VESC-based board(s) for sale....

If you plan to make a group order, if you have spare VESCs or parts for sale etc. you can post that here.
rew
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Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

VESC-based board(s) for sale....

Postby rew » 25 Mar 2016, 14:14

I'm building a VESC-based ESC.

VESC is split into three separate modules. For each module there currently are two choices.

Modules:
CPU:
* STM32F405
* STM32F072 (not VESC software compatible)
* adapter module for TI launchpad (not VESC software compatible)

FET driver and current sense amplification
* DRV8302 based (discouraged now the other one works)
* LM5109 based

power mosfets
* IRFS7437 compatible.
* SO8 compatible (This includes NXP and other's variations in similar formfactor). PSMN1R2-30 for example fits.

Disadvantages above VESC:
* larger.
* Currently not guaranteed much above 30A motorcurrent.

Advantages above "real" VESC:
* easier to change components / modules.
* more points accessible for debugging.

The whole, or a derivative will, in the future, become available for normal purchase. In the meanwhile, I'm willing to sell a few prototypes to people who want to help beta-test the system. Knowledge of electronics, ESC and chibios-firmware is a bonus!

I get EUR 60,- as the cost-of-the-components. You pay EUR 60 + shipping. This includes a '405 CPU module, a LM5109 based driver-module and two power-fet modules.

Any takers?
Last edited by rew on 27 Mar 2016, 14:00, edited 1 time in total.

hexakopter
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Joined: 24 Dec 2015, 15:24
Location: Germany

Re: VESC-based board(s) for sale....

Postby hexakopter » 27 Mar 2016, 12:01

I think that is not enough info for someone to buy something where he don't know what he got exactly.
Can you maybe take pictures or upload the KiCad files so one knows what to get?

The LM5109 is a 100V driver. As you are saying in the VESC V5.0 thread that I am wrong with the supposition that it is not easy to replace the DRV8302 with something else to use higher voltages, it is correct that your design works up to 100V?
You solved the internal switching regulator of the DRV8302 with a new up to 100V switching regulator?
What shunt design are you using?
What do you mean with the point that it "become available for normal purchase in the future"?

I think there are a lot more questions, but these are the first ones came to my mind.
Because your design is build on the same principle like the VESC V5.0 (split it into parts) one can maybe learn something from your design to put it in the new V5.0 one.

rew
Posts: 937
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: VESC-based board(s) for sale....

Postby rew » 27 Mar 2016, 14:00

First: Feel free to ask questions here, or in PM or through Email (if you can find it :D ).
Yeah, I'm a bit stupid in that I don't always realize what people need to know. So please help me by asking the questions that come up.

No pictures available now or tomorrow. Hopefully Tuesday. I'm not ready to put the design up for download.

My personal target is to go "above 50V" (but below 60V: 12 or 13S). So for me the LM5109 is sufficient, it has some "headroom". I am currently running with 40V FETs so I'm not using any of the headroom that the LM5109 provides.

The DRV has a builtin regulator for the 12V. My board has a connector for this function. My current testing at 24V could solder a 7812 into that slot (the connector is pin-compatible with 78xx). In reality I have a 35V rated step-down board from Ebay. Writing here on the forums has made me realize that 35V limit.... If I hadn't been doing this, I probably would have blown it up when moving on to higher voltages....

I also have a 60V switching-step-down board of my own design (78xx pinout compatible! :-) ). It is rated for 0.5A IIRC. Should be enough to handle the 12V requirements of the FET drivers.

If you want to increase the working voltage beyond 60V you have to figure out a 12V power supply somehow.

My current power-board has 1mOhm shunt resistors. Three of them. The current DRV (fet drivers and current amp) board has three current amplifiers.

My current setup is geared towards being able to improve the modules one-by-one, so I don't have to spend money on components like the STM32F045 or DRV8302 when I just want to change something on the power-side. Or like now, I have an improved DRV module coming this way soon. I'll just reuse the existing CPU and POWER modules.

When I've settled on a working setup, I'll throw everything together and make a single PCB. That will then become available for "normal sale".

hexakopter
Posts: 86
Joined: 24 Dec 2015, 15:24
Location: Germany

Re: VESC-based board(s) for sale....

Postby hexakopter » 27 Mar 2016, 15:15

Thanks for the answer. That makes it clearer for me. I think the best is asking in the public form, because when PM or Email you the knowledge isn't accessible for others.

I am tensed to see the pictures. You are not ready means that you will upload it sometime? When I got it from an other post of you, you are not using KiCad right? I'm inclined to the view that you are using Altium because of your job. :D

When you don't want to go above 60V why using something else then the DRV8302 then? Just because of the handling of bigger total gate charges for "bigger" FETs and the voltage "headroom"?

The 35V limit in your case is exactly what I mean that the TI DRV with 60V isn't that easy to replace when also PCB space plays a role. I think the cheap switching step downs from china aren't the best in case of noise and 100V ones are also bigger and not good available.

