godzukihop

iTrader: (32)

I called Minipro today to inquire on the dyno and all that I can say is wow.
Jose, took his time and answered all of my questions and concerns.
He explained in depth the functions and options and as soon as I save up enough I will be buying a MiniPro Dyno.

cdub_OffRoad

iTrader: (1)

I've had great support from Jose thus far. I had a few more questions and some self inflicted issues and he was on it right away. Very impressed so far.

I'm having trouble with my punch control kicking in on the ESC What ESC's are folks using with the dyno and what are you using for either punch control or current limiting?

Randy_Pike

iTrader: (6)

I'm using the RS Gen2 on mine. If you turn off torque control, it's off.

cdub_OffRoad

iTrader: (1)

I'm currently using an old HobbyWing V2 60A ESC that I had in my parts box.

Which flywheel are you using? I'm assuming you are evaluating a range of motors, from 17.5T all the way to 4.5T?

I've got the steel flywheel. If I run with the punch control all the way off, I'm right at the edge of the 180A current measuring device. Frankly, I'm afraid I will burn something up. If I turn the punch control on, I get this awkward discontinuity in the data, as the punch control kicks in mid run and dials back the power and then slams back on again.

I used to run RX8's in my 1/8th scale stuff, and I really liked the way current limiting worked on those (at least how they were used in a car application).

My thought process is to run with the heaviest flywheel in order to get the longest possible spool up times (and the highest number of good data points). The trouble then is that you must limit the power electronics in a graceful manner so that they don't burn themselves up. I'm looking at a range of motors, 17.5T down to around 6.5T.

robk

iTrader: (22)

BROAD TECH ONLINE SHOP

Warren Weaver

iTrader: (49)

That unit is for brushed motors only

PizzaDude

Cannot get the linkeproperly instered as a link sorry
this is the BL version

[URL="http://broadtechonlineshop.com/eagleshop/shop/ShopProductDetail.aspx?id=3800"]

robk

iTrader: (22)

Crap, you're right. That is where I got my BL unit from though.

cdub_OffRoad

iTrader: (1)

I think there is some theory that needs to be explained and documented with regards to the operation of this style of dyno. Depending on what your end goal is, I believe you will want to set your dyno up (specifically the flywheel, esc, power source, etc) in different manners. I don't have all of the answers, but I think I have a handle on the questions. Perhaps we could get some constructive dialog going?

the scenarios I can think of are -

1) I want an apples to apples comparison of different motors. Potentially data that is so apples to apples I could compare my quantitative results with someone else. I want to be able to determine if and when a given motor is getting "tired". I could test it as received and test it periodically to validate it is still performing as expected.

2) I want to understand what my complete powertrain from my racecar is capable of on the track. I want to understand the differences in performance between different batteries, escs, and motors. I want to know if my batteries are still up to snuff for racing.

My instinct is that scenario number 2 is pretty straightforward and is likely what most folks will do upon receipt of the machine. Rip the powertrain out of a car, hook it up, and give it a spin. Of course, the immediate problem is you have lots of unknowns and only the output of the motor to look at. I think this quickly drives folks to start thinking about scenario 1.

A first pass at dealing with number 1 would be to pick an ESC and some batteries and set them "aside" to be your dyno setup. Then, you could test all your motors and their variations with a consistent driver. There will be areas where this may lead you astray though. I was looking at battery options, and found some 8 Volt golf cart batteries that might be a nice compromise with regards to current capability and cost (versus a power supply). If you are typically running 2S Lipo, the 8V nominal Lead acid battery would give data at a representative voltage. It would be large enough in capacity to deliver the current required with no trouble and not suffer from voltage droop over a large number of runs. Just an idea.

I poked at the flywheel sizing/current limiting topic on here a bit. Personally, I'm not convinced that the error introduced through the process of data acquisition can be controlled enough to get meaningful data from a dyno run with a spool up of 1 second or 1.5 seconds. My instinct is that it would be best to run a very large flywheel, and then control the current electronically to some consistent limit in order to avoid damage to the motor or esc. This way, you could get potentially very long spool times and thus a large number of measured data points. Anyone aware of a commercially available ESC that has an explicit current limit setting?

robk

iTrader: (22)

Tekin has current limiting, but you would probably have to run it through an ammeter or datalogger to see what the settings were. Or maybe Tekin might tell you.

howardcano

iTrader: (37)

Given fine enough resolution of time measurement for each motor revolution, a flywheel large enough for the motor to spool up to 90% of free-running speed in just ten revolutions will give calculated power results repeatable to better than 0.06%. In other words, the power calculated at the ninth or eleventh revolution (since we don't necessarily know at what angle the motor starts at) is within 0.06% of the power calculated at the tenth revolution. I would call that meaningful, but your requirement may vary.

This does, however, require a very high resolution of time measurement between revolutions: a 1us change in the measured period corresponds to about 0.1% error in the power calculation. I believe the Minipro is several orders of magnitude shy of this resolution, so a larger flywheel is more appropriate.

cdub_OffRoad

iTrader: (1)

Interesting, I take it you have a spreadsheet or two on this topic?
Let's say the time measurement error is 100 uS, how much does this impact the measurement?

There is also external drag being applied to the motor. On this particular dyno, you have the belt drive system (and it's tension). On other dynos, you have the weight of the flywheel being directly applied to the poor little output shaft of the motor. There's also drag in the main bearings and churning losses in the air.

So, in reality, the flywheel sizing becomes a game of making it large enough that the power required to spool up greatly outweighs all of these other sources of noise by orders of magnitude.

howardcano

iTrader: (37)

Yes, I have made a spreadsheet. It's not terribly complicated to do for yourself, but I can send mine to you via email if you so desire. It is a simple matter to change the data by an arbitrary amount to see how the power calculation is affected.

While it would be nice to have all of the frictional and aerodynamic losses far below the power calculated without their inclusion, it is more practical to simply take data during the spool-down period, then subtract the spool-down power numbers from the spool-up power numbers. The equations work the same both ways. The losses for a directly-driven flywheel are only a few percent of the motor power, so that works pretty well.

To keep from cluttering up this thread, you can reply here:
http://www.rctech.net/forum/radio-el...no-thread.html

cplus

iTrader: (11)

Thread Dig

Interested to know what type of ESC everyone is using for their minipro dyno?

Currently setting one up. Have options!

HW V3.1
R1 digital 2
ORCA VX3
LRP Flow

Plus others!

MDawson

iTrader: (27)

I found it helpful to use the same hardware and software running in my cars - ORCA R32X.