Karen Nakamura: January 2009 Archives

I had gotten so used to thinking HarborFreight was the cheapest game in town, I was surprised when I dropped into my local welding supply store and found that welding wire was much cheaper there.

HF sells flux core MIG steel wire (E71T-GS) for $19.95 for a 2 lb. reel. My local welding store had it for $15 for the 2 pound reel. Just a side note, Lowes was $9.95 for a single pound reel.

Pays to shop around and not assume the discounters always have the best price, especially on consumables. And the local store has much more expertise than any of the big box shop drones.

One of my best purchases last year was a little MIG welder from HarborFreight. It was around $100 with coupons. It doesn't come with any accessories, so I bought an auto-darkening welding helmet for around $40, leather welding gloves, slag chipper, etc. also at HF.


The MIG welder is flux core only with no gas option. This means you get a lot of splatter and slag, but you can always grind those off. I'm happy with the increasing quality of my welds on iron and steel. I used it to make the rear carrier on my scooter EV -- and most recently, a firewood rack for 1/2 cord of firewood. The little MIG welder runs on 120 VAC which is very handy since I can just use the current power outlet in my back yard.

Unfortunately a flux core MIG welder means that I can't weld aluminium (which needs gas), which is a bummer since the weight/strength ratio of AL is ideal for EV use. I need to upgrade to a gas MIG welder -- or a TIG welder. I'm leaning towards the latter but I really need to ge a 240/220 volt outlet installed since it's not worth trying to buy a 120 VAC TIG. But getting a TIG welder would be great. I could even weld titanium if I wanted to. :-) Maybe Santa will get me a Lincoln TIG welder for Christmas....

I use steel from a local steel reseller, Logan Steel. They sell surplus steel bar and sheet for $1 a pound, which is quite reasonable. Their billboards are ubiquitous in southern CT.

The other useful tools I'm using are an offset grinder to prep my welding stock. Also, I converted my HarborFreight compound sliding miter saw to be a metal cutting saw by putting in a 10" metal cutting disk. Very useful, especially when I'm cutting a lot of stock. What I like about my miter saw conversion is that I retained the ability to do 45° cuts (or any arbitrary degree) as well as relatively long cross-cuts, which a lot of dedicated metal chopsaws can't do.

PU140-00900-2T.jpgI recently installed an Engine Block Heater (EBH) into my 2008 Prius -- just in time before this artic frigid weather struck New England. The part is a stock Prius Canada part that fits directly into American Prii without modification -- you don't even have to drain the antifreeze or remove an engine block plug like you do in other cars.

The part itself was US$59 from PriusChat Shop and the installation was around $45 (half an hour's labor) at my local dealer, A-1 Toyota of New Haven, CT. I could have done it myself, but I get nervous working underneath a car on jack stands.

Here are some online instructions:

About two hours of 120 VAC juice brings the engine up to around 30°C which I think is a good break-even point. The engine block heater consumes 400 watts so....... 2 hours = 0.8 kWh @ roughly 22 cents/kWh = 16 cents per "charge."

According to my ScanGauge II, even with $1.70 gasoline, I'm saving around 20 cents on each startup with a faster warm-up using less fossil fuels. As the price of gas goes up again, I'll save more -- and I plan on hooking the EBH up to my (future) garage solar panel system. What's more important to me is:

  • Less CO2 emissions for future generations
  • Less wear and tear on the engine, especially in terms of having to crank up at subzero temps
  • Warmer cabin as soon as I get in... brrr!

Today it's -10°C during the daytime in New Haven CT, brrr!

Screw the Brammo, me wantee an A5:

Li-Po batteries have the best power/weight performance of all of the mini battery sizes. If only they'd come down in price more, they'd have more utility. In any case, I'm using small Zippy brand 11.1 volt (3S) 2200 mAh battery packs. The only problem I found is that the balancing connectors on them aren't nearly long enough to reach from my Turnigy charger to my bomb-proof charging container (an old army-surplus ammo case). I tried to see if anyone sold 3S lipo battery connector extensions, but no luck.

Also, my Turnigy charger requires two connections for LiPo balancing -- the main Dean's connector and the balancing connector. This is a pain in the waddle since you can do it with only one connector -- as long as you remain within the relatively low amp constraits of the balancing connector (likely < 5 amp).

To make life difficult, there are apparently four (4) different LiPo balancing connectors in use. My Zippy batteries use the Align standard, which is a JST XH connector. Here's a very handy chart describing the various connectors and which batteries use which connector: http://www.rcaccessory.com/pdf/Battery%20Tap%20Configuration%20Guide.pdf

Now that I know that both my Turnigy charger and my Zippy batteries use JST XH, I just had to go to Digi-Key and order the right parts:

1	10	455-2249-ND	CONN HEADER XH TOP 4POS 2.5MM	JST XH SHROUDED HEADER	0	0.13500	$1.35
2	10	455-2267-ND	CONN HOUSING 2.5MM 4POS	JST XH HOUSING	0	0.05700	$0.57
3	100	455-2261-1-ND	CONN TERM CRIMP XH 26-30AWG	JST CRIMP CONNECTOR	0	0.03340	$3.34
4	10	455-2219-ND	CONN HOUSING 2.5MM XH 3POS	JST XH HOUSING 3 PIN	0	0.05700	$0.57
5	10	455-2248-ND	CONN HEADER XH TOP 3POS 2.5MM	JST XH HEADER 3 PIN	0	0.10000	$1.00

Once the connectors arrive, I'll have enough to play around with them for quite a while!

p.s. Bonus, the same connectors can also be used to create extensions for my LiPo battery monitors.

