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[hama]

Not only a great tug-model, but he's planing to build the motors too! Never heard of it but seems very cool, there is a YouTube link to another solenoid motor build.
http://modeltugforum.com/index.php?topic=6187.msg75954;topicseen#msg75954
Hama

[Brian60]

I watched the film. I fail to see how you can build a crankshaft (and conrods and pistons) without the indexing capability of a lathe. You just cannot make the tolerances needed with handtools as he is saying - I am open to being proved wrong but the heat generated would also need a cooling system which there is no sign of either. I know its not internal combustion but the fact that parts are in moving contact with each other creates heat - lots of it.

[grendel]

because the solenoid and piston it drives does not need to be a tolerance fit, it can be made easily the solenoid just pulls the piston as far as it will travel, then the next solenoid takes over - the tricky bit is the timing. After that I watched a second video, where the crankshaft was bent up with a pair of pliers
you can see here how close a tolerance you dont need for one of these engines - https://www.youtube.com/watch?v=X3J4WkUxsSQ

[Plastic - RIP]

WOW - that is amazing! love that engine. 

Dead simple concept - no need to worry about timing - just need a trigger pulse for No1 and sequence from there. Could be driven with a simple bit of electronics for variable speed & torque. (variable clock for speed & variable voltage (more current) for torque.
Could use a 4017 decade counter driving into a DRV8860 8-channel power driver connected to the solenoids.
Just need a variable clock to make it go. 555 timer?

[dreadnought72]

My physics teacher made one of these about 35 years ago. Timing was by commutator on the crankshaft. Horribly inefficient way of doing things, and sparks-a-plenty, but good fun, and a great way to demonstrate electromagnetism.


Andy

[Geoff]

I've never heard of these before. Quite fascinating and with a bit of care it could look just like a steam engine! All you need to do then is build a boiler casing round the battery and away you go - no steam though!


I wonder how much power they develop and how much current they use but either way an interesting concept.


I enjoyed this one!


Cheers


Geoff

[malcolmfrary]

I wonder how much power they develop and how much current they use but either way an interesting concept.

Geoff

Not much power for the current involved, i would expect short run times and a big battery.
To self start, it would need at least three coils.  Distribution of current could be controlled by a sensor on the crank by an ESC that would supply a pulse of current to each coil in turn which could also determine the direction of rotation.  If that sounds a bit like a brushless motor without the advantages of simplicity, compactness and efficiency, it is.

[Plastic - RIP]

Not much power for the current involved, i would expect short run times and a big battery.
To self start, it would need at least three coils.  Distribution of current could be controlled by a sensor on the crank by an ESC that would supply a pulse of current to each coil in turn which could also determine the direction of rotation.  If that sounds a bit like a brushless motor without the advantages of simplicity, compactness and efficiency, it is.

I don't think you need a crank sensor or any need to worry about timing or feedback from the motor - just a sequenced output to each coil in turn - the motor would soon sync up - it has no choice.

By altering the pulse width or voltage you can control torque and by adjusting the clock you control speed.

[malcolmfrary]

Yes, thats how sensorless motors work, but if you expect any useful efficiency, a sensor will be needed plus at least 3 cylinders coils to ensure self starting without something extra giving it a kick.

[Plastic - RIP]

Yes, thats how sensorless motors work, but if you expect any useful efficiency, a sensor will be needed plus at least 3 cylinders coils to ensure self starting without something extra giving it a kick.

I don't understand why you would need any sensors - if you energise solenoid 1, 'piston' 1 will be at the top - it can't be anywhere else!

By sequencing the solenoids in the forward 'firing' order, it wil go forwards - reverse the order will reverse the motor. There is no need to care what the motor thinks it is doing, it has to follow the drive pulses. There is no cam shaft or sparkplugs to synchronise to the crank - the crank follows the 'pistons' order.

[dreadnought72]

To self start, it would need at least three coils.

I might be having a grey moment, but surely two is enough, 90° apart. If one's at TDC or BDC, the other can be driven on starting?


Andy

[Plastic - RIP]

I might be having a grey moment, but surely two is enough, 90° apart. If one's at TDC or BDC, the other can be driven on starting?


Andy

As it's a V8 and there is no exhaust cycle, each piston will fire once every revolution so it will have 45° between triggering pistons - quite a smooth and easily controlled rotation.

[malcolmfrary]

I might be having a grey moment, but surely two is enough, 90° apart. If one's at TDC or BDC, the other can be driven on starting?


Andy

It will always stop on the dead spot so that no matter what voltage is applied to it, the current has nowhere to go.  That's why two pole motors never found much use in the real world - they always need something to move them to a spot where current can flow.  Once moving, flywheel action moves them over to the next segment or switch contact.  It isn't going to act as a double acting steamer, the pull only happens on the up stroke, so that at 90° between coils, there is still 180° of dead space unless there is some really fancy commutation to reverse the current in the coils.  3 at 120° to ensure that one is ready to go, hopefully in the right direction.
A V-8 will should not have this problem.  Just the problem of getting tolerances fine enough that the magnetic field gaps are small enough to ensure enough efficiency for a reasonable size of battery to last long enough.