125cc ATV Conversion

H2Guy

100 mW
Joined
Dec 8, 2020
Messages
45
I’ve had mobility issues over the past several years following back surgery and miss going on those long walks with the dogs (and my wife). So I picked up a beater Chinese 125cc ATV brought it back to life and now I cruise along side the pack every night. It’s noisy and am getting lots of questionable looks as we trek through the various paths and fields so I’m starting my electric conversion. All parts are on order and I’ll post pictures and progress over the coming month(s).

2000w BLDC motor and controller (off shore manufacturer)
Dual EGO 56V 7.5Ah batteries (switchable banks: 1 for the drive and 1 for accessories and can be electrically switched)
11:60 sprocket configuration
Power monitor on drive battery

Am not going to cannibalize the existing ATV other than pull the motor and sort out the various mounting challenges of motor, controller and supporting components. I’ll leave the wiring harness in place and connect the accessory power directly to the ATV battery wires (with the ICE out that should just leave the passive accessories : lights, horn).

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Got all the key components assembled and tested ...

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Push button switches for fwd/rev as well as hard/soft start. Have a video and as soon as I figure out how to post that I will. Still waiting on the sprockets so will switch my attention to how to mount it all on the ATV. More to come.
 
Moving on to the mounting challenges. Motor bracket fab is underway and should fit nicely on the rear swing arm. Some mounting holes once I get the new rear sprocket and have it positioned then paint.
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Have the basic “dash” display fab’d and ready for mounting.868701B6-2930-456C-A297-DFB5FDCC93C2.jpeg
 
Still waiting on my sprockets so time to do some hacker fabrication. I need a chain guard and here is my attempt.

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Have two batteries to find a home for in the build and landed on this for the accessory battery. Using a gutted charger for the connection on this one but have a 3D printed adapter for the main power source ...6C168143-6213-4343-A631-637863C765DA.jpeg
 
All parts are now in so it’s time. I’ve stripped it down and pulled the engine. Will do a thorough cleaning and start to place the components. Still have to find mounting solutions for the main battery, controller and assortment of misc hardware. Once assembled and tested I’ll strip it down again after any adjustments and clean up the frame and plastics.

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Lots of work over the last couple of days and still not happy with the motor/sprocket alignment so will tear it down and get that sorted over the next few days You can see from the pics there’s lots of final assembly to go but did take it for it’s first road test. It’s NOT a beast but knew that going in based on battery selection and motor ratings however it is supposed to be a “touring” machine and it’s going to do that perfectly. No info on range yet but will post all the performance info once it’s closer to being fully road worthy.
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First substantial road test this morning. Was too cold (-5c) to stay out cruising too long but went about 7km over 30 minutes and used about 50% of my EGO 56V 7.5ah battery (also have a switchable 5ah on board for reserve). Top speed was 37km/h. Again, the design parameters were to cruise for long walks with the family and dogs so I’m pleased with the performance. Still more final assembly to go to button up all the wiring and aesthetics. Will post more pictures of that progress.
 
Done till spring when I can strip it down and refurb the plastics and paint. It is fully functional and this will be the last update until I can do some full performance testing. Here are some pics ...173CD18B-F148-4D30-B8FF-1FDF1452E518.jpegE29874C1-4D57-4D61-B714-0A8364FE8792.jpeg830A72C3-1B3A-4D0C-9246-C69DCE641210.jpeg
 
Done some tweaks over the past few weeks : swapped out the master switch for a 4 position that allows off:Battery A:Battery B: Battery A&B paralleled(along with some diodes to control cross charging if they are at different SOCs), added blue LED under frame running lights and installed an 11 tooth front sprocket. All continues to run fine with good range / run time but still can't get the amps through the batteries for decent low end torque. Think the BMSs in the EGO batteries must limit this. So I've gotten my hands on a few hundred 18650's and am going through them to find and categorize their capacity to build my own pack. Thinking 14SP6 and will post any significant updates as I go but it takes a long time to test each cell so will be a while before I start spot welding and packaging that up.

Have updated the wiring diagram as well.

ATV Wiring Feb 2021.PNG
 
Hi there, I just posted a thread about doing something similar possibly using a 2000w 48v kit from amazon. Was thinking of using a similar sized rear sprocket 11:74. Does your gearing config allow you to go slow and steady and give enough torque to slowly ascend hills? Thanks!

Here is my first post. Pretty sure I will end up doing the project and will put status in this thread.
https://endless-sphere.com/forums/viewtopic.php?f=34&t=112404
 
The primary issue I found with using the 2000W “cheap” motor/controller is the solid rear axle requires more torque from the motor than it can deliver while slow turning to overcome the tire slip required. I added a jack shaft further gear reduction since the initial build and it now has “acceptable” performance to maneuver up hills and around corners. Don’t have the info in front of me but I’m probably at a 1:10 ratio on gearing to the wheels.

My design parameters was for smooth quiet performance at walking speeds and I’m there now (other than the creaks and groans from the 10 year old suspension components of the ATV).

If I were to do it again I would have gone with a better system that had the torque but a lot goes into this … amps delivered from your battery, controller and then ultimately motor.

Enjoy the journey
 
Thanks for the info. Hate to ask but do you have a pic of the motor to jackshaft to rear sprocket? It sounds like this would work for me but having a hard time visualizing where the jackshaft would be mounted on the atv and chain positions. It looks like you have a similar size atv to what I am working with. Thanks again.
 
Don’t have any pictures and it’s buttoned up with all the plastic. Basically I created a “module” with the motor and jack shaft mounted as a single unit that then bolts in where the ICE was. I mounted the motor on the vertical plane and jack shaft on the horizontal plane of the “module”. The height of the module has to be considered so it clears all the frame components and maintains a relatively constant chain tension through the suspension travel. Designing with left/right/fwd/back adjustments of the module to the frame easily allows for alignment to the rear sprocket and chain length.
 
I appreciate the reply. Im prob a few months away from starting but will def add a jack shaft to the equation and post what i come up with in my thread. Thanks again.
 
Actually, one more question. Do you have any videos of you running it? I think you have something that is very similar to what I am thinking of going for and it would be nice to see a video of it to understand if the performance is acceptable. Im really at a crossroads here where if I can get the performance to be 'acceptable' I will prob continue but if its going to be a total dog I may just sell it or hold onto it till the kids get more used to its gas motor. Early in the thread it (before jackshaft?) you said its top speed was 37kmph, just curious what your performance is now with the jackshaft. Im def not looking for anything close to 37kmph. I think if it can do 16-20kmph and be able to 'turn' the wheels in turns and go up small hills i would be happy with it.

Thanks again!
 
I don’t have a video but if I get a chance I’ll post one. I’ve seen plenty of builds that deliver impressive performance on an ATV platform. I went into it with very different performance requirements than matching what it was pre conversion. I’m confident that as long as you don’t under spec the battery so you can deliver to the controller/motor current limits you will be pleased. The secret is torque for a good solid axle ATV build so select components and design parameters to maximize that and the top end won’t matter :)
 
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