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robo
18 April 2014, 2009
Apologies for the new thread here. I'm hoping this is easier for others to find later. Also, it may help folks invent a different substitute they like better.

Details for a PB-6 potentiometer replacement:

Part: PMC98191 or CM44675
Resistance 5K Ohm
Tracking: 45-degrees (although the mechanical rotation is ~312 degees)
Shaft length: 0.825 inches
Bushing length: 0.5 inches (uses a 3/8-32 NEF nut & lockwasher)
Operating temp: -55C to 120C
Rotational life: 1,500,000 (in theory)

This pot has a conductive plastic resistive element. Tolerance is +/- 10% and linearity is +/- 5%. The variable resistance band is approximately at the center of mechanical travel (I mentioned above the pot actually travels 312-degrees, but the active region is only 45-degrees).

My pot's labeled Clarostat. I think that's related to Honeywell, but others might manufacture the part. It appears to be a custom potentiometer...it's not like most rotary potentiometers in terms of travel & tracking. So, either you have to get this pot as a replacement, or you're on your own to invent another solution.

The pot is not sealed, so in an exposed electric motorcycle like mine, the pot will get dirty well before the predicted 1,500,000 cycle lifetime....like mine did at ~1000 miles. Symptoms are jerky throttle response or worse.

I've also attached some pictures on the pot in my PB-6. I hope this info is useful.

569556965697

later edit: much of this info came from:

http://www.potentiometers.com/pdf/CustomResistiveTracks.pdf

podolefsky
18 April 2014, 2023
Good stuff, thanks Rob.

I wonder if you could extend the life by sealing the PB-6 box. Take the box apart, squeeze some gasket maker along the seams and put it back together.

robo
19 April 2014, 0823
...I wonder if you could extend the life by sealing the PB-6 box.

Seems like a good idea to me. Seal the box and/or maybe enclose it. The shaft extends out of the box, so sealing the box and enclosing it would address both.

Better to do this earlier than later.

Knowing what I know now and given the price of a PB-6, I'd just start with a hall effect solution instead.

But if you have a PB-6, the above should help. Good idea.

robo
19 April 2014, 1304
For completeness, here is what the PB-6 potentiometer looks like inside (it's definitely not sealed). This shows why it's a "custom tracked" 45-degree pot unlike most pots and why alternative "generic" PB-6 pot replacements aren't easily available.

In the pictures, you can see the smaller black 45-degree electrical throw region compared to the much larger overall mechanical travel area (that isn't used in the PB-6):

56985699

If that's not useful, if anything, hopefully it's interesting.

In the meantime, I've cleaned this one with contact cleaner and I've sealed the outside up with rubber cement (cheap & easy to get back in). The math says the pot should have a LOT of cycles left and the meter says it's now working fine. This is a temporary fix while I consider a hall effect replacement.

podolefsky
19 April 2014, 1724
I think it's interesting... It would be nice if cleaning the pot and sealing the box did the trick. My two PB-6's are still working fine, but I suspect they'll go at some point.


Here are two relevant threads on using a Hall effect.

http://www.diyelectriccar.com/forums/showthread.php/tps-vs-hall-effect-throttle-61543.html

-Main point, what Frodus points out, if you're using a Hall with a controller set up for a 2-wire pot, you need a 5V source. That source should be isolated so you don't tie the 12V system to pack negative.


http://www.diyelectriccar.com/forums/showthread.php/alltrax-axe-7245-hall-effect-throttle-69237.html

-Just read the first page - there are pros and cons to Hall vs pot. A good pot is better than a bad Hall (and vice versa).

robo
19 April 2014, 1927
Great links Noah. A high quality sealed pot (or automotive grade TPS) doesn't sound bad after reading those. I have a large 2/0 cable very near the PB-6 and a hall effect unit could be influenced by the cable's magnetic field during current draws. Installing an isolated 5v dc supply as you previously described is also extra work for a hall effect sensor (for use with Alltrax at least).

