Rear All-Axle, Fst HG Grin Hubmotor with Phaserunner, CAv3, and 52V in FS 29inch MTB

[hjns]

Hi all,

I will document here my experiences with building a kit from Grin into a FS MTB over the next month or two.
Main user requirements are:

1. Relatively stealthy build (I know, this is highly subjective ).
2. Top-speed 40mph / 60kmh.
3. Range at 45km/h >30km.
4. Removable and easy-to-charge battery for charging inside.
5. Full suspension frame with large triangle for the battery.
6. Budget: USD 6'000.00

So, no. This is not a cheap project. The e-bike will be used to commute on a daily basis over a distance of 15km. My point of reference is a car. The financial aspect (only a part of my consideration) means costs of the new e-bike + charging should break even with the costs of gasoline (not selling the car...., just not driving it) within one year.

This e-bike build will compete against the myriad of off-the-shelf e-bikes currently available. For most people, this budget would be really better spent on exactly such an off-the-shelf e-bike. The main differentiators of my e-bike will of course be the top-speed (15kmh faster than any off-the-shelf version) and overall power (crazy higher acceleration), i.e., all the things that make e-bikes fun!

 

[E-HP]

Did you try modeling these components in the Grin simulator? I’m not seeing 40mph from this system.

 

[Zambam]

I'll be following your build.

Assuming you'll ride 6,000 miles / year, how did you calculate payoff within one year ($6,000 build + $ charging) of not driving the car?

 

[Mclewis1]

Did you try modeling these components in the Grin simulator? I’m not seeing 40mph from this system.

Fast wind v3 all axle, Phaserunner, 52v battery, 29" wheels, MTB tuck position, and 100w of human power seems to be able to get to 60kph (surprised me too). Motor Simulator - Tools

I'll bet it will take a bit to get up to that top speed but with Statorade it appears to be able to run there for a while. However at 28wh/km it will suck even a large battery down pretty quickly (but much better at the OPs suggested 45kph).

 

[E-HP]

I don’t see 40. I see 38.6. Add 400w of pedaling and it will do 40.

 

[Mclewis1]

What's 1.4mph between friends?

It always amazes me the amount of additional power required to achieve even small speed gains when running flat out.

 

[smitty2k1]

At that speed it's all wind resistance. Find a car to draft behind.

 

[hjns]

Did you try modeling these components in the Grin simulator? I’m not seeing 40mph from this system.

The batterypack HoC is at 58.8V, hence gets me above 60kph. Sorry about the rounding error when calculating mph, indeed it is only 39mph...

 

[hjns]

edited to allow for re-calculations...

 

[hjns]

I'll be following your build.

Assuming you'll ride 6,000 miles / year, how did you calculate payoff within one year ($6,000 build + $ charging) of not driving the car?

You are correct. It is impossible. I had made a calculation error. Here are the assumptions:

Item	value	unit
Workable days/month	24​	days
distance/day	30​	km
Distance/month	720​	km/month
Gasoline price/Liter	2​	CHF
Car efficiency (AMG V8 biturbo)	25​	Liter/100km
Costs per 100km	50​	CHF/100km
Gasoline costs per month	360​	CHF/month
Electricity price per charge	5​	CHF
Km per charge	20​	km
Electricity costs per km	0.25​	CHF
Electricity costs per month	180​	CHF
E-bike build	6000​	CHF

And here are the results:



Break-even point is only after 3 years, not within one year.
Thanks for challenging me on this! I stand corrected and will continue with the build with a more realistic forecast

 

[hjns]

I had ordered this FS MTB for EUR 1'999.00 and it came in earlier this week.
Key specs:

• 29inch/700c (ETRTO 622) wheels.
• Formula Cura X brakes.
• Rear axis 148x12mm.
• Fox 34 front suspension fork.
• RockShox SIDLuxe Select+ rear suspension.
• Large triangle.
• Carbon frame.

I am aware that the carbon frame is the "weak link". I will use the Triple Bob with Hose Clamps to securely mount the battery onto the downtube of the frame, so as not to rely on the eyelets only. The battery is 5.38 kg according to Grin, therefore I believe that when it is well mounted, it should not be a problem for the carbon frame.

The tires will be replaced by Schwalbe marathon plus MTB performance 29"x2.1 tires rated for E-bikes up to 50kph.

 

[offGridDownUnder]

View attachment 369510
The batterypack HoC is at 58.8V, hence gets me above 60kph. Sorry about the rounding error when calculating mph, indeed it is only 39mph...

If you ride 5 days/week commuting 15km each way for 30km/day you will be buying a new large battery each year. Approximately. That is 100% charge usage every day.

If you size the battery to keep the usage within the 20% (minimum) to 80% (maximum) then you would require a 33Ah battery. This could extend the battery life to 3 years or more, and thus reduce your cost, albeit costing more now.

