Quark VS. MGM? - Page 2 - RC-Monster Forums

BrianG · 08.29.2007, 09:38 AM

Quote:

Originally Posted by Sower

You think? Even with my higher kv motor (2700)? I know the MGM can pull a 200 amp spike for 5 seconds, but I just get nervous with my past experience of a company saying they have certain specs and then not performing.

The motor kv is only part of the story as much of the current draw depends on gearing, weight, tire size, rolling resistance, etc. But, if you are currently pulling 200A @ 5s, then maybe a higher current setup is needed. I was just trying to save you a few bucks.

I understand your concern though. I usually try to over-engineer my setups so the ESC has a higher current rating than I think I will need. You may never need the amperage rating, but it's nice to be there just in case. Plus, higher current ESC means more FETs, means less overall ESC output resistance (total Rdson), means less heat for a given current. And we can't forget that these FETs have a temperature derating curve, so it's better to keep temps as low as possible.

As far as contacting Mike, I would email and wait for a response. I know it can take some time, but he gets a TON of emails a day and tries to get to them FIFO (first in, first out). Unless he has email notifications when he receives a PM, the only time he'll see those is if he logs in - and you've seen how many times he does that!

Sower · 08.29.2007, 10:04 AM

Thanks for the info Brian. I guess I don't really know how many amps I'm pulling and that's part of the problem. How can I tell? My setup is actually a 4s (instead of 5s) Flightpower 25C 5000, CRT pro truggy w/Crimefighters, Neu 1515 . . . and whatever ESC I decide. And my gearing is stock in the diffs, but the center is 10/51. Is there any way I (meaning you :) ) can guestimate the amp draw?

Oh, and by the way, I emailed Mike last night and he replied. He said he thought he had replied to one PM so I think there was just a problem with the PMs. But he said he has the MGM's on order. Not sure how long it takes them to arrive though.

GorillaMaxx360 · 08.28.2007, 10:37 PM

you can try emailing mike

Sower · 08.28.2007, 10:46 PM

I thought that was the same as a PM. Shouldn't he get both? Is there a preference for him to check one or the other? In the past he might take a couple days to get back to me, but never this long. It's not like I've never bought anything from him either. I thought I was a "good customer". I'm sure he's just really busy. But I sure would like to know when the MGM's will be in.

GorillaMaxx360 · 08.28.2007, 11:02 PM

yeah i am not sure but i think that the email he checks more frequently than the pms. BUt i could be wrong give it a try (the email).

jhautz · 08.28.2007, 11:13 PM

I think Mike is really insanely busy lately. Theres more work than he can do in a day and hes been killing himself trying to do it all. He really does bust his hump to get back to everyone, but lately rather than answering email in little batches I think he sits down and batch process them in one long session when he gets some time.

Last time I talked to him (a couple weeks ago) he told me he was working 60hrs a week just to keep up and then the rest of the time on all of the custom work and such. All I can say is I'm glad I'm not him.... but I'm sure glad he's there.

Sower · 08.28.2007, 11:23 PM

I hear ya. I'm not trying to come down on the guy by any means so I hope it doesn't sound that way. I think the he's awesome and I'm waiting as long as I can to give him business because I love this site and what he's doing. It would be nice if he had someone help him out a little though. I just sent him an email, so we'll see if that gets any reply.

BrianG · 08.29.2007, 10:24 AM

It is VERY tough to estimate current draw without a measuring device like an Eagletree. At best, you can determine the average current draw by your battery capacity and runtime, but it's VERY rough since BL cars are very peaky with current spikes. But, I can say that you aren't drawing 200A constantly since runtime would only be 1.5 minutes.

What seems to be pretty accurate is to figure out your average current draw by:
(battery_Ah X 60) / runtime_minutes
Then, multiply this value by about 6 to get the approximate peak current. It's not scientific, but from the various graphs I've seen, it seems to be pretty close.

4s, 4.3:1 F/R diffs, 1515/1.5d (2700kv), 5.1:1 CD gearing, 5.75" tires should give you a speed around 40mph. Is this what you are shooting for?

Sower · 08.29.2007, 10:53 AM

That's exactly what I've been shooting for, and that's about what it was doing when I was running it with my MM.

My run times were usually a little more than 1.5 minutes . . . more like 3 or 4 minutes. Just kidding. The pack is pretty new so I don't know for sure but I would say it was close to 15 to 20 minutes depending on the driving style.

BrianG · 08.29.2007, 11:11 AM

Assuming 15 minutes for runtime, that means your average current draw is ~20A, which seems a little high for that vehicle, but not too bad. I would've thought the average would be ~15-17A, but that's OK. Anyway, using the rough 6 multiplier, the peak current is 120A. Again, this is approximate, but is probably pretty darn close.

Sower · 08.29.2007, 11:19 AM

Well, that at least gives me some kind of idea though. That basically tells me that the MGM 160 should work just fine - even under racing conditions when my run time will be more like 10 minutes on a wet/high-traction track. Thanks a ton Brian.

I would really like to get an Eagletree though. That would be sweet. Are they very expensive or difficult to use? Is there just a little box that plugs into your reciever or what? I've never seen one.

BrianG · 08.29.2007, 11:42 AM

The Eagletree is a small device that plugs in between your batteries and the ESC. It samples current and voltage every 100ms (sample rate is adjustable). From that information, it can compute power and other things. You hook it to a PC and can generate graphs showing these values.

http://www.eagletreesystems.com/MicroPower/micro.htm

The unit itself is ~$70 and has other sensors you can add to measure rpm, temperature, etc. The manual can be found here.

It is rated for 100A, but can log up to 130A IIRC. Eagletree makes another recorder (in the "Pro Products" section) that has an optional hookup to measure up to 300A, but is more expensive. Just the 300A measurement add-on is $130, but not sure if is compatible with the e-logger unit. You might want to call/write them to see what your options are for your application.

Sower · 08.29.2007, 11:57 AM

Nice, thanks Brian. I'll look into that.

sleebus.jones · 08.29.2007, 01:59 PM

+1 for the eagletree. I've got one and it's been really revealing on how my systems perform. I went ahead and got the RPM sensor and the temp sensor too. All together, it gives you a really darn good picture of what's going on. The unit itself is $65, add'l sensors range from $10 for the temp to $14 for the rpm. I think it may even be possible to add a G meter to it too. :) Hottest spike I've recorded is 116A with my setup.

Sleeb

Sower · 08.29.2007, 02:30 PM

Quote:

Originally Posted by sleebus.jones

+1 for the eagletree. I've got one and it's been really revealing on how my systems perform. I went ahead and got the RPM sensor and the temp sensor too. All together, it gives you a really darn good picture of what's going on. The unit itself is $65, add'l sensors range from $10 for the temp to $14 for the rpm. I think it may even be possible to add a G meter to it too. :) Hottest spike I've recorded is 116A with my setup.

Sleeb

Nice . . . so what's your setup Sleeb?