DPV research

[Jona Silverstein]

Noise takes energy, period. Conservation of energy is a thing.

How much is lost via noise, I have no idea, nor how to quantify it.

Perhaps @Jon Nellis or @Jona Silverstein have data on this?

Does noise equate to inefficiency?

Dive Xtras released a firmware update on the Blacktip which massively quietened it down. Something to so with a sinusoidal waveform to the motor.

TLDR; Squares are super inefficient when dealing with sine waves.


So a few things on this. When DX updated from V1.15 to V1.18 all they changed was driving the motor from BLDC to Sensorless FOC. What that does is takes input from the motor to depict "Where" in the rotational cycle it is to more effectively send power to it. and the difference between Sensored (ie Smart-dpv, seacraft etc) and sensorless is how the ESC receives that data.

For sensored, its easy either via a magnetic encoder, a physical encoder, or hall sensors, the esc knows where the motor is relative to the motor poles, the magnetic encoders we use measure to within 0.01 Deg.

For Sensorless, it drives based off the eddy currents that are generated by the motor spinning. Think spin motor, lightbulb lights up. this back flow of voltage is called BEMF (back electromotive force) and the esc can measure that to determine (kinda) where the motor is located but it still has the issues of BLDC being no low speed torque and slightly less efficient. for Sensorless, the motor is started in openloop (BLDC) then once it generates BEMF and is stable (typically over a certain duty or ERPM) it switches over to closed loop and runs FOC

not having a hard sensor is what causes the problems that many have faced with the BT being jittery and awkward startups vs smooth and elegant spool up and instant torque at any rpm.


As for the efficiency, there isnt much difference between sensorless and sensored, only a few % but the difference between those and BLDC is pretty significant.
"In summary, high-side MOSFET power losses for sensorless FOC are about 10 percent lower than block commutation, but considerable lower – almost a 70 percent reduction – for low-side MOSFETs. Under the described conditions, total power losses on the power MOSFETs when utilizing sensorless FOC (about 5.2 W) are about 33 percent lower than block commutation losses (about 7.9 W), and the three-phase power inverter efficiency of sensorless FOC is therefore higher than BLDC block commutation."

https://www.infineon.com/dgdl/Infineon-Motor_power_tool_Block_Commutation_vs_FOC-ApplicationNotes-v01_00-EN.pdf?fileId=5546d4626eab8fbf016ed37fee474a65

 

[stuartv]

I thought using Power Tool Batteries was a great idea ... until I had my BlackTip for a while.

Now, I think they have these problems:

If the scooter uses more than 1 (as all BlackTips do), then they can easily get out of balance with each other and you end up having your scooter shut off at very inopportune times. I've had this happen with mine numerous times and my batteries are DeWalt 12 Ah that were bought new, together. They have only ever been used in my scooter and only charged on my DeWalt 4-bay charger. So, they have identical usage and charging history. There is no reason they should ever be out of balance, but I've had it shut down on me several times when I was working the scooter hard (e.g. speed 6 or 7 against the current in the Saint Lawrence River). Maybe I just got a "bad" PTB, but if that's it, then how can you ever trust them? I mean, mine seem to work fine when I just putt around at speed 3 or 4. But, when it's Go Time, sometimes they do okay, and SOME times, they have caused my scooter to just shut off while displaying an indicator of one or the other battery having an issue. I let it stay off for a short time and then it will start up and go again for another stint.

You have to open the hull every time you want to charge the batteries. That kinda sucks. Especially if you are trying to use smaller battery packs and swap between dives. It's not AS bad when the batteries last all day and you only have to open the hull at the end of the day to charge them overnight. Opening the hull is an opportunity to get drops of water inside, which can cause problems (especially if it's salt water), and also it's an opportunity to mess up an O-ring and have a flood.

They are not as space-efficient as custom battery packs. That is why the biggest PTB setup you can put in a BlackTip Tech is 12 Ah, but you can get a custom battery pack for the same scooter from @Jona Silverstein that is 20 Ah in the same space.

So, after owning a DPV that uses PTBs, my ideal setup would be what the Logic Genesis 2.x and 3.x have. Their battery pack is proprietary, but it uses individual 18650 batteries that the user can replace themselves. And there is a smartphone app that lets you check the battery status and identify if you have one bad cell that you need to replace. At least, that is my understanding. And they are TSA-compliant, so you can fly with them. Right now, my wallet says I can only aspire to own a Genesis.

