mx 400 build log

[shortcircuit911]

So its been a while since I've posted here. It looks like may of you have made some cool stuff. My last build was an E300 with a 6500w turnigy motor. The scooter has been scrapped and the parts have been given to friends/burnt out lol. About 8 months ago I had my first kid and have been busy with him. Now he's to the point where we can start doing cool stuff together. I picked up an mx400 on CL for $100 that was in pretty good shape. I bought it so we can cruise around on it together, and it'll eventually be his when he's big enough. The first obvious mods were to over-volt to 48v and change the speed controller. I picked up a 48v 800w controller on ebay for $15, as well as 2 9ah batteries ($40) and a 48v charger ($25). Let the modding begin! I wanted the bike to look as stock as possible (mainly so his mother wouldn't know its got some extra juice). The bike has a U shaped bracket that holds the batteries down, so I started out with making a longer version so I could stack the additional batteries on top of the others. Wiring up the controller was pretty simple so I wont get into that. The bars were a bit of a problem, so I made some 1" riser to help make it more ride-able. The results were pretty good, the top speed shot through the roof but I knew the motor wouldn't last long. I think I'll stop here and add more pics and details on the next post.

 

[shortcircuit911]

I've been lagging on posting results of this build. I've done quite a bit and will get everything posted here soon. I knew the motor wouldn't hold up very long. Our combined weight is about 175lbs, we live on an incline, and 24v motors don't like 48v. After a few hard rides the motor began to smell really bad, so I ordered a 36v 800w motor. I went with a brushed motor because they are virtually problem free. When I installed the 6500w motor on my e300 project, I was blowing hall sensors weekly on that motor. Those motors can be run without them, but they loose sync frequently, so sensored commutation is the way to go on those. Also I just want something cheap and reliable to go out with my kid, not a bike for drag racing. Just before the motor came in we rode it hard and smoked (literally) the stock motor. Luckily the new motor came in the other day and I did the motor swap. This required some custom mounts to lift the motor up 3/4" of an inch to clear the swingarm. I used 3/4" square tubing with through holes drilled in it, and used longer bolts. I kept the location of the two bolts closest to the sprocket the same (because the distance from the endbell to the sprocket is the same as the stock motor) and drilled the new holes on the commutator side of the motor (hope I explained that ok). I can add pics of the mounts if anyone is interested. The bike is so much more fun to ride now, we can go up anything in our neighborhood at at least 15mph. I bought a speedo at target, but it was meant for bigger wheels. I programmed the wheel circumference in but the speedo freaks out at speeds above 8mph. I ordered a new one off of ebay that should work better, haven't had a chance to gps the bike on my phone. Last thing I installed was a variable speed throttle from ebay. This one is pretty sweet it has aluminum end caps, pack voltage read out, and an on/off switch, all of that for $21. I also need to install my watt meter so I can monitor battery consumption and input power. after that I'll probably start on the cosmetics.

 

[shortcircuit911]

I was able to gps the bike today and it topped out at 21mph it hit 23 but we were starting to go downhill. I would squeeze a few more mph's out of it if I change the motor sprocket to a 13t but I'll leave it alone. I'd actually like to put a bigger sprocket on the rear so I have more torque. On the ride the brakes began to make lots of noise and eventually became useless. So I dug up a tektro disc brake caliper from my stash and ordered a rotor and adapter (allows you to add a disc brake rotor to wheels that have band brakes) from electricscooterparts.com. I should be able to do that conversion pretty easily so it's just a waiting game for now. I was also able to take a few more pics of the bike with the new motor in there.

 

[DAND214]

Nice! Looks like he's ready to go.

Dan

 

[shortcircuit911]

Ya man, he is. I put him in the chest carrier, throw a helmet on him and we go for rides a few times a week, he loves it!

I did another top speed run today alone on another street and I hit 22 mph consistently, 23 here and there so we'll call it 22. I've been unhappy with the acceleration and remembered I left the 30 amp fuse inline with the battery pack. So I decided to remove it and solder up the shunt on the controller. Taking it apart was a breeze and the board was much smaller than I thought it would be. Forgot to mention that I installed my watt meter and did a baseline of motor performance. Max current was 25 amps and max power was 1,200 ish watts. After I soldered the shunt I went for a spin to see what the mod did for performance. I was able to hit 45amps and pull over 2,000 watts. I pulled into the driveway and wasn't completely satisfied so I decided to do a WOT cycle up the street from a dead stop. I smashed the throttle and rode a wheelie, after about 5ft I left off to keep the wheelie going and to keep from flipping. When I let off the bike kept accelerating and I knew immediately that the controller failed (in the on position). So I jumped off the bike while keeping my hands on the bars, the bike stayed wide open and would stay in the 12 o clock position as the rear tire bounced on and off the ground burning rubber when hitting the ground. I was able to get one hand off and disconnect the watt meter/motor plug and stopped the bike. I was expecting to eventually burn out the MOSFET's, but didn't think it would be that soon. I checked the watt meter when I got home and saw that the motor pulled over 3,200 watts and 114 amps! I knew I put a little too much solder on the shunt, but honestly didn't care at the time. Luckily I had a stash of 4110 MOSFETs and went home and swapped out the burnt ones for fresh ones. Took it for another spin and it felt nice. Decided to be a D-bag again and did another WOT cycle up the hill again and it failed in the on position again. Luckily this time it didn't ride a wheelie and I was able to pull the plug again. So I'm thinking the freewheel diodes are part of the problem. I think I'm just going to get a bad buttocks kelly controller and be done with the cheap stuff. I like to beat on my stuff, so I usually try to buy the best stuff when possible. I only paid $15 for the controller so I'm not really mad that it burned out. I think I might fix it again and just go easy on it until the new controller comes in.