If you have a charger at each end and time to recharge, you can probably manage this with your currently specified 20Ah battery by using only 50% charge for each leg of the trip, thus remaining above 20% minimum and recharging to 80% at each end of the commute.

You would also need a charger that can maintain this, or just pay attention while charging to stop when 80% is reached. As you are using Grin tech, the Satiator charger will do this for you.

 

[hjns]

If you ride 5 days/week commuting 15km each way for 30km/day you will be buying a new large battery each year. Approximately. That is 100% charge usage every day.

If you size the battery to keep the usage within the 20% (minimum) to 80% (maximum) then you would require a 33Ah battery. This could extend the battery life to 3 years or more, and thus reduce your cost, albeit costing more now.

If you have a charger at each end and time to recharge, you can probably manage this with your currently specified 20Ah battery by using only 50% charge for each leg of the trip, thus remaining above 20% minimum and recharging to 80% at each end of the commute.

You would also need a charger that can maintain this, or just pay attention while charging to stop when 80% is reached. As you are using Grin tech, the Satiator charger will do this for you.

Completely agree. I did not mention it, but I do indeed want to charge both at home and in the office. Given the price of two Satiator chargers versus a new battery every year or two, I agree that this makes sense on the long term.

 

[E-HP]

View attachment 369510
The batterypack HoC is at 58.8V, hence gets me above 60kph. Sorry about the rounding error when calculating mph, indeed it is only 39mph...

So 40 fully charged, but a topped off fully charged pack will drop a volt or two in the first mile, which is why the simulator uses the nominal pack voltage for the real world speed. It’s easier than saying my bike goes 40 when I’m near my house.

 

[Zambam]

View attachment 369513

I had ordered this FS MTB for EUR 1'999.00 and it came in earlier this week.
Key specs:

• 29inch/700c (ETRTO 622) wheels.
• Formula Cura X brakes.
• Rear axis 148x12mm.
• Fox 34 front suspension fork.
• RockShox SIDLuxe Select+ rear suspension.
• Large triangle.
• Carbon frame.

I am aware that the carbon frame is the "weak link". I will use the Triple Bob with Hose Clamps to securely mount the battery onto the downtube of the frame, so as not to rely on the eyelets only. The battery is 5.38 kg according to Grin, therefore I believe that when it is well mounted, it should not be a problem for the carbon frame.

The tires will be replaced by Schwalbe marathon plus MTB performance 29"x2.1 tires rated for E-bikes up to 50kph.

Looks nice but what was your rationale for choosing a carbon frame?

 

[ZeroEm]

Hi all,

I will document here my experiences with building a kit from Grin into a FS MTB over the next month or two.
Main user requirements are:

1. Relatively stealthy build (I know, this is highly subjective ).
2. Top-speed 40mph / 60kmh.
3. Range at 45km/h >30km.
4. Removable and easy-to-charge battery for charging inside.
5. Full suspension frame with large triangle for the battery.
6. Budget: USD 6'000.00

So, no. This is not a cheap project. The e-bike will be used to commute on a daily basis over a distance of 15km. My point of reference is a car. The financial aspect (only a part of my consideration) means costs of the new e-bike + charging should break even with the costs of gasoline (not selling the car...., just not driving it) within one year.

This e-bike build will compete against the myriad of off-the-shelf e-bikes currently available. For most people, this budget would be really better spent on exactly such an off-the-shelf e-bike. The main differentiators of my e-bike will of course be the top-speed (15kmh faster than any off-the-shelf version) and overall power (crazy higher acceleration), i.e., all the things that make e-bikes fun!

Think it is a great idea to replace the car. The cost of insurance alone will pay for all the batteries. Would think about going 72V, would give you the extra speed.

 

[hjns]

Looks nice but what was your rationale for choosing a carbon frame?

Mostly weight. But it was also part of the package for the most cost-effective FS MTB with good groups and good brakes.

 

[hjns]

Think it is a great idea to replace the car. The cost of insurance alone will pay for all the batteries. Would think about going 72V, would give you the extra speed.

Yes, I thought about that, too. But of all the requirements, the top-speed is the least important. It is just a very nice to have from fun perspective.

 

[ZeroEm]

Yes, I thought about that, too. But of all the requirements, the top-speed is the least important. It is just a very nice to have from fun perspective.

I run 72V but it was not for the speed, have a 7T leafmotor. It was for pulling a steep hill. But was over kill. This year or next going to quit driving cars. Still have my 2013 Leaf, but going to get my E-trike back out and sell the car. Good luck, Note: I keep it under 30 with out full suspension.

 

[hjns]

The project has started..... .... now waiting for the Grin kit to come in.

.... however, I am traveling for the next two weeks. I.e., you will only see the next updates in the second half of May.