Advice on building a custom off road bike.

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MichaelMcginnis

New Member
I am new to electric bikes. I am looking to build an electric bike for a dedicated purpose, on a budget. Basically, I would like to use the bike to access my garden down a trail, which is about 1/4 mile long. Most of the trail is level. But, there is one hill that is about 100 foot long. I dont care about range, and I don't care about top speed. My concern is getting up the hill. Are there any motors available that will get me up this hill without pedaling? If I prune some trees back, I could probably get a 30 ft run on level ground to gain some momentum before I hit the hill. It's the kind of hill that I could pedal up if I had to. But, after working in the garden for a while on a hot day, I'm not gonna feel like pedaling. I am very mechanical , and I do not mind doing custom work.
 
Your weight matters. The steepness of the hill matters. Both my 1000 W geared hubmotor, and my 1000 W direct drive hubmotor, will start 320 lb on a 15% grade. That is 7/8" rise on a 6" level. The 300 lb includes me, the bike, the motor & battery, & 60 lb supplies.
I converted the bike left with a $189 dd power wheel kit from e-bay, and a $630 battery from Luna. If you're in canada buy battery & motor from grintech, if you're in Hong Kong buy from em3ev. I got a defective battery that would take me 7 miles from amazon, and another defective battery that would take me 12 miles from e-bay. The power wheel controller does drop out after 12-15 miles, until it cools down. Sounds as if that is not a problem for you. A battery of 7.5 to 10 AH should be fine your your purpose.
Make sure your frame has a fork spacing compatible with the one on the kit. Sometimes the slot in the fork has to be widened to get the axle of a hub motor in it. I used a 4 1/2' body grinder. Use safety glasses with power tools. I made the torque arms out of scrap steel. I used Dorman bullitt connectors crimped on 12 ga wire with a klein tool for the battery connection. I made the battery mount out of aluminum angle. I hung the controller wires down under the seat with brackets made of SPAM can lids, also aluminum angle.
 
Thanks for the info. I did not even know that there were 2 different types of hubs. I assume that a geared hub would be what I'm looking for? I will have to come up with some way to measure the grade. The least thing that I want to do is drop a bunch of money on this project, and it not meet my needs.
 
See this thread from grintech about bike conversions: https://electricbikereview.com/forums/threads/why-an-ebike-kit.27333/
Large geared hubs are excellent at grades, and allow one to pedal unpowered without a drag penalty. Small geared hubs are very cheap and not available from US vendors. DD hubs are most of what is sold on e-bay and amazon in cheap power wheel conversion kits. They are heavy, about 15 lb, and in the 1000 W variety as I said, competent at starting on grades. Mine drags me down about 2 sprockets and about 25% of speed versus no motor when I ride it unpowered.
I measured the grade with a 6" level from K-mart, and a scale. Hold the level with one end on the ground, make it level, and measure the distance from the ground of the other end with a scale or ruler. Divide the height measurement by the length measurement. Multiply by 100 to get percent grade.
Fat tire bike geared hub motors have been generally available, but ones that fit a 130 mm rear fork with a 7 speed sprocket cluster have been hard to find in the US. Last month luna had one, but didn't have any when I was buying my geared hub motor. Other vendors are overseas, and I don't send my debit card # to servers that aren't protected by the FBI & US law.
I did the conversion left for $860, with a much bigger battery than you need. As I said, the $189 DD controller is not competent at long trips, but that is not what you are doing, so the low end kits should be fine. My DD power wheel has no PAS, just a throttle, which is not a problem on short trips. Outside of nanny states like Massachusetts & NJ where throttles are illegal. I don't like cheap PAS, the one on my geared hub was too fast (11 mph minimum ) and accelerated too fast (500 w minimum). $5000 torque sensing e-bikes are supposed to be much more natural feeling, but one cannot pedal those bikes unpowered. I pedal most of the time and at age 67, after a $5000 heart evaluation before shoulder surgery, "there is nothing wrong with (my) heart".
 
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Measure your grade. Front wheel should be fine up to 10%, above that I'd stick with rear hub motor.
I had to buy a front hub motor for my 10 speed 90's huffy savannah because 5 speed rear sprocket clusters are no longer available. I used that frame because it was strong. You can't mix a 7 speed rear cluster with a 10 speed front sprocket & chain.
It may be easier to find a rear hub motor in stock @ luna ( if you're a US resident). I think probably the luna controller will be more civilized than the one from ebikeling.com where I bought my front hub motor. Don't count on getting your 7 speed cluster off the old axle, they are usually stuck. Also a new ****ese rear cluster is cheaper than the park tool to remove them.
 
For grass, or a dirt path, you will do better with rear hub. You'll get less weight on the front hub going uphill and from my experience, they can lose traction. In addition, front hubs are better done on steel forks,

You don't need fatbike tires. A wider tire with an aggressive tread ought to work. And that lets you work with a regular frame. A mountain bike frame has an axle width of 135mm, which is the standard width of a rear motor, Front axles are 100mm. WIth fat bikes, those increase to 175mm and 135 mm respectively, although there are fat bike frames out at 190 mm. Most people prefer to have the motor drop right in. You can spread/squeeze a steel frame, but alloy can crack.

Ever ridden a regular bike up that hill? If you can, it shouldn't be a big issue with a geared motor. I've got two 20" folders that have 250W motors with 12:1 gearing. The small wheels and high gearing lets these bikes climb well. I'm always amused when my wife charges up a (short) hill in the wrong gear, sitting straight up, but the motor lets her pass regular cyclists.

I wonder if this low end bike could meet your needs. I bought it earlier this year. Certainly less money than building an ebike.
https://www.amazon.com/gp/product/B073WBF8Z9/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1

This morning, I rode it up our local sledding hill. Not very tall, maybe 20 feet. No pedaling. Just throttle on a half depleted battery. It got pretty slow, but made it.
 
