Brushless Bump Box Build

[tudordewolf]

I love my bump box, but it weighs as much as a whole RC car. I figured I could get the same torque from a single 3660 motor as its double 550 brushed motors, so I set about building the most superfluous brushless conversion ever.

A 10BL60 ESC with the fan removed, an arduino pro mini, and a 1400kv 3660 brushless motor are the guts of the conversion. The low KV is to match the RPM's of the original setup while running on 3S, which I measured at 5400 RPM fully charged. My conversion does just over 5000 RPM, which I am completely satisfied with.

The stated goal was to cut weight. The final weight is 2180g, down from 2860, a savings of 680g. Not bad, though the majority of that could be accomplished by just swapping out the NiMh cells for the lipo- but the Kyosho manual explicitly states that lipos are not recommended and may cause fire, so that's part of my excuse to do this conversion. Considering the stock bump box just dumps the battery voltage through the motors with a physical contactor, it's a big upgrade to longevity since now the contactor and power switch are exposed to sensing levels of current instead of the full amperage the motors are drawing.

I've coded for an arduino before, but this time I described my goals to ChatGPT and had it produce the code. One or two tweaks later and it ran perfectly.
It reads the push-plate and generates a PWM signal for the ESC. Seems simple enough, but of course it got more complicated as I added smooth transitions between PWM states, a button for reverse to calibrate the ESC, and a function to show the output state with the onboard LED.

Key details & challenges:
Reverse-engineering the tooth profile (FHT-3, compatible with HTD-3M) and finding a belt of the exact length (55 teeth) to work with 1 motor instead of 2.

Rewiring the ESC's power switch to the bump box's switch, including wiring in a "set" button.

Incorporating a diode to drop the ESC's 6V to a level safe for the arduino (<5.5V) - I originally considered using the fan port voltage, which is directly from the battery, to the arduino's onboard regulator via the RAW pin, but I couldn't get the arduino to boot, only by giving it 5V on VCC. Using the BEC is cleaner anyway since that eliminates any connections to the fan port.

Incorporating forward & reverse test buttons directly onto the arduino.

Using the arduino's indicator LED to give visual confirmation of forward / reverse reads.
Using only the pins along the edge of the arduino for a very clean package & heat shrunk for that professional look:

The servo port goes to the ESC, and green/yellow reads the push-plate.

Videos to follow, preliminary tests have been promising. Fingers crossed that it doesn't suffer cogging issues.

 

[J’sCrawler]

I love my bump box, but it weighs as much as a whole RC car. I figured I could get the same torque from a single 3660 motor as its double 550 brushed motors, so I set about building the most superfluous brushless conversion ever.
View attachment 173704

A 10BL60 ESC with the fan removed, an arduino pro mini, and a 1400kv 3660 brushless motor are the guts of the conversion. The low KV is to match the RPM's of the original setup while running on 3S, which I measured at 5400 RPM fully charged. My conversion does just over 5000 RPM, which I am completely satisfied with.

The stated goal was to cut weight. The final weight is 2180g, down from 2860, a savings of 680g. Not bad, though the majority of that could be accomplished by just swapping out the NiMh cells for the lipo- but the Kyosho manual explicitly states that lipos are not recommended and may cause fire, so that's part of my excuse to do this conversion. Considering the stock bump box just dumps the battery voltage through the motors with a physical contactor, it's a big upgrade to longevity since now the contactor and power switch are exposed to sensing levels of current instead of the full amperage the motors are drawing.

I've coded for an arduino before, but this time I described my goals to ChatGPT and had it produce the code. One or two tweaks later and it ran perfectly.
It reads the push-plate and generates a PWM signal for the ESC. Seems simple enough, but of course it got more complicated as I added smooth transitions between PWM states, a button for reverse to calibrate the ESC, and a function to show the output state with the onboard LED.

Key details & challenges:
Reverse-engineering the tooth profile (FHT-3, compatible with HTD-3M) and finding a belt of the exact length (55 teeth) to work with 1 motor instead of 2.
View attachment 173700

Rewiring the ESC's power switch to the bump box's switch, including wiring in a "set" button.

Incorporating a diode to drop the ESC's 6V to a level safe for the arduino (<5.5V) - I originally considered using the fan port voltage, which is directly from the battery, to the arduino's onboard regulator via the RAW pin, but I couldn't get the arduino to boot, only by giving it 5V on VCC. Using the BEC is cleaner anyway since that eliminates any connections to the fan port.
View attachment 173701

Incorporating forward & reverse test buttons directly onto the arduino.

Using the arduino's indicator LED to give visual confirmation of forward / reverse reads.
Using only the pins along the edge of the arduino for a very clean package & heat shrunk for that professional look:
View attachment 173702
The servo port goes to the ESC, and green/yellow reads the push-plate.

Videos to follow, preliminary tests have been promising. Fingers crossed that it doesn't suffer cogging issues.

I like it. Great job. I have seen all these brushed powered starter boxes and I just think why not brushless?

 

[Greywolf74]

I love my bump box, but it weighs as much as a whole RC car. I figured I could get the same torque from a single 3660 motor as its double 550 brushed motors, so I set about building the most superfluous brushless conversion ever.
View attachment 173704

A 10BL60 ESC with the fan removed, an arduino pro mini, and a 1400kv 3660 brushless motor are the guts of the conversion. The low KV is to match the RPM's of the original setup while running on 3S, which I measured at 5400 RPM fully charged. My conversion does just over 5000 RPM, which I am completely satisfied with.