For the record, dis-assembling and cleaning the PB-6 pot with contact cleaner worked very well. Following a sound engineering method, I also added a small film of WD-40 to the track using a Q-tip. Yes, this sounded like a terrible idea to me too. I also wouldn't have done it without sealing the pot (oil attracts dirt). But, throttle response is now very smooth.

The problematic throttle ranges are completely gone. Smooth. At least for now.

podolefsky
19 April 2014, 2112
I've been using the EVnetics throttle in a project that is about as dirty an environment as you will find, and it's held up great. It's also beautiful and completely over-engineered, which I love.

If there were a good drop-in pot for the PB-6 I would just change it out, but given that there isn't I'll probably replace mine with two EVnetics at some point.

IMO, the PB-6 just isn't a good motorcycle throttle. It's huge considering what's inside (one little cheapo pot), way too expensive, and not sealed. At all. Maybe OK in a reasonably clean environment like the trunk of a car, but not on a bike.

robo
19 April 2014, 2220
Agreed. For an el moto, the PB-6 is not the best choice.

I wanted to explore exactly why to see what could be addressed for us who have them. Sealing up should help a bit.

Clearly, the EVnetics and others address all these issues and then some.

Noah, you know me...I have a ghetto engineering bias for diy low-cost with reliability. It's just my bias...it's by no means "better". Just what I typically explore.

That's why I waste an afternoon's effort rehabbing a cheap $20 pot.

Can't recommend the wd-40 thing though. That's dicier. The solvent may eat the conductive plastic...or the oil may make it last longer. Don't know.

podolefsky
20 April 2014, 0835
I fully support any ghetto engineering that makes things work better.

podolefsky
25 April 2014, 2033
Cross linking to this thread on a Hall effect throttle adapter:

http://www.elmoto.net/showthread.php?3548-Hall-effect-throttle-adapter

podolefsky
09 May 2014, 1541
This Hall effect throttle is a drop in replacement for the PB-6. I asked a rep from EV West and they said it works great (I doubt they would sell it if it didn't).

http://www.evwest.com/catalog/product_info.php?cPath=25&products_id=94

robo
13 May 2014, 0757
That's pretty slick. Can't get away from having to provide 5v DC though.

Brief update. My rebuilt and ghetto sealed pb6 pot has worked very well for the last 220mi. I'm going to see how long it goes.

furyphoto
13 May 2014, 0910
For 5v you could use a RC u-BEC (universal battery Eliminator Circuit). Its a little 5v voltage regulator for running an RC receiver off the main motor battery instead of having a separate 5v battery for the receiver and the servos of an RC plane/heli/car. A separate battery is what they did in the old days when most RC was gas powered. Once everything started to go electric these BEC's showed up to eliminate the weight of an extra receiver battery pack.

They are REALLY inexpensive and would put out a solid 5v, pulled off your 12v system for only a few bucks. In fact, you can easily afford to run two in parallel for redundancy.

I trust these things to keep $5000 worth of RC quadcopter and camera in the air, so I can vouch for them. You can get them and just about any RC store (brick & mortar, or online). Pick one up from somewhere close for fast shipping.

Here are some on e-Bay (http://www.ebay.com/sch/i.html?_odkw=5v+ubec&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.X5v+ubec+-esc&_nkw=5v+ubec+-esc&_sacat=0)

frodus
13 May 2014, 0914
That may work in some cases.... But throttles on Curtis 1238 and alltrax (not sure about sevcon and kelly) are not isolated from pack negative.... So a regulator would now link the ground from 12V stuff to the pack negative. A lot of builds use isolated dc-dc converters and using a 12V-5V converter would break isolation.

furyphoto
13 May 2014, 0924
OH, well that's a problem then! I figured it couldn't be that simple. It's probably about time for me to start making a wiring diagram for my bike to figure that stuff out.