing setup. I think in fact they allude to the difficulty of getting same in affordable quantities. Roy

The definitive source on high performance model engine design is the FMV Story. Although it is 40 years old the principles don't change. They include a detailed description of the main bearing design referencing most of the techniques discussed above.

Roy

http://bmpra.bmfa.org/wp-content/uploads/2016/12/FMV-Engine-history.pdf

Thanks for that insight Martin, not worth potentially spoiling the ship for a h'p'orth of tar.

Re the motor controller, is it always necessary to set it up from a PC or are they normally supplied pre-configured? I'm thinking particularly of the hybrid stepper kits from Stepperonline?

Roy

Thanks Phil for the TI steer and John for the installation info.

Tony, can you tell us a bit more about your stepper problems and how you resolved them? Are the torque specs not to be believed?

Roy

Michael, I'm not an expert either but clicking on the Ebay link in the encoder line item on the Clough42 web site takes me to something with what looks like an identical spec. Not worth ordering anything else and risking problems for the sake of a couple of weeks in my view. The big ticket item is the stepper motor and controller.

Zan, thanks for the link, looks like very comprehensive description of the mods. For reference in full (sorry I don't know how to make it clickable), it's:

http://www.jeffree.co.uk/pages/ml7-cnc/part-1-files/myfordcncpt1.htm

Roy