When the battery setup is enough to last me all day, then using power tool batteries does not offer ME any advantage. I can charge overnight, in which case it doesn't matter whether I'm charging PTBs or something proprietary. It would only be an advantage if the battery did not last all day and I wanted to swap between dives to instantly get back to a full charge.

I have yet to burn all the way through my one set of 12 Ah batteries in a day, so I'm not getting any advantage from having PTBs. In fact, they are a disadvantage because, as I said, I have to open the hull to charge them overnight. That means I'm much more likely to have a flood at some point than I would be if I had a proprietary battery pack in a scooter that supported through-hull charging (like the Genesis and the Seacraft Future, and, I'm sure, others). Opening the hull every night versus never opening the hull at all, unless I need to change weighting from salt water to fresh water (or vice versa).

Going back to the space efficiency issue again for a moment. Because of the form factor, the most I can put in my BlackTip (using PTBs) is 2 x 12 Ah. That gives me (18V x 12Ah x 2=) 432 W-Hr of capacity. A Genesis 2.1 is roughly the same size and weight as a BlackTip Travel (okay, between a Travel and Tech, I think), and it is 850 W-Hr of capacity. Basically, double the capacity, so double the range/runtime. Since I have yet to burn through my 432 W-Hr in one day, I think having 850 would be MORE than enough for me for the foreseeable future. MORE then enough. I probably would not even need to charge a Genesis at all during a weekend of diving. I don't dive caves (yet).

So, what would I want in a new scooter. Well, basically, exactly what a Genesis 3.1 is, with a few enhancements:

A throttle that can be easily controlled with either hand without needing to be "reversed". But, I'll take the current Genesis throttle setup over any other one I've actually seen (note that my experience here is not very broad).

A built-in display that shows all the info the Logic Sentry shows, plus having a leak detector integrated into it.

Built-in cruise control. One that is VERY easy to disengage. Easier to disengage than how I understand the current Genesis throttle lock to work. Maybe even automatically disengage if the tow cord goes slack at all or the prop gets fouled?

Some kind of integrated mount options, so a camera or light mount doesn't have to rely on a cam band to hold it in place. Or maybe that's easy enough to accomplish with hose clamps and not necessary to be integrated into the hull/nose....

Totally silent. I had my BlackTip before the "quiet" firmware. The "quiet" firmware made it SO much nicer!

User-updateable, open source firmware. That is a GREAT feature of the BlackTip.

And then, of course, if it were even smaller and lighter, with the same battery capacity and max thrust, that would make it even more awesome.

 

[Wibble]

There's a couple of benefits of the Blacktip. Principally it's cheap, less than half the price of its cousins. With cheap comes some disadvantages which one has to live with. The benefit is I've got one; I would never have bought a full-price scooter. A scooter in the hand is worth two in the shop.

The power tool batteries are, IMHO, an excellent idea. It means that for me as an occasional scooter user I can use the batteries for other things or just replace them and even sell them on.

In general the DPV manufacturers aren't in the market of making and selling batteries. Hence they're expensive -- have seen replacements for various scooters priced at $1k or more. PTBs are a fraction of that price, my 9AH DeWalt batteries were $300 for the pair. I've never managed to consume a fraction of their power in one dive, although to be fair I'm a light user, only using it for wreck diving or hooning around some picturesque dive site, definitely not in high-current river settings!


Is there a reason for the system to shut down when batteries are "unbalanced"? If one battery gets depleted before the other, won't that bring down the voltage which, I guess, would mean the motor shuts down to "protect the batteries". It seems that only the v.expensive full-sized scooters have that "sod the batteries, run that motor now so I can get the heck out of this cave" mode. One of the consequences of a cheap unit.

Is there a software setting to reduce its sensitivity? Or maybe one of your batteries has a duff cell which is just dying. Wonder if there's a DeWalt battery checker that has load resistors for timing?

 

[broncobowsher]

I remember seeing a setting for cell balance check.
One of the issues of running cells too far out of balance is you could actually push a cell into negative voltage. If you damage it to the point it turns into an open circuit, you have nothing.

I'm with the Black tip users. While it is not a big boy scooter, it is very capable. It has put a lot of good scooters into the hands of people who otherwise would never have dropped that much coin. While the overall performance isn't as good as the big ones, it is more than enough for all but the most hard core needs. I don't know of anything else that offers that much performance per dollar spent in the DPV market. And it is all the performance most people will ever need as well.

 

[Whitrzac]

I thought using Power Tool Batteries was a great idea ... until I had my BlackTip for a while.

