Razor MX350 low on torque

[maurtis]

Hi all,

It seems we are having an issue with my son's well loved Razor MX350, the older model with suspension and 350W motor. When I say "well loved" I mean it has seen a LOT of use over the last two years, a non-zero amount of time was my son riding two-up on it with a buddy... Lately I have noticed it was giving less and less torque, and on our last ride it was constantly getting stuck in the smallest of holes/tall grass/etc. My son is 7 and weighs 74 lbs. I am pretty vigilant about getting the SLAs on the charger after each run and not overcharging them, and these batteries are only about a year old, but my first guess was that the batteries were going.

So yesterday I swapped out the batteries for a known good set from our Razor Dune Buggy, but the same issue. When we got the bike used 2 years ago it would easily loft the front wheel when standing over it and holding onto the bars, and if you blocked the front wheel, the rear wheel would spin. Now it will barely lift the front wheel and the rear wheel will not spin out.

I checked the connections for melting, corrosion, and fit. They were all clean and tight. So assuming it is either the controller not letting enough amps through, or the brushed motor is dying. The rear wheel spins freely, so no bearing issues or brake dragging.

Any easy way to narrow down which it might be, or should I just throw a dart and order the cheaper of the two (the controller) and replace it?

Thanks!

 

[kfong]

I'm willing to bet the motor overheated when riding with more than 1 person. That would weaken the magnets. Motors are easy to replace.

 

[Dauntless]

When I was 7 I'd have been ready for something bigger.

http://austin.craigslist.org/mcy/3833975282.html

My perception is that with the same controller on both, the MX500 and the MX650 are identical even though the 650 is supposed to have a more powerful motor. I have had a few of each. Uh, I haven't exactly outgrown riding these in my own yard. Don't have room to ride a fullsize bike. You don't seem to have many out around you, in California I pick them up broken for $75 or such on occasion.

 

[maurtis]

Thanks kfong, I think you might be right about the motor. It looks like tncscooters is still sold out of them and none of the 350W are showing up on eBay, so time to do some digging.

Dauntless, you are right, there are not many MX500s and MX650s around here. I have an RSS reader pulling CL posts with "Razor" in them since I like to pick up cheap Razor electric scooters to fix and flip. When those MXs show up for less than $200, they go pretty much immediately. Size-wise my son could probably handle a MX500 just fine, but his confidence level is not there yet. The smaller size of the MX350 makes him feel safer. He does the same thing with bicycles. He has a 16" bike, 20" BMX, and 20" mountain bike and still gravitates to the much smaller 16" bike. I just need to spend more saddle time with him.

 

[sololb45@gmail.com]

I have a Razor MX350 in which I just replaced the batteries, brand new, and replaced the motor, brand new. After one day of my son riding it just fine, the torque just went low. I can lift the back tire off the ground and give it some throttle and it will spin the tire pretty good as it should, but as soon as there is a little weight on the bike, the scooter won't move, low torque.

No its not the motor.

Not its not the battery.

Maybe the speed controller, maybe. What else could it be? Any suggestions?

 

[gogo]

If the magnets in the motor did get too hot, the no-load speed of the motor would be higher. Is there any way for you to check this parameter?

 

[amberwolf]

First bet is the connections, especially if it uses spade lugs on the batteries.

 

[John in CR]

No its not the motor.
Not its not the battery.

Without load testing each. Like AW said check the wiring and connections first. Then check the battery by spinning it up no-load and see what voltage does while you apply more and more rear brake. If voltage sags deeply, then the batteries are the culprit. Give the motor a good sniff. Those little brushed motors put off a foul smell as the varnish on the windings starts to fry. I don't think it has neo magnets, so I doubt your cooked magnets.

Whatever ends up wrong, do yourself a huge favor and don't dump any more money into lead batteries or a brushed motor system. Those little frames have great fun potential once you add lithium batteries and a brushless motor, so much so that then you'll want to upgrade the suspension and push it well beyond being a cheap kids toy.

 

[dirkdiggler]

Freewheel is shot. Lift it off the ground and give throttle. Drop the bike and watch the wheel stop. I've had a bujch break on me.