The stated goal was to cut weight. The final weight is 2180g, down from 2860, a savings of 680g. Not bad, though the majority of that could be accomplished by just swapping out the NiMh cells for the lipo- but the Kyosho manual explicitly states that lipos are not recommended and may cause fire, so that's part of my excuse to do this conversion. Considering the stock bump box just dumps the battery voltage through the motors with a physical contactor, it's a big upgrade to longevity since now the contactor and power switch are exposed to sensing levels of current instead of the full amperage the motors are drawing.

I've coded for an arduino before, but this time I described my goals to ChatGPT and had it produce the code. One or two tweaks later and it ran perfectly.
It reads the push-plate and generates a PWM signal for the ESC. Seems simple enough, but of course it got more complicated as I added smooth transitions between PWM states, a button for reverse to calibrate the ESC, and a function to show the output state with the onboard LED.

Key details & challenges:
Reverse-engineering the tooth profile (FHT-3, compatible with HTD-3M) and finding a belt of the exact length (55 teeth) to work with 1 motor instead of 2.
View attachment 173700

Rewiring the ESC's power switch to the bump box's switch, including wiring in a "set" button.

Incorporating a diode to drop the ESC's 6V to a level safe for the arduino (<5.5V) - I originally considered using the fan port voltage, which is directly from the battery, to the arduino's onboard regulator via the RAW pin, but I couldn't get the arduino to boot, only by giving it 5V on VCC. Using the BEC is cleaner anyway since that eliminates any connections to the fan port.
View attachment 173701

Incorporating forward & reverse test buttons directly onto the arduino.

Using the arduino's indicator LED to give visual confirmation of forward / reverse reads.
Using only the pins along the edge of the arduino for a very clean package & heat shrunk for that professional look:
View attachment 173702
The servo port goes to the ESC, and green/yellow reads the push-plate.

Videos to follow, preliminary tests have been promising. Fingers crossed that it doesn't suffer cogging issues.

Your a man after my own heart!! I absolutely love this conversion! I've been tempted to play around with Arduinos for several years now. I need to look into doing a conversion of my own.

 

[tudordewolf]

I like it. Great job. I have seen all these brushed powered starter boxes and I just think why not brushless?

Your a man after my own heart!! I absolutely love this conversion! I've been tempted to play around with Arduinos for several years now. I need to look into doing a conversion of my own.

Thanks! Field testing revealed a few issues..

It works, and starts cars, but it's prone to cogging. It helps if I spin up before the flywheel enagages, but that's not ideal.

I'm tempted to try a sensored brushed motor, but I can only find those in 3650 sizes or 42mm+ cans that won't fit available space. I'm not sure a single 3650 would cut it, even sensored.

There is something to be said for the raw low-end torque of brushed motors no matter how close you get them to stalling, and the analog simplicity of a push-plate driving them straight off the battery.

I could go back to brushed motors and use an ESC with my Arduino to spare the contactors the arcing from using lipos, but by that point I will have completely lost sight of the original goal.

 

[Greywolf74]

How hard would it be to add a second ESC and brushless motor?

 

[tudordewolf]

How hard would it be to add a second ESC and brushless motor?

Totally doable; but by that point, it would probably be over the original weight, not to mention ballooning project costs. Kind of a textbook case of mission creep. And if the engine hydrolocks after the brushless motors get up to speed with good contact on the flywheel, they'll probably blow it apart.

The single 3660 has more than enough torque once it's spinning to crank any motor I throw at it, the issue is just when there's extra resistance to getting started, like the compression stroke on a high-pinch engine, and that torque just isn't available. I even have it on a slightly smaller pulley (by 1 tooth...) than stock to get as much torque advantage as I can.

I'm considering a hobbywing fusion system, brushless & sensored all-in-one intended for crawlers. It has all the right features to cram everything into the smaller side of the bump box, and I expect it would have the right "jump from a standstill" capabilities to overcome the cogging issues.

What this was really for was to see it I could make a miniature bump-box, with supports that either slide or swing out and lock into place, so it can go in a backpack or carry case instead of being its own piece of luggage...

 

[J’sCrawler]

Totally doable; but by that point, it would probably be over the original weight, not to mention ballooning project costs. Kind of a textbook case of mission creep. And if the engine hydrolocks after the brushless motors get up to speed with good contact on the flywheel, they'll probably blow it apart.

The single 3660 has more than enough torque once it's spinning to crank any motor I throw at it, the issue is just when there's extra resistance to getting started, like the compression stroke on a high-pinch engine, and that torque just isn't available. I even have it on a slightly smaller pulley (by 1 tooth...) than stock to get as much torque advantage as I can.

I'm considering a hobbywing fusion system, brushless & sensored all-in-one intended for crawlers. It has all the right features to cram everything into the smaller side of the bump box, and I expect it would have the right "jump from a standstill" capabilities to overcome the cogging issues.

What this was really for was to see it I could make a miniature bump-box, with supports that either slide or swing out and lock into place, so it can go in a backpack or carry case instead of being its own piece of luggage...

Oh I like that idea.