Now, I think they have these problems:

If the scooter uses more than 1 (as all BlackTips do), then they can easily get out of balance with each other and you end up having your scooter shut off at very inopportune times. I've had this happen with mine numerous times and my batteries are DeWalt 12 Ah that were bought new, together. They have only ever been used in my scooter and only charged on my DeWalt 4-bay charger. So, they have identical usage and charging history. There is no reason they should ever be out of balance, but I've had it shut down on me several times when I was working the scooter hard (e.g. speed 6 or 7 against the current in the Saint Lawrence River). Maybe I just got a "bad" PTB, but if that's it, then how can you ever trust them? I mean, mine seem to work fine when I just putt around at speed 3 or 4. But, when it's Go Time, sometimes they do okay, and SOME times, they have caused my scooter to just shut off while displaying an indicator of one or the other battery having an issue. I let it stay off for a short time and then it will start up and go again for another stint.

You have to open the hull every time you want to charge the batteries. That kinda sucks. Especially if you are trying to use smaller battery packs and swap between dives. It's not AS bad when the batteries last all day and you only have to open the hull at the end of the day to charge them overnight. Opening the hull is an opportunity to get drops of water inside, which can cause problems (especially if it's salt water), and also it's an opportunity to mess up an O-ring and have a flood.

They are not as space-efficient as custom battery packs. That is why the biggest PTB setup you can put in a BlackTip Tech is 12 Ah, but you can get a custom battery pack for the same scooter from @Jona Silverstein that is 20 Ah in the same space.

So, after owning a DPV that uses PTBs, my ideal setup would be what the Logic Genesis 2.x and 3.x have. Their battery pack is proprietary, but it uses individual 18650 batteries that the user can replace themselves. And there is a smartphone app that lets you check the battery status and identify if you have one bad cell that you need to replace. At least, that is my understanding. And they are TSA-compliant, so you can fly with them. Right now, my wallet says I can only aspire to own a Genesis.

When the battery setup is enough to last me all day, then using power tool batteries does not offer ME any advantage. I can charge overnight, in which case it doesn't matter whether I'm charging PTBs or something proprietary. It would only be an advantage if the battery did not last all day and I wanted to swap between dives to instantly get back to a full charge.

I have yet to burn all the way through my one set of 12 Ah batteries in a day, so I'm not getting any advantage from having PTBs. In fact, they are a disadvantage because, as I said, I have to open the hull to charge them overnight. That means I'm much more likely to have a flood at some point than I would be if I had a proprietary battery pack in a scooter that supported through-hull charging (like the Genesis and the Seacraft Future, and, I'm sure, others). Opening the hull every night versus never opening the hull at all, unless I need to change weighting from salt water to fresh water (or vice versa).

Going back to the space efficiency issue again for a moment. Because of the form factor, the most I can put in my BlackTip (using PTBs) is 2 x 12 Ah. That gives me (18V x 12Ah x 2=) 432 W-Hr of capacity. A Genesis 2.1 is roughly the same size and weight as a BlackTip Travel (okay, between a Travel and Tech, I think), and it is 850 W-Hr of capacity. Basically, double the capacity, so double the range/runtime. Since I have yet to burn through my 432 W-Hr in one day, I think having 850 would be MORE than enough for me for the foreseeable future. MORE then enough. I probably would not even need to charge a Genesis at all during a weekend of diving. I don't dive caves (yet).

So, what would I want in a new scooter. Well, basically, exactly what a Genesis 3.1 is, with a few enhancements:

A throttle that can be easily controlled with either hand without needing to be "reversed". But, I'll take the current Genesis throttle setup over any other one I've actually seen (note that my experience here is not very broad).

A built-in display that shows all the info the Logic Sentry shows, plus having a leak detector integrated into it.

Built-in cruise control. One that is VERY easy to disengage. Easier to disengage than how I understand the current Genesis throttle lock to work. Maybe even automatically disengage if the tow cord goes slack at all or the prop gets fouled?

Some kind of integrated mount options, so a camera or light mount doesn't have to rely on a cam band to hold it in place. Or maybe that's easy enough to accomplish with hose clamps and not necessary to be integrated into the hull/nose....

Totally silent. I had my BlackTip before the "quiet" firmware. The "quiet" firmware made it SO much nicer!

User-updateable, open source firmware. That is a GREAT feature of the BlackTip.

And then, of course, if it were even smaller and lighter, with the same battery capacity and max thrust, that would make it even more awesome.

