hanulec

iTrader: (28)

last year we were using the v3, but i just picked up a v4. once it stops raining on the east coast every weekend (argh!) i'll hopefully get to try this model out...

John Stranahan

iTrader: (27)

Be sure and go here where we reawakened this thread.

http://www.rctech.net/forum/8993633-post232.html

James35

iTrader: (1)

Thanks John. You are the man!

FYI: For those doing single cell testing, I've been thrilled with the Mean Well 5V 120A (HRP-600-5)_power supply (120A continuous, 162A peak). It cost me $180. I was able to adjust the voltage down to 4.220V.

I recently discovered the SE-600-5 model for only $115 or so. (Currently, there's 10 available on ebay for only $67!) Not sure why the 2 models are so different in price. Mean Well also offers 7.5V versions which can be adjusted to 8.440V. I'm sure there are other brands out there to, but Mean Well was the best I've found yet for the price.

John Stranahan

iTrader: (27)

James -Thanks

McPappy Dyno
Note the McPappy dyno is actually a production unit and can be purchased now.
http://www.mcpappyracing.com/dyno.php

John Stranahan

iTrader: (27)

McPappy Dyno Progress

I tried ordering the Eagle Tree v4 but it is backordered until May.

I plan to order an LRP 21.5 so there will be some delay.

I plan to order that Mean Well power supply reccomended by James above so we are on an even Playing field.

I was asked by e-mail what is a good voltage. Fantom used to use 5.0 volts. The Competition Electronics used a user selectable voltage. I used the latter tool to show that power increased in a straight line with Voltage. This means testing at lower voltages should be helpful even when the motor is used at higher voltage. These days 1 cell is common. 5 Volts from a power supply seems like a good compromise. 4.2 Volts is fine as well. You will probably need a voltage booster to run an older speed control.

If you have a link for a spur gear adaptor used to run spur gears on the motor, Please supply a link, maybe I will do a gear test later on.

Resistance
It looks like youc can wire your resistors a couple of ways and at the same time use all three poles. The method pictured in a previous post and in photo two here gives a .002 Ohm path for the current from a pole using .001 ohm resisistors. This is only approximate as there are alternate paths to bleed off current. I can also think of a way to get a .001 ohm path where the left end of the resistors are not shunted together but instead run to the adjacent tab on the motor. I will try both and try to get the motor into a decent running RPM near race condition.

Build
The build went well. zip ties hold the fans satisfactorily secure. Notice in comparing picture one and two that we lose some rubber tubing contact if we screw on the motors. I think there is enough metal in the little motor supports to use a bigger radius in the shaft clearance cutout, and gain back the extra contact. It was a very good idea to use the bushings to increase the inner diameter and thickness of the tubing and thus getting rid of the need for zip ties here. Now I want the extra contact length when screwing on the motor. I will probably mill mine, a running correction could be made at McPappy for future lots. Nice quality.

John

joeqsmith

John,

I saw your ad on the UK site and was curious about a few things. It's a very good idea IMO, to give the customer some way to easily put something together to try. Yours is well thought out with being able to do so many combos.

Why use the weights at all? You have the absorber. If the absorber can handle the entire load of the motor, why not just control the absorber rather than use the fixed resistors?

If you did not care about the motoring aspect when slowing down, seems like you could easily model it with out too much electronics. This would allow the user to change the simulated weight electronically.

Or do you feel the weight doing something else for you?

This is my attempt at making a similar dyno. There is a link to a video at the end. Nothing real fancy yet. Because it is fully computer controlled, it can do some pretty nice things (model tire shake for instance).

I guess I am not allowed to post the link.... So
www
msuk-forum
co
uk
/topic
/81512-self-built-rc-dyno
/page__st__135

Bob~H

iTrader: (13)

James, I called Mean Well asking the difference in the two power supplies. The HRP you have is medical grade, minuscule voltage variation and higher efficiency than the SE. The SE although in the 600 series is 100 amps, not 120. I asked if the SE 600 would possibly peak at 120 amps and was told no, that it will work at a continuous 100 amps but that is also the peak amperage. I have one on order from eBay that should be here Monday so I can see how well it works.

Bob

John Stranahan

iTrader: (27)

Thanks for the post guys-
JoeqSmith- Firstly the dyno kit is a McPappy Kit. I am only associated with the software. I am satisfied with simple spin up of the flywheel, as very accurate power numbers and the entire power curve can be generated along with efficiency and torque.

Personally I would not use the flywheel and the absorber together, but the the dyno kit has this capability. I have not pictured it.

Here is my plan at this time. I have ordered the power supply. I have the 21.5 in hand now.