 

[shortcircuit911]

So I woke up this morning determined to fix the controller and get the bike running (I get stressed out when my stuff is broken). Got the controller apart and saw only one FET blew so I replaced it and also added some thermal grease to the back of all the FETs to help with heat dissipation. I also removed most of the solder so I don't blow the darn thing up again. Took it for a ride and it ran fine (boring with only 30 amps of power). Checked the mail and saw that I got my new speedo in as well as my disc brake parts. I was able to get the rotor mounted to the wheel and both mounting brackets made for the caliper. I'll try and weld them in the morning so I can take my kid for a ride tomorrow . Kelly also emailed me and said my controller is on the way so I can't wait to get that thing wired up. Also ordered an 18-56v 200 amp controller from kelly.
http://kellycontroller.com/kds48200e200 ... p-286.html

 

[shortcircuit911]

I didn't like the look of the tabs, so I decided to give them more of an organic shape. Next step is to re-install everything and make some spacers for the caliper on the lathe. I hope to have the brakes all dialed in by next weekend. Hopefully the controller will be in by then and I can get that all wired up.I received a nice little package from Kelly yesterday, which was pretty quick. The controller is just about the same size and the POS I have on there now. Unfortunately I've been slammed at work this week and probably won't have time to do anything until this weekend. Three main goals for the weekend are:
1.Get controller programmed and mounted
2.Re-install motor
3.Finish brakes

We'll see how it goes.

 

[shortcircuit911]

I re-mounted the motor and made the spacers for the brake caliper. It took some fine tuning getting the spacers turned down to the correct length, but they turned out perfect. Brakes feel good but didn't get to test ride. I was able to program the kelly and get it wired for a bench test. It took a long time to get it right, after troubleshooting I realized that my throttle was working intermittently. I still need to finish the mounts and weld them to the frame. I also received my hella switch which is a high power switch you turn by hand, a mount also needs to be made for that. Also picked up some bad ass connectors at lowes that should handle the high current nicely.

 

[shortcircuit911]

Finally got enough time to work on the bike and got it pretty much done. I welded some brackets on the frame for the controller but am not too happy with them, so I'll redo them later. I still need to make a mount for the hella switch but zip ties will do for now. As far as the firmware, i programmed it last week so I don't remember all the settings. I do remember setting the the throttle on the aggressive side, and will probably program it so it is maxed out on sensitivity. I'm pretty comfortable on a motorcycle and prefer a twitchy throttle. I used a momentary switch hooked up to a 1K resistor (which I think is too much resistance, will probably put a smaller one in) to pre-charge the controller caps. After the caps are charged I flip the switch (main contactor) then I hit another power switch that sends power to the logic side of the controller. We went for a test ride and it was awesome! It had nice power just like I expected. We can climb every hill here at almost full speed. The brakes are also working very well, they have lots of grab. I was a bit surprised but the bike can actually pull wheelies. I was going about 3 mph and pinned the throttle and felt the front end come up, I set it back down because my wife was watching, going to explore that later. All in all this thing is bad buttocks, everything feels solid on the bike. The watt meter says it pulled 57 amps and 2,450 watts. I'm pretty sure the batteries are whats holding this thing back but they'll have to do for now.

 

[shortcircuit911]

The bike is running so good, I couldn't be happier with the performance and reliability. There's still a few small things I want to do to it, but will probably wait until my scooter is complete. My son and I go ride every weekend and he loves it! So far we have over 30 miles clocked on the speedo, but probably closer to 60 miles since I bought the bike. Each run is only 2-3 miles depending on how hard I'm on the throttle. The 7ah batteries are really bringing down the 9ahs so it would be wise to swap them out. Since recently discovering the multistar packs from hobbyking, I'm temped to run 12s 20ah in this thing and dramatically extend the ride time (and cut weight). Anyway I'll post updates on improvements soon.

 

[shortcircuit911]

So I've been playing around with this thing for the past couple of days. Today I was able to set new parameters in the firmware. I maxed out throttle sensitivity, lowered the lvc to 40v, and set the throttle effective range from 0 (starting) to 100 (ending), amps were also maxed out. I have to say, I did notice slight difference in torque and performance from a dead stop. I've notice the batteries dropping off a bit more and its so annoying! I found a deal on hobbyking for 6s, 20c cells for $30, and I almost pulled the trigger, but I still need to get more parts for my scooter so I'm holding off for now. I was able to get a 13t sprocket on order so it should be in next week. Hopefully it will get me in the 25-26 mph range.