Yes, a self build step down with a suitable voltage would be the best case for higher voltage when using an other FET driver, but the noise and HF part is maybe not to underestimate.

I can understand to split it into parts so one can improve it one by one. Maybe you will also remain then on two splitted parts (like V5.0) in the finished version and not going for a single PCB. ;)

Are you planning to port the VESC firmware to the STM32F072 or why have this possibility in your design?

Regards

rew
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Joined: 25 Mar 2016, 12:29
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Re: VESC-based board(s) for sale....

Postby rew » 27 Mar 2016, 18:06

RE PM/email vs posting here: Agreed. But if for some reason you prefer PM or Email I'm game too.

No not altium. Eagle.

Why not DRV8302? Well, I calculated the 12V current for VESC and found we were already close to or over the allowed current for the DRV8302. I asked TI what could be done about about this, suggesting an external 12V source to prevent the DRV getting hot from the linear regulator. They indicated that this was not an option, and that using fets as big as the ones on the VESC was not something the DRV was designed for. Eventually I need to go above 50A, bigger fets are not possible so I'll have to put them in parallel too! That is going to rule out the DRV completely.

As it stands VESC already uses the DRV outside the allowed safe-operating-area. Because Benjamin and I think the 30mA limit for the gate drives is due to the power dissipation of the linear regulator, we agree that it's probably OK if you don't go up to 60V but stay with 50.4V max.....

In my experience, if you try a big project without any intermediate steps, you will fail. "I'm going to build myself a castle, I'm going to live like a king". If you don't have any building experience that will fail. In electronics projects I have to be a bit careful, even though I have experience. When I take on something "too big" it always ends up getting stuck in a not-working state. So I'm slowly moving up the power-scale towards my target. At 12 or 24V I can run off my lab powersupply and prevent frying the mosfets. During those tests, the lab powersupply would click into currentlimit when reprogramming the STM. Turns out the fet drive signals float to "high" during programming. Oops. A pulldown solved that. Starting immediately with a 12S 5A LIPO would have cost me a whole bunch of FETs before I'd have figured out what was wrong. So building up slowly means a more reliable road to the full-power version later on. (And I know myself I get irritated when I blow a bunch of hardware and don't know why, and then the project gets scrapped).

So my current testing stands at 35V with the ebay DCDC converters. I don't share your concerns with "noise" on those regulators. The 12V is just meant to drive the gates. Anything between say 10V and 18V is fine. 12V +/- 1V ripple? Great!

The 5V is used... nowhere. Well, almost. In my design there is an MCP9700 on the power board that measures the temperature there. The critical stuff runs off the 3.3V regulator, which is a nice stable linear one. I'm planning to measure the current draw on the 12V line. To verify the calculations that we've done. Similarly, I want to know the current on the 5V line. I expect to replace the 5V DCDC converter with a 7805. The space for a DCDC converter is not worth the power savings.

If someone wants a 55V version tomorrow, I'd have to speed up those measurements and run a test with my own DCDC stepdown. As I'm currently using a "60V" stepdown chip, if it turns out a significant number of people are interested in >60V versions, then I'd have to think about that. I have several options:
* find a chip that works up to 100V. Possibly use a cheaper version for < 60V.
* Allow external stepdown for > 60V operation.
* a few more.

Re: split boards: Yes, I'm seriously considering splitting the power part in the final version. One of the advantages is that you end up with a large surface with the power-part, that is good for cooling. IRF has told me: Cool the back of the PCB, not the top of the FETs. (Benjamin are you listening?) Experimental verification required!

Re: 072... I have other boards that are able to use STM32FxxxR chips. My notes list 23 chips that I think are compatible, I've physically tried 6 of them. The list is outdated. e.g. I haven't looked at any STM32L devices for compatibility. The 072 is a nice "beginners model". It has USB, plenty of flash and RAM and is not as peripheral-starved as the earlier "value line" chips. (e.g. it has a DAC that previously was only available on more expensive chips).

My CPU board is '072 (and '405 and probably 21+ other) CPU-compatible. When bringing up the CPU board, there was something stupid. The USB connector was bad or something like that. So then we built another '405 board and that didn't work either. So then we built two of those boards with the '072. Those worked, showing that the board-layout was OK. But running VESC on them is going to be a challenge as they only have one ADC peripheral. And no FPU. And runs 2.5 times slower. However it CAN be done. ST's FOC library is able to do it.

Anyway, Benjamin's decision to simply go with the more powerful CPU means that you have the ease-of-programming not worrying about the flash filling up, etc. That's a good engineering decision. When you're going to make thousands that decision needs to be rethought (not necessarily revised!). The "expensive" '405 also has FP. In this application FP is not useful at all! Any variables can be scaled to work with integers. So instead of storing 23.4V as (float)23.4, you store 23400 mV. (or 1000x more in microvolts). There is never going to be a huge range of numbers required. And if the difference between 51.1 and 51.2 matters to you, so does the difference between 12.2 and 12.3. A fixed-point format works just fine. But it requires a bit of "effort" on the part of the programmer. And as our lead-programmer is doing it for the fun of it we must respect his decision to use floats and simplify the programming a bit. Totally worth it! :-)

hexakopter
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Location: Germany

Re: VESC-based board(s) for sale....