You're comparing a $2k scooter with $7k+ ones. If you want the features of a $7k scooter, you're not going to be happy with the BT.

The BT can not sustain any speed above 5 indefinitely in stock configuration. If you cruise around for 30min of 5 and try to go 6+ it will cut out and slow down after a few min. Its not a battery limitation, but a motor/esc one. The esc/motor gets hot and they power limit the DPV.

 

[Whitrzac]

If you leave the batteries in the scooter, it will discharge the one farther in the tube even if the outside one is disconected. The blue/balanace wire is always drawing power.

 

[Wibble]

If you leave the batteries in the scooter, it will discharge the one farther in the tube even if the outside one is disconected. The blue/balanace wire is always drawing power.

Interesting.

Wonder if it's worth marking them up and ensuring that they're switched round each time so that one battery doesn't take the battering.

 

[broncobowsher]

Interesting.

Wonder if it's worth marking them up and ensuring that they're switched round each time so that one battery doesn't take the battering.

Just take them out of the tube. It is only a draw when they are plugged into the tube.

 

[stuartv]

Is there a reason for the system to shut down when batteries are "unbalanced"? If one battery gets depleted before the other, won't that bring down the voltage which, I guess, would mean the motor shuts down to "protect the batteries". It seems that only the v.expensive full-sized scooters have that "sod the batteries, run that motor now so I can get the heck out of this cave" mode. One of the consequences of a cheap unit.

Is there a software setting to reduce its sensitivity? Or maybe one of your batteries has a duff cell which is just dying. Wonder if there's a DeWalt battery checker that has load resistors for timing?

I ASSUME (and we both know what that can do) that it shuts off for unbalanced batteries for SOME reason, or they wouldn't have put that feature in.

Yes, there is a firmware setting that can be changed to tell it to ignore battery balance. But, I have not used that because I assume there is a reason it works the way it does out of the box, but I don't know what it is. So, turning that feature off means (in my mind, anyway) that I am risking damaging the scooter, the batteries, or both. Not REALLY knowing why it works that way in the first place has made me unwilling to turn the feature off.

I remember seeing a setting for cell balance check.
One of the issues of running cells too far out of balance is you could actually push a cell into negative voltage. If you damage it to the point it turns into an open circuit, you have nothing.

I'm with the Black tip users. While it is not a big boy scooter, it is very capable. It has put a lot of good scooters into the hands of people who otherwise would never have dropped that much coin. While the overall performance isn't as good as the big ones, it is more than enough for all but the most hard core needs. I don't know of anything else that offers that much performance per dollar spent in the DPV market. And it is all the performance most people will ever need as well.

100% agree.

I have very limited knowledge of electrical and electronics. My total GUESS is that it uses the 2 batteries to drive Push and Pull sides of something in the motor. So, if the Push got to be too much bigger than the Pull, it could damage something in the motor. Just a guess. Probably totally wrong, now that I contemplate the fact there is only one pair of power wires (plus the one blue wire) going to the motor.

Regardless, I am also guessing that there is SOME way to enhance the electronics so that it could work just fine with any batteries - maybe even totally different voltages. But, presumably, that would make the scooter more expensive (and probably less energy efficient, as well), so it's understandable that they didn't do that.

You're comparing a $2k scooter with $7k+ ones. If you want the features of a $7k scooter, you're not going to be happy with the BT.

The BT can not sustain any speed above 5 indefinitely in stock configuration. If you cruise around for 30min of 5 and try to go 6+ it will cut out and slow down after a few min. Its not a battery limitation, but a motor/esc one. The esc/motor gets hot and they power limit the DPV.

I was comparing all the scooters. The OP asked about the DPV market in general - not one specific price point. My post talked specifically about the issues I have experienced with using PTBs. Then it went on to try and address the OP's question in a comprehensive way.

Your implication that I am not happy with the BT is an incorrect conclusion. I am very happy with my BT. I would NOT be if I had paid $7K for it. But, for the less than $2K, all in, that I have in it, I am very happy with it. That doesn't mean I can't recognize and call out what I would LIKE to have in a scooter, that the BlackTip does not bring to the table. Just because I WANT filet mignon does not mean I am not happy to eat a Quarter Pounder. I try not to let my unfulfilled "wants" ruin my happiness with what I have.

 

[TooCold]

I have a gear driven piranha, it's loud as phawk. My buddies say that they love it cause they know when I am

I'm curious: in the context of the OP's question, is noisiness really a desirable feature you look for in a DPV?