I'd rather build than buy for a few reasons. Although this bike has a dedicated purpose now, I want the option to upgrade individual parts in the future if my needs change. Also, if any 1 part breaks, I want to be able to replace it with off the shelf parts. Also, I'd assume that the battery included with that bike is bottom end. I've had bad experiences with bottom end batteries with many other products. So, I can tell you that the battery is one thing that I do not want to skimp on. That being said, since batteries are going to be the largest expense of this project, I had the idea of using Dewalt 20v (20v nominal 18v under load) power tool batteries to power the bike. I alread own at least a dozen of these batteries, and have only had only 1 go bad over the 8 years or so that I have been using them. Wired in series, I could get 36v, 54v, or 72v. Have you seen anyone else successfully use power tool batteries for an electric bike?
 
Bike batteries have 7 to 14 stacks of cells, managed by a BMS board to make the charge even up when the cells develop voltage differences. Dewalt batteries have one stack. If you parallel 7 dewalt batteries and stack up 3 or 4 each to make 48 v, you are lacking the BMS board. The charging will stop when the highest voltage stack reaches cutoff voltage.
 
Most people use lithium power tool batteries. I think Dewalt Nicad or NiMh are going to be relatively weak, but you could put three or four in parallel and then make a second group in series for a nominal 36V battery. Ebike motors will pull 20A or more when climbing but you're not going very far. Then you have to break it apart to recharge.

You cannot mix lithium packs with NiMH if you put them in parallel. DIscharge is different and I believe the terminal voltage differs. Series would work. One problem to solve is all the connectors. I've seen pics where people mount them on a plank with holes for the pack towers.

Anyway, people were riding NiMH packs 10 years ago, so if you have enough of them, it could be done.

Here's my found_in_the_dumpster 26" Schwinn with a Ryobi 40V battery. Free bike. $250 motor. Could it climb your hill? I dunno.
 

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If you use Facebook find DIY ebikes. More experienced builders there.
If the hill is 100' a geared rear hub 36V will get your job done. 48V for more speed. MAC would be my preferred choice, or eZee if you can afford it from Grin. Riding with good shifting practices my BBS01 250W-500W would definitely climb that hill. OR TSDZ2. Or BBSHD for a climbing beast.
 
Thanks for the info. I will review the spoke calculator, when I make my final decision on what I am going to order. Let me clarify how I want to use the Dewalt batteries. I do not want to hack the battery cases apart and rewire the cells. I want to use battery docks like this one: https://www.ebay.com/itm/1x-battery...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649 This will enable me to use the Dewalt chargers that I already own, and also be able to continue to use the Dewalt batteries on my power tools, when I'm not riding the bike. Wiring these 20v max (18v under load) batteries in series, I will have the option to go 18v, 36v, 54v... Since, nothing in the bike world seems to operate on 54v, 36v seems the way to go. I am confident that the larger dewalt batteries put out well over 20A. Every 36v geared motor that I have seen is rated for only 500 watts though. I am thinking that I would try a 36v 500 watt geared hub on the rear, and then add a matching front hub motor to front of it needs more power. I have no problem problem shifting my weight if one of the wheels is slipping. Has anyone had any experience with these hubs? https://www.ebay.com/itm/36V-250W-3...hash=item2616553359:m:mfxi3eE6y1QBoloeTWFO1Og
 
MichaelMcginnis said:
Assuming that I buy a hub that does not include a wheel, how do I know what spokes to buy?
Click to expand...
Two different spoke calculators enabled me to buy two wrong length sets of spokes when I was putting a Sturmey-Archer IGH (hub) in a wheel. The vendor couldn't tell me what to buy, niagaracycle, now they are out of business: funny thing. As if 26" wheels are really unusual.
One unexplained trick to spoke calculators, when they ask "# of crosses" they mean crosses of one spoke. Not the entire set. I ended up buying 10 mm shorter spokes than the 2nd set that was too long, and using extral long nuts (20 mm) to make up the variations.
Two motor bikes are squirrelly to ride, especially in the wet. If you need 1000 W for 15% grade, buy 1000 W. Measure your grade.
Chargers come with the battery. I think you will done months before a dewalt build if you buy an entire set battery wheel controller PAS sensor throttle from luna (US). You don't need but a 7 AH battery to go a mile, save you hundreds over my 80 mile setup. The cheap luna wheel, and all the wheels on e-bay, take an extra long stem shrader valve tube, available to me only out of state (e-bay).
 
I purchased this kit for the rear wheel: https://www.amazon.com/gp/product/B07MG7LK9F/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
If I go the 2 motor method, I would do a 2nd throttle for the front wheel that I only activate on the straight sections. Going the Dewalt route won’t cost me any time using the battery docks. I’ve used the dewalt docks for other projects. But, yes, I am limited to 36volts. I will post photos of the build when I am finished. I may even settle for one motor and having to pedal a little on the hill. I’ve had nothing but trouble with batteries in the past, which is why I’m making every effort to use batteries that I’m familiar with.
 
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I have several ebikeling motors! One on my first ebike conversion. Second on a 2WD bike. Third in that bike posted above. Now you won't need to spoke the wheels.

Did you get the LCD or LED kit. I've not used any of his new kits with the waterproof connectors.
 
indianajo said:
Two different spoke calculators enabled me to buy two wrong length sets of spokes when I was putting a Sturmey-Archer IGH (hub) in a wheel.
Click to expand...

Yeah, first set of spokes were ordered from China and they were too long. Now I get them for twice the price from a guy in downstate Illinois or another guy in Chicago. Better quality spokes too.

.
 
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