Del Monte's Double Agent

[TSK]

Originally Posted by JohnRobHolmes

I would prefer they didn't stick at all, but we are already at 140% back iron thickness VS a regular motor. The better it works at being a fridge magnet, the worse it is at being a motor.


I'll post up specs on the pair tomorrow. In the mean time, ponder that the KV of these 35t motors are 20% higher than a 540, but the rotor length is 30% shorter. Its a net positive torque density increase, and net reduction in waste watts per unit of torque output. Peak torque at armature saturation goes down by 30%, but the batteries in use don't come close to outputting enough amperage to hit saturation nor could the gears take it anyway.

Ummm.... So in layman's terms, these should be good motors?

And why does a good fridge magnet make for a bad motor?

[Curcal]

Originally Posted by Del Monte

Got a ton of goodies from the postman today, among them was these little gems from Holmes Hobbies.



I remember seeing some other gravity defying, fridge related pictures before, so I had to try it

Its going to be a fast and furious week of building before we leave for AZ next week. The clock is running. Tick, tick, tick...

Colbalt mags?

[JohnRobHolmes]

Neo mags. Cobalt is best served in 150c+ applications that can take advantage of the higher heat resistance and hci. These motors will see 5 minute runs, a perfect candidate for high mgo neo.

Any magnetic force that leaves the motor is not used for motive force. Ceramic magnets can get away with thin cans, even fb12 is pretty weak next to a low grade cobalt or neo magnet. The grade in these 400s is 4x stronger than fb12, but less than half as thick. Still a net increase in airgap flux density (torque density) when back iron is thick enough to support it, as these have been designed.

The effects can be measured in speed changes (not including commutator and brush tweaks, but including timing). Torque per amp is relative to speed. If rpm per volt doubles, amperage doubles for a given torque output. So a 35t that is built into a 2000kv and a 1000kv version for example. For any given situation the 1000kv version will need half the amperage to produce said torque. Heat in the coil is the square of amperage (joule heating law), thus our 2000kv version makes 4x the heat inside the coil. Voltage drop in the fast motor is twice as much for a given torque output, another downside.

Flipping our example, we fix speed at 2000kv. Our fast motor is 35t and the slow build is 17.5 turn. Both use equal amperage. The 17.5 has half the voltage drop and 4x less coil heating if copper fill isn't changed.

Another aspect is peak torque and magnet demagnetizing. Without enough back iron a magnet can be easily demagged. Longer rotors get around this, as flux density is lower for a load and the point of magnet damage is beyond what an MOA can create.




In every aspect, producing a motor that is as slow as possible for a certain turn gains performance and efficiency. Thus, we want to keep that precious flux contained and usable. But it must have low losses and good startup too, while balancing weight and cost. If somebody wants to spend $350 per motor we can knock an ounce off with no detriment to power and torque, with more exotic materials. If somebody wants even higher torque we can add some back iron and adjust the magnets, at a weight penalty. I could halve the no load losses if peak torque could be sacrificed. It's all a balance of the application of install.


So the basic answer is that fridge magnets are wasting amperage as heat instead of making force. These 400s were over 50% faster with a 30 thou thin can and 3.5 ounce weight, practically unfit. We would have needed a 50t to be useful. Probably good enough for an average person, but not for me. I'll be working on getting these slower still

[JohnRobHolmes]

And these are already obsolete if anybody is wondering what is next. We have engineered and tested a 2 ounce motor with equal torque output and higher power output. It was a contract engineering job we will share later. Don't hold your breath, we have another project to finish before it will be useful.

[chevotafun]

So I guess Jake will be dropping another 4 or so oz's putting him around 2.5lbs mark LOL that's just nuts but I like it

[Calderwood]

Originally Posted by JohnRobHolmes

The better it works at being a fridge magnet, the worse it is at being a motor.

I mentioned this once before and was met with hostility. Glad to see I'm not the only one of this opinion.

[Del Monte]

Love the tech John!

We've talked about them for long enough, it will be nice to see what happens on the rocks. I can only imagine what crazy ideas you have for something even lighter...just let me know when theyre ready and I'll build a rig to work around them

[chevotafun]

Can't wait to here your review of these motor.

Just got my crawler 500's and dam there just so smooth and pack a good punch as well

[TSK]

Originally Posted by nigels_world

I mentioned this once before and was met with hostility. Glad to see I'm not the only one of this opinion.

Do you receall what thread this was in? I would like to read more into this fridge magnet debate. JRH has posted a lot of tech, but it's a bit too out of my scope of technical motor knowledge to understand.

[sally1800]

Originally Posted by chevotafun

Can't wait to here your review of these motor.

Just got my crawler 500's and dam there just so smooth and pack a good punch as well

There's number 3

[Calderwood]

Originally Posted by TheSCorpionKing

Do you receall what thread this was in? I would like to read more into this fridge magnet debate. JRH has posted a lot of tech, but it's a bit too out of my scope of technical motor knowledge to understand.

Magnet strength testing

[ROWDY RACING]

Originally Posted by nigels_world

I mentioned this once before and was met with hostility. Glad to see I'm not the only one of this opinion.

Originally Posted by nigels_world

Magnet strength testing

I hardley see any hostility in that thread.

[TSK]

Originally Posted by nigels_world

Magnet strength testing

Thanks

[Calderwood]

Originally Posted by ROWDY RACING

I hardley see any hostility in that thread.

Hence the:


Rowdy, you of all people should understand sarcasm.

[krawlfreak]

Originally Posted by Del Monte

Got a ton of goodies from the postman today, among them was these little gems from Holmes Hobbies.



I remember seeing some other gravity defying, fridge related pictures before, so I had to try it

Its going to be a fast and furious week of building before we leave for AZ next week. The clock is running. Tick, tick, tick...

the best part in this pic is holding the spoon to the motor

sneaky

[ROWDY RACING]

Originally Posted by nigels_world

Hence the:


Rowdy, you of all people should understand sarcasm.

Ah, ok.

Hmm what could those be between the motor and the spoon...

[Harvo]

Originally Posted by ROWDY RACING

Ah, ok.

Hmm what could those be between the motor and the spoon...

Oh...oh...oh...I know ....I know




















It's a wraith driveshaft.

[sally1800]

Originally Posted by chevotafun

So I guess Jake will be dropping another 4 or so oz's putting him around 2.5lbs mark LOL that's just nuts but I like it

So where are we at with weight?

[chevotafun]

Originally Posted by sally1800

There's number 3

Huh?

[sally1800]

Originally Posted by chevotafun

Huh?

wasn't meant to you.