I plan to run 4 motors (decreasing winds) using the flywheel and generating the complete Power vs RPM curve. Then I can run the same four motors on the absorber. Each motor will achieve its own unique RPM on the absorber. I can use the power curves to find its power at this unique RPM. ( I can also determine if the absorber has a proper resistance.) This will give me four data points. I can then fit a mathematical model to the points generated. The result will be a formula that you can plug in your test motors unique RPM and the spreadsheet (or calculator) will calculate its power. This avoids trying to figure out efficiencies of the slave motors windings and the amount of inefficiency brought in through the alternate current paths that do not include the main pole and its corresponding resistor. I would not want to add a computer to the machine other than to process a spreadsheet. The advantage here over a flywheel test is the motor can be run for 3 minutes and then a RPM determined while hot. You could generate a RPM vs time chart to look at motor fade.

The ideal situation would be like the Competition Electronics dyno. A controller would vary the load until a certain amp is reached. A load sensor would measure torque at the slave at that amperage. Then all the motor properties,(power, torque, efficiency, RPM) could be calculated.
Joh

joeqsmith

Ok, I see where your heading with it. Seems prone to a lot of errors, but then again most people are just looking for repeatable numbers, not absolute. I assume you would recommend which motor people would purchse for the absorber so they don't have to remodel it? It would be very interesting to have some "standard" motors we could swap just to compare absolute numbers between the two types of dynos. With these motors not using any air, we could do a fair job comparing...

The other dyno you mention is similar to my homemade setup. My balance is rated for 100 grams which is about double what my little test motor can put out. Obviously the cost of a balance would put it out of reach for most DYS'ers, but it is accurate and traceable. I can vary the test motors input voltage as well as the load.

Was thinking that for these hobby motors that you could use a spring and LVDT to measure force. You could calibrate it and you could offer different springs for different motor power levels. The sensor could be made rather than purchased. I plan to make a sensor like this for my dyno to replace the balance. Seems like you could get under $500 for a dyno system that would give you direct torque numbers.

John Stranahan

iTrader: (27)

I do plan to reccomend the LRP 21.5 slave and the Meanwell Power supply. Errors in the Power estimate with this motor and the Meanwell power supply should be low. The spreadsheet can be setup at the bottom of the page to allow data from different slave motos to be entered. The formula will be self generating. For better accuracy a flywheel run could be used. Repeatability with the flywheel is within a couple of percent on three runs. Repeatability with the slave will be determined.

I have my power supply and slave in hand now. I will be able to do a run in a few days.

The theory behind using a flywheel and a slave is to have the motor undergo chassis rotational inertia drag and then follow up with a change to aero and friction drag.
john

joeqsmith

How do you handle the power factor correction? What do you do for the controller (how do you model the losses)? Is the plan to assume a PF of 1 and recommend a controller as well?

Currently I have only tested the brush motors I have. I use sense wires to compensate for the drop in the harness and have a bulk cap sitting next to the motor. The current and voltage are in phase with this setup, so no big deal to figure power in. Yours will be more complex.

Agree, a sweep with a flywheel is good for a small electric motor. Not so good for motor break in and simulating track conditions .

Very interesting project. Keep the updates coming.

John Stranahan

iTrader: (27)

I plan to reccomend the meanwell HRP-600-5 if you want the motor power to be close to the ones I publish. The power formula I generate, however, will predict power accurately for any power supply or battery given the same slave motor and resistor setup. The motor will obviously make more power if the supply voltage is higher, but it will then generate a higher RPM to plug in to the formula and a higher power will be calculated.

Power input to the motor will be measured before the speed control. Some losses in the speed control which are small will not be accounted for.

Efficiency of the motor can then be calculated.

The greatest use of the dyno will be to compare two or more motors that you have in hand. Accuracy is not so important here as precision or repeatability.
john

EddieO

iTrader: (6)

I would think that some how making it where you can vary the load at say 10,15,20, 25, 30, 35 amps would be beneficial. I've see a lot of these brushless motors look great at 15 or 20, but like crap at 25 and 30.......

I would imagine some type of switchable load system could be produced so it can changed over easily and quickly.

Later EddieO

joeqsmith

John, could you explain what you mean by the three terms, accuracy, precision and repeatability. Just want to make sure I understand.

I have never looked at one of these brushless controllers. I would not have thought that there was any sort of filtering and with the currents you talk about, I would have thought that you would have to do some sort of power factor correction. Is this not the case?

Sorry for all the questions.

EddieO

iTrader: (6)

I think what he is saying, he doesn't mind if its 200 rpm off actual RPM, or 1% off in efficiency, as long as its the same for all motors.....that way, he knows the baseline of what a good motor is on the dyno.

All the speed controllers have inherent losses........not anything crazy, but its still there.

Later EddieO