I was trying to decide which servo to use in my project. I had some JR NES-241s lying around from my JR radio kit. They are nice analog servos.

I also had some E-sky EK2-508 digital servos which I had also just ordered.

I wanted to see what the speed difference might be between the two. The JR is rated at 0.23 / 60° arc while the E-sky is rated at 0.10 / 60°. But there are ratings and there are ratings.

So I fired up my servo tester and pitted them head to head in this very short video (1 minute; 5 mb). As you can see, the E-sky is considerably faster.

The e-sky is only rated to 1.0 kg / cm torque while the JR has 1.3 kg/cm. But I think that difference is negligible.

Picture 2.png

I'm beginning a new project that uses micro servos. Here's a little table that I'm using to compare various options.

HTX900Analog21.0x12.0x22.0mm9.0g0.12 sec/60°1.6kg/cm0.11secNylon$4
Towerpro SG90Analog21.0x11.5x27.0mm9.0g0.12 sec/60°1.2kg/cmYesNylon$5
E-sky EK2-0508Digital22.8x11.5x20.8mm7.5g0.10 sec/60°1.0kg/cmYesNylon$10
Towerpro MG90Analog23.0x12.2x29.0mm14.0g0.11 sec/60°2.2kg/cm0.10 secMetal$12
E-flite S75Analog23.0x12.0x24.0mm7.5g0.12 sec/60°1.17kg/cmNoNylon$14
Spektrum DSP75Analog23.0x12.0x24.0mm7.5g0.11 sec/60°1.17kg/cmNoNylon$20
Futaba S3114Analog21.8x11.0x19.8mm7.8g0.10 sec/60°1.5kg/cm0.09secNylon$15
Power HD-2216HBDigital22.8x12.0x25.4mm13.6g0.13sec/60°1.8kg/cmYesMetal$20
Align DS410Digital22.8x12.0x25.4mm12.7g0.13 sec/60°1.8kg/cm0.09secMetal/Plastic$26
JR NES-241Analog21.5x11.5x22.0mm9.0g0.23 sec/60°1.3kg/cmYesPlastic$30
JR DS290GDigital21.0x11.0x21.0mm7.0g0.08 sec/60°0.9kg/cm0.07 secNylon$35
Futaba S3154Digital21.8x11.0x19.8mm7.8g0.10 sec/60°1.5kg/cm0.09secNylon$35
Ino-Lab HG-D202MGDigital23.0x11.4x24.1mm9.8g0.16 sec/60°2.5kg/cm0.13 secMetal$35
Align DS410MDigital22.8x12.0x25.4mm13.5g0.13 sec/60°1.8kg/cm0.09secMetal$37
HiTec HS-65MGAnalog24.0x12.0x24.0mm11.2g0.16 sec/60°1.6kg/cm0.13secMetal$37
HiTec HS-5065MGDigital23.6x11.6x24.0mm11.9g0.14 sec/60°1.8kg/cm0.11secMetal$47

The conversion for torque from kg/cm to oz/in is to multiply by 14.7. So a servo with a torque of 1.0 kg/cm has an imperial torque of 14.7 oz/in.


Futaba S9257Digital36.0x15.0x29.0mm26g0.08 sec/60°2.0kg/cmNoNylon$60

I just had a nice conversation with one of the staff at BatterySpec.com, which is where I bought my Tempest TR22-12 sealed-lead acid (SLA) battery. I had inquired about a warranty exchange. They denied it but they gave me a really good reason why -- which is why I'm giving them two thumbs up.

The reason my TR22-12 died on my Piaggio is because I had it in a 2 serial 2 parallel configuration with slightly lower capacity Rhino batteries. I had them configured as a bank of Rhinos and a bank of Tempests. The internal resistance of the Tempests is lower than the Rhinos, so the Tempests were discharging faster and this is why one of them failed.

If anything, I should have done a mixed bank of Rhino-Tempest paired with another Rhino-Tempest. This would have protected the Tempests. But in general, mixing different capacity batteries is a big no-no -- which is why my warranty claim was denied.

In any case, my TR35-12 should be good for its purpose so we'll see where to go from there!

All in all, I'm very happy with BatterySpec and glad that they took the trouble to call me to tell me why my warranty claim was denied and why I shouldn't be doing what I had been doing.

About this Archive

This page is a archive of recent entries written by Karen Nakamura in January 2009.

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