Postby hexakopter » 27 Mar 2016, 20:55

Thank you a lot for this extensive answer. I really appreciate it. Great knowledge you are sharing with us. I can learn a lot from these words.

rew wrote:Re: split boards: Yes, I'm seriously considering splitting the power part in the final version. One of the advantages is that you end up with a large surface with the power-part, that is good for cooling. IRF has told me: Cool the back of the PCB, not the top of the FETs. (Benjamin are you listening?) Experimental verification required!

I think cooling the back of the PCB is the best for any FET in a "plastic package on the top", when you know what I mean. The current D2Pak package (IRFS7530 etc.) or HSOF package (IPT007N06N) have their thermal isolating "plastic" between a mounted heat sink on top of the packages. When there are a lot of vias under the package footprint the thermal conduction between a PCB back mounted heat sink should be a lot better. When you are searching for heat sinks for the named packages you will also see that they normally are mounted on the PCB and not connected to the top of the package.
Put all six FETs on one site of the PCB is a big advantage to be able to cool the MOSFETs better.
I don't know if you already have read the idea to use IRF7749 in a directFET package, but when using these mounting the heat sink directly on top of the package is the way to go in my opinion.
(I should notice here, that all what I am saying here in the forum are just the thoughts of a young inexperienced student and that these thoughts are maybe wrong, but it is just possible to learn when one gets corrected and is asking.)

Also your words about the STMs are really interesting and helpful. Thanks a lot.

You will definitely got a PM about your beta-testing offer. :)

Regards

rew
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Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: VESC-based board(s) for sale....

Postby rew » 28 Mar 2016, 08:59

The IRF7749 shows as "no longer stocked" here at Farnell (EU). i.e. they think there are better products available.

I searched for "directfet" and got a load of results. When I selected >=60V, there was just one that wasn't "no longer stocked". I want to be able to get the components for a while to come... This sounds like a hit that these are not such a good idea.

Another thing that worries me is their current rating. The LFPAK FETs from NXP are about the same size but rated at 100A when the RDSON is like below 1.5mOhm. These have larger RDSON, and current ratings on the order of 10A.

Hmm. Doing parametric search on IRF.com lead me to "active and preferred" IRF7749 and second place IRF7748. Ah. Also, farnell have a datasheet-reading problem. IRF claims 200A for the '7749, farnell lists 33A. Ah. Found it. With a heatsink, case temp of 100C is already on the high side... 140A continuous current sounds promising.

hexakopter
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Joined: 24 Dec 2015, 15:24
Location: Germany

Re: VESC-based board(s) for sale....

Postby hexakopter » 28 Mar 2016, 10:58

I don't know if this FET topic is in the right place here, but because you are the TO i think it is no thread hijack. :)

I don't know why Farnell don't list the new IRF7749L1. They just list the old replaced IRF7749L2. That is the reason why it is "no longer stocked". It is outdated and replaced by new L1 version.
So as you found out on the IRF.com website the IRF7749L1 should be "active and preferred".

You should also not forget when comparing with the nxp FETs, to look at the voltage rating. I can't find a 60V LFPAK FET with RDSON lower than 1.5mOhm. As an example: When you looking for 40V FETs the IRL7472L1 with 0.59 mOhm looks like top-notch. It is also in a Direct-FET package. That means good cooling is possible directly on the FETs, and also on the back of the PCB. (They called it Dual Cooling)
They are looking not easy to solder, but as you are talking about "When you're going to make thousands that decision needs to be rethought (not necessarily revised!)" so I think the soldering should not be a problem for you. ;)

As you told that you are using eagle. How much layer are you using for each individual PCB?

Edit.: Maybe this paper http://irf.com/technical-info/whitepaper/directfet.pdf is interesting for you.

lizardmech
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Location: Australia

Re: VESC-based board(s) for sale....

Postby lizardmech » 28 Mar 2016, 15:37

I sent you a PM, in case you don't see it, I'm up for buying one.

rew
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Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: VESC-based board(s) for sale....

Postby rew » 28 Mar 2016, 20:04

hexakopter wrote:As you told that you are using eagle. How much layer are you using for each individual PCB?

Edit.: Maybe this paper http://irf.com/technical-info/whitepaper/directfet.pdf is interesting for you.

I will take a look at the whitepaper. I try to stick to two layers. PCB manufacture is easier and cheaper that way. My endresult may end up being a bit larger than Benjamins. If so: tough luck. :-)

40V is a whole lot easier to find fets for!

Thanks for the heads-up for the PM. I thought the forum would send me an email on PM, but I have to notice the "PM waiting" at the top.


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