12 replies to this topic

[rmjlmartin]

I have a couple of questions about this motor that I built. I got a pair of identical arms as an added freebie from an Ebay seller a year or so ago. They appear to be intended for some sort of cobalt motor, and I didn't have a setup to put them in, so they've just sat in a parts box since. There is some engraving on the stack, what looks like ProSlot, 470, and either 16TD or 16T0. The arm is .470" diameter, the stack is .390", and the overall length, including the comm, is .881". I'm assuming the engraving means that it's a ProSlot arm, 470 is the diameter, and the 16TD or 16T0 is some sort of spec for the wind.

 

First, does anyone know for certain what these arms are? I recently rediscovered them in my parts box and decided to see if I could find a setup without spending a lot of money, just to have some fun with them. I showed one to a local long time wing car racer (Ed Gibson, who I believe just won C12 and 27L at the Western States race at Piranha Speedway in CA- Congratulations Ed!), and, at a first impression, he said he thinks it's an early '90s open arm, and suggested seeing if it would fit in a Euro/FK can with shimmed magnets.

 

So, I pulled out an old ProSlot setup from a 4002fk, cut the can so it was more open, similar to the newer Speedball-style can, installed some hard neo magnets from an old Phoenix motor, and trimmed the brush hoods to clear the larger American comm. The magnets are shimmed, and the air gap is .505". The arm fits perfectly.

 

The problem I'm running into is that I have no idea what amperage it should be pulling. The other motors I'm familiar with, mostly ProSlot 4002fk/Scorpion, Speedball/Crazy Eagle, and 16D, all pull less than 2A on my power supply. This motor pulls 8A at 2v.

 

I've analyzed it as well as I can, but I don't have enough information to say anything definite. The motor will start at about 1v, and pulls 7A. It's up to 8A at 2v, and my inexpensive 10A power supply limits it to just under 3v, when it hits the 10A limit. A friend suggested trying it with a controller connected to a car battery, to get a little higher voltage (while also being careful not to put too much voltage to it), but I haven't had a chance to do it yet. I have a lab scope (my day job is an automotive tech), and I've monitored the motor with it using an amp probe. The current pattern looks good and even, no spikes like a shorted pole might show, just much higher than I'm used to seeing. The motor also doesn't get almost instantly piping hot.

 

So the second question is whether or not this is normal for this type of motor. I know it's a completely different, much hotter motor than I'm used to running, but 8A at 2v still seems pretty high to me. Or did I likely do something wrong in the process of building it that's causing the high amperage draw? Or maybe this arm just really isn't suitable for this type of setup?

 

I've attached a picture of the motor, alongside the second arm.

Attached Images

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[breese]

What does the engravings on the arm say?

Looks very similar to a few open motors I have from the 80's...

[rmjlmartin]

What does the engravings on the arm say?

 

 

There are three, what looks like "ProSlot", "470", and either "16TD" or "16T0".

[Ramcatlarry]

Try running the motor backwards an see if the amps go up or down. This will confirm what direction the motor should run to coincide with the timing advance.

The stronger magnets may be too strong for that air gap, causing the hi amp reading.

 

16T might be 16 turns.  D for double?

[rmjlmartin]

Thanks Larry. I tried running it the other way (CCW, viewed from the can end), and it does pull slightly less amperage. However, after running it that way for a minute, it seems to pull a little less in the normal CW direction.

 

I got brave enough at that point to run it a bit longer, and it seems to run fine at low voltage, at least. Just for kicks, I pulled out and ran the next hottest motor I have, and old G27 cobalt motor that I picked up awhile back but haven't had a chance to put in a car yet, and it pulls about 5A at 2v. From my reading of the G27 arm specs in the USRA rules, a G27 arm has a significantly milder wind (38t27), so 8A at 2v might be normal. A friend told me yesterday that 16t24 is a common open arm wind, so I'm going to tentatively assume that's likely what this is.

 

Since it seems likely that the motor isn't actually about to blow up, I guess I'll go ahead and swap out the bushings for bearings, install shunts, and put it in a car and run it.

 

However, if anyone else has anything to add, please feel free to do so. As I said, this is fairly far out of my normal field of experience, and I'm hoping to avoid burning anything up, even if the arm didn't actually cost me anything.

[Dave_12]

depends on  what wind the arm has and  is it on a bench power supply or under track load?

[rmjlmartin]

depends on  what wind the arm has and  is it on a bench power supply or under track load?

One of the engravings on the arm is what appears to be 16TD or 16T0, so I'm assuming the wind is 16 turns of some fairly heavy wire, from the looks of it. I'm told 16t24 is a common open arm wind, so I'm tentatively assuming that's what it is.

 

This is on a bench power supply.

[Dave_12]

sounds like it is a 64 .   Sixteen turns of 24g.   Now days the number 64 would be engraved on a stack. 

[MSwiss]

8 amps is high for a 64 road race arm which will be about 15-18 degrees timing and draw 4-5 amps.

 

But if it's .470 diameter,  it might be a drag arm which might also be higher timing and would explain the higher amperage draw.

[rmjlmartin]

Thanks Mike, I appreciate it.

 

So, assuming this arm was a road race arm, this arm should have a similar amperage draw to the G27 motor I compared it to? (5A at 2v on my power supply)

 

Forgive my ignorance, but would the timing in an open wing car or Eurosport motor actually be less than 20 degrees? When the local wing car guy told me it was likely an old open arm, my mind went to open wing cars. The only experience I have with something like that is some mostly older G12 and G15 that I've been tinkering with to teach myself some motor building skills, and they're generally running significantly higher timing, at least these days.

 

It certainly wouldn't be the first time I've operated on assumptions that turned out not to be correct.

[MSwiss]

Open arms and G12/15/27 arms are totally different animals.

 

For torque you either need turns or mild timing.

 

50T on the G12/15 provides that just as 38T provides it with a G27. Hence, you can time them 32 - 45  degrees.

 

A 15-19 turn armature with bigger wire has much lower resistance and less torque.  Hence the lower 12-18 timing  and the need to gear it higher numerically. 

(4.5 or 4.8 -1 on .760 tires)

 

A Eurosport arm might have timing in the 20's but that works because they are gearing the car astronomically high and on short tires.(8-1 on .650(?)  tires)

 

IMO, you are investing too many keystrokes on a free arm.

 

Gear it 8-38 or 8-39 and try running it.

[rmjlmartin]

Thanks Mike, I appreciate it. That makes sense and is very helpful.

 

I am planning on running it as my next step, but that's on hold for the moment, since my local raceway is closed for the next few weeks while they move to a new location.

 

You may well be right about the keystrokes, but for me, this is also a learning experience. Very few people below wing car racers and Eurosport are building motors any more. Building motors interests me, though both of those classes are well above my means at the moment. But older C cans are cheap, and I have lots of parts left over from worn-out sealed motors. Thus the willingness to experiment with the odd free arm that's probably not really worth much otherwise...

[MSwiss]

Glad you are looking to learn.

 

That's why I gave you a semi-lengthy response.